[Code of Federal Regulations]
[Title 14, Volume 1]
[Revised as of January 1, 2004]
From the U.S. Government Printing Office via GPO Access
[CITE: 14CFR36.1583]
[Page 813-872]
TITLE 14--AERONAUTICS AND SPACE
CHAPTER I--FEDERAL AVIATION ADMINISTRATION, DEPARTMENT OF TRANSPORTATION
PART 36--NOISE STANDARDS: AIRCRAFT TYPE AND AIRWORTHINESS CERTIFICATION--Table
of Contents
Subpart O--Operating Limitations and Information
Sec. 36.1583 Noncomplying agricultural and fire fighting airplanes.
(a) This section applies to propeller-driven, small airplanes that--
(1) Are designed for ``agricultural aircraft operations'' (as
defined in Sec. 137.3 of this chapter, effective on January 1, 1966) or
for dispensing fire fighting materials; and
(2) Have not been shown to comply with the noise levels prescribed
under appendix F of this part--
(i) For which application is made for the original issue of a
standard airworthiness certificate and that do not have any flight time
before January 1, 1980; or
(ii) For which application is made for an acoustical change
approval, for airplanes which have a standard airworthiness certificate
after the change in the type design, and that do not have any flight
time in the changed configuration before January 1, 1980.
(b) For airplanes covered by this section an operating limitation
reading as follows must be furnished in the manner prescribed in
Sec. 36.1581:
Noise abatement: This airplane has not been shown to comply with the
noise limits in FAR Part 36 and must be operated in accordance with the
noise operating limitation prescribed under FAR Sec. 91.815.
[Amdt. 36-11, 45 FR 67066, Oct. 9, 1980. Redesignated by Amdt. 36-14, 53
FR 3540, Feb. 5, 1988; Amdt. 36-18, 54 FR 34330, Aug. 18, 1989]
Appendix A to Part 36--Aircraft Noise Measurement and Evaluation Under
Sec. 36.101
Sec.
A36.1 Introduction.
A36.2 Noise Certification Test and Measurement Conditions.
A36.3 Measurement of Airplane Noise Received on the Ground.
A36.4 Calculations of Effective Perceived Noise Level From Measured
Data.
A36.5 Reporting of Data to the FAA.
A36.6 Nomenclature: Symbols and Units.
A36.7 Sound Attenuation in Air.
A36.8 [Reserved]
A36.9 Adjustment of Airplane Flight Test Results.
Section A36.1 Introduction
A36.1.1 This appendix prescribes the conditions under which
airplane noise certification tests must be conducted and states the
measurement procedures that must be used to measure airplane noise. The
procedures that must be used to determine the noise evaluation quantity
designated as effective perceived noise level, EPNL, under Secs. 36.101
and 36.803 are also stated.
A36.1.2 The instructions and procedures given are intended to
ensure uniformity during compliance tests and to permit comparison
between tests of various types of airplanes conducted in various
geographical locations.
A36.1.3 A complete list of symbols and units, the mathematical
formulation of perceived noisiness, a procedure for determining
atmospheric attenuation of sound, and detailed procedures for correcting
noise levels from non-reference to reference conditions are included in
this appendix.
Section A36.2 Noise Certification Test and Measurement Conditions
A36.2.1 General.
A36.2.1.1 This section prescribes the conditions under which noise
certification must be conducted and the measurement procedures that must
be used.
Note: Many noise certifications involve only minor changes to the
airplane type design. The resulting changes in noise can often be
established reliably without resorting to a complete test as outlined in
this appendix. For this reason, the FAA permits the use of approved
equivalent procedures. There are also equivalent procedures that may be
used in full certification tests, in the interest of reducing costs and
providing reliable results. Guidance material on the use of equivalent
procedures in the noise certification of subsonic jet and propeller-
driven large airplanes is provided in the current advisory circular for
this part.
A36.2.2 Test environment.
[[Page 814]]
A36.2.2.1 Locations for measuring noise from an airplane in flight
must be surrounded by relatively flat terrain having no excessive sound
absorption characteristics such as might be caused by thick, matted, or
tall grass, shrubs, or wooded areas. No obstructions that significantly
influence the sound field from the airplane must exist within a conical
space above the point on the ground vertically below the microphone, the
cone being defined by an axis normal to the ground and by a half-angle
80 deg. from this axis.
Note: Those people carrying out the measurements could themselves
constitute such obstruction.
A36.2.2.2 The tests must be carried out under the following
atmospheric conditions.
(a) No precipitation;
(b) Ambient air temperature not above 95 deg.F (35 deg.C) and not
below 14 deg.F (-10 deg.C), and relative humidity not above 95% and
not below 20% over the whole noise path between a point 33 ft (10 m)
above the ground and the airplane;
Note: Care should be taken to ensure that the noise measuring,
airplane flight path tracking, and meteorological instrumentation are
also operated within their specific environmental limitations.
(c) Relative humidity and ambient temperature over the whole noise
path between a point 33 ft (10 m) above the ground and the airplane such
that the sound attenuation in the one-third octave band centered on 8
kHz will not be more than 12 dB/100 m unless:
(1) The dew point and dry bulb temperatures are measured with a
device which is accurate to 0.9 deg.F (0.5
deg.C) and used to obtain relative humidity; in addition layered
sections of the atmosphere are used as described in section A36.2.2.3 to
compute equivalent weighted sound attenuations in each one-third octave
band; or
(2) The peak noy values at the time of PNLT, after adjustment to
reference conditions, occur at frequencies less than or equal to 400
Hz.;
(d) If the atmospheric absorption coefficients vary over the PNLTM
sound propagation path by more than 1.6 dB/1000 ft
(0.5 dB/100m) in the 3150Hz one-third octave band from the
value of the absorption coefficient derived from the meteorological
measurement obtained at 33 ft (10 m) above the surface, ``layered''
sections of the atmosphere must be used as described in section
A36.2.2.3 to compute equivalent weighted sound attenuations in each one-
third octave band; the FAA will determine whether a sufficient number of
layered sections have been used. For each measurement, where multiple
layering is not required, equivalent sound attenuations in each one-
third octave band must be determined by averaging the atmospheric
absorption coefficients for each such band at 33 ft (10 m) above ground
level, and at the flight level of the airplane at the time of PNLTM, for
each measurement;
(e) Average wind velocity 33 ft (10 m) above ground may not exceed
12 knots and the crosswind velocity for the airplane may not exceed 7
knots. The average wind velocity must be determined using a 30-second
averaging period spanning the 10 dB-down time interval. Maximum wind
velocity 33 ft (10 m) above ground is not to exceed 15 knots and the
crosswind velocity is not to exceed 10 knots during the 10 dB-down time
interval;
(f) No anomalous meteorological or wind conditions that would
significantly affect the measured noise levels when the noise is
recorded at the measuring points specified by the FAA; and
(g) Meteorological measurements must be obtained within 30 minutes
of each noise test measurement; meteorological data must be interpolated
to actual times of each noise measurement.
A36.2.2.3 When a multiple layering calculation is required by
section A36.2.2.2(c) or A36.2.2.2(d) the atmosphere between the airplane
and 33 ft (10 m) above the ground must be divided into layers of equal
depth. The depth of the layers must be set to not more than the depth of
the narrowest layer across which the variation in the atmospheric
absorption coefficient of the 3150 Hz one-third octave band is not
greater than 1.6 dB/1000 ft (0.5 dB/100m), with
a minimum layer depth of 100 ft (30 m). This requirement must be met for
the propagation path at PNLTM. The mean of the values of the atmospheric
absorption coefficients at the top and bottom of each layer may be used
to characterize the absorption properties of each layer.
A36.2.2.4 The airport control tower or another facility must be
aproved by the FAA for use as the central location at which measurements
of atmospheric parameters are representative of those conditions
existing over the geographical area in which noise measurements are
made.
A36.2.3 Flight path measurement.
A36.2.3.1 The airplane height and lateral position relative to the
flight track must be determined by a method independent of normal flight
instrumentation such as radar tracking, theodolite triangulation, or
photographic scaling techniques, to be approved by the FAA.
A36.2.3.2 The airplane position along the flight path must be
related to the noise recorded at the noise measurement locations by
means of synchronizing signals over a distance sufficient to assure
adequate data during the period that the noise is within 10 dB of the
maximum value of PNLT.
A36.2.3.3 Position and performance data required to make the
adjustments referred to in section A36.9 of this appendix must be
[[Page 815]]
automatically recorded at an approved sampling rate. Measuring equipment
must be approved by the FAA.
Section A36.3 Measurement of Airplane Noise Received on the Ground
A36.3.1 Definitions.
For the purposes of section A36.3 the following definitions apply:
A36.3.1.1 Measurement system means the combination of instruments
used for the measurement of sound pressure levels, including a sound
calibrator, windscreen, microphone system, signal recording and
conditioning devices, and one-third octave band analysis system.
Note: Practical installations may include a number of microphone
systems, the outputs from which are recorded simultaneously by a multi-
channel recording/analysis device via signal conditioners, as
appropriate. For the purpose of this section, each complete measurement
channel is considered to be a measurement system to which the
requirements apply accordingly.
A36.3.1.2 Microphone system means the components of the measurement
system which produce an electrical output signal in response to a sound
pressure input signal, and which generally include a microphone, a
preamplifier, extension cables, and other devices as necessary.
A36.3.1.3 Sound incidence angle means in degrees, an angle between
the principal axis of the microphone, as defined in IEC 61094-3 and IEC
61094-4, as amended and a line from the sound source to the center of
the diaphragm of the microphone.
Note: When the sound incidence angle is 0 deg., the sound is said to
be received at the microphone at ``normal (perpendicular) incidence;''
when the sound incidence angle is 90 deg., the sound is said to be
received at ``grazing incidence.''
A36.3.1.4 Reference direction means, in degrees, the direction of
sound incidence specified by the manufacturer of the microphone,
relative to a sound incidence angle of 0 deg., for which the free-field
sensitivity level of the microphone system is within specified tolerance
limits.
A36.3.1.5 Free-field sensitivity of a microphone system means, in
volts per Pascal, for a sinusoidal plane progressive sound wave of
specified frequency, at a specified sound incidence angle, the quotient
of the root mean square voltage at the output of a microphone system and
the root mean square sound pressure that would exist at the position of
the microphone in its absence.
A36.3.1.6 Free-field sensitivity level of a microphone system
means, in decibels, twenty times the logarithm to the base ten of the
ratio of the free-field sensitivity of a microphone system and the
reference sensitivity of one volt per Pascal.
Note: The free-field sensitivity level of a microphone system may be
determined by subtracting the sound pressure level (in decibels re 20
[mu]Pa) of the sound incident on the microphone from the voltage level
(in decibels re 1 V) at the output of the microphone system, and adding
93.98 dB to the result.
A36.3.1.7 Time-average band sound pressure level means in decibels,
ten times the logarithm to the base ten, of the ratio of the time mean
square of the instantaneous sound pressure during a stated time interval
and in a specified one-third octave band, to the square of the reference
sound pressure of 20 [mu]Pa.
A36.3.1.8 Level range means, in decibels, an operating range
determined by the setting of the controls that are provided in a
measurement system for the recording and one-third octave band analysis
of a sound pressure signal. The upper boundary associated with any
particular level range must be rounded to the nearest decibel.
A36.3.1.9 Calibration sound pressure level means, in decibels, the
sound pressure level produced, under reference environmental conditions,
in the cavity of the coupler of the sound calibrator that is used to
determine the overall acoustical sensitivity of a measurement system.
A36.3.1.10 Reference level range means, in decibels, the level
range for determining the acoustical sensitivity of the measurement
system and containing the calibration sound pressure level.
A36.3.1.11 Calibration check frequency means, in hertz, the nominal
frequency of the sinusoidal sound pressure signal produced by the sound
calibrator.
A36.3.1.12 Level difference means, in decibels, for any nominal
one-third octave midband frequency, the output signal level measured on
any level range minus the level of the corresponding electrical input
signal.
A36.3.1.13 Reference level difference means, in decibels, for a
stated frequency, the level difference measured on a level range for an
electrical input signal corresponding to the calibration sound pressure
level, adjusted as appropriate, for the level range.
A36.3.1.14 Level non-linearity means, in decibels, the level
difference measured on any level range, at a stated one-third octave
nominal midband frequency, minus the corresponding reference level
difference, all input and output signals being relative to the same
reference quantity.
A36.3.1.15 Linear operating range means, in decibels, for a stated
level range and frequency, the range of levels of steady sinusoidal
electrical signals applied to the input of the entire measurement
system, exclusive of the microphone but including the microphone
preamplifier and any other signal-conditioning elements that are
considered to be part of the microphone system, extending from a lower
to an upper boundary, over
[[Page 816]]
which the level non-linearity is within specified tolerance limits.
Note: Microphone extension cables as configured in the field need
not be included for the linear operating range determination.
A36.3.1.16 Windscreen insertion loss means, in decibels, at a
stated nominal one-third octave midband frequency, and for a stated
sound incidence angle on the inserted microphone, the indicated sound
pressure level without the windscreen installed around the microphone
minus the sound pressure level with the windscreen installed.
A36.3.2 Reference environmental conditions.
A36.3.2.1 The reference environmental conditions for specifying the
performance of a measurement system are:
(a) Air temperature 73.4 deg.F (23 deg.C);
(b) Static air pressure 101.325 kPa; and
(c) Relative humidity 50%.
A36.3.3. General.
Note: Measurements of aircraft noise that are made using instruments
that conform to the specifications of this section will yield one-third
octave band sound pressure levels as a function of time. These one-third
octave band levels are to be used for the calculation of effective
perceived noise level as described in section A36.4.
A36.3.3.1 The measurement system must consist of equipment approved
by the FAA and equivalent to the following:
(a) A windscreen (See A36.3.4.);
(b) A microphone system (See A36.3.5):
(c) A recording and reproducing system to store the measured
aircraft noise signals for subsequent analysis (see A36.3.6);
(d) A one-third octave band analysis system (see A36.3.7); and
(e) Calibration systems to maintain the acoustical sensitivity of
the above systems within specified tolerance limits (see A36.3.8).
A36.3.3.2. For any component of the measurement system that
converts an analog signal to digital form, such conversion must be
performed so that the levels of any possible aliases or artifacts of the
digitization process will be less than the upper boundary of the linear
operating range by at least 50 dB at any frequency less than 12.5 kHz.
The sampling rate must be at least 28 kHz. An anti-aliasing filter must
be included before the digitization process.
A36.3.4 Windscreen.
A36.3.4.1 In the absence of wind and for sinusoidal sounds at
grazing incidence, the insertion loss caused by the windscreen of a
stated type installed around the microphone must not exceed
1.5 dB at nominal one-third octave midband frequencies from
50 Hz to 10 kHz inclusive.
A36.3.5 Microphone system.
A36.3.5.1 The microphone system must meet the specifications in
sections A36.3.5.2 to A36.3.5.4. Various microphone systems may be
approved by the FAA on the basis of demonstrated equivalent overall
electroacoustical performance. Where two or more microphone systems of
the same type are used, demonstration that at least one system conforms
to the specifications in full is sufficient to demonstrate conformance.
Note: An applicant must still calibrate and check each system as
required in section A36.3.9.
A36.3.5.2 The microphone must be mounted with the sensing element 4
ft (1.2 m) above the local ground surface and must be oriented for
grazing incidence, i.e., with the sensing element substantially in the
plane defined by the predicted reference flight path of the aircraft and
the measuring station. The microphone mounting arrangement must minimize
the interference of the supports with the sound to be measured. Figure
A36-1 illustrates sound incidence angles on a microphone.
A36.3.5.3 The free-field sensitivity level of the microphone and
preamplifier in the reference direction, at frequencies over at least
the range of one-third-octave nominal midband frequencies from 50 Hz to
5 kHz inclusive, must be within 1.0 dB of that at the
calibration check frequency, and within 2.0 dB for nominal
midband frequencies of 6.3 kHz, 8 kHz and 10 kHz.
A36.3.5.4 For sinusoidal sound waves at each one-third octave
nominal midband frequency over the range from 50 Hz to 10 kHz inclusive,
the free-field sensitivity levels of the microphone system at sound
incidence angles of 30 deg., 60 deg., 90 deg., 120 deg. and 150 deg.,
must not differ from the free-field sensitivity level at a sound
incidence angle of 0 deg. (``normal incidence'') by more than the values
shown in Table A36-1. The free-field sensitivity level differences at
sound incidence angles between any two adjacent sound incidence angles
in Table A36-1 must not exceed the tolerance limit for the greater
angle.
[[Page 817]]
[GRAPHIC] [TIFF OMITTED] TR08JY02.000
A36.3.6 Recording and reproducing systems.
A36.3.6.1 A recording and reproducing system, such as a digital or
analog magnetic tape recorder, a computer-based system or other
permanent data storage device, must be used to store sound pressure
signals for subsequent analysis. The sound produced by the aircraft must
be recorded in such a way that a record of the complete acoustical
signal is retained. The recording and reproducing systems must meet the
specifications in sections A36.3.6.2 to A36.3.6.9 at the recording
speeds and/or data sampling rates used for the noise certification
tests. Conformance must be demonstrated for the frequency bandwidths and
recording channels selected for the tests.
A36.3.6.2 The recording and reproducing systems must be calibrated
as described in section A36.3.9.
(a) For aircraft noise signals for which the high frequency spectral
levels decrease rapidly with increasing frequency, appropriate pre-
emphasis and complementary de-emphasis networks may be included in the
measurement system. If pre-emphasis is included, over the range of
nominal one-third octave midband frequencies from 800 Hz to 10 kHz
inclusive, the electrical gain provided by the pre-emphasis network must
not exceed 20 dB relative to the gain at 800 Hz.
A36.3.6.3 For steady sinusoidal electrical signals applied to the
input of the entire measurement system including all parts of the
microphone system except the microphone at a selected signal level
within 5 dB of that corresponding to the calibration sound pressure
level on the reference level range, the time-average signal level
indicated by the readout device at any one-third octave nominal midband
frequency from 50 Hz to 10 kHz inclusive must be within 1.5
dB of that at the calibration check frequency. The frequency response of
a measurement system, which includes components that convert analog
signals to digital form, must be within 0.3 dB of the
response at 10 kHz over the frequency range from 10 kHz to 11.2 kHz.
Note: Microphone extension cables as configured in the field need
not be included for the frequency response determination. This
[[Page 818]]
allowance does not eliminate the requirement of including microphone
extension cables when performing the pink noise recording in section
A36.3.9.5.
A36.3.6.4 For analog tape recordings, the amplitude fluctuations of
a 1 kHz sinusoidal signal recorded within 5 dB of the level
corresponding to the calibration sound pressure level must not vary by
more than 0.5 dB throughout any reel of the type of magnetic
tape used. Conformance to this requirement must be demonstrated using a
device that has time-averaging properties equivalent to those of the
spectrum analyzer.
A36.3.6.5 For all appropriate level ranges and for steady
sinusoidal electrical signals applied to the input of the measurement
system, including all parts of the microphone system except the
microphone, at one-third-octave nominal midband frequencies of 50 Hz, 1
kHz and 10 kHz, and the calibration check frequency, if it is not one of
these frequencies, the level non-linearity must not exceed
0.5 dB for a linear operating range of at least 50 dB below
the upper boundary of the level range.
Note 1: Level linearity of measurement system components may be
tested according to the methods described in IEC 61265 as amended.
Note 2: Microphone extension cables configured in the field need not
be included for the level linearity determination.
A36.3.6.6 On the reference level range, the level corresonding to
the calibration sound pressure level must be at least 5 dB, but no more
than 30 dB less than the upper boundary of the level range.
A36.3.6.7 The linear operating ranges on adjacent level ranges must
overlap by at least 50 dB minus the change in attenuation introduced by
a change in the level range controls.
Note: It is possible for a measurement system to have level range
controls that permit attenuation changes of either 10 dB or 1 dB, for
example. With 10 dB steps, the minimum overlap required would be 40 dB,
and with 1 dB steps the minimum overlap would be 49 dB.
A36.3.6.8 An overload indicator must be included in the recording
and reproducing systems so that an overload indication will occur during
an overload condition on any relevant level range.
A36.3.6.9 Attenuators included in the measurement system to permit
range changes must operate in known intervals of decibel steps.
A36.3.7 Analysis systems.
A36.3.7.1 The analysis system must conform to the specifications in
sections A36.3.7.2 to A36.3.7.7 for the frequency bandwidths, channel
configurations and gain settings used for analysis.
A36.3.7.2 The output of the analysis system must consist of one-
third octave band sound pressure levels as a function of time, obtained
by processing the noise signals (preferably recorded) through an
analysis system with the following characteristics:
(a) A set of 24 one-third octave band filters, or their equivalent,
having nominal midband frequencies from 50 Hz to 10 kHz inclusive;
(b) Response and averaging properties in which, in principle, the
output from any one-third octave filter band is squared, averaged and
displayed or stored as time-averaged sound pressure levels;
(c) The interval between successive sound pressure level samples
must be 500 ms 5 milliseconds(ms) for spectral analysis with
or without slow time-weighting, as defined in section A36.3.7.4;
(d) For those analysis systems that do not process the sound
pressure signals during the period of time required for readout and/or
resetting of the analyzer, the loss of data must not exceed a duration
of 5 ms; and
(e) The analysis system must operate in real time from 50 Hz through
at least 12 kHz inclusive. This requirement applies to all operating
channels of a multi-channel spectral analysis system.
A36.3.7.3 The minimum standard for the one-third octave band
analysis system is the class 2 electrical performance requirements of
IEC 61260 as amended, over the range of one-third octave nominal midband
frequencies from 50 Hz through 10 kHz inclusive.
Note: IEC 61260 specifies procedures for testing of one-third octave
band analysis systems for relative attenuation, anti-aliasing filters,
real time operation, level linearity, and filter integrated response
(effective bandwidth).
A36.3.7.4 When slow time averaging is performed in the analyzer,
the response of the one-third octave band analysis system to a sudden
onset or interruption of a constant sinusoidal signal at the respective
one-third octave nominal midband frequency, must be measured at sampling
instants 0.5, 1, 1.5 and 2 seconds(s) after the onset and 0.5 and 1s
after interruption. The rising response must be -4 1 dB at
0.5s, -1.75 0.75 dB at 1s, -1 0.5 dB at 1.5s and
-0.5 0.5 dB at 2s relative to the steady-state level. The
falling response must be such that the sum of the output signal levels,
relative to the initial steady-state level, and the corresponding rising
response reading is -6.5 1 dB, at both 0.5 and 1s. At
subsequent times the sum of the rising and falling responses must be -
7.5 dB or less. This equates to an exponential averaging process (slow
time-weighting) with a nominal 1s time constant (i.e., 2s averaging
time).
A36.3.7.5 When the one-third octave band sound pressure levels are
determined from the output of the analyzer without slow time-weighting,
slow time-weighting must be simulated in the subsequent processing.
[[Page 819]]
Simulated slow time-weighted sound pressure levels can be obtained using
a continuous exponential averaging process by the following equation:
Ls (i,k)=10 log [(0.60653) 100.1 Ls[i, (k-1)] +
(0.39347) 100.1 L (i, k)]
where Ls(i,k) is the simulated slow time-weighted sound
pressure level and L(i,k) is the as-measured 0.5s time average sound
pressure level determined from the output of the analyzer for the k-th
instant of time and i-th one-third octave band. For k=1, the slow time-
weighted sound pressure Ls[i, (k-1=0)] on the right hand side
should be set to 0 dB. An approximation of the continuous exponential
averaging is represented by the following equation for a four sample
averaging process for k [ge] 4:
Ls (i,k)=10 log [(0.13) 100.1 L[i,(k-3)] + (0.21)
100.1 L[i, (k-2)] + (0.27) 100.1 L[i, (k-1)] +
(0.39) 100.1 L[i, k]]
where Ls (i, k) is the simulated slow time-weighted sound
pressure level and L (i, k) is the as measured 0.5s time average sound
pressure level determined from the output of the analyzer for the k-th
instant of time and the i-th one-third octave band.
