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 system must comply with the requirements in
IEC 651 and IEC 561 (incorporated by reference, see Section 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-emphasis must be added to the recording channel with the converse de-emphasis on playback. The pre-emphasis must be applied such
that the instantaneous recorded sound pressure level of the noise signal between 800 and
11,200 Hz does not vary more than 20 dB between the maximum and minimum one-third
octave bands.
(e) The output noise signal must be read
through an  - A -  filter with dynamic characteristics designated  - slow -  as defined in IEC
651. A graphic recorder, sound level meter, or
digital equipment may be used.
(f) The equipment must be acoustically
calibrated using facilities for acoustic freefield calibration and if analysis of the tape
recording is requested by the Administrator,
the analysis equipment shall be electronically calibrated by a method approved by the
FAA. Calibrations shall be performed, as appropriate, in accordance with paragraphs
A36.3.8 and A36.3.9 of appendix A of this part.
(g) A windscreen must be employed with
the microphone during all measurements of
aircraft noise when the wind speed is in excess of 5 knots (9 km/hr).

spaschal on DSK3GDR082PROD with CFR

Sec. G36.107 Noise Measurement Procedures.
(a) The microphone must be a pressure
type, 12.7 mm in diameter, with a protective
grid, mounted in an inverted position such
that the microphone diaphragm is 7 mm
above and parallel to a white-painted metal
circular plate. This white-painted metal
plate shall be 40 cm in diameter and at least
2.5 mm thick. The plate shall be placed horizontally and flush with the surrounding

ground surface with no cavities below the
plate. The microphone must be located
three-quarters of the distance from the center to the back edge of the plate along a radius normal to the line of flight of the test
airplane.
(b) Immediately prior to and after each
test, a recorded acoustic calibration of the
system must be made in the field with an
acoustic calibrator for the purposes of
checking system sensitivity and providing
an acoustic reference level for the analysis
of the sound level data. If a tape recorder or
graphic level recorder is used, the frequency
response of the electrical system must be determined at a level within 10 dB of the fullscale reading used during the test, utilizing
pink or pseudorandom noise.
(c) The ambient noise, including both
acoustic background and electrical systems
noise, must be recorded and determined in
the test area with the system gain set at levels which will be used for aircraft noise
measurements. If aircraft sound pressure levels do not exceed the background sound pressure levels by at least 10 dB(A), a takeoff
measurement point nearer to the start of the
takeoff roll must be used and the results
must be adjusted to the reference measurement point by an approved method.
Sec. G36.109 Data Recording, Reporting, and
Approval.
(a) Data representing physical measurements and adjustments to measured data
must be recorded in permanent form and appended to the record, except that corrections
to measurements for normal equipment response deviations need not be reported. All
other adjustments must be approved. Estimates must be made of the individual errors
inherent in each of the operations employed
in obtaining the final data.
(b) Measured and corrected sound pressure
levels obtained with equipment conforming
to the specifications in section G36.105 of
this appendix must be reported.
(c) The type of equipment used for measurement and analysis of all acoustical, airplane performance, and meteorological data
must be reported.
(d) The following atmospheric data, measured immediately before, after, or during
each test at the observation points prescribed in section G36.101 of this appendix
must be reported:
(1) Ambient temperature and relative humidity.
(2) Maximum and average wind speeds and
directions for each run.
(e) Comments on local topography, ground
cover, and events that might interfere with
sound recordings must be reported.
(f) The aircraft position relative to the
takeoff reference flight path must be determined by an approved method independent of
normal flight instrumentation, such as radar

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