[Code of Federal Regulations]

[Title 14, Volume 3]

[Revised as of January 1, 2006]

From the U.S. Government Printing Office via GPO Access

[CITE: 14CFR171.109]



[Page 228-230]

 

                     TITLE 14--AERONAUTICS AND SPACE

 

CHAPTER I--FEDERAL AVIATION ADMINISTRATION, DEPARTMENT OF TRANSPORTATION 

                               (CONTINUED)

 

PART 171_NON-FEDERAL NAVIGATION FACILITIES--Table of Contents

 

             Subpart F_Simplified Directional Facility (SDF)

 

Sec. 171.109  Performance requirements.



    (a) The Simplified Directional Facility must perform in accordance 

with the following standards and practices:

    (1) The radiation from the SDF antenna system must produce a 

composite field pattern which is amplitude modulated by a 90 Hz and a 

150 Hz tone. The radiation field pattern must produce a course sector 

with the 90 Hz tone predominating on one side of the course and with the 

150 Hz tone predominating on the opposite side.

    (2) When an observer faces the SDF from the approach end of runway, 

the depth of modulation of the radio frequency carrier due to the 150 Hz 

tone must predominate on his right hand and that due to the 90 Hz tone 

must predominate on his left hand.

    (3) All horizontal angles employed in specifying the SDF field 

patterns must originate from the center of the antenna system which 

provides the signals used in the front course sector.

    (4) The SDF must operate on odd tenths or odd tenths plus a 

twentieth MHz within the frequency band 108.1 MHz to 111.95 MHz. The 

frequency tolerance of the radio frequency carrier must not exceed plus 

or minus 0.002 percent.

    (5) The radiated emission from the SDF must be horizontally 

polarized. The vertically polarized component of the radiation on the 

course line must not exceed that which corresponds to an error one-

twentieth of the course sector width when an aircraft is positioned on 

the course line and is in a roll attitude of 20[deg] from the 

horizontal.

    (6) The SDF must provide signals sufficient to allow satisfactory 

operation of a typical aircraft installation within the sector which 

extends from the center of the SDF antenna system to distances of 18 

nautical miles within a plus or minus 10[deg] sector and 10 nautical 

miles within the remainder of the coverage when alternative navigational 

facilities provide satisfactory coverage within the intermediate 

approach area. SDF signals must be receivable at the distances specified 

at and above a height of 1,000 feet above the elevation of the 

threshold, or the lowest altitude authorized for transition, whichever 

is higher. Such signals must be receivable, to the distances specified, 

up to a surface extending outward from the SDF antenna and inclined at 

7[deg] above the horizontal.

    (7) The modulation tones must be phase-locked so that within the 

half course sector, the demodulated 90 Hz and 150 Hz wave forms pass 

through zero in the same direction within 20[deg] of phase relative to 

the 150 Hz component, every half cycle of the combined 90 Hz and 150 Hz 

wave form. However, the phase need not be measured within the half 

course sector.

    (8) The angle of convergence of the final approach course and the 

extended runway centerline must not exceed 30[deg]. The final approach 

course must be aligned to intersect the extended runway centerline 

between points A1 and the runway threshold. When an operational 

advantage can be achieved, a final approach course that does not 

intersect the runway or that intersects it at a distance greater than 

point A1 from the threshold, may be established, if that course lies 

within 500 feet laterally of the extended runway centerline at a point 

3,000 feet outward from the runway threshold. The mean course line must 

be maintained within 10 percent of the course 

sector width.

    (9) The nominal displacement sensitivity within the half course 

sector must be 50 microamperes/degree. The nominal course sector width 

must be 6[deg]. When an operational advantage can be achieved, a nominal 

displacement sensitivity of 25 microamperes/degree may be established, 

with a nominal course sector width of 12[deg] with proportional 

displacement sensitivity. The lateral displacement sensitivity must be 

adjusted and maintained within the limits of plus or minus 17 percent of 

the nominal value.

    (10) The off-course (clearance) signal must increase at a 

substantially linear rate with respect to the angular displacement from 

the course line up to an angle on either side of the course



[[Page 229]]



line where 175 microamperes of deflection is obtained. From that angle 

to 10[deg], the off-course deflection must not be 

less than 175 microamperes. From 10[deg] to 35[deg] the off-course deflection must not be less than 

150 microamperes. With the course adjusted to cause any of several 

monitor alarm conditions, the aforementioned values of 175 microamperes 

in the sector 10[deg] each side of course and 150 microamperes in the 

sector 10[deg] to 35[deg] 

may be reduced to 160 microamperes and 135 microamperes, respectively. 

These conditions must be met at a distance of 18 nautical miles from the 

SDF antenna within the sector 10[deg] each side of course line and 10 

nautical miles from the SDF antenna within the sector 10[deg] to 35[deg] each side of 

course line.