The sum of the weighting factors is 1.0 in the two equations. Sound
pressure levels calculated by means of either equation are valid for the
sixth and subsequent 0.5s data samples, or for times greater than 2.5s
after initiation of data analysis.
Note: The coefficients in the two equations were calculated for use
in determining equivalent slow time-weighted sound pressure levels from
samples of 0.5s time average sound pressure levels. The equations do not
work with data samples where the averaging time differs from 0.5s.
A36.3.7.6 The instant in time by which a slow time-weighted sound
pressure level is characterized must be 0.75s earlier than the actual
readout time.
Note: The definition of this instant in time is needed to correlate
the recorded noise with the aircraft position when the noise was emitted
and takes into account the averaging period of the slow time-weighting.
For each 0.5 second data record this instant in time may also be
identified as 1.25 seconds after the start of the associated 2 second
averaging period.
A36.3.7.7 The resolution of the sound pressure levels, both
displayed and stored, must be 0.1 dB or finer.
A36.3.8 Calibration systems.
A36.3.8.1 The acoustical sensitivity of the measurement system must
be determined using a sound calibrator generating a known sound pressure
level at a known frequency. The minimum standard for the sound
calibrator is the class 1L requirements of IEC 60942 as amended.
A36.3.9 Calibration and checking of system.
A36.3.9.1 Calibration and checking of the measurement system and
its constituent components must be carried out to the satisfaction of
the FAA by the methods specified in sections A36.3.9.2 through
A36.3.9.10. The calibration adjustments, including those for
environmental effects on sound calibrator output level, must be reported
to the FAA and applied to the measured one-third-octave sound pressure
levels determined from the output of the analyzer. Data collected during
an overload indication are invalid and may not be used. If the overload
condition occurred during recording, the associated test data are
invalid, whereas if the overload occurred during analysis, the analysis
must be repeated with reduced sensitivity to eliminate the overload.
A36.3.9.2 The free-field frequency response of the microphone
system may be determined by use of an electrostatic actuator in
combination with manufacturer's data or by tests in an anechoic free-
field facility. The correction for frequency response must be determined
within 90 days of each test series. The correction for non-uniform
frequency response of the microphone system must be reported to the FAA
and applied to the measured one-third octave band sound pressure levels
determined from the output of the analyzer.
A36.3.9.3 When the angles of incidence of sound emitted from the
aircraft are within 30 deg. of grazing incidence at the
microphone (see Figure A36-1), a single set of free-field corrections
based on grazing incidence is considered sufficient for correction of
directional response effects. For other cases, the angle of incidence
for each 0.5 second sample must be determined and applied for the
correction of incidence effects.
A36.3.9.4 For analog magnetic tape recorders, each reel of magnetic
tape must carry at least 30 seconds of pink random or pseudo-random
noise at its beginning and end. Data obtained from analog tape-recorded
signals will be accepted as reliable only if level differences in the 10
kHz one-third-octave-band are not more than 0.75 dB for the signals
recorded at the beginning and end.
A36.3.9.5 The frequency response of the entire measurement system
while deployed in the field during the test series, exclusive of the
microphone, must be determined at a level within 5 dB of the level
corresponding to the calibration sound pressure level on the level range
used during the tests for each one-third octave nominal midband
frequency from 50 Hz to 10 kHz inclusive, utilizing pink random or
pseudo-random noise. Within six months of each test series the output of
the noise generator must be determined by a method traceable to the U.S.
National Institute of Standards and Technology or to an equivalent
national standards laboratory as
[[Page 820]]
determined by the FAA. Changes in the relative output from the previous
calibration at each one-third octave band may not exceed 0.2 dB. The
correction for frequency response must be reported to the FAA and
applied to the measured one-third octave sound pressure levels
determined from the output of the analyzer.
A36.3.9.6 The performance of switched attenuators in the equipment
used during noise certification measurements and calibration must be
checked within six months of each test series to ensure that the maximum
error does not exceed 0.1 dB.
A36.3.9.7 The sound pressure level produced in the cavity of the
coupler of the sound calibrator must be calculated for the test
environmental conditions using the manufacturer's supplied information
on the influence of atmospheric air pressure and temperature. This sound
pressure level is used to establish the acoustical sensitivity of the
measurement system. Within six months of each test series the output of
the sound calibrator must be determined by a method traceable to the
U.S. National Institute of Standards and Technology or to an equivalent
national standards laboratory as determined by the FAA. Changes in
output from the previous calibration must not exceed 0.2 dB.
A36.3.9.8 Sufficient sound pressure level calibrations must be made
during each test day to ensure that the acoustical sensitivity of the
measurement system is known at the prevailing environmental conditions
corresponding with each test series. The difference between the
acoustical sensitivity levels recorded immediately before and
immediately after each test series on each day may not exceed 0.5 dB.
The 0.5 dB limit applies after any atmospheric pressure corrections have
been determined for the calibrator output level. The arithmetic mean of
the before and after measurements must be used to represent the
acoustical sensitivity level of the measurement system for that test
series. The calibration corrections must be reported to the FAA and
applied to the measured one-third octave band sound pressure levels
determined from the output of the analyzer.
A36.3.9.9 Each recording medium, such as a reel, cartridge,
cassette, or diskette, must carry a sound pressure level calibration of
at least 10 seconds duration at its beginning and end.
A36.3.9.10 The free-field insertion loss of the windscreen for each
one-third octave nominal midband frequency from 50 Hz to 10 kHz
inclusive must be determined with sinusoidal sound signals at the
incidence angles determined to be applicable for correction of
directional response effects per section A36.3.9.3. The interval between
angles tested must not exceed 30 degrees. For a windscreen that is
undamaged and uncontaminated, the insertion loss may be taken from
manufacturer's data. Alternatively, within six months of each test
series the insertion loss of the windscreen may be determined by a
method traceable to the U.S. National Institute of Standards and
Technology or an equivalent national standards laboratory as determined
by the FAA. Changes in the insertion loss from the previous calibration
at each one-third-octave frequency band must not exceed 0.4 dB. The
correction for the free-field insertion loss of the windscreen must be
reported to the FAA and applied to the measured one-third octave sound
pressure levels determined from the output of the analyzer.
A36.3.10 Adjustments for ambient noise.
A36.3.10.1 Ambient noise, including both a acoustical background
and electrical noise of the measurement system, must be recorded for at
least 10 seconds at the measurement points with the system gain set at
the levels used for the aircraft noise measurements. Ambient noise must
be representative of the acoustical background that exists during the
flyover test run. The recorded aircraft noise data is acceptable only if
the ambient noise levels, when analyzed in the same way, and quoted in
PNL (see A36.4.1.3 (a)), are at least 20 dB below the maximum PNL of the
aircraft.
A36.3.10.2 Aircraft sound pressure levels within the 10 dB-down
points (see A36.4.5.1) must exceed the mean ambient noise levels
determined in section A36.3.10.1 by at least 3 dB in each one-third
octave band, or must be adjusted using a method approved by the FAA; one
method is described in the current advisory circular for this part.
Section A36.4 Calculation of Effective Perceived Noise Level From
Measured Data
A36.4.1 General.
A36.4.1.1 The basic element for noise certification criteria is the
noise evaluation measure known as effective perceived noise level, EPNL,
in units of EPNdB, which is a single number evaluator of the subjective
effects of airplane noise on human beings. EPNL consists of
instantaneous perceived noise level, PNL, corrected for spectral
irregularities, and for duration. The spectral irregularity correction,
called ``tone correction factor'', is made at each time increment for
only the maximum tone.
A36.4.1.2 Three basic physical properties of sound pressure must be
measured: level, frequency distribution, and time variation. To
determine EPNL, the instantaneous sound pressure level in each of the 24
one-third octave bands is required for each 0.5 second increment of time
during the airplane noise measurement.
[[Page 821]]
A36.4.1.3 The calculation procedure that uses physical measurements
of noise to derive the EPNL evaluation measure of subjective response
consists of the following five steps:
(a) The 24 one-third octave bands of sound pressure level are
converted to perceived noisiness (noy) using the method described in
section A36.4.2.1 (a). The noy values are combined and then converted to
instantaneous perceived noise levels, PNL(k).
(b) A tone correction factor C(k) is calculated for each spectrum to
account for the subjective response to the presence of spectral
irregularities.
(c) The tone correction factor is added to the perceived noise level
to obtain tone-corrected perceived noise levels PNLT(k), at each one-
half second increment:
PNLT(k)=PNL(k) + C(k)
The instantaneous values of tone-corrected perceived noise level are
derived and the maximum value, PNLTM, is determined.
(d) A duration correction factor, D, is computed by integration
under the curve of tone-corrected perceived noise level versus time.
(e) Effective perceived noise level, EPNL, is determined by the
algebraic sum of the maximum tone-corrected perceived noise level and
the duration correction factor:
EPNL=PNLTM + D
A36.4.2 Perceived noise level.
A36.4.2.1 Instantaneous perceived noise levels, PNL(k), must be
calculated from instantaneous one-third octave band sound pressure
levels, SPL(i, k) as follows:
(a) Step 1: For each one-third octave band from 50 through 10,000
Hz, convert SPL(i, k) to perceived noisiness n(i, k), by using the
mathematical formulation of the noy table given in section A36.4.7.
(b) Step 2: Combine the perceived noisiness values, n(i, k),
determined in step 1 by using the following formula:
[GRAPHIC] [TIFF OMITTED] TR08JY02.001
where n(k) is the largest of the 24 values of n(i, k) and N(k) is the
total perceived noisiness.
(c) Step 3: Convert the total perceived noisiness, N(k), determined
in Step 2 into perceived noise level, PNL(k), using the following
formula:
[GRAPHIC] [TIFF OMITTED] TR08JY02.002
Note: PNL(k) is plotted in the current advisory circular for this
part.
A36.4.3 Correction for spectral irregularities.
A36.4.3.1 Noise having pronounced spectral irregularities (for
example, the maximum discrete frequency components or tones) must be
adjusted by the correction factor C(k) calculated as follows:
(a) Step 1: After applying the corrections specified under section
A36.3.9, start with the sound pressure level in the 80 Hz one-third
octave band (band number 3), calculate the changes in sound pressure
level (or ``slopes'') in the remainder of the one-third octave bands as
follows:
s(3,k)=no value
s(4,k)=SPL(4,k)-SPL(3,k)
s(i,k)=SPL(i,k)-SPL(i-1,k)
s(24,k)=SPL(24,k)-SPL(23,k)
(b) Step 2: Encircle the value of the slope, s(i, k), where the
absolute value of the change in slope is greater than five; that is
where:
[bond][Delta]s(i,k)[bond]=[bond]s(i,k)-s(i-1,k)[bond]5
(c) Step 3:
(1) If the encircled value of the slope s(i, k) is positive and
algebraically greater than the slope s(i-1, k) encircle SPL(i, k).
(2) If the encircled value of the slope s(i, k) is zero or negative
and the slope s(i-1, k) is positive, encircle SPL(i-1, k).
(3) For all other cases, no sound pressure level value is to be
encircled.
(d) Step 4: Compute new adjusted sound pressure levels SPL'(i, k) as
follows:
(1) For non-encircled sound pressure levels, set the new sound
pressure levels equal to the original sound pressure levels, SPL'(i,
k)=SPL(i, k).
(2) For encircled sound pressure levels in bands 1 through 23
inclusive, set the new sound pressure level equal to the arithmetic
average of the preceding and following sound pressure levels as shown
below:
SPL'(i,k)=\1/2\[SPL(i-1,k)+SPL(i+1,k)]
(3) If the sound pressure level in the highest frequency band (i=24)
is encircled, set the new sound pressure level in that band equal to:
SPL'(24,k)=SPL(23,k)+s(23,k)
(e) Step 5: Recompute new slope s'(i, k), including one for an
imaginary 25th band, as follows:
s'(3,k)=s'(4,k)
s'(4,k)=SPL'(4,k)-SPL'(3,k)
s'(i,k)=SPL'(i,k)-SPL'(i-1,k)
s'(24,k)=SPL'(24,k)-SPL'(23,k)
[[Page 822]]
s'(25,k)=s'(24,k)
(f) Step 6: For i, from 3 through 23, compute the arithmetic average
of the three adjacent slopes as follows:
s(i,k)=\1/3\[s'(i,k)+s'(i+1,k)+s'(i+2,k)]
(g) Step 7: Compute final one-third octave-band sound pressure
levels, SPL' (i,k), by beginning with band number 3 and proceeding to
band number 24 as follows:
SPL'(3,k)=SPL(3,k)
SPL'(4,k)=SPL'(3,k)+s(3,k)
SPL'(i,k)=SPL'(i-1,k)+s(i-1,k)
SPL'(24,k)=SPL'(23,k)+s(23,k)
(h) Setp 8: Calculate the differences, F (i,k), between the original
sound pressure level and the final background sound pressure level as
follows:
F(i,k)=SPL(i,k)-SPL'(i,k)
and note only values equal to or greater than 1.5.
(i) Step 9: For each of the relevant one-third octave bands (3
through 24), determine tone correction factors from the sound pressure
level differences F (i, k) and Table A36-2.
[[Page 823]]
[GRAPHIC] [TIFF OMITTED] TR08JY02.003
(j) Step 10: Designate the largest of the tone correction factors,
determined in Step 9, as C(k). (An example of the tone correction
procedure is given in the current advisory circular for this part).
Tone-corrected perceived noise levels PNLT(k) must be determined by
adding the C(k) values to corresponding PNL(k) values, that is:
PNLT(k)=PNL(k)+C(k)
For any i-th one-third octave band, at any k-th increment of time, for
which the tone correction factor is suspected to result from something
other than (or in addition to) an actual tone (or any spectral
irregularity other than airplane noise), an additional analysis may be
made using a filter with a bandwidth narrower than one-third of an
octave. If the narrow band analysis corroborates these suspicions, then
a revised value for the background sound pressure level
[[Page 824]]
SPL'(i,k), may be determined from the narrow band analysis and used to
compute a revised tone correction factor for that particular one-third
octave band. Other methods of rejecting spurious tone corrections may be
approved.
A36.4.3.2 The tone correction procedure will underestimate EPNL if
an important tone is of a frequency such that it is recorded in two
adjacent one-third octave bands. An applicant must demonstrate that
either:
(a) No important tones are recorded in two adjacent one-third octave
bands; or
(b) That if an important tone has occurred, the tone correction has
been adjusted to the value it would have had if the tone had been
recorded fully in a single one-third octave band.
A36.4.4 Maximum tone-corrected perceived noise level
A36.4.4.1 The maximum tone-corrected perceived noise level, PNLTM,
must be the maximum calculated value of the tone-corrected perceived
noise level PNLT(k). It must be calculated using the procedure of
section A36.4.3. To obtain a satisfactory noise time history,
measurements must be made at 0.5 second time intervals.
Note 1: Figure A36-2 is an example of a flyover noise time history
where the maximum value is clearly indicated.
Note 2: In the absence of a tone correction factor, PNLTM would
equal PNLM.
[GRAPHIC] [TIFF OMITTED] TR08JY02.004
A36.4.4.2 After the value of PNLTM is obtained, the frequency band
for the largest tone correction factor is identified for the two
preceding and two succeeding 500 ms data samples. This is performed in
order to identity the possibility of tone suppression at PNLTM by one-
third octave band sharing of that tone. If the value of the tone
correction factor C(k) for PNLTM is less than the average value of C(k)
for the five consecutive time intervals, the average value of C(k) must
be used to compute a new value for PNLTM.
A36.4.5 Duration correction.
A36.4.5.1 The duration correction factor D determined by the
integration technique is defined by the expression:
[[Page 825]]
[GRAPHIC] [TIFF OMITTED] TR08JY02.005
where T is a normalizing time constant, PNLTM is the maximum value of
PNLT, t(1) is the first point of time after which PNLT becomes greater
than PNLTM-10, and t(2) is the point of time after which PNLT remains
constantly less than PNLTM-10.
A36.4.5.2 Since PNLT is calculated from measured values of sound
pressure level (SPL), there is no obvious equation for PNLT as a
function of time. Consequently, the equation is to be rewritten with a
summation sign instead of an integral sign as follows:
[GRAPHIC] [TIFF OMITTED] TR08JY02.006
where [Delta]t is the length of the equal increments of time for which
PNLT(k) is calculated and d is the time interval to the nearest 0.5s
during which PNLT(k) remains greater or equal to PNLTM-10.
A36.4.5.3 To obtain a satisfactory history of the perceived noise
level use one of the following:
(a) Half-Second time intervals for [Delta]t; or
(b) A shorter time interval with approved limits and constants.
A36.4.5.4 The following values for T and [Delta]t must be used in
calculating D in the equation given in section A36.4.5.2:
T=10 s, and
[Delta]t=0.5s (or the approved sampling time interval).
Using these values, the equation for D becomes:
[GRAPHIC] [TIFF OMITTED] TR08JY02.007
where d is the duration time defined by the points corresponding to the
values PNLTM-10.
A36.4.5.5 If in using the procedures given in section A36.4.5.2,
the limits of PNLTM-10 fall between the calculated PNLT(k) values (the
usual case), the PNLT(k) values defining the limits of the duration
interval must be chosen from the PNLT(k) values closest to PNLTM-10. For
those cases with more than one peak value of PNLT(k), the applicable
limits must be chosen to yield the largest possible value for the
duration time.
A36.4.6 Effective perceived noise level.
The total subjective effect of an airplane noise event, designated
effective perceived noise level, EPNL, is equal to the algebraic sum of
the maximum value of the tone-corrected perceived noise level, PNLTM,
and the duration correction D. That is:
EPNL=PNLTM+D
where PNLTM and D are calculated using the procedures given in sections
A36.4.2, A36.4.3, A36.4.4. and A36.4.5.
A36.4.7 Mathematical formulation of noy tables.
A36.4.7.1 The relationship between sound pressure level (SPL) and
the logarithm of perceived noisiness is illustrated in Figure A36-3 and
Table A36-3.
A36.4.7.2 The bases of the mathematical formulation are:
(a) The slopes (M(b), M(c), M(d) and M(e)) of the straight lines;
(b) The intercepts (SPL(b) and SPL(c)) of the lines on the SPL axis;
and
(c) The coordinates of the discontinuities, SPL(a) and log n(a);
SPL(d) and log n=-1.0; and SPL(e) and log n=log (0.3).
A36.4.7.3 Calculate noy values using the following equations:
(a)
SPL [ge] SPL (a)
n=antilog {(c)[SPL-SPL(c)]{time}
[[Page 826]]
(b)
SPL(b) [le] SPL < SPL(a)
n=antilog {M(b)[SPL-SPL(b)]{time}
(c)
SPL(e) [le] SPL < SPL(b)
n=0.3 antilog {M(e)[SPL-SPL(e)]{time}
(d)
SPL(d) [le] SPL < SPL(e)
n=0.1 antilog {M(d)[SPL-SPL(d)]{time}
A36.4.7.4 Table A36-3 lists the values of the constants necessary
to calculate perceived noisiness as a function of sound pressure level.
[GRAPHIC] [TIFF OMITTED] TR08JY02.008
[[Page 827]]
[GRAPHIC] [TIFF OMITTED] TR08JY02.009
Section A36.5 Reporting of Data to the FAA
A36.5.1 General.
A36.5.1.1 Data representing physical measurements and data used to
make corrections to physical measurements must be recorded in an
approved permanent form and appended to the record.
A36.5.1.2 All corrections must be reported to and approved by the
FAA, including corrections to measurements for equipment response
deviations.
A36.5.1.3 Applicants may be required to submit estimates of the
individual errors inherent in each of the operations employed in
obtaining the final data.
A36.5.2 Data reporting.
An applicant is required to submit a noise certification compliance
report that includes the following.
A36.5.2.1 The applicant must present measured and corrected sound
pressure levels in one-third octave band levels that are obtained with
equipment conforming to the standards described in section A36.3 of this
appendix.
A36.5.2.2 The applicant must report the make and model of equipment
used for measurement and analysis of all acoustic performance and
meteorological data.
A36.5.2.3 The applicant must report the following atmospheric
environmental data, as measured immediately before, after, or during
each test at the observation points prescribed in section A36.2 of this
appendix.
(a) Air temperature and relative humidity;
(b) Maximum, minimum and average wind velocities; and
(c) Atmospheric pressure.
[[Page 828]]
A36.5.2.4 The applicant must report conditions of local topography,
ground cover, and events that might interfere with sound recordings.
A36.5.2.5 The applicant must report the following:
(a) Type, model and serial numbers (if any) of airplane, engine(s),
or propeller(s) (as applicable);
(b) Gross dimensions of airplane and location of engines;
(c) Airplane gross weight for each test run and center of gravity
range for each series of test runs;
(d) Airplane configuration such as flap, airbrakes and landing gear
positions for each test run;
(e) Whether auxiliary power units (APU), when fitted, are operating
for each test run;
(f) Status of pneumatic engine bleeds and engine power take-offs for
each test run;
(g) Indicated airspeed in knots or kilometers per hour for each test
run;
(h) Engine performance data:
(1) For jet airplanes: engine performance in terms of net thrust,
engine pressure ratios, jet exhaust temperatures and fan or compressor
shaft rotational speeds as determined from airplane instruments and
manufacturer's data for each test run;
(2) For propeller-driven airplanes: engine performance in terms of
brake horsepower and residual thrust; or equivalent shaft horsepower; or
engine torque and propeller rotational speed; as determined from
airplane instruments and manufacturer's data for each test run;
(i) Airplane flight path and ground speed during each test run; and
(j) The applicant must report whether the airplane has any
modifications or non-standard equipment likely to affect the noise
characteristics of the airplane. The FAA must approve any such
modifications or non-standard equipment.
A36.5.3 Reporting of noise certification reference conditions.
A36.5.3.1 Airplane position and performance data and the noise
measurements must be corrected to the noise certification reference
conditions specified in the relevant sections of appendix B of this
part. The applicant must report these conditions, including reference
parameters, procedures and configurations.
A36.5.4 Validity of results.
A36.5.4.1 Three average reference EPNL values and their 90 percent
confidence limits must be produced from the test results and reported,
each such value being the arithmetical average of the adjusted
acoustical measurements for all valid test runs at each measurement
point (flyover, lateral, or approach). If more than one acoustic
measurement system is used at any single measurement location, the
resulting data for each test run must be averaged as a single
measurement. The calculation must be performed by:
(a) Computing the arithmetic average for each flight phase using the
values from each microphone point; and
(b) Computing the overall arithmetic average for each reference
condition (flyover, lateral or approach) using the values in paragraph
(a) of this section and the related 90 percent confidence limits.
A36.5.4.2 For each of the three certification measuring points, the
minimum sample size is six. The sample size must be large enough to
establish statistically for each of the three average noise
certification levels a 90 percent confidence limit not exceeding
1.5 EPNdB. No test result may be omitted from the averaging
process unless approved by the FAA.
Note: Permitted methods for calculating the 90 percent confidence
interval are shown in the current advisory circular for this part.
A36.5.4.3 The average EPNL figures obtained by the process
described in section A36.5.4.1 must be those by which the noise
performance of the airplane is assessed against the noise certification
criteria.
Section A36.6 Nomenclature: Symbols and Units
------------------------------------------------------------------------
Symbol Unit Meaning
------------------------------------------------------------------------
antilog............... ...................... Antilogarithm to the
base 10.
C(k).................. dB.................... Tone correction factor.
The factor to be added
to PNL(k) to account
for the presence of
spectral irregularities
such as tones at the k-
th increment of time.
d..................... s..................... Duration time. The time
interval between the
limits of t(1) and t(2)
to the nearest 0.5
second.
D..................... dB.................... Duration correction. The
factor to be added to
PNLTM to account for
the duration of the
noise.
EPNL.................. EPNdB................. Effective perceived
noise level. The value
of PNL adjusted for
both spectral
irregularities and
duration of the noise.
(The unit EPNdB is used
instead of the unit
dB).
