Appendix J to Part 36 - Alternative Noise Certification Procedure for Helicopters Under Subpart H Having a Maximum Certificated Takeoff Weight of Not More Than 7,000 Pounds
14:1.0.1.3.20.14.283.1.43 : Appendix J
Appendix J to Part 36 - Alternative Noise Certification Procedure
for Helicopters Under Subpart H Having a Maximum Certificated
Takeoff Weight of Not More Than 7,000 Pounds part a - reference
conditions Sec. J36.1
General. J36.3
Reference Test
Conditions. J36.5 [Reserved] part b - noise measurement
procedure under § 36.801 J36.101
Noise certification test and
measurement conditions. J36.103 [Reserved] J36.105
Flyover
test conditions. J36.107 [Reserved] J36.109
Measurement of
helicopter noise received on the ground. J36.111
Reporting
requirements. J36.113 [Reserved] part c - noise evaluation and
calculation under § 36.803 J36.201
Noise evaluation in SEL.
J36.203
Calculation of noise levels. J36.205
Detailed
data correction procedures. part d - noise limits procedure
under § 36.805 J36.301
Noise measurement, evaluation, and
calculation. J36.303 [Reserved] J36.305
Noise limits.
part a - reference conditions Section J36.1 General.
This appendix prescribes the alternative noise certification
requirements identified under § 36.1 of this part and subpart H of
this part for helicopters in the primary, normal, transport, and
restricted categories having maximum certificated takeoff weight of
not more than 7,000 pounds including:
(a) The conditions under which an alternative noise
certification test under subpart H of this part must be conducted
and the alternative measurement procedure that must be used under §
36.801 of this part to measure the helicopter noise during the
test;
(b) The alternative procedures which must be used under § 36.803
of this part to correct the measured data to the reference
conditions and to calculate the noise evaluation quantity
designated as Sound Exposure Level (SEL); and
(c) The noise limits for which compliance must be shown under §
36.805 of this part.
Section J36.3 Reference Test Conditions.
(a) Meteorological conditions. The following are the
noise certification reference atmospheric conditions which shall be
assumed to exist from the surface to the helicopter altitude:
(1) Sea level pressure of 2116 pounds per square foot (76
centimeters mercury);
(2) Ambient temperature of 77 degrees Fahrenheit (25 degrees
Celsius);
(3) Relative humidity of 70 percent; and
(4) Zero wind.
(b) Reference test site. The reference test site is flat
and without line-of-sight obstructions across the flight path that
encompasses the 10 dB down points of the A-weighted time
history.
(c) Level flyover reference profile. The reference
flyover profile is a level flight, 492 feet (150 meters) above
ground level as measured at the noise measuring station. The
reference flyover profile has a linear flight track and passes
directly over the noise monitoring station. Airspeed is stabilized
at 0.9VH; 0.9VNE; 0.45VH + 65 kts (120 km/h); or 0.45VNE + 65 kts
(120 km/h), whichever of the four airspeeds is least, and
maintained throughout the measured portion of the flyover. Rotor
speed is stabilized at the maximum normal operating RPM throughout
the 10 dB-down time interval.
(1) For noise certification purposes, VH is defined as the
airspeed in level flight obtained using the minimum specification
engine power corresponding to maximum continuous power available
for sea level pressure of 2,116 psf (1,013.25 hPa) at 77 °F (25 °C)
ambient conditions at the relevant maximum certificated weight. The
value of VH and VNE used for noise certification must be included
in the Flight Manual.
(2) VNE is the never-exceed airspeed.
(d) The weight of the helicopter shall be the maximum takeoff
weight at which noise certification is requested.
Section J36.5 [Reserved] Part B - Noise Measurement Procedure Under
§ 36.801 Section J36.101 Noise certification test and measurement
conditions.
(a) General. This section prescribes the conditions under
which helicopter noise certification tests must be conducted and
the measurement procedures that must be used to measure helicopter
noise during each test.
(b) Test site requirements. (1) The 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.
