813 

Federal Aviation Administration, DOT 

Pt. 36, App. G 

and accuracy requirements of section G36.105 
of this appendix. 

(d) Acoustic calibrators using sine wave or 

broadband noise of known sound pressure 
level. If broadband noise is used, the signal 
must be described in terms of its average and 
maximum root-mean-square (rms) value for 
non-overload signal level. 

Sec. G36.105 Sensing, Recording, and 

Reproducing Equipment. 

(a) The noise produced by the airplane 

must be recorded. A magnetic tape recorder, 
graphic level recorder, or sound level meter 
is acceptable when approved by the regional 
certificating authority. 

(b) The characteristics of the complete sys-

tem must comply with the requirements in 
IEC 651 and IEC 561 (incorporated by ref-
erence, see § 36.6). Sound level meters must 
comply with the requirements for Type 1 
sound level meters as specified in IEC 651. 

(c) The response of the complete system to 

a sensibly plane progressive sinusoidal wave 
of constant amplitude must be within the 
tolerance limits specified in IEC 651, over the 
frequency range 45 to 11,200 Hz. 

(d) If equipment dynamic range limitations 

make it necessary, high frequency pre-em-
phasis must be added to the recording chan-
nel with the converse de-emphasis on play-
back. The pre-emphasis must be applied such 
that the instantaneous recorded sound pres-
sure level of the noise signal between 800 and 
11,200 Hz does not vary more than 20 dB be-
tween the maximum and minimum one-third 
octave bands. 

(e) The output noise signal must be read 

through an ‘‘A’’ filter with dynamic charac-
teristics designated ‘‘slow’’ as defined in IEC 
651. A graphic recorder, sound level meter, or 
digital equipment may be used. 

(f) The equipment must be acoustically 

calibrated using facilities for acoustic free- 
field calibration and if analysis of the tape 
recording is requested by the Administrator, 
the analysis equipment shall be electroni-
cally calibrated by a method approved by the 
FAA. Calibrations shall be performed, as ap-
propriate, in accordance with paragraphs 
A36.3.8 and A36.3.9 of appendix A of this part. 

(g) A windscreen must be employed with 

the microphone during all measurements of 
aircraft noise when the wind speed is in ex-
cess of 5 knots (9 km/hr). 

Sec. G36.107 Noise Measurement Procedures. 

(a) The microphone must be a pressure 

type, 12.7 mm in diameter, with a protective 
grid, mounted in an inverted position such 
that the microphone diaphragm is 7 mm 
above and parallel to a white-painted metal 
circular plate. This white-painted metal 
plate shall be 40 cm in diameter and at least 
2.5 mm thick. The plate shall be placed hori-
zontally and flush with the surrounding 

ground surface with no cavities below the 
plate. The microphone must be located 
three-quarters of the distance from the cen-
ter to the back edge of the plate along a ra-
dius normal to the line of flight of the test 
airplane. 

(b) Immediately prior to and after each 

test, a recorded acoustic calibration of the 
system must be made in the field with an 
acoustic calibrator for the purposes of 
checking system sensitivity and providing 
an acoustic reference level for the analysis 
of the sound level data. If a tape recorder or 
graphic level recorder is used, the frequency 
response of the electrical system must be de-
termined at a level within 10 dB of the full- 
scale reading used during the test, utilizing 
pink or pseudorandom noise. 

(c) The ambient noise, including both 

acoustic background and electrical systems 
noise, must be recorded and determined in 
the test area with the system gain set at lev-
els which will be used for aircraft noise 
measurements. If aircraft sound pressure lev-
els do not exceed the background sound pres-
sure levels by at least 10 dB(A), a takeoff 
measurement point nearer to the start of the 
takeoff roll must be used and the results 
must be adjusted to the reference measure-
ment point by an approved method. 

Sec. G36.109 Data Recording, Reporting, and 

Approval. 

(a) Data representing physical measure-

ments and adjustments to measured data 
must be recorded in permanent form and ap-
pended to the record, except that corrections 
to measurements for normal equipment re-
sponse deviations need not be reported. All 
other adjustments must be approved. Esti-
mates must be made of the individual errors 
inherent in each of the operations employed 
in obtaining the final data. 

(b) Measured and corrected sound pressure 

levels obtained with equipment conforming 
to the specifications in section G36.105 of 
this appendix must be reported. 

(c) The type of equipment used for meas-

urement and analysis of all acoustical, air-
plane performance, and meteorological data 
must be reported. 

(d) The following atmospheric data, meas-

ured immediately before, after, or during 
each test at the observation points pre-
scribed in section G36.101 of this appendix 
must be reported: 

(1) Ambient temperature and relative hu-

midity. 

(2) Maximum and average wind speeds and 

directions for each run. 

(e) Comments on local topography, ground 

cover, and events that might interfere with 
sound recordings must be reported. 

(f) The aircraft position relative to the 

takeoff reference flight path must be deter-
mined by an approved method independent of 
normal flight instrumentation, such as radar 

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