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Annex I6 - Environmental Proleetion Volume Z
of normal flight instrumentation, such as radar tracking,
theodolite triangulation or photographic scaling techniques,
approved by the certificating authorities.
2.3.5 The aeroplane height when directly over the microphone
shall be measured by an approved technique. The
aeroplane shall pass over the microphone within *lo0 from the
vertical and within k20 per cent of the reference height (see
Figure A6-1).
2.3.6 Aeroplane speed, position and performance data
required to make the adjustments referred to in Section 5 of
this appendix shall be recorded when the aeroplane is directly
over the measurement site. Measuring equipment shall be
approved by the certificating authority.
2.3.7 An independent device accurate to within *1 per
cent shall be used for the measurement of propeller rotational
speed to avoid orientation and installation errors when the test
aeroplane is equipped with mechanical tachometers.
3. NOISE UNIT DEFINITION
The Lh,, is defined as the maximum level, in decibels, of the
A-weighted sound pressure (slow response) with reference to
the square of the standard reference sound pressure (Po) of
20 micropascals (pPa).
4. MEASUREMENT OF AEROPLANE
NOISE RECEIVED ON THE GROUND
4.1 General
4.1.1 All measuring equipment shall be approved by the
certificating authority.
4.1.2 Sound pressure level data for noise evaluation
purposes shall be obtained with acoustical equipment and
measurement practices that conform to the specifications given
in 4.2.
4.2 Measurement system
The acoustical measurement system shall consist of approved
equipment equivalent to the following:
a) a microphone system with frequency response compatible
with measurement and analysis system accuracy as
stated in 4.3;
b) tripods or similar microphone mountings that minimize
interference with the sound being measured;
c) recording and reproducing equipment characteristics,
frequency response, and dynamic range compatible with
the response and accuracy requirements of 4.3; and
Height (rn)
I
o FIRST PHASE ' SECOND PHASE 2 iO0
Distance from brake release (rn)
Figure A6-1. Typird test and reference profiles
APP 6-2
Appendix 6 Annex 16 - Environmental Protection
d) acoustic calibrators using sine wave or broadband noise
of known sound pressure level. If broadband noise is
used, the signal shall be described in terms of its average
and maximum root-mean-squarc (rms) value for nonoverload
signal level.
4.3 Sensing, recording and
reproducing equipment
4.3.1 The sound level produced by the aeroplane shall
be recorded. A magnetic tape recorder, graphic level recorder
or sound level meter is acceptable at the option of the
certificating authority.
4.3.2 The characteristics of the complete system shall
comply with the recommendations given in International
Electrotechnical Commission (IEC) Publication No. 65 1 ' with
regard to the sections concerning microphone, amplifier and
indicating instrument characteristics. The text and specifications
of IEC Publication No. 651 entitled "Sound Level
Meters" are incorporated by reference into this section and are
made a part hereof.
Note.- q a tape recording is required by the certijicating
authority, the tape recorder shall comply with IEC
Recommendation 561.
4.3.3 The response of the complete system to a sensibly
plane progressive sinusoidal wave of constant amplitude shall
lie within the tolerance limits specified in Table IV and
Table V for Type 1 instruments in IEC Publication No. 651, for
weighting curve "A" over the frequency range 45 to 11 500 Hz.
4.4 Noise measurement
procedures
4.4.1 The microphone shall be a 12.7 mm diameter
pressure type, with its protective grid, mounted in an inverted
position such that the microphone diaphragm is 7 mrn above
and parallel to a circular metal plate. This white-painted metal
plate shall be 40 cm in diameter and at least 2.5 mm thick and
shall be placed horizontally and flush with the surrounding
ground surface with no cavities below the plate. The microphone
shall be located three-quarters of the distance from the
centre to the edge along a radius normal to the line of flight of
the test aeroplane.
4.4.2 If the noise signal is tape-recorded, the frequency
response of the electrical system shall be determined, during
each test series, at a level within 10 dB of the fill-scale
reading used during the tests, utilizing random or pseudorandom
pink noise. The output of the noise generator shall
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