(2) During the period when the flyover noise measurement is
within 10 dB of the maximum A-weighted sound level, no obstruction
that significantly influences the sound field from the helicopter
may exist within a conical space above the noise measuring position
(the point on the ground vertically below the microphone), the cone
is defined by an axis normal to the ground and by half-angle 80
degrees from this axis.
(c) Weather restrictions. The test must be conducted
under the following atmospheric conditions:
(1) No rain or other precipitation;
(2) Ambient air temperature between 36 degrees and 95 degrees
Fahrenheit (2 degrees and 35 degrees Celsius), inclusively, and
relative humidity between 20 percent and 95 percent inclusively,
except that testing may not take place where combinations of
temperature and relative humidity result in a rate of atmospheric
attenuation greater than 10 dB per 100 meters (30.5 dB per 1000 ft)
in the one-third octave band centered at 8 kiloHertz.
(3) Wind velocity that does not exceed 10 knots (19 km/h) and a
crosswind component that does not exceed 5 knots (9 km/h). The wind
shall be determined using a continuous averaging process of no
greater than 30 seconds;
(4) Measurements of ambient temperature, relative humidity, wind
speed, and wind direction must be made between 4 feet (1.2 meters)
and 33 feet (10 meters) above the ground. Unless otherwise approved
by the FAA, ambient temperature and relative humidity must be
measured at the same height above the ground.
(5) No anomalous wind conditions (including turbulence) or other
anomalous meteorological conditions that will significantly affect
the noise level of the helicopter when the noise is recorded at the
noise measuring station; and
(6) If the measurement site is within 6560 feet (2,000 meters)
of a fixed meteorological station (such as those found at airports
or other facilities) the weather measurements reported for
temperature, relative humidity and wind velocity may be used, if
approved by the FAA.
(d) Helicopter testing procedures. (1) The helicopter
testing procedures and noise measurements must be conducted and
processed in a manner which yields the noise evaluation measure
designated Sound Exposure Level (SEL) as defined in section
J36.109(b) of this appendix.
(2) The helicopter height relative to the noise measurement
point sufficient to make corrections required under section J36.205
of this appendix must be determined by an FAA-approved method that
is independent of normal flight instrumentation, such as radar
tracking, theodolite triangulation, laser trajectography, or
photographic scaling techniques.
(3) If an applicant demonstrates that the design characteristics
of the helicopter would prevent flight from being conducted in
accordance with the reference test conditions prescribed under
section J36.3 of this appendix, then with FAA approval, the
reference test conditions used under this appendix may vary from
the standard reference test conditions, but only to the extent
demanded by those design characteristics which make compliance with
the reference test conditions impossible.
Section J36.103 [Reserved] Section J36.105 Flyover test conditions.
(a) This section prescribes the flight test conditions and
allowable random deviations for flyover noise tests conducted under
this appendix.
(b) A test series must consist of at least six flights. The
number of level flights made with a headwind component must be
equal to the number of level flights made with a tailwind component
over the noise measurement station:
(1) In level flight and in cruise configuration;
(2) At a height of 492 feet ±50 feet (150 ±15 meters) above the
ground level at the noise measuring station; and
(3) Within ±10 degrees from the zenith.
(c) Each flyover noise test must be conducted:
(1) At the reference airspeed specified in section J36.3(c) of
this appendix, with such airspeed adjusted as necessary to produce
the same advancing blade tip Mach number as associated with the
reference conditions;
(i) Advancing blade tip Mach number (MAT) is defined as the
ratio of the arithmetic sum of blade tip rotational speed (VR) and
the helicopter true air speed (VT) over the speed of sound (c) at
77 degrees Fahrenheit (1135.6 ft/sec or 346.13 m/sec) such that MAT
= (VR + VT)/c; and
(ii) The airspeed shall not vary from the adjusted reference
airspeed by more than ±3 knots (±5 km/hr) or an equivalent
FAA-approved variation from the reference advancing blade tip Mach
number. The adjusted reference airspeed shall be maintained
throughout the measured portion of the flyover.
