spaschal on DSK3GDR082PROD with CFR

Pt. 36, App. A

14 CFR Ch. I (1-1-19 Edition)

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 Section1.6 dB/1000
ft (Section0.5 dB/100m), with a minimum layer
depth of 100 ft (30 m). This requirement must
be met for the propagation path at PNLTM.
The mean of the values of the atmospheric
absorption coefficients at the top and bottom of each layer may be used to characterize the absorption properties of each
layer.
A36.2.2.4 The airport control tower or another facility must be aproved by the FAA
for use as the central location at which
measurements of atmospheric parameters
are representative of those conditions existing over the geographical area in which noise
measurements are made.
A36.2.3 Flight path measurement.
A36.2.3.1 The airplane height and lateral
position relative to the flight track must be
determined by a method independent of normal flight instrumentation such as radar
tracking, theodolite triangulation, or photographic scaling techniques, to be approved
by the FAA.
A36.2.3.2 The airplane position along the
flight path must be related to the noise re-

corded 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 (incorporated by reference, see Section 36.6).
NOTE: When the sound incidence angle is
0Section, the sound is said to be received at the
microphone at  - normal (perpendicular) incidence; -  when the sound incidence angle is
90Section, 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 0Section, 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

778

VerDate Sep<11>2014

12:50 Apr 30, 2019

Jkt 247046

PO 00000

Frm 00788

Fmt 8010

Sfmt 8002

Y:\SGML\247046.XXX

247046