EPNLr................. EPNdB................. Effective perceived
noise level adjusted
for reference
conditions.
f(i).................. Hz.................... Frequency. The
geometrical mean
frequency for the i-th
one-third octave band.
[[Page 829]]
F (i, k).............. dB.................... Delta-dB. The difference
between the original
sound pressure level
and the final
background sound
pressure level in the i-
th one-third octave
band at the k-th
interval of time. In
this case, background
sound pressure level
means the broadband
noise level that would
be present in the one-
third octave band in
the absence of the
tone.
h..................... dB.................... dB-down. The value to be
subtracted from PNLTM
that defines the
duration of the noise.
H..................... Percent............... Relative humidity. The
ambient atmospheric
relative humidity.
i..................... ...................... Frequency band index.
The numerical indicator
that denotes any one of
the 24 one-third octave
bands with geometrical
mean frequencies from
50 to 10,000 Hz.
k..................... ...................... Time increment index.
The numerical indicator
that denotes the number
of equal time
increments that have
elapsed from a
reference zero.
Log................... ...................... Logarithm to the base
10.
log n(a).............. ...................... Noy discontinuity
coordinate. The log n
value of the
intersection point of
the straight lines
representing the
variation of SPL with
log n.
M(b), M(c), etc....... ...................... Noy inverse slope. The
reciprocals of the
slopes of straight
lines representing the
variation of SPL with
log n.
n..................... noy................... The perceived noisiness
at any instant of time
that occurs in a
specified frequency
range.
n(i,k)................ noy................... The perceived noisiness
at the k-th instant of
time that occurs in the
i-th one-third octave
band.
n(k).................. noy................... Maximum perceived
noisiness. The maximum
value of all of the 24
values of n(i) that
occurs at the k-th
instant of time.
N(k).................. noy................... Total perceived
noisiness. The total
perceived noisiness at
the k-th instant of
time calculated from
the 24-instantaneous
values of n (i, k).
p(b), p(c), etc....... ...................... Noy slope. The slopes of
straight lines
representing the
variation of SPL with
log n.
PNL................... PNdB.................. The perceived noise
level at any instant of
time. (The unit PNdB is
used instead of the
unit dB).
PNL(k)................ PNdB.................. The perceived noise
level calculated from
the 24 values of SPL
(i, k), at the k-th
increment of time. (The
unit PNdB is used
instead of the unit
dB).
PNLM.................. PNdB.................. Maximum perceived noise
level. The maximum
value of PNL(k). (The
unit PNdB is used
instead of the unit
dB).
PNLT.................. TPNdB................. Tone-corrected perceived
noise level. The value
of PNL adjusted for the
spectral irregularities
that occur at any
instant of time. (The
unit TPNdB is used
instead of the unit
dB).
PNLT(k)............... TPNdB................. The tone-corrected
perceived noise level
that occurs at the k-th
increment of time.
PNLT(k) is obtained by
adjusting the value of
PNL(k) for the spectral
irregularities that
occur at the k-th
increment of time. (The
unit TPNdB is used
instead of the unit
dB).
PNLTM................. TPNdB................. Maximum tone-corrected
perceived noise level.
The maximum value of
PNLT(k). (The unit
TPNdB is used instead
of the unit dB).
PNLTr................. TPNdB................. Tone-corrected perceived
noise level adjusted
for reference
conditions.
s (i, k).............. dB.................... Slope of sound pressure
level. The change in
level between adjacent
one-third octave band
sound pressure levels
at the i-th band for
the k-th instant of
time.
[Delta]s (i, k)....... dB.................... Change in slope of sound
pressure level.
s' (i, k)............. dB.................... Adjusted slope of sound
pressure level. The
change in level between
adjacent adjusted one-
third octave band sound
pressure levels at the
i-th band for the k-th
instant of time.
s (i, k).............. dB.................... Average slope of sound
pressure level.
SPL................... dB re................. Sound pressure level.
20 [mu]Pa............. The sound pressure
level that occurs in a
specified frequency
range at any instant of
time.
SPL(a)................ dB re................. Noy discontinuity
20 [mu]Pa............. coordinate. The SPL
value of the
intersection point of
the straight lines
representing the
variation of SPL with
log n.
SPL(b)................ dB re................. Noy intercept. The
SPL (c)............... 20 [mu]Pa............. intercepts on the SPL-
axis of the straight
lines representing the
variation of SPL with
log n.
SPL (i, k)............ dB re................. The sound pressure level
20 [mu]Pa............. at the k-th instant of
time that occurs in the
i-th one-third octave
band.
[[Page 830]]
SPL' (i, k)........... dB re................. Adjusted sound pressure
20 [mu]Pa............. level. The first
approximation to
background sound
pressure level in the i-
th one-third octave
band for the k-th
instant of time.
SPL(i)................ dB re................. Maximum sound pressure
20 [mu]Pa............. level. The sound
pressure level that
occurs in the i-th one-
third octave band of
the spectrum for PNLTM.
SPL(i)r............... dB re................. Corrected maximum sound
20 [mu]Pa............. pressure level. The
sound pressure level
that occurs in the i-th
one-third octave band
of the spectrum for
PNLTM corrected for
atmospheric sound
absorption.
SPL' (i, k)........... dB re................. Final background sound
20 [mu]Pa............. pressure level. The
second and final
approximation to
background sound
pressure level in the i-
th one-third octave
band for the k-th
instant of time.
t..................... s..................... Elapsed time. The length
of time measured from a
reference zero.
t(1), t(2)............ s..................... Time limit. The
beginning and end,
respectively, of the
noise time history
defined by h.
[Delta]t.............. s..................... Time increment. The
equal increments of
time for which PNL(k)
and PNLT(k) are
calculated.
T..................... s..................... Normalizing time
constant. The length of
time used as a
reference in the
integration method for
computing duration
corrections, where
T=10s.
t( deg.F) ( deg.C).. deg.F, deg.C....... Temperature. The ambient
air temperature.
[alpha](i)............ dB/1000ft db/100m..... Test atmospheric
absorption. The
atmospheric attenuation
of sound that occurs in
the i-th one-third
octave band at the
measured air
temperature and
relative humidity.
[alpha](i)o........... dB/1000ft db/100m..... Reference atmospheric
absorption. The
atmospheric attenuation
of sound that occurs in
the i-th one-third
octave band at a
reference air
temperature and
relative humidity.
A1.................... Degrees............... First constant climb
angle (Gear up, speed
of at least V2+10 kt
(V2+19 km/h), takeoff
thrust).
A2.................... Degrees............... Second constant climb
angle (Gear up, speed
of at least V2+10 kt
(V2+19 km/h), after cut-
back).
[delta]............... Degrees............... Thrust cutback angles.
[epsi]................ The angles defining the
points on the takeoff
flight path at which
thrust reduction is
started and ended
respectively.
[eta]................. Degrees............... Approach angle.
[eta]r................ Degrees............... Reference approach
angle.
[thetas].............. Degrees............... Noise angle (relative to
flight path). The angle
between the flight path
and noise path. It is
identical for both
measured and corrected
flight paths.
[psi]................. Degrees............... Noise angle (relative to
ground). The angle
between the noise path
and the ground. It is
identical for both
measured and corrected
flight paths.
[mu].................. ...................... Engine noise emission
parameter.
[mu]r................. ...................... Reference engine noise
emission parameter.
[Delta]1.............. EPNdB................. PNLT correction. The
correction to be added
to the EPNL calculated
from measured data to
account for noise level
changes due to
differences in
atmospheric absorption
and noise path length
between reference and
test conditions.
[Delta]2.............. EPNdB................. Adjustment to duration
correction. The
adjustment to be made
to the EPNL calculated
from measured data to
account for noise level
changes due to the
noise duration between
reference and test
conditions.
[Delta]3.............. EPNdB................. Source noise adjustment.
The adjustment to be
made to the EPNL
calculated from
measured data to
account for noise level
changes due to
differences between
reference and test
engine operating
conditions.
------------------------------------------------------------------------
Section A36.7 Sound Attenuation in Air
A36.7.1 The atmospheric attenuation of sound must be determined in
accordance with the procedure presented in section A36.7.2.
A36.7.2 The relationship between sound attenuation, frequency,
temperature, and humidity is expressed by the following equations.
A36.7.2(a) For calculations using the English System of Units:
[GRAPHIC] [TIFF OMITTED] TR08JY02.010
and
[GRAPHIC] [TIFF OMITTED] TR08JY02.011
[[Page 831]]
where
[eta]([delta]) is listed in Table A36-4 and f0 in Table A36-
5;
[alpha](i) is the attenuation coefficient in dB/1000 ft;
[thetas] is the temperature in deg.F; and
H is the relative humidity, expressed as a percentage.
A36.7.2(b) For calculations using the International System of Units
(SI):
[GRAPHIC] [TIFF OMITTED] TR08JY02.012
and
[GRAPHIC] [TIFF OMITTED] TR08JY02.013
where
[eta]([delta]) is listed in Table A36-4 and f0 in Table A36-
5;
[alpha](i) is the attenuation coefficient in dB/100 m;
[thetas] is the temperature in deg.C; and
H is the relative humidity, expressed as a percentage.
A36.7.3 The values listed in table A36-4 are to be used when
calculating the equations listed in section A36.7.2. A term of quadratic
interpolation is to be used where necessary.
Section A36.8 [Reserved]
[[Page 832]]
[GRAPHIC] [TIFF OMITTED] TR08JY02.014
Section A36.9 Adjustment of Airplane Flight Test Results.
A36.9.1 When certification test conditions are not identical to
reference conditions, appropriate adjustments must be made to the
measured noise data using the methods described in this section.
A36.9.1.1 Adjustments to the measured noise values must be made
using one of the methods described in sections A36.9.3 and A36.9.4 for
differences in the following:
(a) Attenuation of the noise along its path as affected by ``inverse
square'' and atmospheric attenuation
(b) Duration of the noise as affected by the distance and the speed
of the airplane relative to the measuring point
[[Page 833]]
(c) Source noise emitted by the engine as affected by the
differences between test and reference engine operating conditions
(d) Airplane/engine source noise as affected by differences between
test and reference airspeeds. In addition to the effect on duration, the
effects of airspeed on component noise sources must be accounted for as
follows: for conventional airplane configurations, when differences
between test and reference airspeeds exceed 15 knots (28 km/h) true
airspeed, test data and/or analysis approved by the FAA must be used to
quantify the effects of the airspeed adjustment on resulting
certification noise levels.
A36.9.1.2 The ``integrated'' method of adjustment, described in
section A36.9.4, must be used on takeoff or approach under the following
conditions:
(a) When the amount of the adjustment (using the ``simplified''
method) is greater than 8 dB on flyover, or 4 dB on approach; or
(b) When the resulting final EPNL value on flyover or approach
(using the simplified method) is within 1 dB of the limiting noise
levels as prescribed in section B36.5 of this part.
A36.9.2 Flight profiles.
As described below, flight profiles for both test and reference
conditions are defined by their geometry relative to the ground,
together with the associated airplane speed relative to the ground, and
the associated engine control parameter(s) used for determining the
noise emission of the airplane.
A36.9.2.1 Takeoff Profile.
Note: Figure A36-4 illustrates a typical takeoff profile.
(a) The airplane begins the takeoff roll at point A, lifts off at
point B and begins its first climb at a constant angle at point C. Where
thrust or power (as appropriate) cut-back is used, it is started at
point D and completed at point E. From here, the airplane begins a
second climb at a constant angle up to point F, the end of the noise
certification takeoff flight path.
(b) Position K1 is the takeoff noise measuring station
and AK1 is the distance from start of roll to the flyover
measuring point. Position K2 is the lateral noise measuring
station, which is located on a line parallel to, and the specified
distance from, the runway center line where the noise level during
takeoff is greatest.
(c) The distance AF is the distance over which the airplane position
is measured and synchronized with the noise measurements, as required by
section A36.2.3.2 of this part.
A36.9.2.2 Approach Profile.
Note: Figure A36-5 illustrates a typical approach profile.
(a) The airplane begins its noise certification approach flight path
at point G and touches down on the runway at point J, at a distance OJ
from the runway threshold.
(b) Position K3 is the approach noise measuring station
and K3O is the distance from the approach noise measurement
point to the runway threshold.
(c) The distance GI is the distance over which the airplane position
is measured and synchronized with the noise measurements, as required by
section A36.2.3.2 of this part.
[[Page 834]]
[GRAPHIC] [TIFF OMITTED] TR08JY02.015
The airplane reference point for approach measurements is the instrument
landing system (ILS) antenna. If no ILS antenna is installed an
alternative reference point must be approved by the FAA.
A36.9.3 Simplified method of adjustment.
A36.9.3.1 General. As described below, the simplified adjustment
method consists of applying adjustments (to the EPNL, which is
calculated from the measured data) for the differences between measured
and reference conditions at the moment of PNLTM.
A36.9.3.2 Adjustments to PNL and PNLT.
(a) The portions of the test flight path and the reference flight
path described below, and illustrated in Figure A36-6, include the noise
time history that is relevant to the calculation of flyover and approach
EPNL. In figure A36-6:
[[Page 835]]
(1) XY represents the portion of the measured flight path that
includes the noise time history relevant to the calculation of flyover
and approach EPNL; XrYr represents the
corresponding portion of the reference flight path.
(2) Q represents the airplane's position on the measured flight path
at which the noise was emitted and observed as PNLTM at the noise
measuring station K. Qr is the corresponding position on the
reference flight path, and Kr the reference measuring
station. QK and QrKr are, respectively, the
measured
[GRAPHIC] [TIFF OMITTED] TR08JY02.016
and reference noise propagation paths, Qr being determined
from the assumption that QK and QrKr form the same
angle [thetas] with their respective flight paths.
(b) The portions of the test flight path and the reference flight
path described in paragraph (b)(1) and (2), and illustrated in Figure
A36-7(a) and (b), include the noise time history that is relevant to the
calculation of lateral EPNL.
(1) In figure A36-7(a), XY represents the portion of the measured
flight path that includes the noise time history that is relevant to the
calculation of lateral EPNL; in figure A36-7(b),
XrYr represents the corresponding portion of the
reference flight path.
(2) Q represents the airplane position on the measured flight path
at which the noise was emitted and observed as PNLTM at the noise
measuring station K. Qr is the corresponding position on the
reference flight path, and Kr the reference measuring
station. QK and QrKr are, respectively, the
measured and reference noise propagation paths. In this case
Kr is only specified as being on a particular Lateral line;
Kr and Qr are therefore determined from the
assumptions that QK and QrKr:
(i) Form the same angle [thetas] with their respective flight paths;
and
(ii) Form the same angle [psi] with the ground.
Note: For the lateral noise measurement, sound propagation is
affected not only by inverse square and atmospheric attenuation, but
also by ground absorption and reflection effects which depend mainly on
the angle [psi].
[[Page 836]]
[GRAPHIC] [TIFF OMITTED] TR08JY02.017
A36.9.3.2.1 The one-third octave band levels SPL(i) comprising PNL
(the PNL at the moment of PNLTM observed at K) must be adjusted to
reference levels SPL(i)r as follows:
A36.9.3.2.1(a) For calculations using the English System of Units:
SPL(i)r=SPL(i)+0.001[[alpha](i)-[alpha](i)0]QK
+0.001[alpha](i)0(QK-QrKr)
+20log(QK/QrKr)
In this expression,
(1) The term 0.001[[alpha](i)-[alpha](i)0]QK is the
adjustment for the effect of the change in sound attenuation
coefficient, and [alpha](i) and [alpha](i)0 are the
coefficients for the test and reference atmospheric conditions
respectively, determined under section A36.7 of this appendix;
(2) The term 0.001[alpha](i)0(QK -
QrKr) is the adjustment for the effect of the
change in the noise path length on the sound attenuation;
(3) The term 20 log(QK/QrKr) is the adjustment
for the effect of the change in the noise path length due to the
``inverse square'' law;
(4) QK and QrKr are measured in feet and
[alpha](i) and [alpha](i)0 are expressed in dB/1000 ft.
A36.9.3.2.1(b) For calculations using the International System of
Units:
SPL(i)r=SPL(i)+0.01[[alpha](i)-[alpha](i)0]QK
+0.01[alpha](i)0 (QK - QrKr)
+20 log(QK/QrKr)
In this expression,
[[Page 837]]
(1) The term 0.01[[alpha](i) - [alpha](i)0]QK is the
adjustment for the effect of the change in sound attenuation
coefficient, and [alpha](i) and [alpha](i)0 are the
coefficients for the test and reference atmospheric conditions
respectively, determined under section A36.7 of this appendix;
(2) The term 0.01[alpha](i)0(QK -
QrKr) is the adjustment for the effect of the
change in the noise path length on the sound attenuation;
(3) The term 20 log(QK/QrKr) is the adjustment
for the effect of the change in the noise path length due to the inverse
square law;
(4) QK and QrKr are measured in meters and
[alpha](i) and [alpha](i)0 are expressed in dB/100 m.
A36.9.3.2.1.1 PNLT Correction.
(a) Convert the corrected values, SPL(i)r, to
PNLTr;
(b) Calculate the correction term [Delta]1 using the
following equation:
[Delta]1=PNLTr - PNLTM
A36.9.3.2.1.2 Add [Delta]1 arithmetically to the EPNL
calculated from the measured data.
A36.9.3.2.2 If, during a test flight, several peak values of PNLT
that are within 2 dB of PNLTM are observed, the procedure defined in
section A36.9.3.2.1 must be applied at each peak, and the adjustment
term, calculated according to section A36.9.3.2.1, must be added to each
peak to give corresponding adjusted peak values of PNLT. If these peak
values exceed the value at the moment of PNLTM, the maximum value of
such exceedance must be added as a further adjustment to the EPNL
calculated from the measured data.
A36.9.3.3 Adjustments to duration correction.
A36.9.3.3.1 Whenever the measured flight paths and/or the ground
velocities of the test conditions differ from the reference flight paths
and/or the ground velocities of the reference conditions, duration
adjustments must be applied to the EPNL values calculated from the
measured data. The adjustments must be calculated as described below.
A36.9.3.3.2 For the flight path shown in Figure A36-6, the
adjustment term is calculated as follows:
[Delta]2=-7.5 log(QK/QrKr)+10 log(V/
Vr)
(a) Add [Delta]2 arithmetically to the EPNL calculated
from the measured data.
A36.9.3.4 Source noise adjustments.
A36.9.3.4.1 To account for differences between the parameters
affecting engine noise as measured in the certification flight tests,
and those calculated or specified in the reference conditions, the
source noise adjustment must be calculated and applied. The adjustment
is determined from the manufacturer's data approved by the FAA. Typical
data used for this adjustment are illustrated in Figure A36-8 that shows
a curve of EPNL versus the engine control parameter [mu], with the EPNL
data being corrected to all the other relevant reference conditions
(airplane mass, speed and altitude, air temperature) and for the
difference in noise between the test engine and the average engine (as
defined in section B36.7(b)(7)). A sufficient number of data points over
a range of values of [mu]r is required to calculate the
source noise adjustments for lateral, flyover and approach noise
measurements.
[GRAPHIC] [TIFF OMITTED] TR08JY02.018
A36.9.3.4.2 Calculate adjustment term [Delta]3 by
subtracting the EPNL value corresponding to the parameter [mu] from the
EPNL value corresponding to the parameter
[[Page 838]]
[mu]r. Add [Delta]3 arithmetically to the EPNL
value calculated from the measured data.
A36.9.3.5 Symmetry adjustments.
A36.9.3.5.1 A symmetry adjustment to each lateral noise value
(determined at the section B36.4(b) measurement points), is to be made
as follows:
(a) If the symmetrical measurement point is opposite the point where
the highest noise level is obtained on the main lateral measurement
line, the certification noise level is the arithmetic mean of the noise
levels measured at these two points (see Figure A36-9(a));
(b) If the condition described in paragraph (a) of this section is
not met, then it is assumed that the variation of noise with the
altitude of the airplane is the same on both sides; there is a constant
difference between the lines of noise versus altitude on both sides (see
figure A36-9(b)). The certification noise level is the maximum value of
the mean between these lines.
[GRAPHIC] [TIFF OMITTED] TR08JY02.019
A36.9.4 Integrated method of adjustment
A36.9.4.1 General. As described in this section, the integrated
adjustment method consists of recomputing under reference conditions
points on the PNLT time history corresponding to measured points
obtained during the tests, and computing EPNL directly for the new time
history obtained in this way. The main principles are described in
sections A36.9.4.2 through A36.9.4.4.1.
A36.9.4.2 PNLT computations.
(a) The portions of the test flight path and the reference flight
path described in paragraph (a)(1) and (2), and illustrated in Figure
A36-10, include the noise time history that is relevant to the
calculation of flyover and approach EPNL. In figure A36-10:
[[Page 839]]
[GRAPHIC] [TIFF OMITTED] TR08JY02.020
(1) XY represents the portion of the measured flight path that
includes the noise time history relevant to the calculation of flyover
and approach EPNL; XrYr represents the
corresponding reference flight path.
(2) The points Q0, Q1, Qn represent
airplane positions on the measured flight path at time t0,
t1 and tn respectively. Point Q1 is the
point at which the noise was emitted and observed as one-third octave
values SPL(i)1 at the noise measuring station K at time
t1. Point Qr1 represents the corresponding
position on the reference flight path for noise observed as
SPL(i)r1 at the reference measuring station Kr at
time tr1. Q1K and Qr1Kr are
respectively the measured and reference noise propagation paths, which
in each case form the angle [thetas]1 with their respective
flight paths. Qr0 and Qrn are similarly the points
on the reference flight path corresponding to Q0 and
Qn on the measured flight path. Q0 and
Qn are chosen so that between Qr0 and
Qrn all values of PNLTr (computed as described in
paragraphs A36.9.4.2.2 and A36.9.4.2.3) within 10 dB of the peak value
are included.
(b) The portions of the test flight path and the reference flight
path described in paragraph (b)(1) and (2), and illustrated in Figure
A36-11(a) and (b), include the noise time history that is relevant to
the calculation of lateral EPNL.
(1) In figure A36-11(a) XY represents the portion of the measured
flight path that includes the noise time history that is relevant to the
calculation of lateral EPNL; in figure A36-11(b),
XrYr represents the corresponding portion of the
reference flight path.
(2) The points Q0, Q1 and Qn
represent airplane positions on the measured flight path at time
t0, t1 and tn respectively. Point
Q1 is the point at which the noise was emitted and observed
as one-third octave values SPL(i)1 at the noise measuring
station K at time t1. The point Qr1 represents the
corresponding position on the reference flight path for noise observed
as SPL(i)r1 at the measuring station Kr at time
tr1. Q1K and Qr1Kr are
respectively the measured and reference noise propagation paths.
Qr0 and Qrn are similarly the points on the
reference flight path corresponding to Q0 and Qn
on the measured flight path.
[[Page 840]]
[GRAPHIC] [TIFF OMITTED] TR08JY02.021
Q0 and Qn are chosen to that between
Qro and Qrn all values of PNLTr
(computed as described in paragraphs A36.9.4.2.2 and A36.9.4.2.3) within
10 dB of the peak value are included. In this case Kr is only
specified as
[[Page 841]]
being on a particular lateral line. The position of Kr and
Qr1 are determined from the following requirements.
(i) Q1K and Qr1Kr form the same
angle [thetas]1 with their respective flight paths; and
(ii) The differences between the angles 1 and
r1 must be minimized using a method, approved by the FAA. The
differences between the angles are minimized since, for geometrical
reasons, it is generally not possible to choose Kr so that
the condition described in paragraph A36.9.4.2(b)(2)(i) is met while at
the same time keeping 1 and r1 equal.
Note: For the lateral noise measurement, sound propagation is
affected not only by ``inverse square'' and atmospheric attenuation, but
also by ground absorption and reflection effects which depend mainly on
the angle.
A36.9.4.2.1 In paragraphs A36.9.4.2(a)(2) and (b)(2) the time
tr1 is later (for Qr1Kr
Q1K) than t1 by two separate amounts:
(1) The time taken for the airplane to travel the distance
Qr1Qr0 at a speed Vr less the time
taken for it to travel Q1Q0 at V;
(2) The time taken for sound to travel the distance
Qr1Kr-Q1K.