(2) At rotor speed stabilized at the power on maximum normal
operating rotor RPM (±1 percent); and
(3) With the power stabilized during the period when the
measured helicopter noise level is within 10 dB of the maximum
A-weighted sound level (LAMAX).
(d) The helicopter test weight for each flyover test must be
within plus 5 percent or minus 10 percent of the maximum takeoff
weight for which certification under this part is requested.
(e) The requirements of paragraph (b)(2) of this section
notwithstanding, flyovers at an FAA-approved lower height may be
used and the results adjusted to the reference measurement point by
an FAA-approved method if the ambient noise in the test area,
measured in accordance with the requirements prescribed in section
J36.109 of this appendix, is found to be within 15 dB(A) of the
maximum A-weighted helicopter noise level (LAMAX) measured at the
noise measurement station in accordance with section J36.109 of
this appendix.
Section J36.107 [Reserved] Section J36.109 Measurement of
helicopter noise received on the ground.
(a) General. (1) The helicopter noise measured under this
appendix for noise certification purposes must be obtained with
FAA-approved acoustical equipment and measurement practices.
(2) Paragraph (b) of this section identifies and prescribes the
specifications for the noise evaluation measurements required under
this appendix. Paragraphs (c) and (d) of this section prescribe the
required acoustical equipment specifications. Paragraphs (e) and
(f) of this section prescribe the calibration and measurement
procedures required under this appendix.
(b) Noise unit definition. (1) The value of sound
exposure level (SEL, or as denoted by symbol, LAE), is defined as
the level, in decibels, of the time integral of squared
‘A’-weighted sound pressure (PA) over a given time period or event,
with reference to the square of the standard reference sound
pressure (PO) of 20 micropascals and a reference duration of one
second.
(2) This unit is defined by the expression:
Where TO is the reference integration time of
one second and (t2-t1) is the integration time interval.
(3) The integral equation of paragraph (b)(2) of this section
can also be expressed as:
Where LA(t) is the time varying A-weighted
sound level.
(4) The integration time (t2-t1) in practice shall not be less
than the time interval during which LA(t) first rises to within 10
dB(A) of its maximum value (LAMAX) and last falls below 10 dB(A) of
its maximum value.
(5) The SEL may be approximated by the following expression:
LAE = LAMAX + <delta>A where <delta>A is the duration
allowance given by: <delta>A = 10 log10 (T) where T =
(t2-t1)/2 and LAMAX is defined as the maximum level, in decibels,
of the A-weighted sound pressure (slow response) with reference to
the square of the standard reference sound pressure (P0).
(c) Measurement system. The acoustical measurement system
must consist of FAA-approved equipment equivalent to the
following:
(1) A microphone system with frequency response that is
compatible with the measurement and analysis system accuracy
prescribed in paragraph (d) of this section;
(2) Tripods or similar microphone mountings that minimize
interference with the sound energy being measured;
(3) Recording and reproducing equipment with characteristics,
frequency response, and dynamic range that are compatible with the
response and accuracy requirements of paragraph (d) of this
section; and
(4) The calibration and checking of measurement systems must use
the procedures described in Section A36.3.9.
(d) Sensing, recording, and reproducing equipment. (1)
The noise levels measured from helicopter flyovers under this
appendix may be determined directly by an integrating sound level
meter, or the A-weighted sound level time history may be written
onto a graphic level recorder set at “slow” response from which the
SEL value may be determined. With the approval of the FAA, the
noise signal may be tape recorded for subsequent analysis.
(i) The SEL values from each flyover test may be directly
determined from an integrating sound level meter complying with the
standards of IEC 804 (Incorporated by reference, see § 36.6) for a
Type 1 instrument set at “slow” response.
