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statistically a 90 per cent confidence limit not exceeding
+1.5 &(A). No test result shall be omitted from the averaging
process, unless otherwise specified by the certificating
authority.
Note.- Methods for calculating the 90 per cent confidence
interval are given in Appendix 1 of Doc 9501.
APP 3-4
APPENDIX 4. EVALUATION METHOD FOR NOISE CERTIFICATION
OF HELICOPTERS NOT EXCEEDING 3 175 kg MAXIMUM
CERTIFICATED TAKE-OFF MASS
Note.- See Part ZI, Chapter 11.
1. INTRODUCTION space above the test noise measurement position, the cone
being defined by an axis normal to the ground and by a half-
Note 1.- This noise evaluation method includes: angle of 80" from this axis.
a) noise certijication test and measurement conditions; Note.- Those people carrying out the measurements could
themselves constitute such obstructions.
b) definition of sound exposure level using measured noise
data; 2.2.2 The tests shall be carried out under the following
atmospheric conditions:
c) measurement of helicopter noise received on the
ground; a) no precipitation;
d) adjustment offight test results; and
e) reporting of data to the certificating authority.
Note 2.- The instructions and procedures given in the
method are intended to ensure uniformity during compliance
tests of various types of helicopters conducted in various
geographical locations. The method applies only to helicopters
meeting the applicability clauses of Part II, Chapter 11, of this
Annex.
2. NOISE CERTIFICATION
TEST AND MEASUREMENT
CONDITIONS
2.1 General
This section prescribes the conditions under which noise
certification shall be conducted and the meteorological and
flight path measurement procedures that shall be used.
b) relative humidity not higher than 95 per cent or lower
than 20 per cent and ambient temperature not above
35°C and not below 2°C at a height between 1.2 m and
10 m above ground (if the measurement site is within
2 000 m of aerodrome weather measuring equipment,
the aerodrome reported temperature, relative humidity
and wind speed may be used). Combinations of
tcmpcrature and humidity which lead to an absorption
coefficient in the 8 KHz one-third octave band of greater
than 10 dB1100 m shall be avoided. Absorption
coefficients as a function of temperature and relative
humidity are given in Section 7 of Appendix 2 or SAE
ARP 866 A;
c) at a height between 1.2 m (4 ft) and 10 m (33 ft) above
ground, average wind speed shall not exceed 19 kmh
(10 kt) and the crosswind average wind speed component
at right angles to the direction of flight shall not
exceed 9 krnh (5 kt) at a height between 1.2 m (4 it)
and 10 m (33 ft) above ground; and
Note.- Average wind speed is defined over a 30-
second time period.
d) no other anomalous meteorological conditions that
would significantly affect the noise level when recorded
2.2 Test environment at the measuring points specified by the certificating
authority.
2.2.1 The location for measuring noise from the helicopter
in flight shall be surrounded by relativcly flat terrain
having no excessive ground absorption characteristics such as 2.3 Flight path measurement
might be caused by thick, matted or tall grass, shrubs or
wooded areas. No obstructions which significantly influence 2.3.1 The helicopter position relative to the flight path
the sound field from the helicopter shall exist within a conical reference point shall be determined by a method independent
ANNEX 16 - VOLUME I APP 4-1 24/11/05
Annex I6 - Environmental Protection Volume I
of normal flight instrumentation, such as radar tracking,
theodolite triangulation or photographic scaling techniques,
approved by the certificating authority.
2.3.2 The helicopter noise shall be measured over a
distance sufficient to ensure adequate data during the period
that the noise is within 10 dB(A) of the maximum value of
&(A).
2.3.3 Position and performance data required to make the
adjustments referred to in Section 5 of this appendix shall be
recorded at an approved sampling rate. Measuring equipment
shall be approved by the certificating authority.
2.4 Flight test conditions
2.4.1 The helicopter flyover noise test shall be conducted
at the airspeed referred to in Part 11, Chapter 11, 11.5.2 with
such airspeed adjusted as necessary to produce the same
advancing blade tip Mach number as associated with the
reference conditions.
2.4.2 Advancing blade tip Mach number (Mat) is defined
as the ratio of the arithmetic sum of blade tip rotational speed
(Vt) and the helicopter true airspeed (Vr) divided by the speed
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