Note: For the flight paths described in paragraphs A36.9.4.2(a) and
(b), the use of thrust or power cut-back will result in test and
reference flight paths at full thrust or power and at cut-back thrust or
power. Where the transient region between these thrust or power levels
affects the final result, an interpolation must be made between them by
an approved method such as that given in the current advisory circular
for this part.
A36.9.4.2.2 The measured values of SPL(i)1 must be
adjusted to the reference values SPL(i)r1 to account for the
differences between measured and reference noise path lengths and
between measured and reference atmospheric conditions, using the methods
of section A36.9.3.2.1 of this appendix. A corresponding value of
PNLr1 must be computed according to the method in section
A36.4.2. Values of PNLr must be computed for times
t0 through tn.
A36.9.4.2.3 For each value of PNLr1, a tone correction
factor C1 must be determined by analyzing the reference
values SPL(i)r using the methods of section A36.4.3 of this
appendix, and added to PNLr1 to yield PNLTr1.
Using the process described in this paragraph, values of
PNLTr must be computed for times t0 through
tn.
A36.9.4.3 Duration correction.
A36.9.4.3.1 The values of PNLTr corresponding to those
of PNLT at each one-half second interval must be plotted against time
(PNLTr1 at time tr1). The duration correction must
then be determined using the method of section A36.4.5.1 of this
appendix, to yield EPNLr.
A36.9.4.4 Source Noise Adjustment.
A36.9.4.4.1 A source noise adjustment, [Delta]3, must be
determined using the methods of section A36.9.3.4 of this appendix.
A36.9.5 Flight Path Identification Positions
------------------------------------------------------------------------
Position Description
------------------------------------------------------------------------
A............................... Start of Takeoff roll.
B............................... Lift-off.
C............................... Start of first constant climb.
D............................... Start of thrust reduction.
E............................... Start of second constant climb.
F............................... End of noise certification Takeoff
flight path.
G............................... Start of noise certification Approach
flight path.
H............................... Position on Approach path directly
above noise measuring station.
I............................... Start of level-off.
J............................... Touchdown.
K............................... Noise measurement point.
Kr.............................. Reference measurement point.
K1.............................. Flyover noise measurement point.
K2.............................. Lateral noise measurement point.
K3.............................. Approach noise measurement point.
M............................... End of noise certification Takeoff
flight track.
O............................... Threshold of Approach end of runway.
P............................... Start of noise certification Approach
flight track.
Q............................... Position on measured Takeoff flight
path corresponding to apparent PNLTM
at station K See section A36.9.3.2.
Qr.............................. Position on corrected Takeoff flight
path corresponding to PNLTM at
station K. See section A36.9.3.2.
V............................... Airplane test speed.
Vr.............................. Airplane reference speed.
------------------------------------------------------------------------
A36.9.6 Flight Path Distances
------------------------------------------------------------------------
Distance Unit Meaning
------------------------------------------------------------------------
AB................. Feet (meters).......... Length of takeoff roll.
The distance along the
runway between the start
of takeoff roll and lift
off.
AK................. Feet (meters).......... Takeoff measurement
distance. The distance
from the start of roll to
the takeoff noise
measurement station along
the extended center line
of the runway.
AM................. Feet (meters).......... Takeoff flight track
distance. The distance
from the start of roll to
the takeoff flight track
position along the
extended center line of
the runway after which
the position of the
airplane need no longer
be recorded.
QK................. Feet (meters).......... Measured noise path. The
distance from the
measured airplane
position Q to station K.
QrKr............... Feet (meters).......... Reference noise path. The
distance from the
reference airplane
position Qr to station
Kr.
K3H................ Feet (meters).......... Airplane approach height.
The height of the
airplane above the
approach measuring
station.
OK3................ Feet (meters).......... Approach measurement
distance. The distance
from the runway threshold
to the approach
measurement station along
the extended center line
of the runway.
[[Page 842]]
OP................. Feet (meters).......... Approach flight track
distance. The distance
from the runway threshold
to the approach flight
track position along the
extended center line of
the runway after which
the position of the
airplane need no longer
be recorded.
------------------------------------------------------------------------
[Amdt. 36-54, 67 FR 45212, July 8, 2002; Amdt. 36-24, 67 FR 63195,
63196, Oct. 10, 2002; 68 FR 1512, Jan 10, 2003]
Appendix B to Part 36--Noise Levels for Transport Category and Jet
Airplanes Under Sec. 36.103
Sec.
B36.1 Noise Measurement and Evaluation.
B36.2 Noise Evaluation Metric.
B36.3 Reference Noise Measurement Points.
B36.4 Test Noise Measurement Points.
B36.5 Maximum Noise Levels.
B36.6 Trade-Offs.
B36.7 Noise Certification Reference Procedures and Conditions.
B36.8 Noise Certification Test Procedures.
Section B36.1 Noise Measurement and Evaluation
Compliance with this appendix must be shown with noise levels
measured and evaluated using the procedures of appendix A of this part,
or under approved equivalent procedures.
Section B36.2 Noise Evaluation Metric
The noise evaluation metric is the effective perceived noise level
expressed in EPNdB, as calculated using the procedures of appendix A of
this part.
Section B36.3 Reference Noise Measurement Points
When tested using the procedures of this part, except as provided in
section B36.6, an airplane may not exceed the noise levels specified in
section B36.5 at the following points on level terrain:
(a) Lateral full-power reference noise measurement point:
(1) For jet airplanes: The point on a line parallel to and 1,476
feet (450 m) from the runway centerline, or extended centerline, where
the noise level after lift-off is at a maximum during takeoff. For the
purpose of showing compliance with Stage 1 or Stage 2 noise limits for
an airplane powered by more than three jet engines, the distance from
the runway centerline must be 0.35 nautical miles (648 m). For jet
airplanes, when approved by the FAA, the maximum lateral noise at
takeoff thrust may be assumed to occur at the point (or its approved
equivalent) along the extended centerline of the runway where the
airplane reaches 985 feet (300 meters) altitude above ground level. A
height of 1427 feet (435 meters) may be assumed for Stage 1 or Stage 2
four engine airplanes. The altitude of the airplane as it passes the
noise measurement points must be within +328 to -164 feet (+100 to -50
meters) of the target altitude. For airplanes powered by other than jet
engines, the altitude for maximum lateral noise must be determined
experimentally.
(2) For propeller-driven airplanes: The point on the extended
centerline of the runway above which the airplane, at full takeoff
power, reaches a height of 2,133 feet (650 meters). For tests conducted
before August 7, 2002, an applicant may use the measurement point
specified in section B36.3(a)(1) as an alternative.
(b) Flyover reference noise measurement point: The point on the
extended centerline of the runway that is 21,325 feet (6,500 m) from the
start of the takeoff roll;
(c) Approach reference noise measurement point: The point on the
extended centerline of the runway that is 6,562 feet (2,000 m) from the
runway threshold. On level ground, this corresponds to a position that
is 394 feet (120 m) vertically below the 3 deg. descent path, which
originates at a point on the runway 984 feet (300 m) beyond the
threshold.
Section B36.4 Test noise measurement points.
(a) If the test noise measurement points are not located at the
reference noise measurement points, any corrections for the difference
in position are to be made using the same adjustment procedures as for
the differences between test and reference flight paths.
(b) The applicant must use a sufficient number of lateral test noise
measurement points to demonstrate to the FAA that the maximum noise
level on the appropriate lateral line has been determined. For jet
airplanes, simultaneous measurements must be made at one test noise
measurement point at its symmetrical point on the other side of the
runway. Propeller-driven airplanes have an inherent asymmetry in lateral
noise. Therefore, simultaneous measurements must be made at each and
every test noise measurement point at its symmetrical position on the
opposite side of the runway. The measurement points are considered to be
symmetrical if they are longitudinally within 33 feet (10
meters) of each other.
Section B36.5 Maximum Noise Levels
Except as provided in section B36.6 of this appendix, maximum noise
levels, when determined in accordance with the noise evaluation methods
of appendix A of this part, may not exceed the following:
[[Page 843]]
(a) For acoustical changes to Stage 1 airplanes, regardless of the
number of engines, the noise levels prescribed under Sec. 36.7(c) of
this part.
(b) For any Stage 2 airplane regardless of the number of engines:
(1) Flyover: 108 EPNdB for maximum weight of 600,000 pounds or more;
for each halving of maximum weight (from 600,000 pounds), reduce the
limit by 5 EPNdB; the limit is 93 EPNdB for a maximum weight of 75,000
pounds or less.
(2) Lateral and approach: 108 EPNdB for maximum weight of 600,000
pounds or more; for each halving of maximum weight (from 600,000
pounds), reduce the limit by 2 EPNdB; the limit is 102 EPNdB for a
maximum weight of 75,000 pounds or less.
(c) For any Stage 3 airplane:
(1) Flyover.
(i) For airplanes with more than 3 engines: 106 EPNdB for maximum
weight of 850,000 pounds or more; for each halving of maximum weight
(from 850,000 pounds), reduce the limit by 4 EPNdB; the limit is 89
EPNdB for a maximum weight of 44,673 pounds or less;
(ii) For airplanes with 3 engines: 104 EPNdB for maximum weight of
850,000 pounds or more; for each halving of maximum weight (from 850,000
pounds), reduce the limit by 4 EPNdB; the limit is 89 EPNdB for a
maximum weight of 63,177 pounds or less; and
(iii) For airplanes with fewer than 3 engines: 101 EPNdB for maximum
weight of 850,000 pounds or more; for each halving of maximum weight
(from 850,000 pounds), reduce the limit by 4 EPNdB; the limit is 89
EPNdB for a maximum weight of 106,250 pounds or less.
(2) Lateral, regardless of the number of engines: 103 EPNdB for
maximum weight of 882,000 pounds or more; for each halving of maximum
weight (from 882,000 pounds), reduce the limit by 2.56 EPNdB; the limit
is 94 EPNdB for a maximum weight of 77,200 pounds or less.
(3) Approach, regardless of the number of engines: 105 EPNdB for
maximum weight of 617,300 pounds or more; for each halving of maximum
weight (from 617,300 pounds), reduce the limit by 2.33 EPNdB; the limit
is 98 EPNdB for a maximum weight of 77,200 pounds or less.
Section B36.6 Trade-Offs
Except when prohibited by sections 36.7(c)(1) and 36.7(d)(1)(ii), if
the maximum noise levels are exceeded at any one or two measurement
points, the following conditions must be met:
(a) The sum of the exceedance(s) may not be greater than 3 EPNdB;
(b) Any exceedance at any single point may not be greater than 2
EPNdB, and
(c) Any exceedance(s) must be offset by a corresponding amount at
another point or points.
Section B36.7 Noise Certification Reference Procedures and Conditions
(a) General conditions:
(1) All reference procedures must meet the requirements of section
36.3 of this part.
(2) Calculations of airplane performance and flight path must be
made using the reference procedures and must be approved by the FAA.
(3) Applicants must use the takeoff and approach reference
procedures prescribed in paragraphs (b) and (c) of this section.
(4) [Reserved]
(5) The reference procedures must be determined for the following
reference conditions. The reference atmosphere is homogeneous in terms
of temperature and relative humidity when used for the calculation of
atmospheric absorption coefficients.
(i) Sea level atmospheric pressure of 2116 pounds per square foot
(psf) (1013.25 hPa);
(ii) Ambient sea-level air temperature of 77 deg.F (25 deg.C, i.e.
ISA+10 deg.C);
(iii) Relative humidity of 70 per cent;
(iv) Zero wind.
(v) In defining the reference takeoff flight path(s) for the takeoff
and lateral noise measurements, the runway gradient is zero.
(b) Takeoff reference procedure:
The takeoff reference flight path is to be calculated using the
following:
(1) Average engine takeoff thrust or power must be used from the
start of takeoff to the point where at least the following height above
runway level is reached. The takeoff thrust/power used must be the
maximum available for normal operations given in the performance section
of the airplane flight manual under the reference atmospheric conditions
given in section B36.7(a)(5).
(i) For Stage 1 airplanes and for Stage 2 airplanes that do not have
jet engines with a bypass ratio of 2 or more, the following apply:
(A): For airplanes with more than three jet engines--700 feet (214
meters).
(B): For all other airplanes--1,000 feet (305 meters).
(ii) For Stage 2 airplanes that have jet engines with a bypass ratio
of 2 or more and for Stage 3 airplanes, the following apply:
(A): For airplanes with more than three engines--689 feet (210
meters).
(B): For airplanes with three engines--853 feet (260 meters).
(C): For airplanes with fewer than three engines--984 feet (300
meters).
(2) Upon reaching the height specified in paragraph (b)(1) of this
section, airplane thrust or power must not be reduced below that
required to maintain either of the following, whichever is greater:
(i) A climb gradient of 4 per cent; or
[[Page 844]]
(ii) In the case of multi-engine airplanes, level flight with one
engine inoperative.
(3) For the purpose of determining the lateral noise level, the
reference flight path must be calculated using full takeoff power
throughout the test run without a reduction in thrust or power. For
tests conducted before August 7, 2002, a single reference flight path
that includes thrust cutback in accordance with paragraph (b)(2) of this
section, is an acceptable alternative in determining the lateral noise
level.
(4) The takeoff reference speed is the all-engine operating takeoff
climb speed selected by the applicant for use in normal operation; this
speed must be at least V2+10kt (V2+19km/h) but may not be greater than
V2+20kt (V2+37km/h). This speed must be attained as soon as practicable
after lift-off and be maintained throughout the takeoff noise
certification test. For Concorde airplanes, the test day speeds and the
acoustic day reference speed are the minimum approved value of V2+35
knots, or the all-engines-operating speed at 35 feet, whichever speed is
greater as determined under the regulations constituting the type
certification basis of the airplane; this reference speed may not exceed
250 knots. For all airplanes, noise values measured at the test day
speeds must be corrected to the acoustic day reference speed.
(5) The takeoff configuration selected by the applicant must be
maintained constantly throughout the takeoff reference procedure, except
that the landing gear may be retracted. Configuration means the center
of gravity position, and the status of the airplane systems that can
affect airplane performance or noise. Examples include, the position of
lift augmentation devices, whether the APU is operating, and whether air
bleeds and engine power take-offs are operating;
(6) The weight of the airplane at the brake release must be the
maximum takeoff weight at which the noise certification is requested,
which may result in an operating limitation as specified in
Sec. 36.1581(d); and
(7) The average engine is defined as the average of all the
certification compliant engines used during the airplane flight tests,
up to and during certification, when operating within the limitations
and according to the procedures given in the Flight Manual. This will
determine the relationship of thrust/power to control parameters (e.g.,
N1 or EPR). Noise measurements made during certification
tests must be corrected using this relationship.
(c) Approach reference procedure:
The approach reference flight path must be calculated using the
following:
(1) The airplane is stabilized and following a 3 deg. glide path;
(2) For subsonic airplanes, a steady approach speed of
Vref + 10 kts (Vref + 19 km/h) with thrust and
power stabilized must be established and maintained over the approach
measuring point. Vref is the reference landing speed, which
is defined as the speed of the airplane, in a specified landing
configuration, at the point where it descends through the landing screen
height in the determination of the landing distance for manual landings.
For Concorde airplanes, a steady approach speed that is either the
landing reference speed + 10 knots or the speed used in establishing the
approved landing distance under the airworthiness regulations
constituting the type certification basis of the airplane, whichever
speed is greater. This speed must be established and maintained over the
approach measuring point.
(3) The constant approach configuration used in the airworthiness
certification tests, but with the landing gear down, must be maintained
throughout the approach reference procedure;
(4) The weight of the airplane at touchdown must be the maximum
landing weight permitted in the approach configuration defined in
paragraph (c)(3) of this section at which noise certification is
requested, except as provided in Sec. 36.1581(d) of this part; and
(5) The most critical configuration must be used; this configuration
is defined as that which produces the highest noise level with normal
deployment of aerodynamic control surfaces including lift and drag
producing devices, at the weight at which certification is requested.
This configuration includes all those items listed in section A36.5.2.5
of appendix A of this part that contribute to the noisiest continuous
state at the maximum landing weight in normal operation.
Section B36.8 Noise Certification Test Procedures
(a) All test procedures must be approved by the FAA.
(b) The test procedures and noise measurements must be conducted and
processed in an approved manner to yield the noise evaluation metric
EPNL, in units of EPNdB, as described in appendix A of this part.
(c) Acoustic data must be adjusted to the reference conditions
specified in this appendix using the methods described in appendix A of
this part. Adjustments for speed and thrust must be made as described in
section A36.9 of this part.
(d) If the airplane's weight during the test is different from the
weight at which noise certification is requested, the required EPNL
adjustment may not exceed 2 EPNdB for each takeoff and 1 EPNdB for each
approach. Data approved by the FAA must be used to determine the
variation of EPNL with weight for both takeoff and approach test
conditions. The necessary EPNL adjustment for variations in approach
flight path from the reference flight path must not exceed 2 EPNdB.
[[Page 845]]
(e) For approach, a steady glide path angle of 3 deg.
0.5 deg. is acceptable.
(f) If equivalent test procedures different from the reference
procedures are used, the test procedures and all methods for adjusting
the results to the reference procedures must be approved by the FAA. The
adjustments may not exceed 16 EPNdB on takeoff and 8 EPNdB on approach.
If the adjustment is more than 8 EPNdB on takeoff, or more than 4 EPNdB
on approach, the resulting numbers must be more than 2 EPNdB below the
limit noise levels specified in section B36.5.
(g) During takeoff, lateral, and approach tests, the airplane
variation in instantaneous indicated airspeed must be maintained within
3% of the average airspeed between the 10 dB-down points.
This airspeed is determined by the pilot's airspeed indicator. However,
if the instantaneous indicated airspeed exceeds 3 kt
(5.5 km/h) of the average airspeed over the 10 dB-down
points, and is determined by the FAA representative on the flight deck
to be due to atmospheric turbulence, then the flight so affected must be
rejected for noise certification purposes.
Note: Guidance material on the use of equivalent procedures is
provided in the current advisory circular for this part.
[Amdt. 36-54, 67 FR 45235, July 8, 2002; Amdt. 36-24, 67 FR 63196, Oct.
10, 2002; 68 FR 1512, Jan. 10, 2003]
Appendixes C-E to Part 36 [Reserved]
Appendix F to Part 36--Flyover Noise Requirements for Propeller-Driven
Small Airplane and Propeller-Driven, Commuter Category Airplane
Certification Tests Prior to December 22, 1988
part a--general
Sec.
F36.1 Scope.
part b--noise measurement
F36.101 General test conditions.
F36.103 Acoustical measurement system.
F36.105 Sensing, recording, and reproducing equipment.
F36.107 Noise measurement procedures.
F36.109 Data recording, reporting, and approval.
F36.111 Flight procedures.
part c--data correction
F36.201 Correction of data.
F36.203 Validity of results.
part d--noise limits
F36.301 Aircraft noise limits.
part a--general
Section F36.1 Scope. This appendix prescribes noise level limits and
procedures for measuring and correcting noise data for the propeller
driven small airplanes specified in Secs. 36.1 and 36.501(b).
part b--noise measurement
Sec. F36.101 General test conditions.
(a) The test area must be relatively flat terrain having no
excessive sound absorption characteristics such as those caused by
thick, matted, or tall grass, by shrubs, or by wooded areas. No
obstructions which significantly influence the sound field from the
airplane may exist within a conical space above the measurement
position, the cone being defined by an axis normal to the ground and by
a half-angle 75 degrees from this axis.
(b) The tests must be carried out under the following conditions:
(1) There may be no precipitation.
(2) Relative humidity may not be higher than 90 percent or lower
than 30 percent.
(3) Ambient temperature may not be above 86 degrees F. or below 41
degrees F. at 33[foot] above ground. If the measurement site is within 1
n.m. of an airport thermometer the airport reported temperature may be
used.
(4) Reported wind may not be above 10 knots at 33[foot] above
ground. If wind velocities of more than 4 knots are reported, the flight
direction must be aligned to within 15 degrees of wind
direction and flights with tail wind and head wind must be made in equal
numbers. If the measurement site is within 1 n.m. of an airport
anemometer, the airport reported wind may be used.
(5) There may be no temperature inversion or anomalous wind
conditions that would significantly alter the noise level of the
airplane when the noise is recorded at the required measuring point.
(6) The flight test procedures, measuring equipment, and noise
measurement procedures must be approved by the FAA.
(7) Sound pressure level data for noise evaluation purposes must be
obtained with acoustical equipment that complies with section F36.103 of
this appendix.
Sec. F36.103 Acoustical measurement system. The acoustical measurement
system must consist of approved equipment equivalent to the following:
(a) A microphone system with frequency response compatible with
measurement and analysis system accuracy as prescribed in section
F36.105 of this appendix.
(b) Tripods or similar microphone mountings that minimize
interference with the sound being measured.
(c) Recording and reproducing equipment characteristics, frequency
response, and dynamic range compatible with the response
[[Page 846]]
and accuracy requirements of section F36.105 of this appendix.
(d) Acoustic calibrators using sine wave or broadband noise of known
sound pressure level. If broadband noise is used, the signal must be
described in terms of its average and maximum root-mean-square (rms)
value for nonoverload signal level.
Sec. F36.105 Sensing, recording, and reproducing equipment.
(a) The noise produced by the airplane must be recorded. A magnetic
tape recorder is acceptable.
(b) The characteristics of the system must comply with the
recommendations in International Electrotechnical Commission (IEC)
Publication No. 179, entitled ``Precision Sound Level Meters'' as
incorporated by reference in Part 36 under Sec. 36.6 of this part.
(c) The response of the complete system to a sensibly plane
progressive sinusoidal wave of constant amplitude must lie within the
tolerance limits specified in IEC Publication No. 179, dated 1973, over
the frequency range 45 to 11,200 Hz.
(d) If limitations of the dynamic range of the equipment make it
necessary, high frequency pre-emphasis must be added to the recording
channel with the converse de-emphasis on playback. The pre-emphasis must
be applied such that the instantaneous recorded sound pressure level of
the noise signal between 800 and 11,200 Hz does not vary more than 20 dB
between the maximum and minimum one-third octave bands.
(e) If requested by the Administrator, the recorded noise signal
must be read through an ``A'' filter with dynamic characteristics
designated ``slow,'' as defined in IEC Publication No. 179, dated 1973.
The output signal from the filter must be fed to a rectifying circuit
with square law rectification, integrated with time constants for charge
and discharge of about 1 second or 800 milliseconds.
(f) The equipment must be acoustically calibrated using facilities
for acoustic freefield calibration and if analysis of the tape recording
is requested by the Administrator, the analysis equipment shall be
electronically calibrated by a method approved by the FAA.
(g) A windscreen must be employed with microphone during all
measurements of aircraft noise when the wind speed is in excess of 6
knots.
Sec. F36.107 Noise measurement procedures.
(a) The microphones must be oriented in a known direction so that
the maximum sound received arrives as nearly as possible in the
direction for which the microphones are calibrated. The microphone
sensing elements must be approximately 4[foot] above ground.
(b) Immediately prior to and after each test; a recorded acoustic
calibration of the system must be made in the field with an acoustic
calibrator for the two purposes of checking system sensitivity and
providing an acoustic reference level for the analysis of the sound
level data.
(c) The ambient noise, including both acoustical background and
electrical noise of the measurement systems, must be recorded and
determined in the test area with the system gain set at levels that will
be used for aircraft noise measurements. If aircraft sound pressure
levels do not exceed the background sound pressure levels by at least 10
dB(A), approved corrections for the contribution of background sound
pressure level to the observed sound pressure level must be applied.
Sec. F36.109 Data recording, reporting, and approval.
(a) Data representing physical measurements or corrections to
measured data must be recorded in permanent form and appended to the
record except that corrections to measurements for normal equipment
response deviations need not be reported. All other corrections must be
approved. Estimates must be made of the individual errors inherent in
each of the operations employed in obtaining the final data.