(ii) The acoustic signal from the helicopter, along with the
calibration signals specified under paragraph (e) of this section
and the background noise signal required under paragraph (f) of
this section, may be recorded on a magnetic tape recorder for
subsequent analysis for an integrating sound level meter identified
in paragraph (d)(1)(i) of this section. The record/playback system
(including the audio tape) of the tape recorder must conform to the
requirements prescribed in section A36.3.6 of appendix A to this
part. The tape recorder shall comply with the specifications of IEC
561 (Incorporated by reference, see § 36.6).
(iii) The characteristics of the complete system shall comply
with the recommendations given in IEC 651 (Incorporated by
reference, see § 36.6) with regard to the specifications concerning
microphone, amplifier, and indicating instrument
characteristics.
(iv) The response of the complete system to a sensibly plane
progressive wave of constant amplitude shall lie within the
tolerance limits specified in Table IV and Table V for Type 1
instruments in IEC 651 for weighting curve “A” over the frequency
range of 45 Hz to 11500 Hz.
(2) [Reserved]
(v) A windscreen must be used with the microphone during each
measurement of the helicopter flyover noise. Correction for any
insertion loss produced by the windscreen, as a function of the
frequency of the acoustic calibration required under paragraph (e)
of this section, must be applied to the measured data and any
correction applied must be reported.
(e) Calibrations. (1) If the helicopter acoustic signal
is tape recorded for subsequent analysis, the measuring system and
components of the recording system must be calibrated as prescribed
under section A36.3.6 of appendix A of this part.
(2) If the helicopter acoustic signal is directly measured by an
integrating sound level meter:
(i) The overall sensitivity of the measuring system shall be
checked before and after the series of flyover tests and at
intervals (not exceeding one-hour duration) during the flyover
tests using an acoustic calibrator using sine wave noise generating
a known sound pressure level at a known frequency.
(ii) The performance of equipment in the system will be
considered satisfactory if, during each day's testing, the
variation in the calibration value does not exceed 0.5 dB. The SEL
data collected during the flyover tests shall be adjusted to
account for any variation in the calibration value.
(iii) A performance calibration analysis of each piece of
calibration equipment, including acoustic calibrators, reference
microphones, and voltage insertion devices, must have been made
during the six calendar months proceeding the beginning of the
helicopter flyover series. Each calibration shall be traceable to
the National Institute of Standards and Technology.
(f) Noise measurement procedures. (1) The microphone
shall be of the pressure-sensitive capacitive type designed for
nearly uniform grazing incidence response. The microphone shall be
mounted with the center of the sensing element 4 feet (1.2 meters)
above the local ground surface and shall be oriented for grazing
incidence such that the sensing element, the diaphragm, is
substantially in the plane defined by the nominal flight path of
the helicopter and the noise measurement station.
(2) If a tape recorder is used, the frequency response of the
electrical system must be determined at a level within 10 dB of the
full-scale reading used during the test, utilizing pink or
pseudorandom noise.
(3) The ambient noise, including both acoustical background and
electrical noise of the measurement systems shall be determined in
the test area and the system gain set at levels which will be used
for helicopter noise measurements. If helicopter sound levels do
not exceed the background sound levels by at least 15 dB(A),
flyovers at an FAA-approved lower height may be used and the
results adjusted to the reference measurement point by an
FAA-approved method.
(4) If an integrating sound level meter is used to measure the
helicopter noise, the instrument operator shall monitor the
continuous A-weighted (slow response) noise levels throughout each
flyover to ensure that the SEL integration process includes, at
minimum, all of the noise signal between the maximum A-weighted
sound level (LAMAX) and the 10 dB down points in the flyover time
history. The instrument operator shall note the actual db(A) levels
at the start and stop of the SEL integration interval and document
these levels along with the value of LAMAX and the integration
interval (in seconds) for inclusion in the noise data submitted as
part of the reporting requirements under section J36.111(b) of this
appendix.
Section J36.111 Reporting Requirements.
(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 is subject to FAA
approval.
