Federal Aviation Administration, DOT

Pt. 36, App. A

APPENDIX A TO PART 36 - AIRCRAFT
NOISE MEASUREMENT AND EVALUATION UNDER Section 36.101
Sec.
A36.1 Introduction.
A36.2 Noise Certification Test and Measurement
Conditions.
A36.3 Measurement of Airplane Noise Received
on the Ground.
A36.4 Calculations of Effective Perceived Noise
Level From Measured Data.
A36.5 Reporting of Data to the FAA.
A36.6 Nomenclature: Symbols and Units.
A36.7 Sound Attenuation in Air.
A36.8 [Reserved]
A36.9 Adjustment of Airplane Flight Test Results.
Section A36.1 Introduction
A36.1.1 This appendix prescribes the conditions under which airplane noise certification tests must be conducted and states
the measurement procedures that must be
used to measure airplane noise. The procedures that must be used to determine the
noise evaluation quantity designated as effective perceived noise level, EPNL, under
SectionSection 36.101 and 36.803 are also stated.
A36.1.2 The instructions and procedures
given are intended to ensure uniformity during compliance tests and to permit comparison between tests of various types of airplanes conducted in various geographical locations.
A36.1.3 A complete list of symbols and
units, the mathematical formulation of perceived noisiness, a procedure for determining
atmospheric attenuation of sound, and detailed procedures for correcting noise levels
from non-reference to reference conditions
are included in this appendix.
A36.1.4 For Stage 4 airplanes, an acceptable
alternative for noise measurement and evaluation is Appendix 2 to ICAO Annex 16, Volume I, Amendment 7 (incorporated by reference, see Section 36.6).
A36.1.5 For Stage 5 airplanes, an acceptable
alternative for noise measurement and evaluation is Appendix 2 to ICAO Annex 16, Volume 1, Amendment 11-B (incorporated by
reference, see Section 36.6).

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Section A36.2 Noise Certification Test and
Measurement Conditions
A36.2.1 General.
A36.2.1.1 This section prescribes the conditions under which noise certification must
be conducted and the measurement procedures that must be used.
NOTE: Many noise certifications involve
only minor changes to the airplane type design. The resulting changes in noise can
often be established reliably without resorting to a complete test as outlined in this appendix. 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 interest of reducing costs and providing reliable
results. Guidance material on the use of
equivalent procedures in the noise certification of subsonic jet and propeller-driven
large airplanes is provided in the current advisory circular for this part.
A36.2.2 Test environment.
A36.2.2.1 Locations for measuring noise
from an airplane in flight must be surrounded 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 obstructions 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 80Section from this axis.
NOTE: Those people carrying out the measurements 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
SectionF (35 SectionC) and not below 14 SectionF (Section10 SectionC), 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;
NOTE: Care should be taken to ensure that
the noise measuring, airplane flight path
tracking, and meteorological instrumentation are also operated within their specific
environmental limitations.
(c) Relative humidity and ambient temperature 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 temperatures are measured with a device which is accurate to Section0.9 SectionF (Section0.5 SectionC) and used to obtain
relative humidity; in addition layered sections of the atmosphere are used as described
in section A36.2.2.3 to compute equivalent
weighted sound attenuations in each onethird octave band; or
(2) The peak noy values at the time of
PNLT, after adjustment to reference conditions, occur at frequencies less than or equal
to 400 Hz.;
(d) If the atmospheric absorption coefficients vary over the PNLTM sound propagation path by more than Section1.6 dB/1000 ft (Section0.5
dB/100m) in the 3150Hz one-third octave band
from the value of the absorption coefficient
derived from the meteorological measurement obtained at 33 ft (10 m) above the surface,  - layered -  sections of the atmosphere
must be used as described in section A36.2.2.3

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