(b) Measured and corrected sound pressure levels obtained with
equipment conforming to the specifications described in section F36.105
of this appendix must be reported.
(c) The type of equipment used for measurement and analysis of all
acoustic, airplane performance, and meteorological data must be
reported.
(d) The following atmospheric data, measured immediately before,
after, or during each test at the observation points prescribed in
section F36.101 of this appendix must be reported:
(1) Air temperature and relative humidity.
(2) Maximum, minimum, and average wind velocities.
(e) Comments on local topography, ground cover, and events that
might interfere with sound recordings must be reported.
(f) The following airplane information must be reported:
(1) Type, model and serial numbers (if any) of airplanes, engines,
and propellers.
(2) Any modifications or nonstandard equipment likely to affect the
noise characteristics of the airplane.
(3) Maximum certificated takeoff weights.
(4) Airspeed in knots for each overflight of the measuring point.
(5) Engine performance in terms of revolutions per minute and other
relevant parameters for each overflight.
(6) Aircraft height in feet determined by a calibrated altimeter in
the aircraft, approved photographic techniques, or approved tracking
facilities.
[[Page 847]]
(g) Aircraft speed and position and engine performance parameters
must be recorded at an approved sampling rate sufficient to ensure
compliance with the test procedures and conditions of this appendix.
Sec. F36.111 Flight procedures.
(a) Tests to demonstrate compliance with the noise level
requirements of this appendix must include at least six level flights
over the measuring station at a height of 1,000[foot]
30[foot] and 10 degrees from the zenith when
passing overhead.
(b) Each test over flight must be conducted:
(1) At not less than the highest power in the normal operating range
provided in an Airplane Flight Manual, or in any combination of approved
manual material, approved placard, or approved instrument markings; and
(2) At stabilized speed with propellers synchronized and with the
airplane in cruise configuration, except that if the speed at the power
setting prescribed in this paragraph would exceed the maximum speed
authorized in level flight, accelerated flight is acceptable.
part c--data correction
Sec. F36.201 Correction of data.
(a) Noise data obtained when the temperature is outside the range of
68 degrees F. 9 degrees F., or the relative humidity is
below 40 percent, must be corrected to 77 degrees F. and 70 percent
relative humidity by a method approved by the FAA.
(b) The performance correction prescribed in paragraph (c) of this
section must be used. It must be determined by the method described in
this appendix, and must be added algebraically to the measured value. It
is limited to 5dB(A).
(c) The performance correction must be computed by using the
following formula:
[GRAPHIC] [TIFF OMITTED] TC28SE91.113
Where:
D50=Takeoff distance to 50 feet at maximum certificated
takeoff weight.
R/C=Certificated best rate of climb (fpm).
Vy=Speed for best rate of climb in the same units as rate of climb.
(d) When takeoff distance to 50[foot] is not listed as approved
performance information, the figures of 2000 for single-engine airplanes
and 1600[foot] for multi-engine airplanes must be used.
Sec. F36.203 Validity of results.
(a) The test results must produce an average dB(A) and its 90
percent confidence limits, the noise level being the arithmetic average
of the corrected acoustical measurements for all valid test runs over
the measuring point.
(b) The samples must be large enough to establish statistically a 90
pecent confidence limit not to exceed 1.5 dB(A). No test
result may be omitted from the averaging process, unless omission is
approved by the FAA.
part d--noise limits
Sec. F36.301 Aircraft noise limits.
(a) Compliance with this section must be shown with noise data
measured and corrected as prescribed in Parts B and C of this appendix.
(b) For airplanes for which application for a type certificate is
made on or after October 10, 1973, the noise level must not exceed 68
dB(A) up to and including aircraft weights of 1,320 pounds (600 kg.).
For weights greater than 1,320 pounds up to and including 3,630 pounds
(1.650 kg.) the limit increases at the rate of 1 dB/165 pounds (1 dB/75
kg.) to 82 dB(A) at 3,630 pounds, after which it is constant at 82
dB(A). However, airplanes produced under type certificates covered by
this paragraph must also meet paragraph (d) of this section for the
original issuance of standard airworthiness certificates or restricted
category airworthiness certificates if those airplanes have not had
flight time before the date specified in that paragraph.
(c) For airplanes for which application for a type certificate is
made on or after January 1, 1975, the noise levels may not exceed the
noise limit curve prescribed in paragraph (b) of this section, except
that 80 dB(A) may not be exceeded.
(d) For airplanes for which application is made for a standard
airworthiness certificate or for a restricted category airworthiness
certificate, and that have not had any flight time before January 1,
1980, the requirements of paragraph (c) of this section apply,
regardless of date of application, to the
[[Page 848]]
original issuance of the certificate for that airplane.
[Doc. No. 13243, 40 FR 1035, Jan. 6, 1975; 40 FR 6347, Feb. 11, 1975, as
amended by Amdt. 36-6, 41 FR 56064, Dec. 23, 1976; Amdt. 36-6, 42 FR
4113, Jan. 24, 1977; Amdt. 36-9, 43 FR 8754, Mar. 2, 1978; Amdt. 36-13,
52 FR 1836, Jan. 15, 1987; Amdt. 36-16, 53 FR 47400, Nov. 22, 1988]
Appendix G to Part 36--Takeoff Noise Requirements for Propeller-Driven
Small Airplane and Propeller-Driven, Commuter Category Airplane
Certification Tests on or After December 22, 1988
part a--general
Sec.
G36.1 Scope.
part b--noise measurement
G36.101 General Test Conditions.
G36.103 Acoustical measurement system.
G36.105 Sensing, recording, and reproducing equipment.
G36.107 Noise measurement procedures.
G36.109 Data recording, reporting, and approval.
G36.111 Flight procedures.
part c--data corrections
G36.201 Corrections to Test Results.
G36.203 Validity of results.
part d--noise limits
G36.301 Aircraft Noise Limits.
part a--general
Section G36.1 Scope. This appendix prescribes limiting noise levels and
procedures for measuring noise and adjusting these data to standard
conditions, for propeller driven small airplanes and propeller-driven,
commuter category airplanes specified in Secs. 36.1 and 36.501(c).
part b--noise measurement
Sec. G36.101 General Test Conditions.
(a) The test area must be relatively flat terrain having no
excessive sound absorption characteristics such as those caused by
thick, matted, or tall grass, by shrubs, or by wooded areas. No
obstructions which significantly influence the sound field from the
airplane may exist within a conical space above the measurement
position, the cone being defined by an axis normal to the ground and by
a half-angle 75 degrees from the normal ground axis.
(b) The tests must be carried out under the following conditions:
(1) No precipitation;
(2) Ambient air temperature between 36 and 95 degrees F (2.2 and 35
degrees C);
(3) Relative humidity between 20 percent and 95 percent,
inclusively;
(4) Wind speed may not exceed 10 knots (19 km/h) and cross wind may
not exceed 5 knots (9 km/h), using a 30-second average;
(5) No temperature inversion or anomalous wind condition that would
significantly alter the noise level of the airplane when the nose is
recorded at the required measuring point, and
(6) The meteorological measurements must be made between 4 ft. (1.2
m) and 33 ft. (10 m) above ground level. If the measurement site is
within 1 n.m. of an airport meteorological station, measurements from
that station may be used.
(c) The flight test procedures, measuring equipment, and noise
measurement procedures must be approved by the FAA.
(d) Sound pressure level data for noise evaluation purposes must be
obtained with acoustical equipment that complies with section G36.103 of
this appendix.
Sec. G36.103 Acoustical Measurement System.
The acoustical measurement system must consist of approved equipment
with the following characteristics: (a) A microphone system with
frequency response compatible with measurement and analysis system
accuracy as prescribed in section G36.105 of this appendix.
(b) Tripods or similar microphone mountings that minimize
interference with the sound being measured.
(c) Recording and reproducing equipment characteristics, frequency
response, and dynamic range compatible with the response and accuracy
requirements of section G36.105 of this appendix.
(d) Acoustic calibrators using sine wave or broadband noise of known
sound pressure level. If broadband noise is used, the signal must be
described in terms of its average and maximum root-mean-square (rms)
value for non-overload signal level.
Sec. G36.105 Sensing, Recording, and Reproducing Equipment.
(a) The noise produced by the airplane must be recorded. A magnetic
tape recorder, graphic level recorder, or sound level meter is
acceptable when approved by the regional certificating authority.
(b) The characteristics of the complete system must comply with the
requirements in International Electrotechnical Commission (IEC)
Publications No. 651, entitled ``Sound Level Meters'' and No. 561,
entitled ``Electro-acoustical Measuring Equipment for Aircraft Noise
Certification'' as incorporated by reference under Sec. 36.6 of this
part. Sound level meters must comply with the requirements for Type 1
sound level meters as specified in IEC Publication No. 651.
[[Page 849]]
(c) The response of the complete system to a sensibly plane
progressive sinusoidal wave of constant amplitude must be within the
tolerance limits specified in IEC Publication No. 651, over the
frequency range 45 to 11,200 Hz.
(d) If equipment dynamic range limitations make it necessary, high
frequency pre-emphasis must be added to the recording channel with the
converse de-emphasis on playback. The pre-emphasis must be applied such
that the instantaneous recorded sound pressure level of the noise signal
between 800 and 11,200 Hz does not vary more than 20 dB between the
maximum and minimum one-third octave bands.
(e) The output noise signal must be read through an ``A'' filter
with dynamic characteristics designated ``slow'' as defined in IEC
Publication No. 651. A graphic level recorder, sound level meter, or
digital equivalent may be used.
(f) The equipment must be acoustically calibrated using facilities
for acoustic free-field calibration and if analysis of the tape
recording is requested by the Administrator, the analysis equipment
shall be electronically calibrated by a method approved by the FAA.
Calibrations shall be performed, as appropriate, in accordance with
paragraphs A36.3.8 and A36.3.9 of appendix A of this part.
(g) A windscreen must be employed with the microphone during all
measurements of aircraft noise when the wind speed is in excess of 5
knots (9 km/hr).
Sec. G36.107 Noise Measurement Procedures.
(a) The microphone must be a pressure type, 12.7 mm in diameter,
with a protective grid, mounted in an inverted position such that the
microphone diaphragm is 7 mm above and parallel to a white-painted metal
circular plate. This white-painted metal plate shall be 40 cm in
diameter and at least 2.5 mm thick. The plate shall be placed
horizontally and flush with the surrounding ground surface with no
cavities below the plate. The microphone must be located three-quarters
of the distance from the center to the back edge of the plate along a
radius normal to the line of flight of the test airplane.
(b) Immediately prior to and after each test, a recorded acoustic
calibration of the system must be made in the field with an acoustic
calibrator for the purposes of checking system sensitivity and providing
an acoustic reference level for the analysis of the sound level data. If
a tape recorder or graphic level recorder is used, the frequency
response of the electrical system must be determined at a level within
10 dB of the full-scale reading used during the test, utilizing pink or
pseudorandom noise.
(c) The ambient noise, including both acoustic background and
electrical systems noise, must be recorded and determined in the test
area with the system gain set at levels which will be used for aircraft
noise measurements. If aircraft sound pressure levels do not exceed the
background sound pressure levels by at least 10 dB(A), a takeoff
measurement point nearer to the start of the takeoff roll must be used
and the results must be adjusted to the reference measurement point by
an approved method.
Sec. G36.109 Data Recording, Reporting, and Approval.
(a) Data representing physical measurements and adjustments to
measured data must be recorded in permanent form and appended to the
record, except that corrections to measurements for normal equipment
response deviations need not be reported. All other adjustments must be
approved. Estimates must be made of the individual errors inherent in
each of the operations employed in obtaining the final data.
(b) Measured and corrected sound pressure levels obtained with
equipment conforming to the specifications in section G36.105 of this
appendix must be reported.
(c) The type of equipment used for measurement and analysis of all
acoustical, airplane performance, and meteorological data must be
reported.
(d) The following atmospheric data, measured immediately before,
after, or during each test at the observation points prescribed in
section G36.101 of this appendix must be reported:
(1) Ambient temperature and relative humidity.
(2) Maximum and average wind speeds and directions for each run.
(e) Comments on local topography, ground cover, and events that
might interfere with sound recordings must be reported.
(f) The aircraft position relative to the takeoff reference flight
path must be determined by an approved method independent of normal
flight instrumentation, such as radar tracking, theodolite
triangulation, or photographic scaling techniques.
(g) The following airplane information must be reported:
(1) Type, model, and serial numbers (if any) of airplanes, engines,
and propellers;
(2) Any modifications or nonstandard equipment likely to affect the
noise characteristics of the airplane;
(3) Maximum certificated takeoff weight;
(4) For each test flight, airspeed and ambient temperature at the
flyover altitude over the measuring site determined by properly
calibrated instruments;
(5) For each test flight, engine performance parameters, such as
manifold pressure or power, propeller speed (rpm) and other relevant
parameters. Each parameter must be determined by properly calibrated
instruments. For instance, propeller RPM must be validated by an
independent device accurate
[[Page 850]]
to within 1 percent, when the airplane is equipped with a
mechanical tachometer.
(6) Airspeed, position, and performance data necessary to make the
corrections required in section G36.201 of this appendix must be
recorded by an approved method when the airplane is directly over the
measuring site.
Sec. G36.111 Flight Procedures.
(a) The noise measurement point is on the extended centerline of the
runway at a distance of 8200 ft (2500 m) from the start of takeoff roll.
The aircraft must pass over the measurement point within 10
degrees from the vertical and within 20% of the reference altitude. The
flight test program shall be initiated at the maximum approved takeoff
weight and the weight shall be adjusted back to this maximum weight
after each hour of flight time. Each flight test must be conducted at
the speed for the best rate of climb (Vy) 5 knots
(9 km/hour) indicated airspeed. All test, measurement, and
data correction procedures must be approved by the FAA.
(b) The takeoff reference flight path must be calculated for the
following atmospheric conditions:
(1) Sea level atmospheric pressure of 1013.25 mb (013.25 hPa);
(2) Ambient air temperature of 59 deg.F (15 deg.C);
(3) Relative humidity of 70 percent; and
(4) Zero wind.
(c) The takeoff reference flight path must be calculated assuming
the following two segments:
(1) First segment.
(i) Takeoff power must be used from the brake release point to the
point at which the height of 50 ft (15m) above the runway is reached.
(ii) A constant takeoff configuration selected by the applicant must
be maintained through this segment.
(iii) The maximum weight of the airplane at brake-release must be
the maximum for which noise certification is requested.
(iv) The length of this first segment must correspond to the
airworthiness approved value for a takeoff on a level paved runway (or
the corresponding value for seaplanes).
(2) Second segment.
(i) The beginning of the second segment corresponds to the end of
the first segment.
(ii) The airplane must be in the climb configuration with landing
gear up, if retractable, and flap setting corresponding to normal climb
position throughout this second segment.
(iii) The airplane speed must be the speed for the best rate of
climb (Vy).
(iv) Maximum continuous installed power and rpm for variable pitch
propeller(s) shall be used. For fixed pitch propeller(s), the maximum
power and rpm that can be delivered by the engine(s) must be maintained
throughout the second segment.
part c--data corrections
Sec. G36.201 Corrections to Test Results.
(a) These corrections account for the effects of:
(1) Differences in atmospheric absorption of sound between
meteorological test conditions and reference conditions.
(2) Differences in the noise path length between the actual airplane
flight path and the reference flight path.
(3) The change in the helical tip Mach number between test and
reference conditions.
(4) The change in the engine power between test and reference
conditions.
(b) Atmospheric absorption correction is required for noise data
obtained when the test conditions are outside those specified in Figure
G1. Noise data outside the applicable range must be corrected to 59 F
and 70 percent relative humidity by an FAA approved method.
[[Page 851]]
[GRAPHIC] [TIFF OMITTED] TR13OC99.001
(c) Helical tip Mach number and power corrections must be made as
follows:
(1) Corrections for helical tip Mach number and power corrections
must be made if--
(i) The propeller is a variable pitch type; or
(ii) The propeller is a fixed pitch type and the test power is not
within 5 percent of the reference power.
(2) No corrections for helical tip Mach number variation need to be
made if the propeller helical tip Mach number is:
(i) At or below 0.70 and the test helical tip Mach number is within
0.014 of the reference helical tip Mach number.
(ii) Above 0.70 and at or below 0.80 and the test helical tip Mach
number is within 0.007 of the reference helical tip Mach number.
(iii) Above 0.80 and the test helical tip Mach number is within
0.005 of the reference helical tip Mach number. For mechanical
tachometers, if the helical tip Mach number is above 0.8 and the test
helical tip Mach number is within 0.008 of the reference helical tip
Mach number.
(d) When the test conditions are outside those specified,
corrections must be applied by an approved procedure or by the following
simplified procedure:
(1) Measured sound levels must be corrected from test day
meteorological conditions to reference conditions by adding an increment
equal to
Delta (M)=(HT [alpha]--0.7 HR)/1000
where HT is the height in feet under test conditions,
HR is the height in feet under reference conditions when the
aircraft is directly over the noise measurement point and [alpha] is the
rate of absorption for the test day conditions at 500 Hz as specified in
SAE ARP 866A, entitled ``Standard Values of Atmospheric Absorption as a
function of Temperature and Humidity for use in Evaluating Aircraft
Flyover Noise'' as incorporated by reference under Sec. 36.6.
(2) Measured sound levels in decibels must be corrected for height
by algebraically adding an increment equal to Delta (1). When test day
conditions are within those specified in figure G1:
Delta (1)=22 log (HT/HR)
where HT is the height of the test aircraft when directly
over the noise measurement point and HR is the reference
height.
When test day conditions are outside those specified in figure G1:
Delta (1)=20 log (HT/HR)
(3) Measured sound levels in decibels must be corrected for helical
tip Mach number by algebraically adding an increment equal to:
Delta (2)=k log (MR/MT)
where MT and MR are the test and reference helical
tip Mach numbers, respectively. The constant ``k'' is equal to the slope
of
[[Page 852]]
the line obtained for measured values of the sound level in dB(A) versus
helical tip Mach number. The value of k may be determined from approved
data. A nominal value of k=150 may be used when MT is smaller
than MR. No correction may be made using the nominal value of
k when MT is larger than MR. The reference helical
tip Mach number MR is the Mach number corresponding to the
reference conditions (RPM, airspeed, temperature) above the measurement
point.
(4) Measured sound levels in decibels must be corrected for engine
power by algebraically adding an increment equal to
Delta (3)=K3 log (PR/PT)
where PR and PT are the test and reference engine
powers respectively obtained from the manifold pressure/torque gauges
and engine rpm. The value of K3 shall be determined from
approved data from the test airplane. In the absence of flight test data
and at the discretion of the Administrator, a value of K3=17
may be used.
Sec. G36.203 Validity of Results.
(a) The measuring point must be overflown at least six times. The
test results must produce an average noise level (LAmax)
value within a 90 percent confidence limit. The average noise level is
the arithmetic average of the corrected acoustical measurements for all
valid test runs over the measuring point.
(b) The samples must be large enough to establish statistically a 90
percent confidence limit not exceeding 1.5 dB(A). No test
results may be omitted from the averaging process unless omission is
approved by the FAA.
part d--noise limits
Sec. G36.301 Aircraft noise limits.
(a) Compliance with this section must be shown with noise data
measured and corrected as prescribed in Parts B and C of this appendix.
(b) The noise level must not exceed 76 dB (A) up to and including
aircraft weights of 1,320 pounds (600 kg). For aircraft weights greater
than 1,320 pounds, the limit increases from that point with the
logarithm of airplane weight at the rate of 9.83 dB (A) per doubling of
weight, until the limit of 88 dB (A) is reached, after which the limit
is constant up to and including 19,000 pounds (8,618 kg). Figure G2
shows noise level limits vs airplane weight.
[GRAPHIC] [TIFF OMITTED] TR13OC99.002
[[Page 853]]
(Secs. 313(a), 603, and 611(b), Federal Aviation Act of 1958 as amended
(49 U.S.C. 1354(a), 1423, and 1431(b)); sec. 6(c), Department of
Transportation Act (49 U.S.C. 1655 (c)); Title I, National Environmental
Policy Act of 1969 (42 U.S.C. 4321 et seq.); E. O. 11514, March 5, 1970
and 14 CFR 11.45).
[Amdt. 36-16, 53 FR 47400, Nov. 22, 1988; 53 FR 50157, Dec. 13, 1988, as
amended by Amdt. 36-22, 64 FR 55602, Oct. 13, 1999; Amdt. 36-54, 67 FR
45236, July 8, 2002]
Appendix H to Part 36--Noise Requirements For Helicopters Under Subpart
H
Part A--Reference Conditions
Sec.
H36.1 General.
H36.3 Reference Test Conditions.
H36.5 Symbols and Units.
Part B--Noise Measurement Under Sec. 36.801
H36.101 Noise certification test and measurement conditions.
H36.103 Takeoff test conditions.
H36.105 Flyover test conditions.
H36.107 Approach test conditions.
H36.109 Measurement of helicopter noise received on the ground.
H36.111 Reporting and correcting measured data.
H36.113 Atmospheric attenuation of sound.
Part C--Noise Evaluation and Calculation Under Sec. 36.803
H36.201 Noise evaluation in EPNdB.
H36.203 Calculation of noise levels.
H36.205 Detailed data correction procedures.
Part D--Noise Limits Under Sec. 36.805
H36.301 Noise measurement, evaluation, and calculation.
H36.303 [Reserved]
H36.305 Noise levels.
Part A--Reference Conditions
Section H36.1 General. This appendix prescribes noise requirements
for helicopters specified under Sec. 36.1, including:
(a) The conditions under which helicopter noise certification tests
under Part H must be conducted and the measurement procedures that must
be used under Sec. 36.801 to measure helicopter noise during each test;
(b) The procedures which must be used under Sec. 36.803 to correct
the measured data to the reference conditions and to calculate the noise
evaluation quantity designated as Effective Perceived Noise Level
(EPNL); and
(c) The noise limits for which compliance must be shown under
Sec. 36.805.
Section H36.3 Reference Test Conditions.
(a) Meteorological conditions. Aircraft position, performance data
and noise measurements must be corrected to the following noise
certification reference atmospheric conditions which shall be assumed to
exist from the surface to the aircraft altitude:
(1) Sea level pressure of 2116 psf (76 cm mercury).
(2) Ambient temperature of 77 degrees F (25 degrees C).
(3) Relative humidity of 70 percent.
(4) Zero wind.
(b) Reference test site. The reference test site is flat and without
line-of-sight obstructions across the flight path that encompasses the
10 dB down points.
(c) Takeoff reference profile. (1) Figure H1 illustrates a typical
takeoff profile, including reference conditions.
(2) The reference flight path is defined as a straight line segment
inclined from the starting point (1640 feet prior to the center
microphone location at 65 feet above ground level) at an angle[beta]
defined by the certificated best rate of climb and Vy for
minimum engine performance. The constant climb angle [beta] is derived
from the manufacturer's data (FAA-approved by the FAA) to define the
flight profile for the reference conditions. The constant climb angle
[beta] is drawn through Cr and continues, crossing over
station A, to the position corresponding to the end of the type
certification takeoff path represented by position Ir.
(d) Level flyover reference profile. The beginning of the level
flyover reference profile is represented by helicopter position D
(Figure H2). The helicopter approaches position D in level flight 492
feet above ground level as measured at station A. Airspeed is stabilized
at either 0.9 VH or 0.45 VH + 65 knots (0.45
VH + 120 km/hr), whichever speed is less. Rotor speed is
stabilized at the maximum continuous RPM throughout the 10 dB down time
period. The helicopter crosses station A in level flight and proceeds to
position J.
(e) For noise certification purposes, VH is defined as
the airspeed in level flight obtained using the minimum specification
engine torque corresponding to maximum continuous power available for
sea level, 25 deg.C ambient conditions at the relevant maximum
certificated weight. The value of VH thus defined must be
listed in the Rotorcraft Flight Manual.
(f) Approach reference profile. (1) Figure H3 illustrates approach
profile, including reference conditions.