(b) Data reporting. After the completion of the test the
following data must be included in the test report furnished to the
FAA:
(1) Measured and corrected sound levels obtained with equipment
conforming to the standards prescribed in section J36.109 of this
appendix;
(2) The type of equipment used for measurement and analysis of
all acoustic, aircraft performance and flight path, and
meteorological data;
(3) The atmospheric environmental data required to demonstrate
compliance with this appendix, measured throughout the test
period;
(4) Conditions of local topography, ground cover, or events
which may interfere with the sound recording;
(5) The following helicopter information:
(i) Type, model, and serial numbers, if any, of helicopter,
engine(s) and rotor(s);
(ii) Gross dimensions of helicopter, location of engines,
rotors, type of antitorque system, number of blades for each rotor,
and reference operating conditions for each engine and rotor;
(iii) Any modifications of non-standard equipment likely to
affect the noise characteristics of the helicopter;
(iv) Maximum takeoff weight for which certification under this
appendix is requested;
(v) Aircraft configuration, including landing gear
positions;
(vi) VH or VNE (whichever is less) and the adjusted reference
airspeed;
(vii) Aircraft gross weight for each test run;
(viii) Indicated and true airspeed for each test run;
(ix) Ground speed, if measured, for each run;
(x) Helicopter engine performance as determined from aircraft
instruments and manufacturer's data; and
(xi) Aircraft flight path above ground level, referenced to the
elevation of the noise measurement station, in feet, determined by
an FAA-approved method which is independent of normal flight
instrumentation, such as radar tracking, theodolite triangulation,
laser trajectography, or photoscaling techniques; and
(6) Helicopter position and performance data required to make
the adjustments prescribed under section J36.205 of this appendix
and to demonstrate compliance with the performance and position
restrictions prescribed under section J36.105 of this appendix must
be recorded at an FAA-approved sampling rate.
Section J36.113 [Reserved] Part C - Noise Evaluation and
Calculations Under § 36.803 Section J36.201 Noise Evaluation in
SEL.
The noise evaluation measure shall be the sound exposure level
(SEL) in units of dB(A) as prescribed under section J36.109(b) of
this appendix. The SEL value for each flyover may be directly
determined by use of an integrating sound level meter.
Specifications for the integrating sound level meter and
requirements governing the use of such instrumentation are
prescribed under section J36.109 of this appendix.
Section J36.203 Calculation of Noise Levels.
(a) To demonstrate compliance with the noise level limits
specified under section J36.305 of this appendix, the SEL noise
levels from each valid flyover, corrected as necessary to reference
conditions under section J36.205 of this appendix, must be
arithmetically averaged to obtain a single SEL dB(A) mean value for
the flyover series. No individual flyover run may be omitted from
the averaging process, unless otherwise specified or approved by
the FAA.
(b) The minimum sample size acceptable for the helicopter
flyover certification measurements is six. The number of samples
must be large enough to establish statistically a 90 percent
confidence limit that does not exceed ±1.5 dB(A).
(c) All data used and calculations performed under this section,
including the calculated 90 percent confidence limits, must be
documented and provided under the reporting requirements of section
J36.111 of this appendix.
Section J36.205 Detailed Data Correction Procedures.
(a) When certification test conditions measured under part B of
this appendix differ from the reference test conditions prescribed
under section J36.3 of this appendix, appropriate adjustments shall
be made to the measured noise data in accordance with the methods
set out in paragraphs (b) and (c) of this section. At minimum,
appropriate adjustments shall be made for off-reference altitude
and for the difference between reference airspeed and adjusted
reference airspeed.
(b) The adjustment for off-reference altitude may be
approximated from:
<delta>J1 = 12.5 log10(HT/492) dB; where <delta>J1 is
the quantity in decibels that must be algebraically added to the
measured SEL noise level to correct for an off-reference flight
path, HT is the height, in feet, of the test helicopter when
directly over the noise measurement point, and the constant (12.5)
accounts for the effects on spherical spreading and duration from
the off-reference altitude.
