[Code of Federal Regulations]
[Title 14, Volume 1]
[Revised as of January 1, 2003]
From the U.S. Government Printing Office via GPO Access
[CITE: 14CFR36.1583]
[Page 789-849]
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.
[[Page 790]]
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.
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
[[Page 791]]
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
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
[[Page 792]]
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 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 793]]
[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 794]]
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 795]]
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 796]]
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 797]]
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 798]]
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 799]]
[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 800]]
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 801]]
[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 802]]
(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 803]]
[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 804]]
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 805]]
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 806]]
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.
[egr]................. 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:
[[Page 807]]
[GRAPHIC] [TIFF OMITTED] TR08JY02.010
and
[GRAPHIC] [TIFF OMITTED] TR08JY02.011
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.
[[Page 808]]
Section A36.8 [Reserved]
[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
[[Page 809]]
(b) Duration of the noise as affected by the distance and the speed
of the airplane relative to the measuring point
(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 810]]
[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 811]]
(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 812]]
[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 813]]
(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 814]]
[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 815]]
[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 816]]
[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 817]]
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.
[[Page 818]]
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.
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; Amdt. 36-24, 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.
[[Page 819]]
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:
(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).
[[Page 820]]
(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
(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
[[Page 821]]
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.
(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; Amdt. 36-24, 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
a