(i) The beginning of the approach profile is represented by
helicopter position E. The position of the helicopter is recorded for a
sufficient distance (EK) to ensure recording of the entire interval
during which the measured helicopter noise level is within 10 dB of
Maximum Tone Corrected Perceived Noise Level (PNLTM), as required. EK
represents a stable flight condition in terms of torque, rpm, indicated
airspeed, and rate of descent resulting in a 6 deg. 0.5 deg.
approach angle.
[[Page 854]]
(ii) The approach profile is defined by the approach angle [beta]
passing directly over the station A at a height of AH, to position K,
which terminates the approach noise certification profile.
(2) The helicopter approaches position H along a constant 6 deg.
approach slope throughout the 10 dB down time period. The helicopter
crosses position E and proceeds along the approach slope crossing over
station A until it reaches position K.
Section H36.5 Symbols and units. The following symbols and units as
used in this appendix for helicopter noise certification have the
following meanings.
Flight Profile Identification--Positions
------------------------------------------------------------------------
Position Description
------------------------------------------------------------------------
A......................... Location of the noise measuring point at the
flight-track noise measuring station
vertically below the reference (takeoff,
flyover, or approach) flight path.
C......................... Start of noise certification takeoff flight
path.
Cr........................ Start of noise certification reference
takeoff flight path.
D......................... Start of noise certification flyover flight
path.
Dr........................ Start of noise certification reference
flyover path.
E......................... Start of noise certification approach flight
path.
Er........................ Start of noise certification reference
approach flight path.
F......................... Position on takeoff flight path directly
above noise measuring station A.
G......................... Position on flyover flight path directly
above noise measuring station A.
H......................... Position on approach flight path directly
above noise measuring station A.
I......................... End of noise type certification takeoff
flight path.
Ir........................ End of noise type certification reference
takeoff flight path.
J......................... End of noise type certification flyover
flight path.
Jr........................ End of noise type certification reference
flyover flight path.
K......................... End of noise certification approach type
flight path.
Kr........................ End of noise type certification reference
approach flight path.
L......................... Position on measured takeoff flight path
corresponding to PNLTM at station A.
Lr........................ Position on reference takeoff flight path
corresponding to PNLTM of station A.
M......................... Position on measured flyover flight path
corresponding to PNLTM of station A.
Mr........................ Position on reference flyover flight path
corresponding to PNLTM of station A.
N......................... Position on measured approach flight path
corresponding to PNLTM at station A.
Nr........................ Position on reference approach flight path
corresponding to PNLTM at station A.
S......................... Position on measured approach path nearest
to station A.
Sr........................ Position on reference approach path nearest
to station A.
T......................... Position on measured takeoff path nearest to
station A.
Tr........................ Position on reference takeoff path nearest
to station A.
------------------------------------------------------------------------
Flight Profile Distances
------------------------------------------------------------------------
Distance Unit Meaning
------------------------------------------------------------------------
AF................. Feet........... Takeoff Height. The vertical
distance between helicopter and
station A.
AG................. Feet........... Flyover Height. The vertical
distance between the helicopter
and station A.
AH................. Feet........... Approach Height. The vertical
distance between the helicopter
and station A.
AL................. Feet........... Measured Takeoff Noise Path. The
distance from station A to the
measured helicopter position L.
ALr................ Feet........... Reference Takeoff Noise Path. The
distance from station A to the
reference helicopter position Lr.
AM................. Feet........... Measured Flyover Noise Path. The
distance from station A to the
measured helicopter position M.
AMr................ Feet........... Reference Flyover Noise Path. The
distance from station A to
helicopter position Mr on the
reference flyover flight path.
AN................. Feet........... Measured Approach Noise Path. The
distance from station A to the
measured helicopter noise
position N.
ANr................ Feet........... Reference Approach Noise Path. The
distance from station A to the
reference helicopter position Nr.
AS................. Feet........... Measured Approach Minimum
Distance. The distance from
station A to the position S on
the measured approach flight
path.
ASr................ Feet........... Reference Approach Minimum
Distance. The distance from
station A to the position Sr on
the reference approach flight
path.
AT................. Feet........... Measured Takeoff Minimum Distance.
The distance from station A to
the position T on the measured
takeoff flight path.
ATr................ Feet........... Reference Takeoff Minimum
Distance. The distance from
station A to the position Tr on
the reference takeoff flight
path.
CI................. Feet........... Takeoff Flight Path Distance. The
distance from position C at which
the helicopter establishes a
constant climb angle on the
takeoff flight path passing over
station A and continuing to
position I at which the position
of the helicopter need no longer
be recorded.
DJ................. Feet........... Flyover Flight Path Distance. The
distance from position D at which
the helicopter is established on
the flyover flight path passing
over station A and continuing to
position J at which the position
of the helicopter need no longer
be recorded.
EK................. Feet........... Approach Flight Path Distance. The
distance from position E at which
the helicopter establishes a
constant angle on the approach
flight path passing over station
A and continuing to position K at
which the position of the
helicopter need no longer be
recorded.
------------------------------------------------------------------------
Part B--Noise Measurement Under Sec. 36.801
Section H36.101 Noise certification test and measurement conditions.
(a) General. This section prescribes the conditions under which
aircraft noise certification tests must be conducted and the measurement
procedures that must be used to measure helicopter noise during each
test.
(b) Test site requirements. (1) Tests to show compliance with
established helicopter noise certification levels must consist of a
series of takeoffs, level flyovers, and approaches during which
measurement must be taken at
[[Page 855]]
noise measuring stations located at the measuring points prescribed in
this section.
(2) Each takeoff test, flyover test, and approach test includes
simultaneous measurements at the flight-track noise measuring station
vertically below the reference flight path and at two sideline noise
measuring stations, one on each side of the reference flight track 492
feet (150m) from, and on a line perpendicular to, the flight track of
the noise measuring station.
(3) The difference between the elevation of either sideline noise
measuring station may not differ from the flight-track noise measuring
station by more than 20 feet.
(4) Each noise measuring station must be surrounded by terrain
having no excessive sound absorption characteristics, such as might be
caused by thick, matted, or tall grass, shrubs, or wooded areas.
(5) During the period when the takeoff, flyover, or approach noise/
time record indicates the noise measurement is within 10 dB of PNLTM, no
obstruction that significantly influences the sound field from the
aircraft may exist--
(i) For any flight-track or sideline noise measuring station, within
a conical space above the measuring position (the point on the ground
vertically below the microphone), the cone being defined by an axis
normal to the ground and by half-angle 80 deg. from this axis; and
(ii) For any sideline noise measuring station, above the line of
sight between the microphone and the helicopter.
(6) If a takeoff or flyover test series is conducted at weights
other than the maximum takeoff weight for which noise certification is
requested, the following additional requirements apply:
(i) At least one takeoff test must be conducted at a weight at, or
above, the maximum certification weight.
(ii) Each test weight must be within +5 percent or -10 percent of
the maximum certification weight.
(iii) FAA-approved data must be used to determine the variation of
EPNL with weight for takeoff test conditions.
(7) Each approach test must be conducted with the aircraft
stabilized and following a 6.0 degree 0.5 degree approach
angle and must meet the requirements of section H36.107 of this part.
(8) If an approach test series is conducted at weights other than
the maximum landing weight for which certification is requested, the
following additional requirements apply:
(i) At least one approach test must be conducted at a weight at, or
above, the maximum landing weight.
(ii) Each test weight must exceed 90 percent of the maximum landing
weight.
(iii) FAA-approved data must be used to determine the variation of
EPNL with weight for approach test conditions.
(9) Aircraft performance data sufficient to make the corrections
required under section H36.205 of this appendix must be recorded at an
FAA-approved sampling rate using FAA approved equipment.
(c) Weather restrictions. The tests must be conducted under the
following atmospheric conditions:
(1) No rain or other precipitation.
(2) Ambient air temperature between 36 deg.F and 95 deg.F (2.2
deg.C and 35 deg.C), inclusively, over that portion of the sound
propagation path between the aircraft and a point 10 meters above the
ground at the noise measuring station. The temperature and relative
humidity measured at aircraft altitude and at 10 meters above ground
shall be averaged and used to adjust for propagation path absorption.
(3) Relative humidity and ambient temperature over the portion of
the sound propagation path between the aircraft and a point 10 meters
above the ground at the noise measuring station is such that the sound
attenuation in the one-third octave band centered at 8 kHz is not
greater than 12 dB/100 meters and the relative humidity is between 20
percent and 95 percent, inclusively.
(4) Wind velocity as measured at 10 meters above ground does not
exceed 10 knots (19 km/h) and the crosswind component does not exceed 5
knots (9 km/h). The wind shall be determined using a continuous thirty-
second averaging period spanning the 10dB down time interval.
(5) No anomalous wind conditions (including turbulence) which will
significantly affect the noise level of the aircraft when the noise is
recorded at each noise measuring station.
(6) The wind velocity, temperature, and relative humidity
measurements required under the appendix must be measured in the
vicinity of noise measuring stations 10 meters above the ground. The
location of the meteorological measurements must be approved by the FAA
as representative of those atmospheric conditions existing near the
surface over the geographical area which aircraft noise measurements are
made. In some cases, a fixed meteorological station (such as those found
at airports or other facilities) may meet this requirement.
(7) Temperature and relative humidity measurements must be obtained
within 25 minutes of each noise test measurement. Meteorological data
must be interpolated to actual times of each noise measurement.
(d) Aircraft testing procedures. (1) The aircraft testing procedures
and noise measurements must be conducted and processed in a manner which
yields the noise evaluation measure designated as Effective Perceived
Noise Level (EPNL) in units of EPNdB, as prescribed in appendix A of
this part.
(2) The aircraft height and lateral position relative to the
centerline of the reference flight-track (which passes through the noise
[[Page 856]]
measuring point) must be determined by an FAA approved method which is
independent of normal flight instrumentation, such as radar tracking,
theodolite triangulation, laser trajectography, or photographic scaling
techniques.
(3) The aircraft position along the flight path must be related to
the noise recorded at the noise measuring stations by means of
synchronizing signals at an approved sampling rate. The position of the
aircraft must be recorded relative to the runway during the entire time
period in which the recorded signal is within 10 dB of PNLTM. Measuring
and sampling equipment must be approved by the FAA.
Section H36.103 Takeoff test conditions.
(a) This section, in addition to the applicable requirements of
sections H36.101 and H36.205(b) of this appendix, applies to all takeoff
noise tests conducted under this appendix to show compliance with Part
36.
(b) A test series must consist of at least six flights over the
flight-track noise measuring station (with simultaneous measurements at
all three noise measuring stations) as follows:
(1) An airspeed of either Vy5 knots or the
lowest approved speed 5 knots for the climb after takeoff,
whichever speed is greater, must be established during the horizontal
portion of each test flight and maintained during the remainder of the
test flight.
(2) The horizontal portion of each test flight must be conducted at
an altitude of 65 feet (20 meters) above the ground level at the flight-
track noise measuring station.
(3) Upon reaching a point 1,640 feet (500 meters) from the noise
measuring station, the helicopter shall be stabilized at:
(i) The torque used to establish the takeoff distance for an ambient
temperature at sea level of 25 deg.C for helicopters for which the
determination of takeoff performance is required by airworthiness
regulations; or
(ii) The torque corresponding to minimum installed power available
for an ambient temperature at sea level of 25 deg.C for all other
helicopters.
(4) The helicopter shall be maintained throughout the takeoff
reference procedure at:
(i) The speed used 5 knots to establish takeoff distance
for an ambient temperature at sea level of 25 deg.C for helicopters for
which the determination of takeoff performance is required by
airworthiness regulations; or
(ii) The best rate of climb speed Vy5 knots,
or the lowest approved speed for climb after takeoff, whichever is
greater, for an ambient temperature at sea level of 25 deg.C for all
other helicopters.
(5) The rotor speed must be stabilized at the normal operating RPM
(1%) during the entire period of the test flight when the
measured helicopter noise level is within 10 dB of PNLTM.
(6) The helicopter must pass over the flight-track noise measuring
station within 10 deg. from the zenith.
Section H36.105 Flyover test conditions.
(a) This section, in addition to the applicable requirements of
sections H36.101 and H36.205(c) of this appendix, applies to all flyover
noise tests conducted under this appendix to show compliance with Part
36.
(b) A test series must consist of at least six flights (three in
each direction) over the flight-track noise measuring station (with
simultaneous measurements at all three noise measuring stations)--
(1) In level flight;
(2) At a height of 492 feet 30 feet (1509
meters) above the ground level at the flight-track noise measuring
station; and
(3) Within 5 deg. from the zenith.
(c) Each flyover noise test must be conducted--
(1) At a speed of 0.9 VH or 0.45 VH+120 km/hr
(0.45 VH+65 kt), whichever is less, maintained throughout the
measured portion of the flyover;
(2) At rotor speed stabilized at the normal operating rotor RPM
(1 percent); and
(3) With the power stabilized during the period when the measured
helicopter noise level is within 10 dB of PNLTM.
(d) The airspeed shall not vary from the reference airspeed by more
than 5 knots (9 km/hr).
Section H36.107 Approach test conditions.
(a) This section, in addition to the requirements of sections
H36.101 and H36.205(d) of this appendix, applies to all approach tests
conducted under this appendix to show compliance with Part 36.
(b) A test series must consist of at least six flights over the
flight-track noise measuring station (with simultaneous measurements at
the three noise measuring stations)--
(1) On an approach slope of 6 deg.0.5 deg.;
(2) At a height of 39430 feet (1209 meters)
above the ground level at the flight-track noise measuring station;
(3) Within 10 deg. of the zenith;
(4) At stabilized airspeed equal to the certificated best rate of
climb Vy, or the lowest approved speed for approach,
whichever is greater, with power stabilized during the approach and over
the flight path reference point, and continued to a normal touchdown;
and
(5) At rotor speed stabilized at the maximum normal operating rotor
RPM (1 percent).
(c) The airspeed shall not vary from the reference airspeed by more
than 5 knots (9 km/hr).
Section H36.109 Measurement of helicopter noise received on the
ground.
(a) General. (1) The measurements prescribed in this section provide
the data needed to determine the one-third octave band noise produced by
an aircraft during testing,
[[Page 857]]
at specific noise measuring stations, as a function of time.
(2) Sound pressure level data for aircraft noise certification
purposes must be obtained with FAA-approved acoustical equipment and
measurement practices.
(3) Paragraphs (b), (c), and (d) of this section prescribe the
required equipment specifications. Paragraphs (e) and (f) prescribe the
calibration and measurement procedures required for each certification
test series.
(b) Measurement system. The acoustical measurement system must
consist of FAA-approved equipment equivalent to the following:
(1) A microphone system with frequency response and directivity
which are compatible with the measurement and analysis system accuracy
prescribed in paragraph (c) of this section.
(2) Tripods or similar microphone mountings that minimize
interference with the sound energy being measured.
(3) Recording and reproducing equipment, the characteristics,
frequency response, and dynamic range of which are compatible with the
response and accuracy requirements of paragraph (c) of this section.
(4) Calibrators using sine wave, or pink noise, of known levels.
When pink noise (defined in paragraph (e)(1) of this section) is used,
the signal must be described in terms of its root-mean-square (rms)
value.
(5) Analysis equipment with the response and accuracy which meets or
exceeds the requirements of paragraph (d) of this section.
(6) Attenuators used for range changing in sensing, recording,
reproducing, or analyzing aircraft sound must be capable of being
operated in equal-interval decibel steps with no error between any two
settings which exceeds 0.2 dB.
(c) Sensing, recording, and reproducing equipment. (1) The sound
produced by the aircraft must be recorded in such a way that the
complete information, including time history, is retained. A magnetic
tape recorder is acceptable.
(2) The microphone must be a pressure-sensitive capacitive type, or
its FAA-approved equivalent, such as a free-field type with incidence
corrector.
(i) The variation of microphone and preamplifier system sensitivity
within an angle of 30 degrees of grazing (60-120 degrees
from the normal to the diaphragm) must not exceed the following values:
------------------------------------------------------------------------
Change in
Frequency (Hz) sensitivity
(dB)
------------------------------------------------------------------------
45 to 1,120............................................. 1
1,120 to 2,240.......................................... 1.5
2,240 to 4,500.......................................... 2.5
4,500 to 7,100.......................................... 4
7,100 to 11,200......................................... 5
------------------------------------------------------------------------
With the windscreen in place, the sensitivity variation in the plane of
the microphone diaphragm shall not exceed 1.0 dB over the frequency
range 45 to 11,200 Hz.
(ii) The overall free-field frequency response at 90 degrees
(grazing incidence) of the combined microphone (including incidence
corrector, if applicable) preamplifier, and windscreen must be
determined by using either (A) an electrostatic calibrator in
combination with manufacturer-provided corrections, or (B) an anechoic
free-field facility. The calibration unit must include pure tones at
each preferred one-third octave frequency from 50 Hz to 10,000 Hz. The
frequency response (after corrections based on that determination) must
be flat and within the following tolerances:
44-3,549 Hz...........
.......................................0.25 dB
3,550-7,099 Hz..........
......................................0.5 dB
7,100-11,200 Hz..........
.....................................1.0 dB
(iii) Specifications concerning sensitivity to environmental factors
such as temperature, relative humidity, and vibration must be in
conformity with the recommendations of International Electrotechnical
Commission (IEC) Publication No. 179, entitled ``Precision Sound Level
Meters'', as incorporated by reference under Sec. 36.6 of this part.
(iv) If the wind speed exceeds 6 knots, a windscreen must be
employed with the microphone during each measurement of aircraft noise.
Correction for any insertion loss produced by the windscreen, as a
function of frequency, must be applied to the measured data and any
correction applied must be reported.
(3) If a magnetic tape recorder is used to store data for subsequent
analysis, the record/replay system (including tape) must conform to the
following:
(i) The electric background noise produced by the system in each
one-third octave must be at least 35 dB below the standard recording
level, which is defined as the level that is either 10 dB below the 3
percent harmonic distortion level for direct recording or 40
percent deviation for frequency modulation (FM) recording.
(ii) At the standard recording level, the corrected frequency
response in each selected one-third octave band between 44 Hz and 180 Hz
must be flat and within 0.75 dB, and in each band between
180 Hz and 11,200 Hz must be flat and within 0.25 dB.
(iii) If the overall system satisfies the requirements of paragraph
(c)(2)(ii) of this section, and if the limitations of the dynamic range
of the equipment are insufficient to obtain adequate spectral
information, high frequency pre-emphasis may be added to the recording
channel with the converse de-emphasis on playback. If pre-emphasis is
added, the instantaneously recorded sound-pressure level between 800 Hz
and 11,200 Hz of the maximum measured noise signal must not
[[Page 858]]
vary more than 20 dB between the levels of the maximum and minimum one-
third octave bands.
(d) Analysis equipment. (1) A frequency analysis of the acoustic
signal must be performed using one-third octave filters which conform to
the recommendations of International Electrotechnical Commission (IEC)
Publication No. 225, entitled ``Octave, Half-Octave, and Third-Octave
Band Filters Intended for Analysis of Sound and Vibrations,'' as
incorporated by reference under Sec. 36.6 of this part.
(2) A set of 24 consecutive one-third octave filters must be used.
The first filter of the set must be centered at a geometric mean
frequency of 50 Hz and the last filter at 10,000 Hz. The output of each
filter must contain less than 0.5 dB ripple.
(3) The analyzer indicating device may be either analog or digital,
or a combination of both. The preferred sequence of signal processing
is:
(i) Squaring the one-third octave filter outputs;
(ii) Averaging or integrating; and
(iii) Converting linear formulation to logarithmic.
(4) Each detector must operate over a minimum dynamic range of 60 dB
and perform as a root-mean-square device for sinusoidal tone bursts
having crest factors of at least 3 over the following dynamic range:
(i) Up to 30 dB below full-scale reading must be accurate within
0.5 dB;
(ii) Between 30 dB and 40 dB below full-scale reading must be
accurate within 1.0 dB; and
(iii) In excess of 40 dB below full-scale reading must be accurate
within 2.5 dB.
(5) The averaging properties of the integrator must be tested as
follows:
(i) White noise must be passed through the 200 Hz one-third octave
band filter and the output fed in turn to each detector/integrator. The
standard deviation of the measured levels must then be determined from a
statistically significant number of samples of the filtered white noise
taken at intervals of not less than 5 seconds. The value of the standard
deviation must be within the interval 0.480.06 dB for a
probability limit of 95 percent. An approved equivalent method may be
substituted for this test on those analyzers where the test signal
cannot readily be fed directly to each detector/integrator.
(ii) For each detector/integrator, the response to a sudden onset or
interruption of a constant amplitude sinusoidal signal at the respective
one-third octave band center frequency must be measured at sampling
times 0.5, 1.0, 1.5, and 2.0 seconds after the onset or interruption.
The rising responses must be in the following amounts before the steady-
state level:
0.5 seconds, 4.01.0 dB
1.0 seconds, 1.750.5 dB
1.5 seconds, 1.00.5 dB
2.0 seconds, 0.60.25 dB
(iii) The falling response must be such that the sum of the decibel
readings below the initial steady-state level, and the corresponding
rising response reading is 6.5 1.0 dB, at both 0.5 and 1.0
seconds and, on subsequent records, the sum of the onset plus decay must
be greater than 7.5 decibels.
Note 1: For analyzers with linear detection, an approximation of
this response would be given by:
SPL (i, k)-10 log................... [0.17 (100.1(Li,k-3))
+10.21 (00.1(Li,k-2))
+0.24 (100.1(Li,k-1))
+0.33 (100.1(Li,k))]
When this approximation is used, the calibration signal should be
established without this weighting.
Note 2: Some analyzers have been shown to have signal sampling rates
that are insufficiently accurate to detect signals with crest factor
ratios greater than three which is common to helicopter noise.
Preferably, such analyzers should not be used for helicopter
certification. Use of analysis systems with high signal sampling rates
(greater than 40KHz) or those with analog detectors prior to
digitization at the output of each one-third octave filter is
encouraged.
(iv) Analyzers using true integration cannot meet the requirements
of (i), (ii), and (iii) directly, because their overall average time is
greater than the sampling interval. For these analyzers, compliance must
be demonstrated in terms of the equivalent output of the data processor.
Further, in cases where readout and resetting require a dead-time during
acquisition, the percentage loss of the total data must not exceed one
percent.
(6) The sampling interval between successive readouts shall not
exceed 500 milliseconds and its precise value must be known to within
1 one percent. The instant in time by which a readout is
characterized shall be the midpoint of the average period where the
averaging period is defined as twice the effective time constant of the
analyzer.
(7) The amplitude resolution of the analyzer must be at least 0.25
dB.
(8) After all systematic errors have been eliminated, each output
level from the analyzer must be accurate within 1.0 dB of
the level of the input signal. The total systematic errors for each of
the output levels must not exceed 3.0 dB. For contiguous
filter systems, the systematic corrections between adjacent one-third
octave channels must not exceed 4.0 dB.
[[Page 859]]
(9) The dynamic range capability of the analyzer to display a single
aircraft noise event, in terms of the difference between full-scale
output level and the maximum noise level of the analyzer equipment, must
be at least 60 dB.
(e) Calibrations. (1) Within five days prior to beginning each test
series, the complete electronic system, as installed in field including
cables, must be electronically calibrated for frequency and amplitude by
the use of a pink noise signal of known amplitudes covering the range of
signal levels furnished by the microphone. For purposes of this section,
``pink noise'' means a noise whose noise-power/unit-frequency is
inversely proportional to frequency at frequencies within the range of
44 Hz to 11,200 Hz. The signal used must be described in terms of its
average root-mean-square (rms) values for a nonoverload signal level.
This system calibration must be repeated within five days of the end of
each test series, or as required by the FAA.
(2) Immediately before and after each day's testing, a recorded
acoustic calibration of the system must be made in the field with an
acoustic calibrator to check the system sensitivity and provide an
acoustic reference level for the sound level data analysis. The
performance of equipment in the system will be considered satisfactory
if, during each day's testing, the variation in the calibration value
does not exceed 0.5 dB.