(c) The adjustment for the difference between reference airspeed
and adjusted reference airspeed is calculated from:
<delta>J3 = 10 log10(VRA/VR) dB; Where <delta>J3 is the
quantity in decibels that must be algebraically added to the
measured SEL noise level to correct for the influence of the
adjustment of the reference airspeed on the duration of the
measured flyover event as perceived at the noise measurement
station, VR is the reference airspeed as prescribed under section
J36.3.(c) of this appendix, and VRA is the adjusted reference
airspeed as prescribed under section J36.105(c) of this appendix.
(d) No correction for source noise during the flyover other than
the variation of source noise accounted for by the adjustment of
the reference airspeed prescribed for under section J36.105(c) of
this appendix need be applied.
(e) No correction for the difference between the reference
ground speed and the actual ground speed need be applied.
(f) No correction for off-reference atmospheric attenuation need
be applied.
(g) The SEL adjustments must be less than 2.0 dB(A) for
differences between test and reference flight procedures prescribed
under section J36.105 of this appendix unless a larger adjustment
value is approved by the FAA.
(h) All data used and calculations performed under this section
must be documented and provided under the reporting requirements
specified under section J36.111 of this appendix.
Part D - Noise Limits Procedure Under § 36.805 Section J36.301
Noise Measurement, Evaluation, and Calculation.
Compliance with this part of this appendix must be shown with
noise levels measured, evaluated, and calculated as prescribed
under parts B and C of this appendix.
Section J36.303 [Reserved] Section J36.305 Noise Limits.
For compliance with this appendix, the calculated noise levels
of the helicopter, at the measuring point described in section
J36.101 of this appendix, must be shown to not exceed the following
(with appropriate interpolation between weights):
(a) For primary, normal, transport, and restricted category
helicopters having a maximum certificated takeoff weight of not
more than 7,000 pounds that are noise tested under this
appendix:
(1) Stage 2 noise limit is constant at 82 decibels SEL for
helicopters up to 1,737 pounds (787 kg) maximum certificated
takeoff weight (mass) and increases linearly with the logarithm of
the helicopter weight at a rate of 3.0 decibels SEL per the
doubling of weight thereafter. The limit may be calculated by the
equation:
LAE(limit) = 82 + 3.0 [log10(MTOW/1737)/log10(2)] dB, where MTOW is
the maximum takeoff weight, in pounds, for which certification
under this appendix is requested.
(2) Stage 3 noise limit is constant at 82 decibels SEL for
helicopters up to 3,125 pounds (1,417 kg) maximum certificated
takeoff weight (mass) and increases linearly with the logarithm of
the helicopter weight at a rate of 3.0 decibels SEL per the
doubling of weight thereafter. The limit may be calculated using
the equation:
LAE(limit) = 82 + 3.0 [log10(MTOW/3125)/log10(2)] dB, where MTOW is
the maximum takeoff weight, in pounds.
(b) The procedures required in this amendment shall be done in
accordance with the International Electrotechnical Commission IEC
Publication No. 804, entitled “Integrating-averaging Sound Level
Meters,” First Edition, dated 1985. This incorporation by reference
was approved by the Director of the Federal Register in accordance
with 5 U.S.C. 552(a) and 1 CFR part 51. Copies may be obtained from
the Bureau Central de la Commission Electrotechnique
Internationale, 1, rue de Varembe, Geneva, Switzerland or the
American National Standard Institute, 1430 Broadway, New York City,
New York 10018, or at the National Archives and Records
Administration (NARA). For information on the availability of this
material at NARA, call 202-741-6030, or go to:
http://www.archives.gov/federal_register/code_of_federal_regulations/ibr_locations.html.
[Doc. No. 26910, 57 FR 42855, Sept. 16, 1992, as amended by Amdt.
36-20, 57 FR 46243, Oct. 7, 1992; 69 FR 18803, Apr. 9, 2004; Amdt.
36-25, 69 FR 31234, June 2, 2004; Amdt. 36-30, 79 FR 12045, Mar. 4,
2014; FAA Doc. No. FAA-2015-3782, Amdt. No. 36-31, 82 FR 46131,
Oct. 4, 2017]