821 

Federal Aviation Administration, DOT 

Pt. 36, App. H 

rotor RPM by more than 

±

1.0 percent during 

the 10 dB-down time interval; and 

(6) The constant approach configuration 

used in airworthiness certification tests, 
with the landing gear extended, must be 
maintained throughout the approach ref-
erence procedure. 

(c) The airspeed shall not vary from the 

reference airspeed by more than 

±

5 knots (

±

9 

km/hr). 

Section H36.109 Measurement of Helicopter 

Noise Received on the Ground. 

The measurement system and the measure-

ment, calibration and general analysis pro-
cedures to be used are provided in Appendix 
A, section A36.3 of this part. 

Section H36.111 Reporting and correcting 

measured data. 

(a) 

General. 

Data representing physical 

measurements, and corrections to measured 
data, including corrections to measurements 
for equipment response deviations, must be 
recorded in permanent form and appended to 
the record. Each correction must be reported 
and is subject to FAA approval. An estimate 
must be made of each individual error inher-
ent in each of the operations employed in ob-
taining the final data. 

(b) 

Data reporting. 

(1) Measured and cor-

rected sound pressure levels must be pre-
sented in one-third octave band levels ob-
tained with equipment conforming to the 
standards prescribed in section H36.109 of 
this appendix. 

(2) The type of equipment used for meas-

urement and analysis of all acoustic, aircraft 
performance, and meteorological data must 
be reported. 

(3) The atmospheric environmental data 

required to demonstrate compliance with 
this appendix, measured throughout the test 
period, must be reported. 

(4) Conditions of local topography, ground 

cover, or events which may interfere with 
sound recording must be reported. 

(5) The following aircraft information 

must be reported: 

(i) Type, model, and serial numbers, if any, 

of aircraft engines and rotors. 

(ii) Gross dimensions of aircraft and loca-

tion of engines. 

(iii) Aircraft gross weight for each test 

run. 

(iv) Aircraft configuration, including land-

ing gear positions. 

(v) Airspeed in knots. 
(vi) Helicopter engine performance as de-

termined from aircraft instruments and 
manufacturer’s data. 

(vii) Aircraft flight path, above ground 

level in feet, determined by an FAA approved 
method which is independent of normal 
flight instrumentation, such as radar track-
ing, theodolite triangulation, laser 

trajectography, or photographic scaling 
techniques. 

(6) Aircraft speed, and position, and engine 

performance parameters must be recorded at 
an approved sampling rate sufficient to cor-
rect to the noise certification reference test 
conditions prescribed in section H36.3 of this 
appendix. Lateral position relative to the 
reference flight-track must be reported. 

(c) 

Data corrections. 

(1) Aircraft position, 

performance data and noise measurement 
must be corrected to the noise certification 
reference conditions as prescribed in sections 
H36.3 and H36.205 of this appendix. 

(2) The measured flight path must be cor-

rected by an amount equal to the difference 
between the applicant’s predicted flight path 
for the certification reference conditions and 
the measured flight path at the test condi-
tions. Necessary corrections relating to heli-
copter flight path or performance may be de-
rived from FAA-approved data for the dif-
ference between measured and reference con-
ditions, together with appropriate allow-
ances for sound attenuation with distance. 
The Effective Perceived Noise Level (EPNL) 
correction may not exceed 2.0 EPNdB except 
for takeoff flight condition, where the cor-
rection may not exceed 4.0 EPNdB, of which 
the arithmetic sum of 

D

1

(described in sec-

tion H36.205(f)(1)) and the term 

¥

7.5 log (AL/ 

AL

r

) from 

D

2

term (described in section 

H36.205(g)(1)(i)) may not exceed 2.0 EPNdB, 
for any combination of the following: 

(i) The helicopter not passing vertically 

above the measuring station. 

(ii) Any difference between the reference 

flight track and the actual test flight track; 
and 

(iii) Detailed correction requirements pre-

scribed in section H36.205 of this appendix. 

(3) Helicopter sound pressure levels within 

the 10 dB-down time interval must exceed 
the mean background sound pressure levels 
determined under section B36.3.9.11 by at 
least 3 dB in each one-third octave band, or 
must be corrected under an FAA-approved 
method. 

(d) 

Validity of results. 

(1) The test results 

must produce three average EPNL values 
within the 90 percent confidence limits, each 
value consisting of the arithmetic average of 
the corrected noise measurements for all 
valid test runs at the takeoff, level flyovers, 
and approach conditions. The 90 percent con-
fidence limit applies separately to takeoff, 
flyover, and approach. 

(2) The minimum sample size acceptable 

for each takeoff, approach, and flyover cer-
tification measurements is six. The number 
of samples must be large enough to establish 
statistically for each of the three average 
noise certification levels a 90 percent con-
fidence limit which does not exceed 

±

1.5 

EPNdB. No test result may be omitted from 
the averaging process, unless otherwise spec-
ified by the FAA. 

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