    (11) The SDF may provide a ground-to-air radiotelephone 

communication channel to be operated simultaneously with the navigation 

and identification signals, if that operation does not interfere with 

the basic function. If a channel is provided, it must conform with the 

following standards:

    (i) The channel must be on the same radio frequency carrier or 

carriers as used for the SDF function, and the radiation must be 

horizontally polarized. Where two carriers are modulated with speech, 

the relative phases of the modulations on the two carriers must avoid 

the occurrence of nulls within the coverage of the SDF.

    (ii) On centerline, the peak modulation depth of the carrier or 

carriers due to the radiotelephone communications must not exceed 50 

percent but must be adjusted so that the ratio of peak modulation depth 

due to the radiotelephone communications to that due to the 

identification signal is approximately 9:1.

    (iii) The audio frequency characteristics of the radiotelephone 

channel must be flat to within 3 db relative to the level at 1,000 Hz 

over the range from 300 Hz to 3,000 Hz.

    (12)(i) The SDF must provide for the simultaneous transmission of an 

identification signal, specific to the runway and approach direction, on 

the same radio frequency carrier or carriers as used for the SDF 

function. The transmission of the identification signal must not 

interfere in any way with the basic SDF function.

    (ii) The identification signal must be produced by Class A2 

modulation of the radio frequency carrier or carriers using a modulation 

tone of 1020 Hz within 50 Hz. The depth of 

modulation must be between the limits of 5 and 15 percent except that, 

where a radiotelephone communication channel is provided, the depth of 

modulation must be adjusted so that the ratio of peak modulation depth 

due to radiotelephone communications to that due to the identification 

signal modulation is approximately 9:1. The emissions carrying the 

identification signal must be horizontally polarized.

    (iii) The identification signal must employ the International Morse 

Code and consist of three letters.

    (iv) The identification signal must be transmitted at a speed 

corresponding to approximately seven words per minute, and must be 

repeated at approximately equal intervals, not less than six times per 

minute. When SDF transmission is not available for operational use, 

including periods of removal of navigational components or during 

maintenance or test transmissions, the identification signal must be 

suppressed.

    (b) It must be shown during ground inspection of the design features 

of the equipment that there will not be conditions that will allow 

unsafe operations because of component failure or deterioration.

    (c) The monitor must be checked periodically during the in-service 

test evaluation period for calibration and stability. These tests, and 

ground checks of SDF radiation characteristics must be conducted in 

accordance with the maintenance manual required by Sec. 171.115(c) and 

must meet the standards and tolerances contained in Sec. 171.111(j).

    (d) The monitor system must provide a warning to the designated 

control point(s) when any of the conditions of Sec. 171.111(j) occur, 

within the time periods specified in that paragraph.

    (e) Flight inspection to determine the adequacy of the facility's 

operational performance and compliance



[[Page 230]]



with applicable performance requirements must be conducted in accordance 

with the ``U.S. Standard Flight Inspection Manual.'' Tolerances 

contained in the U.S. Standard Flight Inspection Manual, section 217, 

must be complied with except as stated in paragraph (f) of this section.

    (f) Flight inspection tolerances specified in section 217 of the 

``U.S. Standard Flight Inspection Manual'' must be complied with except 

as follows:

    (1) Course sector width. The nominal course sector width must be 

6[deg]. When an operational advantage can be achieved, a nominal course 

sector width of 12[deg] may be established. Course sector width must be 

adjusted and maintained within the limits of 17 

percent of the nominal value.

    (2) Course alignment. The mean course line must be adjusted and 

maintained within the limits of 10 percent of the 

nominal course sector width.

    (3) Course structure. Course deviations due to roughness, 

scalloping, or bends must be within the following limitations:

    (i) Front course. (a) Course structure from 18 miles from runway 

threshold to Point A must not exceed 40 

microamperes;

    (b) Point A to Point A-1--linear decrease from not more than 40 microamperes at Point A to not more than 20 microamperes at Point A-1;

    (c) Point A-1 to Missed Approach Point--not more than 20 microamperes;

    (d) Monitor tolerances: width 17 percent of 

nominal; alignment--10 percent of nominal course 

sector width.

    (ii) Back course. (a) Course structure 18 miles from runway 

threshold to 4 miles from runway threshold must not exceed 40 microamperes. Four miles to 1 mile from R/W must not 

exceed 40 microamperes decreasing to not more than 

20 microamperes, at a linear rate.

    (b) Monitor tolerances: width--17 percent of 

nominal; alignment--10 percent of nominal course 

sector width.



[Doc. No. 10116, 35 FR 12711, Aug. 11, 1970, as amended by Amdt. 171-9, 

38 FR 28557, Oct. 15, 1973]