Previous Page Page 929 Next Page  
background image

920 

14 CFR Ch. I (1–1–14 Edition) 

Pt. 36, App. A 

A36.2.1.1 This section prescribes the condi-

tions under which noise certification must 
be conducted and the measurement proce-
dures that must be used. 

N

OTE

: Many noise certifications involve 

only minor changes to the airplane type de-
sign. The resulting changes in noise can 
often be established reliably without resort-
ing to a complete test as outlined in this ap-
pendix. For this reason, the FAA permits the 
use of approved equivalent procedures. There 
are also equivalent procedures that may be 
used in full certification tests, in the inter-
est of reducing costs and providing reliable 
results. Guidance material on the use of 
equivalent procedures in the noise certifi-
cation of subsonic jet and propeller-driven 
large airplanes is provided in the current ad-
visory circular for this part. 

A36.2.2 

Test environment. 

A36.2.2.1 Locations for measuring noise 

from an airplane in flight must be sur-
rounded by relatively flat terrain having no 
excessive sound absorption characteristics 
such as might be caused by thick, matted, or 
tall grass, shrubs, or wooded areas. No ob-
structions that significantly influence the 
sound field from the airplane must exist 
within a conical space above the point on the 
ground vertically below the microphone, the 
cone being defined by an axis normal to the 
ground and by a half-angle 80

° 

from this axis. 

N

OTE

: Those people carrying out the meas-

urements could themselves constitute such 
obstruction. 

A36.2.2.2 The tests must be carried out 

under the following atmospheric conditions. 

(a) No precipitation; 
(b) Ambient air temperature not above 95 

°

F (35 

°

C) and not below 14 

°

F (¥10 

°

C), and 

relative humidity not above 95% and not 
below 20% over the whole noise path between 
a point 33 ft (10 m) above the ground and the 
airplane; 

N

OTE

: Care should be taken to ensure that 

the noise measuring, airplane flight path 
tracking, and meteorological instrumenta-
tion are also operated within their specific 
environmental limitations. 

(c) Relative humidity and ambient tem-

perature over the whole noise path between 
a point 33 ft (10 m) above the ground and the 
airplane such that the sound attenuation in 
the one-third octave band centered on 8 kHz 
will not be more than 12 dB/100 m unless: 

(1) The dew point and dry bulb tempera-

tures are measured with a device which is ac-
curate to 

±

0.9 

°

F (

±

0.5 

°

C) and used to obtain 

relative humidity; in addition layered sec-
tions of the atmosphere are used as described 
in section A36.2.2.3 to compute equivalent 
weighted sound attenuations in each one- 
third octave band; or 

(2) The peak noy values at the time of 

PNLT, after adjustment to reference condi-

tions, occur at frequencies less than or equal 
to 400 Hz.; 

(d) If the atmospheric absorption coeffi-

cients vary over the PNLTM sound propaga-
tion path by more than 

±

1.6 dB/1000 ft (

±

0.5 

dB/100m) in the 3150Hz one-third octave band 
from the value of the absorption coefficient 
derived from the meteorological measure-
ment obtained at 33 ft (10 m) above the sur-
face, ‘‘layered’’ sections of the atmosphere 
must be used as described in section A36.2.2.3 
to compute equivalent weighted sound at-
tenuations in each one-third octave band; 
the FAA will determine whether a sufficient 
number of layered sections have been used. 
For each measurement, where multiple 
layering is not required, equivalent sound at-
tenuations in each one-third octave band 
must be determined by averaging the atmos-
pheric absorption coefficients for each such 
band at 33 ft (10 m) above ground level, and 
at the flight level of the airplane at the time 
of PNLTM, for each measurement; 

(e) Average wind velocity 33 ft (10 m) above 

ground may not exceed 12 knots and the 
crosswind velocity for the airplane may not 
exceed 7 knots. The average wind velocity 
must be determined using a 30-second aver-
aging period spanning the 10 dB-down time 
interval. Maximum wind velocity 33 ft (10 m) 
above ground is not to exceed 15 knots and 
the crosswind velocity is not to exceed 10 
knots during the 10 dB-down time interval; 

(f) No anomalous meteorological or wind 

conditions that would significantly affect 
the measured noise levels when the noise is 
recorded at the measuring points specified 
by the FAA; and 

(g) Meteorological measurements must be 

obtained within 30 minutes of each noise test 
measurement; meteorological data must be 
interpolated to actual times of each noise 
measurement. 

A36.2.2.3 When a multiple layering calcula-

tion is required by section A36.2.2.2(c) or 
A36.2.2.2(d) the atmosphere between the air-
plane and 33 ft (10 m) above the ground must 
be divided into layers of equal depth. The 
depth of the layers must be set to not more 
than the depth of the narrowest layer across 
which the variation in the atmospheric ab-
sorption coefficient of the 3150 Hz one-third 
octave band is not greater than 

±

1.6 dB/1000 

ft (

±

0.5 dB/100m), with a minimum layer 

depth of 100 ft (30 m). This requirement must 
be met for the propagation path at PNLTM. 
The mean of the values of the atmospheric 
absorption coefficients at the top and bot-
tom of each layer may be used to charac-
terize the absorption properties of each 
layer. 

A36.2.2.4 The airport control tower or an-

other facility must be aproved by the FAA 
for use as the central location at which 
measurements of atmospheric parameters 

VerDate Mar<15>2010 

10:12 Mar 18, 2014

Jkt 232046

PO 00000

Frm 00930

Fmt 8010

Sfmt 8002

Y:\SGML\232046.XXX

232046

pmangrum on DSK3VPTVN1PROD with CFR

  Previous Page Page 929 Next Page