(3) A normal incidence pressure calibration of the combined
microphone/preamplifier must be performed with pure tones at each
preferred one-third octave frequency from 50 Hz to 10,000 Hz. This
calibration must be completed within 90 days prior to the beginning of
each test series.
(4) Each reel of magnetic tape must:
(i) Be pistonphone calibrated; and
(ii) At its beginning and end, carry a calibration signal consisting
of at least a 15 second burst of pink noise, as defined in paragraph
(e)(1) of this section.
(5) Data obtained from tape recorded signals are not considered
reliable if the difference between the pink noise signal levels, before
and after the tests in each one-third octave band, exceeds 0.75 dB.
(6) The one-third octave filters must have been demonstrated to be
in conformity with the recommendations of IEC Publication 225 as
incorporated by reference under Sec. 36.6 of this part, during the six
calendar months preceding the beginning of each test series. However,
the correction for effective bandwidth relative to the center frequency
response may be determined for each filter by:
(i) Measuring the filter response to sinusoidal signals at a minimum
of twenty frequencies equally spaced between the two adjacent preferred
one-third octave frequencies; or
(ii) Using an FAA approved equivalent technique.
(7) A performance calibration analysis of each piece of calibration
equipment, including pistonphones, reference microphones, and voltage
insert devices, must have been made during the six calendar months
preceding the beginning of each day's test series. Each calibration must
be traceable to the National Bureau of Standards.
(f) Noise measurement procedures. (1) Each microphone must be
oriented so that the diaphragm is substantially in the plane defined by
the flight path of the aircraft and the measuring station. The
microphone located at each noise measuring station must be placed so
that its sensing element is approximately 4 feet above ground.
(2) Immediately before and immediately after each series of test
runs and each day's testing, acoustic calibrations of the system
prescribed in this section of this appendix must be recorded in the
field to check the acoustic reference level for the analysis of the
sound level data. Ambient noise must be recorded for at least 10 seconds
and be representative of the acoustical background, including system
noise, that exists during the flyover test run. During that recorded
period, each component of the system must be set at the gain-levels used
for aircraft noise measurement.
(3) The mean background noise spectrum must contain the sound
pressure levels, which, in each preferred third octave band in the range
of 50 Hz to 10,000 Hz, are the averages of the energy of the sound
pressure levels in every preferred third octave. When analyzed in PNL,
the resulting mean background noise level must be at least 20 PNdB below
the maximum PNL of the helicopter.
(4) Corrections for recorded levels of background noise are allowed,
within the limits prescribed in section H36.111(c)(3) of this appendix.
Section H36.111 Reporting and correcting measured data
(a) General. Data representing physical measurements, and
corrections to measured data, including corrections to measurements for
equipment response deviations, must be recorded in permanent form and
appended to the record. Each correction must be reported and is subject
to FAA approval. An estimate must be made of each individual error
inherent in each of the operations employed in obtaining the final data.
(b) Data reporting. (1) Measured and corrected sound pressure levels
must be presented in one-third octave band levels obtained with
equipment conforming to the standards prescribed in section H36.109 of
this appendix.
(2) The type of equipment used for measurement and analysis of all
acoustic, aircraft
[[Page 860]]
performance, and meteorological data must be reported.
(3) The atmospheric environmental data required to demonstrate
compliance with this appendix, measured throughout the test period, must
be reported.
(4) Conditions of local topography, ground cover, or events which
may interfere with sound recording must be reported.
(5) The following aircraft information must be reported:
(i) Type, model, and serial numbers, if any, of aircraft engines and
rotors.
(ii) Gross dimensions of aircraft and location of engines.
(iii) Aircraft gross weight for each test run.
(iv) Aircraft configuration, including landing gear positions.
(v) Airspeed in knots.
(vi) Helicopter engine performance as determined from aircraft
instruments and manufacturer's data.
(vii) Aircraft flight path, above ground level in feet, determined
by an FAA approved method which is independent of normal flight
instrumentation, such as radar tracking, theodolite triangulation, laser
trajectography, or photographic scaling techniques.
(6) Aircraft speed, and position, and engine performance parameters
must be recorded at an approved sampling rate sufficient to correct to
the noise certification reference test conditions prescribed in section
H36.3 of this appendix. Lateral position relative to the reference
flight-track must be reported.
(c) Data corrections. (1) Aircraft position, performance data and
noise measurement must be corrected to the noise certification reference
conditions as prescribed in sections H36.3 and H36.205 of this appendix.
(2) The measured flight path must be corrected by an amount equal to
the difference between the applicant's predicted flight path for the
certification reference conditions and the measured flight path at the
test conditions. Necessary corrections relating to aircraft flight path
or performance may be derived from FAA-approved data for the difference
between measured and reference engine conditions, together with
appropriate allowances for sound attenuation with distance. The
Effective Perceived Noise Level (EPNL) correction must be less than 2.0
EPNdB for any combination of the following:
(i) The aircraft's not passing vertically above the measuring
station.
(ii) Any difference between the reference flight-track and the
actual minimum distance of the aircraft's ILS antenna from the approach
measuring station.
(iii) Any difference between the actual approach angle and the noise
certification reference approach flight path.
(iv) Any correction of the measured level flyover noise levels which
accounts for any difference between the test engine thrust or power and
the reference engine thrust or power.
Detailed correction requirements are prescribed in section H36.205 of
this appendix.
(3) Aircraft sound pressure levels within the 10 dB-down points must
exceed the mean background sound pressure levels determined under
section A36.3.10.1 by at least 5 dB in each one-third octave band or be
corrected under an FAA approved method to be included in the computation
of the overall noise level of the aircraft. An EPNL may not be computed
or reported from data from which more than four one-third octave bands
in any spectrum within the 10 dB-down points have been excluded under
this paragraph.
(d) Validity of results. (1) The test results must produce three
average EPNL values within the 90 percent confidence limits, each value
consisting of the arithmetic average of the corrected noise measurements
for all valid test runs at the takeoff, level flyovers, and approach
conditions. The 90 percent confidence limit applies separately to
takeoff, flyover, and approach.
(2) The minimum sample size acceptable for each takeoff, approach,
and flyover certification measurements is six. The number of samples
must be large enough to establish statistically for each of the three
average noise certification levels a 90 percent confidence limit which
does not exceed 1.5 EPNdB. No test result may be omitted
from the averaging process, unless otherwise specified by the FAA.
(3) To comply with this appendix, a minimum of six takeoffs, six
approaches, and six level flyovers is required. To be counted toward
this requirement, each flight event must be validly recorded at all
three noise measuring stations.
(4) The approved values of VH and Vy used in
calculating test and reference conditions and flight profiles must be
reported along with measured and corrected sound pressure levels.
Section H36.113 Atmospheric attenuation of sound.
(a) The values of the one-third octave band spectra measured during
helicopter noise certification tests under this appendix must conform,
or be corrected, to the reference conditions prescribed in section
H36.3(a). Each correction must account for any differences in the
atmospheric attenuation of sound between the test-day conditions and the
reference-day conditions along the sound propagation path between the
aircraft and the microphone. Unless the meteorological conditions are
within the test window prescribed in this appendix, the test data are
not acceptable.
[[Page 861]]
(b) Attenuation rates. The atmospheric attenuation rates of sound
with distance for each one-third octave band from 50 Hz to 10,000 Hz
must be determined in accordance with the formulations and tabulations
of SAE ARP 866A, entitled ``Standard Values of Atmospheric Absorption as
a Function of Temperatures and Humidity for Use in Evaluating Aircraft
Flyover Noise'', as incorporated by reference under Sec. 36.6 of this
part.
(c) Correction for atmospheric attenuation. (1) EPNL values
calculated for measured data must be corrected whenever--
(i) The ambient atmospheric conditions of temperature and relative
humidity do not conform to the reference conditions, 77 deg.F and 70%,
respectively, or
(ii) The measured flight paths do not conform to the reference
flight paths.
(iii) The temperature and relative humidity measured at aircraft
altitude and at 10 meters above the ground shall be averaged and used to
adjust for propagation path absorption.
(2) The mean attenuation rate over the complete sound propagation
path from the aircraft to the microphone must be computed for each one-
third octave band from 50 Hz to 10,000 Hz. These rates must be used in
computing the corrections required in section H36.111(d) of this
appendix.
Part C--Noise Evaluation and Calculation Under Sec. 36.803
Section H36.201 Noise Evaluation in EPNdB.
(a) Effective Perceived Noise Level (EPNL), in units of effective
perceived noise decibels (EPNdB), shall be used for evaluating noise
level values under Sec. 36.803 of this part. Except as provided in
paragraph (b) of this section, the procedures in appendix A of Part 36
must be used for computing EPNL. appendix B includes requirements
governing determination of noise values, including calculations of:
(1) Instantaneous perceived noise levels;
(2) Corrections for spectral irregularities;
(3) Tone corrections;
(4) Duration corrections;
(5) Effective perceived noise levels; and
(6) Mathematical formulation of noy tables.
(b) Notwithstanding the provisions of section A36.4.3.1(a), for
helicopter noise certification, corrections for spectral irregularities
shall start with the corrected sound pressure level in the 50 Hz one-
third octave band.
Section H36.203 Calculation of noise levels.
(a) To demonstrate compliance with the noise level limits of section
H36.305, the noise values measured simultaneously at the three noise
measuring points must be arithmetically averaged to obtain a single
EPNdB value for each flight.
(b) The calculated noise level for each noise test series, i.e.,
takeoff, flyover, or approach must be the numerical average of at least
six separate flight EPNdB values. The 90 percent confidence limit for
all valid test runs under section H36.111(d) of this appendix applies
separately to the EPNdB values for each noise test series.
Section H36.205 Detailed data correction procedures
(a) General. If the test conditions do not conform to those
prescribed as noise certification reference conditions under section
H36.305 of this appendix, the following correction procedure shall
apply:
(1) If a positive value results from any difference between
reference and test conditions, an appropriate positive correction must
be made to the EPNL calculated from the measured data. Conditions which
can result in a positive value include:
(i) Atmospheric absorption of sound under test conditions which is
greater than the reference;
(ii) Test flight path at an altitude which is higher than the
reference; or
(iii) Test weight which is less than maximum certification weight.
(2) If a negative value results from any difference between
reference and test conditions, no correction may be made to the EPNL
calculated from the measured data, unless the difference results from:
(i) An atmospheric absorption of sound under test conditions which
is less than the reference; or
(ii) A test flight path at an altitude which is lower than the
reference.
(3) The following correction procedures may produce one or more
possible correction values which must be added algebraically to the
calculated EPNL to bring it to reference conditions:
(i) The flight profiles must be determined for both reference and
test conditions. The procedures require noise and flight path recording
with a synchronized time signal from which the test profile can be
delineated, including the aircraft position for which PNLTM is observed
at the noise measuring station. For takeoff, the flight profile
corrected to reference conditions may be derived from FAA approved
manufacturer's data.
(ii) The sound propagation paths to the microphone from the aircraft
position corresponding to PNLTM are determined for both the test and
reference profiles. The SPL values in the spectrum of PNLTM must then be
corrected for the effects of--
(A) Change in atmospheric sound absorption;
(B) Atmospheric sound absorption on the linear difference between
the two sound path lengths; and
[[Page 862]]
(C) Inverse square law on the difference in sound propagation path
length. The corrected values of SPL are then converted to PNLTM from
which PNLTM must be subtracted. The resulting difference represents the
correction which must be added algebraically to the EPNL calculated from
the measured data.
(iii) The minimum distances from both the test and reference
profiles to the noise measuring station must be calculated and used to
determine a noise duration correction due to any change in the altitude
of aircraft flyover. The duration correction must be added algebraically
to the EPNL calculated from the measured data.
(iv) From FAA approved data in the form of curves or tables giving
the variation of EPNL with rotor rpm and test speed, corrections are
determined and must be added to the EPNL, which is calculated from the
measured data to account for noise level changes due to differences
between test conditions and reference conditions.
(v) From FAA approved data in the form of curves or tables giving
the variation of EPNL with approach angle, corrections are determined
and must be added algebraically to the EPNL, which is calculated from
measured data, to account for noise level changes due to differences
between the 6 degree and the test approach angle.
(b) Takeoff profiles. (1) Figure H1 illustrates a typical takeoff
profile, including reference conditions.
(i) The reference takeoff flight path is described in section
H36.3(c).
(ii) The test parameters are functions of the helicopter's
performance and weight and the atmospheric conditions of temperature,
pressure, wind velocity and direction.
(2) For the actual takeoff, the helicopter approaches position C in
level flight at 65 feet (20 meters) above ground level at the flight
track noise measuring station and at either Vy5
knots (9 km/hr) or the maximum speed of the curve tangential
at the ordinate of the height-speed envelope plus 3.0 knots
(5 knots), whichever speed is greater. Rotor speed is
stabilized at the normal operating RPM (1 percent),
specified in the flight manual. The helicopter is stabilized in level
flight at the speed for best rate of climb using minimum engine
specifications (power or torque and rpm) along a path starting from a
point located 1640 feet (500 meters) forward of the flight-track noise
measuring station and 65 feet (20 meters) above the ground. Starting at
point B, the helicopter climbs through point C to the end of the noise
certification takeoff flight path represented by position I. The
position of point C may vary within limits allowed by the FAA. The
position of the helicopter shall be recorded for a distance (CI)
sufficient to ensure recording of the entire interval during which the
measured helicopter noise level is within 10 dB of PNLTM, as required by
this rule. Station A is the flight-track noise measuring station. The
relationships between the measured and corrected takeoff flight profiles
can be used to determine the corrections which must be applied to the
EPNL calculated from the measured data.
(3) Figure H1 also illustrates the significant geometrical
relationships influencing sound propagation. Position L represents the
helicopter location on the measured takeoff flight path from which PNLTM
is observed at station A, and Lr is the A and N[rho]
corresponding position on the reference sound propagation path. AL and
ALr both form the angle [Phi] with their respective flight
paths. Position T represents the point on the measured takeoff flight
path nearest station A, and Tr is the corresponding position
on the reference flight path. The minimum distance to the measured and
reference flight paths are indicated by the lines AT and ATr,
respectively, which are normal to their flight paths.
(c) Level flyover profiles. (1) The noise type certification level
flyover profile is shown in Figure H2. Airspeed must be stabilized
within 5 knots of the reference airspeed given in section
H36.3(d). For each run, the difference between airspeed and ground speed
shall not exceed 10 knots between the 10 dB down points. Rotor speed
must be stabilized at the maximum continuous RPM within one percent,
throughout the 10 dB down time period. If the test requirements are
otherwise met, flight direction may be reversed for each subsequent
flyover, to obtain three test runs in each direction.
[[Page 863]]
[GRAPHIC] [TIFF OMITTED] TC28SE91.116
(2) Figure H2 illustrates comparative flyover profiles when test
conditions do not conform to prescribed reference conditions. The
position of the helicopter shall be recorded for a distance (DJ)
sufficient to ensure recording of the entire interval during which the
measured helicopter noise level is
[[Page 864]]
within 10 dB of PNLTM, as required. The flyover profile is defined by
the height AG which is a function of the operating conditions controlled
by the pilot. Position M represents the helicopter location on the
measured flyover flight path for which PNLTM is observed at station A,
and Mr is the corresponding position on the reference flight
path.
(d) Approach profiles. (1) Figure H3 illustrates a typical approach
profile, including reference conditions.
(2) The helicopter approaches position H along a 6 deg.
(0.5 deg.) average approach slope throughout the 10 dB down
period. The approach procedure shall be acceptable to the FAA and shall
be included in the Flight Manual.
(3) Figure H3 illustrates portions of the measured and reference
approach flight paths including the significant geometrical
relationships influencing sound propagation. EK represents the measured
approach path with approach angle [eta], and Er and
Kr represent the reference approach angle of 6 deg.. Position
N represents the helicopter location on the measured approach flight
path for which PNLTM is observed at station A, and Nr is the
corresponding position on the reference approach flight path. The
measured and corrected noise propagation paths are AN and
ANr, respectively, both of which form the same angle with
their flight paths. Position S represents the point on the measured
approach flight path nearest station A, and Sr is the
corresponding point on the reference approach flight path. The minimum
distance to the measured and reference flight paths are indicated by the
lines AS and ASr, respectively, which are normal to their
flight paths.
[GRAPHIC] [TIFF OMITTED] TC28SE91.117
(e) Correction of noise at source during level flyover. (1) For
level overflight, if any combination of the following three factors, 1)
airspeed deviation from reference, 2) rotor speed deviation from
reference, and 3) temperature deviation from reference, results in an
advancing blade tip Mach number which deviates from the reference Mach
value, then source noise adjustments shall be determined. This
adjustment shall be determined from the manufacturer supplied data
approved by the FAA.
(2) Off-reference tip Mach number adjustments shall be based upon a
sensitivity curve of PNLTM versus advancing blade tip Mach number,
deduced from overflights carried out at different airspeeds around the
reference airspeed. If the test aircraft is unable
[[Page 865]]
to attain the reference value, then an extrapolation of the sensitivity
curve is permitted if data cover at least a range of 0.3 Mach units. The
advancing blade tip Mach number shall be computed using true airspeed,
onboard outside air temperature, and rotor speed. A separate PNLTM
versus advancing blade tip Mach number function shall be derived for
each of the three certification microphone locations, i.e., centerline,
sideline left, and sideline right. Sideline left and right are defined
relative to the direction of the flight on each run. PNLTM adjustments
are to be applied to each microphone datum using the appropriate PNLTM
function.
(f) PNLT corrections. If the ambient atmospheric conditions of
temperature and relative humidity are not those prescribed as reference
conditions under this appendix (77 degrees F and 70 percent,
respectively), corrections to the EPNL values must be calculated from
the measured data under paragraph (a) of this section as follows:
(1) Takeoff flight path. For the takeoff flight path shown in Figure
H1, the spectrum of PNLTM observed at station A for the aircraft at
position Lr is decomposed into its individual SPLi values.
(i) Step 1. A set of corrected values are then computed as follows:
SPLic = SPLi + ([alpha] i-[alpha] io)AL
+ ([alpha] io)AL-ALr)
+ 20 log(AL/ALr)
Where SPLi and SPLic are the measured and corrected sound pressure
levels, respectively, in the i-th one-third octave band. The first
correction term accounts for the effects of change in atmospheric sound
absorption where ai and aio are the sound absorption coefficients for
the test and reference atmospheric conditions, respectively, for the -
ith one-third octave band and Lr A is the measured takeoff
sound propagation path. The second correction term accounts for the
effects of atmospheric sound absorption on the change in the sound
propagation path length where Lr A is the corrected takeoff
sound propagation path. The third correction term accounts for the
effects of the inverse square law on the change in the sound propagation
path length.
(ii) Step 2. The corrected values of the SPLic are then converted to
PNLT and a correction term calculated as follows:
[Delta]1=PNLT-PNLTM
Which represents the correction to be added algebraically to the EPNL
calculated from the measured data.
(2) Approach flight path. (i) The procedure described in paragraph
(f)(1) of this section for takeoff flight paths is also used for the
approach flight path, except that the value for SPLic relate to the
approach sound propagation paths shown in Figure H3 as follows:
SPLic = SPLi+([alpha]-[alpha] io) AM+
[alpha] (AM-AMr)+ 20 log (AM/AMr)
Where the lines NS and Nr Sr are the measured and
referenced approach sound propagation paths, respectively.
(ii) The remainder of the procedure is the same as that prescribed
in paragraph (d)(1)(ii) of this section, regarding takeoff flight path.
(3) Sideline microphones. The procedure prescribed in paragraph
(f)(1) of this section for takeoff flight paths is also used for the
propagation to the sideline microphones, except that the values of SPLic
relate only in the measured sideline sound propagation path as follows:
SPLic - SPLi + ([alpha] io-[alpha]+io)KX
+ [alpha] io (KX-KXr) + 20 log (KX/KXr)
K is the sideline measuring station where
X=L and Xr=Ln for takeoff
X=M and Xr=Mn for approach
X=N and Xr=Nr for flyover
(4) Level flyover flight path. The procedure prescribed in paragraph
(f)(1) of this section for takeoff flight paths is also used for the
level flyover flight path, except that the values of SPLic relate only
to the flyover sound propagation paths as follows:
SPLic=SPLi+([alpha]-[alpha] io) AN + [alpha] io (AN-ANr)+20 log (AN/ANr)
(g) Duration corrections. (1) If the measured takeoff and approach
flight paths do not conform to those prescribed as the corrected and
reference flight paths, respectively, under section A36.5(d)(2) it will
be necessary to apply duration corrections to the EPNL values calculated
from the measured data. Such corrections must be calculated as follows:
(i) Takeoff flight path. For the takeoff flight path shown in Figure
H1, the correction term is calculated using the formula--
[Delta]2= -10 log (AT/ATr) + 10 log (V/Vr)
which represents the correction which must be added algebraically to the
EPNL calculated from the measured data. The lengths AT and ATr are the
measured and corrected takeoff minimum distances from the noise
measuring station A to the measured and the corrected flight paths,
respectively. A negative sign indicates that, for the particular case of
a duration correction, the EPNL calculated from the measured data must
be reduced if the measured flight path is at greater altitude than the
corrected flight path.
(ii) Approach flight path. For the approach flight path shown in
Figure H3, the correction term is calculated using the formula--
[Delta]2 = -10 log (AS/ASr) + 10 log (V/Vr)
where AS is the measured approach minimum distance from the noise
measuring station A to the measured flight path and 394 feet is the
minimum distance from station A to the reference flight path.
[[Page 866]]
(iii) Sideline microphones. For the sideline flight path, the
correction term is calculated using the formula--
[Delta]2=-10 log (KX/KXr)+10 log (V/Vr)
K is the sideline measuring station
where X=T and Xr=Tr for takeoff
where X=S and Xr=Sr for approach
where X=G and Xr=Gr for flyover
(iv) Level flyover flight paths. For the level flyover flight path,
the correction term is calculated using the formula--
[Delta]2=-10 log (AG/AGr)+10 log (V/Vr)
where AG is the measured flyover altitude over the noise measuring
station A.
(2) The adjustment procedure described in this section shall apply
to the sideline microphones in the take-off, overflight, and approach
cases. Although the noise emission is strongly dependent on the
directivity pattern, variable from one helicopter type to another, the
propagation angle [thetas] shall be the same for test and reference
flight paths. The elevation angle [psi] shall not be constrained but
must be determined and reported. The certification authority shall
specify the acceptable limitations on [psi]. Corrections to data
obtained when these limits are exceeded shall be applied using FAA
approved procedures.
Part D--Noise Limits Under Sec. 36.805
Section H36.301 Noise measurement, evaluation, and calculation
Compliance with this part of this appendix must be shown with noise
levels measured, evaluated, and calculated as prescribed under Parts B
and C of this appendix.
Section H36.303 [Reserved]
Section H36.305 Noise levels
(a) Limits. For compliance with this appendix, it must be shown by
flight test that the calculated noise levels of the helicopter, at the
measuring points described in section H36.305(a) of this appendix, do
not exceed the following, with appropriate interpolation between
weights:
(1) Stage 1 noise limits for acoustical changes for helicopters are
as follows:
(i) For takeoff, flyover, and approach calculated noise levels, the
noise levels of each Stage 1 helicopter that exceed the Stage 2 noise
limits plus 2 EPNdB may not, after a change in type design, exceed the
noise levels created prior to the change in type design.
(ii) For takeoff, flyover, and approach calculated noise levels, the
noise levels of each Stage 1 helicopter that do not exceed the Stage 2
noise limits plus 2 EPNdB may not, after the change in type design,
exceed the Stage 2 noise limits plus 2 EPNdB.
(2) Stage 2 noise limits are as follows:
(i) For takeoff calculated noise levels--109 EPNdB for maximum
takeoff weights of 176,370 pounds or more, reduced by 3.01 EPNdB per
halving of the weight down to 89 EPNdB for maximum weights of 1,764
pounds or less.
