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is made on or afier 26 November 1981. the noise levels produced
by installed APU and associated aircraft systems should
not e~ceedth ose existing prior to the change, when determined
in accordance with h following guidelines.
2. NOISE EVALUATION
PROCEDURE
The noise evaluation procedure should be according to the
methods specified in Section 4.
3. MAXIMUM NOlSE LEVELS
4. NOISE EVALUATION
PROCEDURES
4.1 General
4.1.1 Test procedures are described for measuring noise
at specific locations (psssenger and cargo doors. and servicing
positions) and for conducting general noise surveys around
aircrafl.
4.1.2 Requirements are identified with respect to instrumentation,
acoustic and amospbenc environment data acquisition.
reduction and presentation, and such other information
sf is needed for reporting the resulk.
4.1 -3 Procedures involve recording data on magnetic tape
for subsequent processing. The use of tape-recorder timeintegrating
analyser systems avoids the need to average by eye
the variations sfsociated with manual readings &om sound
level meters and octave band analysers and therefore yields
more accurate results.
4.1.4 No provision is made for predicting APU noise
from basic engine characteristics. nor for measuring noise of
more than one aircraft operating at the m eti me.
4.2 Cenernl test conditions
4.2.1 Meteorological conditions
Mnd: not more than 19 km/h (10 kt).
The maximum noise levels, when determined in accordnnce Temperuhrre: not lesq than nor more than 3S°C.
with the noise evaluation procedure specified in Scction 4.
should not exceed the following: H~tnrtrlig.:r elative humidity rmt less than 30 per ccnt nor more
than 90 per cent.
a) 85 dB(A) at the points specified in 4.4.2.2 a). b)
and c); Ptrc~piruliori: nonc.
b) 90 dB(A) at any point on the perimctcr of the rectangle Bur-omerric pressure. no1 less than 800 hP4 nor rnorc [hail
shown in Figure C-2. 1 I00 hPa.
ANNEX lb - VOLUME 1 ATT C- l 2411 1/05
Annex I6 - Ent~irontnenralP rotection Volume I
4.2.2 Test site
The ground betwecn microphonc and aircrafl should be a
smooth. hard surface. fro obstructions should bc present
betwcen aucrafi and measurement positrons and no reflecting
surfaces (except the ground nnd sircrdfl) should be near enough
to sound pnths to sipificantly influence results. Surface of thc
p u n d surrounding the aircraft should be sensibly flat and
level at least over an area formed by boundaries parallel to and
60 m bcyond the outermost microphone array identified in
4.4.2.2 d).
4.2.3 Ambient noise
Ambient noise of the measurement system and test ma (that
is. composite of the noise due to environmental background
and the eleclncal noise of the acoustic insuurnentation) should
be determined.
4.2.4 APU i~btallalio~l
Pertinent APU and assoc~ated aircraA systems should be testcd
for each aircraft model for which acoustic data are required.
4.2.5 Aircrafi ground configuration
Aircraft fl~ght control surfaces should be in the "neutral" or
"clean" configuration, with gust locks on. or as stated in the
aircrafl's approved operating manual for aircraft undergoing
servicing.
Operational data identified in 4.5.4 should bc determined from
normal aircraft instruments and controls.
4.3.2 Acoustical
Instrumentat ion and measurement procedures should bc
consisten! with requirements of latest applicable issues of
appropriate standards listcd !n the references (see 4.6). All
data samples should be at least 2.5 tlrnes Lhe dam reduction
integration period which In no case should be Less than 8 s.
All sound pressure levels should be in decikls to a reference
prcssurc of 20 pPa.
lnstmmcntalian systems for record~ng and analysis of nois.
shown in the block diagram of Figure C-1. should meet the
following spec1 fications:
a) Over a frequency range of at lcast 45 Hz to 11 200 Hz
thc system should meet the requirerncnts as oullincd
under microphone systlm specifications in the latest
issue of reference 10 [see 4.6).
b) Mscrophones should be omnidirectional, vented for
pressure equalization if of condenser typc. and should
have known ambient pressure and temperature coefficients.
Microphone amplifier specifications should be
compat~ble with those of the microphone and tape
recorder.
c) Microphone wind screens should be employed when
wind speed is in excess of 11 km/h (6 kt). Corrections
as a function of frequency should b applied to
measured data to account for the presence of microphone
wind screens.
The tapc recorder may be direct record or FM and should have
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