819 

Federal Aviation Administration, DOT 

Pt. 36, App. H 

measurement procedures that must be used 
to measure helicopter noise during each test. 

(b) 

Test site requirements. 

(1) Tests to show 

compliance with established helicopter noise 
certification levels must consist of a series 
of takeoffs, level flyovers, and approaches 
during which measurement must be taken at 
noise measuring stations located at the 
measuring points prescribed in this section. 

(2) Each takeoff test, flyover test, and ap-

proach test includes simultaneous measure-
ments at the flight-track noise measuring 
station vertically below the reference flight 
path and at two sideline noise measuring 
stations, one on each side of the reference 
flight track 492 feet (150m) from, and on a 
line perpendicular to, the flight track of the 
noise measuring station. 

(3) The difference between the elevation of 

either sideline noise measuring station may 
not differ from the flight-track noise meas-
uring station by more than 20 feet. 

(4) Each noise measuring station must be 

surrounded by terrain having no excessive 
sound absorption characteristics, such as 
might be caused by thick, matted, or tall 
grass, shrubs, or wooded areas. 

(5) During the period when the takeoff, fly-

over, or approach noise/time record indicates 
the noise measurement is within 10 dB of 
PNLTM, no obstruction that significantly 
influences the sound field from the aircraft 
may exist— 

(i) For any flight-track or sideline noise 

measuring station, within a conical space 
above the measuring position (the point on 
the ground vertically below the microphone), 
the cone being defined by an axis normal to 
the ground and by half-angle 80

° 

from this 

axis; and 

(ii) For any sideline noise measuring sta-

tion, above the line of sight between the 
microphone and the helicopter. 

(6) If a takeoff or flyover test series is con-

ducted at weights other than the maximum 
takeoff weight for which noise certification 
is requested, the following additional re-
quirements apply: 

(i) At least one takeoff test and one flyover 

test must be conducted at, or above, the 
maximum certification weight. 

(ii) Each test weight must be within + 5 

percent or 

¥

10 percent of the maximum cer-

tification weight. 

(7) Each approach test must be conducted 

with the aircraft stabilized and following a 
6.0 degree 

±

0.5 degree approach angle and 

must meet the requirements of section 
H36.107 of this part. 

(8) If an approach test series is conducted 

at weights other than the maximum landing 
weight for which certification is requested, 
the following additional requirements apply: 

(i) At least one approach test must be con-

ducted at a weight at, or above, the max-
imum landing weight. 

(ii) Each test weight must be between + 5 

percent and 

¥

10 percent of the maximum 

certification weight. 

(c) 

Weather restrictions. 

The tests must be 

conducted under the following atmospheric 
conditions: 

(1) No rain or other precipitation. 
(2) Ambient air temperature between 14 

°

F 

and 95 

°

F (

¥

10 

°

C and 35 

°

C), inclusively, at 

a point 33 feet (10 meters) above the ground 
at the noise measuring station and at the 
aircraft. The temperature and relative hu-
midity measured at a point 33 feet (10 me-
ters) above the ground at the noise meas-
uring station must be used to adjust for 
propagation path absorption. 

(3) Relative humidity and ambient tem-

perature at a point 33 feet (10 meters) above 
the ground at the noise measuring station 
and at the aircraft, is such that the sound at-
tenuation in the one-third octave band cen-
tered at 8 kHz is not greater than 12 dB/100 
meters and the relative humidity is between 
20 percent and 95 percent, inclusively. 

(4) Wind velocity as measured at 10 meters 

above ground does not exceed 10 knots (19 
km/h) and the crosswind component does not 
exceed 5 knots (9 km/h). The wind shall be 
determined using a continuous thirty-second 
averaging period spanning the 10dB down 
time interval. 

(5) No anomalous meteorological condi-

tions (including turbulence) that will signifi-
cantly affect the noise level of the aircraft 
when the noise is recorded at each noise 
measuring station. 

(6) The wind velocity, temperature, and 

relative humidity measurements required 
under the appendix must be measured in the 
vicinity of noise measuring stations 10 me-
ters above the ground. The location of the 
meteorological measurements must be ap-
proved by the FAA as representative of those 
atmospheric conditions existing near the 
surface over the geographical area which air-
craft noise measurements are made. In some 
cases, a fixed meteorological station (such as 
those found at airports or other facilities) 
may meet this requirement. 

(7) Temperature and relative humidity 

measurements must be obtained within 30 
minutes of each noise test. 

(d) 

Aircraft testing procedures. 

(1) The air-

craft testing procedures and noise measure-
ments must be conducted and processed in a 
manner that yields the noise evaluation 
measure designated as Effective Perceived 
Noise Level (EPNL) in units of EPNdB, as 
prescribed in Appendix A of this part. 

(2) The helicopter height and lateral posi-

tion relative to the reference flight track 
(which passes through the flight track noise 
measuring station) must be determined 
using an FAA-approved method. The equip-
ment used to make the determination must 
be independent of normal flight instrumen-
tation. Applicable independent systems are 

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