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octave band.
Adjusted sound pressure level. The first approximation to broadband sound pressure level in the i-th
one-third octave band for the k-th instant of time.
Muximum sound pressure level. The sound pressure level that occurs in the i-th one-third octave band of
the spectrum for PNLTM.
Corrected maximum sound pressure level. The sound pressure level that occurs in the i-th one-third
octave band of the spectrum for PNLTM corrected for atmospheric sound absorption.
APP 2-17
Annex 16 - Environmental Protection Volume I
Symbol Unit Meaning
SPLn(i, k) dB re Final broadband soundpressure level. The second and fmal approximation to broadband sound pressure
20 F P ~ level in the i-th one-third octave band for the k-th instant of time.
t
t l , t2
At
s Elapsed time. The length of time measured f?om a reference zero.
s lime limit. The beginning and end, respectively, of the significant noise time history defmed by h.
s lime increment. The equal increments of time for which PNL(k) and PNLT(k) are calculated.
s Normalizing time constant. The length of time used as a reference in the integration method for computing
duration corrections, where T = 10 s.
t c'c) "C Temperature. The ambient atmospheric temperature.
4 ) dB1100 m Test atmospheric absoiption. The atmospheric attenuation of sound that occurs in the i-th one-third
octave band for the measured atmospheric temperature and relative humidity.
a(90 dB1100 m Reference atmospheric absorption. The atmospheric attenuation of sound that occurs in the i-th one-third
octave band for a reference atmospheric temperature and relative humidity.
GI degrees First constant* climb angle.
*2 degrees Second constant ** climb angle.
6 degrees Thrust cutback angles. The angles defining the points on the take-off flight path at which thrust reduction
E degrees is started and ended respectively.
'l degrees Approach angle.
' l r degrees Reference approach angle.
0 degrees Noise angle (relative to flight path). The angle between the flight path and noise path. It is identical for
both measured and corrected flight paths.
degrees Noise angle (relative to ground). The angle between the noise paths and the ground. It is identified for
both measured and corrected flight paths.
)I degrees Engine noise emission parameter. (See 9.3.4.)
4 EPNdB PNLT correction. The correction to be added to the EPNL calculated fiom measured data to account for
noisc level changes due to differences m atmospheric absorption and noise path length between reference
and test conditions.
A2 EPNdB A@ustment to duration correction. The adjustment to be made to the EPNL calculated from measured
data to account for noise level changes due to the noise duration between reference and test conditions.
4 EPNdB Source noise adjustment. The adjustment to be made to the EPNL calculated kom measured data to
account for noise level changes due to differences between reference and test engine regime.
Gear up, speed of at least V2 + 19 kmm (V2 + 10 kt), take-off thrust.
** Gear up, speed of at least V2 + 19 kmm (V2 + 10 kt), after cutback.
APP 2-18
Appendix 2 Annex 16 - Environmental Protection
7. SOUND ATTENUATION
IN AIR
a) attenuation of the noise along its path as affected by
"inverse square" and atmospheric attenuation;
7.1 The atmospheric attenuation of sound shall be deter- b) duration of the noise as affected by distance and speed of
mined in accordance with the procedure presented below. aircraft relative to the flight path reference point;
7.2 The relationship between sound attenuation, frequency,
temperature and humidity is expressed by the following
equations:
where:
q(6) is given by Table A2-4 and& by Table A2-5;
a(i) being the attenuation coefficient in dB1100 m;
0 being the temperature in "C; and
H being the relative humidity expressed as a percentage.
c) the adjustment procedure described in this section
shall apply to the lateral microphones in the take-off,
ovefflight and approach cases. Although the noise
emission is strongly dependent on the directivity pattern,
variable from one helicopter type to another, the
propagation angle 0, defmed in ~ p ~ e n d2i,x 9 .3.2, Figure
A2-11, shall be the same for the test and rcfercnce
flight paths. The elevation angle iq shall not be constrained
as in the third note of Appendix 2, 9.3.2, but
must be determined and reported. The certification
authority shall specify the acceptable limitations on iq.
Corrections to data obtained when these limits are
exceeded shall be applied using procedures approved by
the certificating authority. In the particular case of lateral
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