Federal Aviation Administration, DOT

Pt. 36, App. H

spaschal on DSK3GDR082PROD with CFR

corrected to reference conditions may be derived from FAA approved manufacturer-s
data.
(ii) The sound propagation paths to the
microphone from the aircraft position corresponding to PNLTM must be determined
for both the test and reference profiles. The
SPL values in the spectrum of PNLTM must
then be corrected for the effects of - 
(A) Change in atmospheric sound absorption;
(B) Atmospheric sound absorption on the
linear difference between the two sound path
lengths; and
(C) Inverse square law on the difference in
sound propagation path length. The corrected values of SPL must then be converted
to a reference condition PNLTM value from
which PNLTM must be subtracted. The resulting difference represents the correction
which must be added algebraically to the
EPNL calculated from the measured data.
(iii) As observed at the noise measuring
station, the measured PNLTM distance is
different from the reference PNLTM distance
and therefore the ratio must be calculated
and used to determine a noise duration cor-

rection factor. Effective perceived noise
level, EPNL, is determined by the algebraic
sum of the maximum tone corrected perceived noise level (PNLTM) and the duration
correction factor.
(iv) For aircraft flyover, alternative source
noise corrections require FAA approval and
must be determined and adjusted to account
for noise level changes caused by the differences between measured test conditions
and reference conditions.
(b) Takeoff profiles. (1) Figure H1 illustrates
a typical takeoff profile, including reference
conditions.
(i) The reference takeoff flight path is described in section H36.3(c).
(ii) The test parameters are functions of
the helicopter-s performance and weight and
the atmospheric conditions of temperature,
pressure, wind velocity and direction.
(2) For the actual takeoff, the helicopter
approaches position C in level flight at 65
feet (20 meters) above ground level at the
flight track noise measuring station and at
either Vy Section5 knots or the lowest approved
speed for the climb after takeoff, whichever
speed is greater.

823

VerDate Sep<11>2014

12:50 Apr 30, 2019

Jkt 247046

PO 00000

Frm 00833

Fmt 8010

Sfmt 8002

Y:\SGML\247046.XXX

247046