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in the one-third octave band centred on 8 kHz will not
be more than 12 dB/ 100 m;
d) if the atmospheric absorption coefficients vary over the
PNLTM sound propagation path by more than
*0.5 dB1100 m in the 3 150 Hz one-third octave band
fiom the value of the absorption coefficient derived fiom
the meteorological measurement obtained at 10 m above
the surface, "layered" sections of the atmosphere must be
used to compute equivalent weighted sound attenuations
in each one-third octave band, sufficient sections being
used to the satisfaction of thc certificating authority;
where multiple layering is not required, equivalent sound
attenuations in each one-thud octave band shall be
determined by averaging the atmospheric absorption
coefficients for each such band at 10 m (33 ft) above
ground level and at the flight level of the test aircraft at
the time of PNLTM, for each measurement;
e) at 10 m (33 ft) above ground, for aeroplanes, average
wind speed shall not exceed 22 km/h (12 kt) and crosswind
average wind speed shall not exceed 13 km/h
(7 kt); for helicopters, average wind speed shall not
exceed 19 kmh (10 kt) and crosswind average wind
speed shall not exceed 9 km/h (5 kt); for aeroplanes, the
wind gust shall not exceed 28 kmlh (1 5 kt) and the crosswind
gust shall not exceed 18 kmm (10 kt);
Note.- Average wind speed is defined over a 30-
second time period.
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 certificating authority; and
g) meteorological measurements must be obtained within
30 minutes of each noise test measurement; meteorological
data shall be interpolated to actual times of each
noise measurement.
2.2.3 When a multiple layering calculation is required by
2.2.2 d), the atmosphere between the aircraft and 10 m (33 ft)
above the ground shall be divided into layers of equal depth.
The depth of the layers shall be set to not more than the depth
of the narrowest layer across which the variation in the atmospheric
absorption coefficient of the 3 150 Hz one-third octave
band is not greater than *0.5 dB1100 m, with a minimum layer
depth of 30 m (100 ft). This shall apply over 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.
2.2.4 The requirements of 2.2.2 b), c) and d) shall only be
applied at a point 10 m (33 ft) above ground for tests of
helicopters.
2.2.5 The aerodrome control tower or another facility
shall be approved 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 ma&.
2.3 Flight path measurement
2.3.1 The aircraft height and lateral position relative to
the flight track shall 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 certificating authority.
2.3.2 The aircraft position along the flight path shall 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.
2.3.3 Position and performance data required to make the
adjustments referred to in Section 8 or 9 of this appendix shall
24/11/05 APP 2-2
Appendix 2 Annex 16 - Environmental Protection
be automatically recorded at an approved sampling rate.
Measuring equipment shall be approved by the certificating
authority.
3. MEASUREMENT OF AIRCRAFT
NOISE RECEIVED ON THE GROUND
3.1 Definitions
For the purposes of this section the following defmitions
apply:
Ambient noise. The acoustical noise from sources other than
the test aircraft present at the microphone site during aircraft
noise measurement. Ambient noise is one component
of background noise.
Free-fied sensitivity of a microphone system. In volts per
pascal, for a sinusoidal plane progressive sound wave of
specified frequency, at a specified sound-incident 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.
Level diflerence. In decibels, for any nominal one-third octave
　
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