(ii) For flyover calculated noise levels--108 EPNdB for maximum
weights of 176,370 pounds or more, reduced by 3.01 EPNdB per halving of
the weight down to 88 EPNdB for maximum weights of 1,764 pounds or less.
(iii) For approach calculated noise levels--110 EPNdB for maximum
weights of 176,370 pounds or more, reduced by 3.01 EPNdB per halving of
the weight down 90 EPNdB for maximum weight of 1,764 pounds or less.
(b) Tradeoffs. Except to the extent limited under Sec. 36.11(b) of
this part, the noise limits prescribed in paragraph (a) of this section
may be exceeded by one or two of the takeoff, flyover, or approach
calculated noise levels determined under section H36.203 of this
appendix if
(1) The sum of the exceedances is not greater than 4 EPNdB;
(2) No exceedance is greater than 3 EPNdB; and
(3) The exceedances are completely offset by reduction in the other
required calculated noise levels.
[Amdt. 36-14, 53 FR 3541, Feb. 5, 1988; 53 FR 4099, Feb. 11, 1988; 53 FR
7728, Mar. 10, 1988, as amended by Amdt. 36-54, 67 FR 45237, July 8,
2002]
Appendix I to Part 36 [Reserved]
Appendix J to Part 36--Alternative Noise Certification Procedure for
Helicopters Under Subpart H Having a Maximum Certificated Takeoff Weight
of Not More Than 6,000 Pounds
Part A--Reference Conditions
J36.1 General.
J36.3 Reference Test Conditions.
J36.5 [Reserved]
Part B--Noise Measurement Procedure Under Sec. 36.801
J36.101 Noise certification test and measurement conditions.
J36.103 [Reserved]
J36.105 Flyover test conditions.
J36.107 [Reserved]
J36.109 Measurement of helicopter noise received on the ground.
J36.111 Reporting requirements.
J36.113 [Reserved]
Part C--Noise Evaluation and Calculation Under Sec. 36.803
J36.201 Noise evaluation in SEL.
J36.203 Calculation of noise levels.
[[Page 867]]
J36.205 Detailed data correction procedures.
Part D--Noise Limits Procedure Under Sec. 36.805
J36.301 Noise measurement, evaluation, and calculation.
J36.303 [Reserved]
J36.305 Noise limits.
Part A--Reference Conditions
Section J36.1 General
This appendix prescribes the alternative noise certification
requirements identified under Sec. 36.1 of this part and subpart H of
this part for helicopters in the primary, normal, transport, and
restricted categories having maximum certificated takeoff weight of not
more than 6,000 pounds including:
(a) The conditions under which an alternative noise certification
test under subpart H of this part must be conducted and the alternative
measurement procedure that must be used under Sec. 36.801 of this part
to measure the helicopter noise during the test;
(b) The alternative procedures which must be used under Sec. 36.803
of this part to correct the measured data to the reference conditions
and to calculate the noise evaluation quantity designated as Sound
Exposure Level (SEL); and
(c) The noise limits for which compliance must be shown under
Sec. 36.805 of this part.
Section J36.3 Reference Test Conditions
(a) Meteorological conditions. The following are the noise
certification reference atmospheric conditions which shall be assumed to
exist from the surface to the helicopter altitude:
(1) Sea level pressure of 2116 pounds per square foot (76
centimeters mercury);
(2) Ambient temperature of 77 degrees Fahrenheit (25 degrees
Celsius);
(3) Relative humidity of 70 percent; and
(4) Zero wind.
(b) Reference test site. The reference test site is flat and without
line-of-sight obstructions across the flight path that encompasses the
10 dB down points of the A-weighted time history.
(c) Level flyover reference profile. The reference flyover profile
is a level flight 492 feet (150 meters) above ground level as measured
at the noise measuring station. The reference flyover profile has a
linear flight track and passes directly over the noise monitoring
station. Airspeed is stabilized at 0.9VH; 0.9VNE;
0.45VH + 65 kts (0.45VH + 120 km/h); or
0.45VNE + 65 kts (0.45VNE + 120 km/h), whichever
of the four speeds is least. Rotor speed is stabilized at the power on
maximum normal operating RPM throughout the 10 dB down time period.
(1) For noise certification purposes, VH is defined as
the airspeed in level flight obtained using the minimum specification
engine power corresponding to maximum continuous power available for sea
level, 77 degree Fahrenheit (25 degrees Celsius) ambient conditions at
the relevant maximum certificated weight. The value of VH
thus defined must be listed in the Rotorcraft Flight Manual.
(2) VNE is the never-exceed airspeed.
(d) The weight of the helicopter shall be the maximum takeoff weight
at which noise certification is requested.
Section J36.5 [Reserved]
Part B--Noise Measurement Procedure Under Sec. 36.801
Section J36.101 Noise certification test and measurement conditions
(a) General. This section prescribes the conditions under which
helicopter noise certification tests must be conducted and the
measurement procedures that must be used to measure helicopter noise
during each test.
(b) Test site requirements. (1) The noise measuring station must be
surrounded by terrain having no excessive sound absorption
characteristics, such as might be caused by thick, matted, or tall
grass, shrubs, or wooded areas.
(2) During the period when the flyover noise measurement is within
10 dB of the maximum A-weighted sound level, no obstruction that
significantly influences the sound field from the helicopter may exist
within a conical space above the noise measuring position (the point on
the ground vertically below the microphone), the cone is defined by an
axis normal to the ground and by half-angle 80 degrees from this axis.
(c) Weather restrictions. The test must be conducted under the
following atmospheric conditions:
(1) No rain or other precipitation;
(2) Ambient air temperature between 36 degrees and 95 degrees
Fahrenheit (2 degrees and 35 degrees Celsius), inclusively, and relative
humidity between 20 percent and 95 percent inclusively, except that
testing may not take place where combinations of temperature and
relative humidity result in a rate of atmospheric attenuation greater
than 10 dB per 100 meters (30.5 dB per 1000 ft) in the one-third octave
band centered at 8 kiloHertz.
(3) Wind velocity that does not exceed 10 knots (19 km/h) and a
crosswind component that does not exceed 5 knots (9 km/h). The wind
shall be determined using a continuous averaging process of no greater
than 30 seconds;
(4) Measurements of ambient temperature, relative humidity, wind
speed, and wind direction must be made between 4 feet (1.2 meters) and
33 feet (10 meters) at the noise
[[Page 868]]
monitoring station. Unless otherwise approved by the FAA, ambient
temperature and relative humidity must be measured at the noise
measuring station at the same height above the ground.
(5) No anomalous wind conditions (including turbulence) or other
anomalous meteorological conditions that will significantly affect the
noise level of the helicopter when the noise is recorded at the noise
measuring station; and
(6) The location of the meteorological instruments must be approved
by the FAA as representative of those atmospheric conditions existing
near the surface over the geographical area where the helicopter noise
measurements are made. In some cases, a fixed meteorological station
(such as those found at airports or other facilities) may meet this
requirement.
(d) Helicopter testing procedures. (1) The helicopter testing
procedures and noise measurements must be conducted and processed in a
manner which yields the noise evaluation measure designated Sound
Exposure Level (SEL) as defined in section J36.109(b) of this appendix.
(2) The helicopter height relative to the noise measurement point
sufficient to make corrections required under section J36.205 of this
appendix must be determined by an FAA-approved method that is
independent of normal flight instrumentation, such as radar tracking,
theodolite triangulation, laser trajectography, or photographic scaling
techniques.
(3) If an applicant demonstrates that the design characteristics of
the helicopter would prevent flight from being conducted in accordance
with the reference test conditions prescribed under section J36.3 of
this appendix, then with FAA approval, the reference test conditions
used under this appendix may vary from the standard reference test
conditions, but only to the extent demanded by those design
characteristics which make compliance with the reference test conditions
impossible.
Section J36.103 [Reserved]
Section J36.105 Flyover test conditions
(a) This section prescribes the flight test conditions and allowable
random deviations for flyover noise tests conducted under this appendix.
(b) A test series must consist of at least six flights with equal
numbers of flights in opposite directions over the noise measuring
station:
(1) In level flight and in cruise configuration;
(2) At a height of 492 feet 50 feet (150 15
meters) above the ground level at the noise measuring station; and
(3) Within 10 degrees from the zenith.
(c) Each flyover noise test must be conducted:
(1) At the reference airspeed specified in section J36.3(c) of this
appendix, with such airspeed adjusted as necessary to produce the same
advancing blade tip Mach number as associated with the reference
conditions;
(i) Advancing blade tip Mach number (MAT) is defined as
the ratio of the arithmetic sum of blade tip rotational speed
(VR) and the helicopter true air speed (VT) over
the speed of sound (c) at 77 degrees Fahrenheit (1135.6 ft/sec or 346.13
m/sec) such that MAT=(VR+VT)/c; and
(ii) The airspeed shall not vary from the adjusted reference
airspeed by more than 3 knots (5 km/hr) or an
equivalent FAA-approved variation from the reference advancing blade tip
Mach number. The adjusted reference airspeed shall be maintained
throughout the measured portion of the flyover.
(2) At rotor speed stabilized at the power on maximum normal
operating rotor RPM (1 percent); and
(3) With the power stabilized during the period when the measured
helicopter noise level is within 10 dB of the maximum A-weighted sound
level (LAMAX).
(d) The helicopter test weight for each flyover test must be within
plus 5 percent or minus 10 percent of the maximum takeoff weight for
which certification under this part is requested.
(e) The requirements of paragraph (b)(2) of this section
notwithstanding, flyovers at an FAA-approved lower height may be used
and the results adjusted to the reference measurement point by an FAA-
approved method if the ambient noise in the test area, measured in
accordance with the requirements prescribed in section J36.109 of this
appendix, is found to be within 15 dB(A) of the maximum A-weighted
helicopter noise level (LAMAX) measured at the noise
measurement station in accordance with section J36.109 of this appendix.
Section J36.107 [Reserved]
Section J36.109 Measurement of helicopter noise received on the ground
(a) General. (1) The helicopter noise measured under this appendix
for noise certification purposes must be obtained with FAA-approved
acoustical equipment and measurement practices.
(2) Paragraph (b) of this section identifies and prescribes the
specifications for the noise evaluation measurements required under this
appendix. Paragraphs (c) and (d) of this section prescribe the required
acoustical equipment specifications. Paragraphs (e) and (f) of this
section prescribe the calibration and measurement procedures required
under this appendix.
(b) Noise unit definition. (1) The value of sound exposure level
(SEL, or as denoted by
[[Page 869]]
symbol, LAE), is defined as the level, in decibels, of the
time integral of squared `A'-weighted sound pressure (PA)
over a given time period or event, with reference to the square of the
standard reference sound pressure (PO) of 20 micropascals and
a reference duration of one second.
(2) This unit is defined by the expression:
[GRAPHIC] [TIFF OMITTED] TC28SE91.118
Where TO is the reference integration time of one second and
(t2-t1) is the integration time interval.
(3) The integral equation of paragraph (b)(2) of this section can
also be expressed as:
[GRAPHIC] [TIFF OMITTED] TC28SE91.119
Where LA(t) is the time varying A-weighted sound level.
(4) The integration time (t2-t1) in practice
shall not be less than the time interval during which LA(t)
first rises to within 10 dB(A) of its maximum value (LAMAX)
and last falls below 10 dB(A) of its maximum value.
(5) The SEL may be approximated by the following expression:
LAE=LAMAX + A
where A is the duration allowance given by:
A=10 log10 (T)
where T=(t2-t1)/2 and LAMAX is
defined as the maximum level, in decibels, of the A-weighted sound
pressure (slow response) with reference to the square of the standard
reference sound pressure (P0).
(c) Measurement system. The acoustical measurement system must
consist of FAA-approved equipment equivalent to the following:
(1) A microphone system with frequency response that is compatible
with the measurement and analysis system accuracy prescribed in
paragraph (d) of this section;
(2) Tripods or similar microphone mountings that minimize
interference with the sound energy being measured;
(3) Recording and reproducing equipment with characteristics,
frequency response, and dynamic range that are compatible with the
response and accuracy requirements of paragraph (d) of this section; and
(4) Acoustic calibrators using sine wave noise and, if a tape
recording system is used, pink noise, of known levels. When pink noise
(defined in section H36.109(e)(1) of appendix H of this part) is used,
the signal must be described in terms of its root-mean-square (rms)
value.
(d) Sensing, recording, and reproducing equipment. (1) The noise
levels measured from helicopter flyovers under this appendix may be
determined directly by an integrating sound level meter, or the A-
weighted sound level time history may be written onto a graphic level
recorder set at ``slow'' response from which the SEL value may be
determined. With the approval of the FAA, the noise signal may be tape
recorded for subsequent analysis.
(i) The SEL values from each flyover test may be directly determined
from an integrating sound level meter complying with the Standards of
the International Electrotechnical Commission (IEC) Publication No. 804,
``Integrating-averaging Sound Level Meters,'' as incorporated by
reference under Sec. 36.6 of this part, for a Type 1 instrument set at
``slow'' response.
(ii) The acoustic signal from the helicopter, along with the
calibration signals specified under paragraph (e) of this section and
the background noise signal required under paragraph (f) of this section
may be recorded on a magnetic tape recorder for subsequent analysis by
an integrating sound level meter identified in paragraph (d)(1)(i) of
this section. The record/playback system (including the audio tape) of
the tape recorder must conform to the requirements prescribed in section
H36.109(c)(3) of appendix H of this part. The tape recorder shall comply
with specifications of IEC Publication No. 561, ``Electro-acoustical
Measuring Equipment for Aircraft Noise Certification,'' as incorporated
by reference under Sec. 36.6 of this part.
(iii) The characteristics of the complete system shall comply with
the recommendations given in IEC Publication No. 651, ``Sound Level
Meters,'' as incorporated by reference under Sec. 36.6 of this part,
with regard to the specifications concerning microphone, amplifier, and
indicating instrument characteristics.
(iv) The response of the complete system to a sensibly plane
progressive wave of constant amplitude shall lie within the tolerance
limits specified in Table IV and Table V for Type 1 instruments in IEC
Publication No. 651, ``Sound Level Meters,'' as incorporated by
reference under Sec. 36.6 of this part, for weighting curve ``A'' over
the frequency range of 45 Hz to 11500 Hz.
(v) A windscreen must be used with the microphone during each
measurement of the helicopter flyover noise. Correction for any
insertion loss produced by the windscreen, as a function of the
frequency of the acoustic calibration required under paragraph (e) of
this section, must be applied to the measured data and any correction
applied must be reported.
[[Page 870]]
(e) Calibrations. (1) If the helicopter acoustic signal is tape
recorded for subsequent analysis, the measuring system and components of
the recording system must be calibrated as prescribed under section
H36.109(e) of appendix H of this part.
(2) If the helicopter acoustic signal is directly measured by an
integrating sound level meter:
(i) The overall sensitivity of the measuring system shall be checked
before and after the series of flyover tests and at intervals (not
exceeding one-hour duration) during the flyover tests using an acoustic
calibrator using sine wave noise generating a known sound pressure level
at a known frequency.
(ii) The performance of equipment in the system will be considered
satisfactory if, during each day's testing, the variation in the
calibration value does not exceed 0.5 dB. The SEL data collected during
the flyover tests shall be adjusted to account for any variation in the
calibration value.
(iii) A performance calibration analysis of each piece of
calibration equipment, including acoustic calibrators, reference
microphones, and voltage insertion devices, must have been made during
the six calendar months proceeding the beginning of the helicopter
flyover series. Each calibration shall be traceable to the National
Institute of Standards and Technology.
(f) Noise measurement procedures. (1) The microphone shall be of the
pressure-sensitive capacitive type designed for nearly uniform grazing
incidence response. The microphone shall be mounted with the center of
the sensing element 4 feet (1.2 meters) above the local ground surface
and shall be oriented for grazing incidence such that the sensing
element, the diaphragm, is substantially in the plane defined by the
nominal flight path of the helicopter and the noise measurement station.
(2) If a tape recorder is used, the frequency response of the
electrical system must be determined at a level within 10 dB of the
full-scale reading used during the test, utilizing pink or pseudorandom
noise.
(3) The ambient noise, including both acoustical background and
electrical noise of the measurement systems shall be determined in the
test area and the system gain set at levels which will be used for
helicopter noise measurements. If helicopter sound levels do not exceed
the background sound levels by at least 15 dB(A), flyovers at an FAA-
approved lower height may be used and the results adjusted to the
reference measurement point by an FAA-approved method.
(4) If an integrating sound level meter is used to measure the
helicopter noise, the instrument operator shall monitor the continuous
A-weighted (slow response) noise levels throughout each flyover to
ensure that the SEL integration process includes, at minimum, all of the
noise signal between the maximum A-weighted sound level
(LAMAX) and the 10 dB down points in the flyover time
history. The instrument operator shall note the actual db(A) levels at
the start and stop of the SEL integration interval and document these
levels along with the value of LAMAX and the integration
interval (in seconds) for inclusion in the noise data submitted as part
of the reporting requirements under section J36.111(b) of this appendix.
Section J36.111 Reporting Requirements
(a) General. Data representing physical measurements, and
corrections to measured data, including corrections to measurements for
equipment response deviations, must be recorded in permanent form and
appended to the record. Each correction is subject to FAA approval.
(b) Data reporting. After the completion of the test the following
data must be included in the test report furnished to the FAA:
(1) Measured and corrected sound levels obtained with equipment
conforming to the standards prescribed in section J36.109 of this
appendix;
(2) The type of equipment used for measurement and analysis of all
acoustic, aircraft performance and flight path, and meteorological data;
(3) The atmospheric environmental data required to demonstrate
compliance with this appendix, measured throughout the test period;
(4) Conditions of local topography, ground cover, or events which
may interfere with the sound recording;
(5) The following helicopter information:
(i) Type, model, and serial numbers, if any, of helicopter,
engine(s) and rotor(s);
(ii) Gross dimensions of helicopter, location of engines, rotors,
type of antitorque system, number of blades for each rotor, and
reference operating conditions for each engine and rotor;
(iii) Any modifications of non-standard equipment likely to affect
the noise characteristics of the helicopter;
(iv) Maximum takeoff weight for which certification under this
appendix is requested;
(v) Aircraft configuration, including landing gear positions;
(vi) VH or VNE (whichever is less) and the
adjusted reference airspeed;
(vii) Aircraft gross weight for each test run;
(viii) Indicated and true airspeed for each test run;
(ix) Ground speed, if measured, for each run;
(x) Helicopter engine performance as determined from aircraft
instruments and manufacturer's data; and
(xi) Aircraft flight path above ground level, referenced to the
elevation of the noise measurement station, in feet, determined by
[[Page 871]]
an FAA-approved method which is independent of normal flight
instrumentation, such as radar tracking, theodolite triangulation, laser
trajectography, or photoscaling techniques; and
(6) Helicopter position and performance data required to make the
adjustments prescribed under section J36.205 of this appendix and to
demonstrate compliance with the performance and position restrictions
prescribed under section J36.105 of this appendix must be recorded at an
FAA-approved sampling rate.
Section J36.113 [Reserved]
Part C--Noise Evaluation and Calculations Under Sec. 36.803
Section J36.201 Noise Evaluation in SEL
The noise evaluation measure shall be the sound exposure level (SEL)
in units of dB(A) as prescribed under section J36.109(b) of this
appendix. The SEL value for each flyover may be directly determined by
use of an integrating sound level meter. Specifications for the
integrating sound level meter and requirements governing the use of such
instrumentation are prescribed under section J36.109 of this appendix.
Section J36.203 Calculation of Noise Levels
(a) To demonstrate compliance with the noise level limits specified
under section J36.305 of this appendix, the SEL noise levels from each
valid flyover, corrected as necessary to reference conditions under
section J36.205 of this appendix, must be arithmetically averaged to
obtain a single SEL dB(A) mean value for the flyover series. No
individual flyover run may be omitted from the averaging process, unless
otherwise specified or approved by the FAA.
(b) The minimum sample size acceptable for the helicopter flyover
certification measurements is six. The number of samples must be large
enough to establish statistically a 90 percent confidence limit that
does not exceed 1.5 dB(A).
(c) All data used and calculations performed under this section,
including the calculated 90 percent confidence limits, must be
documented and provided under the reporting requirements of section
J36.111 of this appendix.
Section J36.205 Detailed Data Correction Procedures
(a) When certification test conditions measured under part B of this
appendix differ from the reference test conditions prescribed under
section J36.3 of this appendix, appropriate adjustments shall be made to
the measured noise data in accordance with the methods set out in
paragraphs (b) and (c) of this section. At minimum, appropriate
adjustments shall be made for off-reference altitude and for the
difference between reference airspeed and adjusted reference airspeed.
(b) The adjustment for off-reference altitude may be approximated
from:
J1=12.5 log10(HT/492)
dB;
where J1 is the quantity in decibels that
must be algebraically added to the measured SEL noise level to correct
for an off-reference flight path, HT is the height, in feet,
of the test helicopter when directly over the noise measurement point,
and the constant (12.5) accounts for the effects on spherical spreading
and duration from the off-reference altitude.
(c) The adjustment for the difference between reference airspeed and
adjusted reference airspeed is calculated from:
J3=10 log10(VRA/
VR) dB;
Where J3 is the quantity in decibels that
must be algebraically added to the measured SEL noise level to correct
for the influence of the adjustment of the reference airspeed on the
duration of the measured flyover event as perceived at the noise
measurement station, VR is the reference airspeed as
prescribed under section J36.3.(c) of this appendix, and VRA
is the adjusted reference airspeed as prescribed under section
J36.105(c) of this appendix.
(d) No correction for source noise during the flyover other than the
variation of source noise accounted for by the adjustment of the
reference airspeed prescribed for under section J36.105(c) of this
appendix need be applied.
(e) No correction for the difference between the reference ground
speed and the actual ground speed need be applied.
(f) No correction for off-reference atmospheric attenuation need be
applied.
(g) The SEL adjustments must be less than 2.0 dB(A) for differences
between test and reference flight procedures prescribed under section
J36.105 of this appendix unless a larger adjustment value is approved by
the FAA.
(h) All data used and calculations performed under this section must
be documented and provided under the reporting requirements specified
under section J36.111 of this appendix.
Part D--Noise Limits Procedure Under Sec. 36.805
Section J36.301 Noise Measurement, Evaluation, and Calculation
Compliance with this part of this appendix must be shown with noise
levels measured, evaluated, and calculated as prescribed under parts B
and C of this appendix.
[[Page 872]]
Section J36.303 [Reserved]
Section J36.305 Noise Limits
For compliance with this appendix, the calculated noise levels of
the helicopter, at the measuring point described in section J36.101 of
this appendix, must be shown to not exceed the following (with
appropriate interpolation between weights):
(a) For primary, normal, transport, and restricted category
helicopters having a maximum certificated takeoff weight of not more
than 6,000 pounds and noise tested under this appendix, the Stage 2
noise limit is 82 decibels SEL for helicopters with maximum certificated
takeoff weight at which the noise certification is requested, of up to
1,764 pounds and increasing at a rate of 3.01 decibels per doubling of
weight thereafter. The limit may be calculated by the equation:
LAE(limit)=82+3.01[log10(MTOW/1764)/
log10(2)] dB;
where MTOW is the maximum takeoff weight, in pounds, for which
certification under this appendix is requested.
(b) The procedures required in this amendment shall be done in
accordance with the International Electrotechnical Commission IEC
Publication No. 804, entitled ``Integrating-averaging Sound Level
Meters,'' First Edition, dated 1985. This incorporation by reference was
approved by the Director of the Federal Register in accordance with 5
U.S.C. 552(a) and 1 CFR part 51. Copies may be obtained from the Bureau
Central de la Commission Electrotechnique Internationale, 1, rue de
Varembe, Geneva, Switzerland or the American National Standard
Institute, 1430 Broadway, New York City, New York 10018, and can be
inspected at the Office of the Federal Register, 800 North Capitol
Street NW., suite 700, Washington, DC.
[Doc. No. 26910, 57 FR 42855, Sept. 16, 1992, as amended by Amdt. 36-20,
57 FR 46243, Oct. 7, 1992]