Appendix H to Part 36 - Noise Requirements For Helicopters Under Subpart H
14:1.0.1.3.20.14.283.1.41 : Appendix H
Appendix H to Part 36 - Noise Requirements For Helicopters Under
Subpart H part a - reference conditions Sec. H36.1 General.
H36.3 Reference Test Conditions. H36.5 Symbols and
Units. part b - noise measurement under § 36.801 H36.101
Noise certification test and measurement conditions. H36.103
Takeoff test conditions. H36.105 Flyover test
conditions. H36.107 Approach test conditions. H36.109
Measurement of helicopter noise received on the ground.
H36.111 Reporting and correcting measured data. H36.113
Atmospheric attenuation of sound. part c - noise evaluation
and calculation under § 36.803 H36.201 Noise evaluation in
EPNdB. H36.203 Calculation of noise levels. H36.205
Detailed data correction procedures. part d - noise limits
under § 36.805 H36.301 Noise measurement, evaluation, and
calculation. H36.303 [Reserved] H36.305 Noise levels.
part a - reference conditions
Section H36.1 General. This appendix prescribes noise
requirements for helicopters specified under § 36.1, including:
(a) The conditions under which helicopter noise certification
tests under Part H must be conducted and the measurement procedures
that must be used under § 36.801 to measure helicopter noise during
each test;
(b) The procedures which must be used under § 36.803 to correct
the measured data to the reference conditions and to calculate the
noise evaluation quantity designated as Effective Perceived Noise
Level (EPNL); and
(c) The noise limits for which compliance must be shown under §
36.805.
Section H36.3 Reference Test Conditions.
(a) Meteorological conditions. Aircraft position,
performance data and noise measurements must be corrected to the
following noise certification reference atmospheric conditions
which shall be assumed to exist from the surface to the aircraft
altitude:
(1) Sea level pressure of 2,116 psf (1,013.25 hPa).
(2) Ambient temperature of 77 degrees F (25 degrees C).
(3) Relative humidity of 70 percent.
(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.
(c) Takeoff reference profile. (1) Figure H1 illustrates
a typical takeoff profile, including reference conditions.
(2) The reference flight path is defined as a straight line
segment inclined from the starting point (1,640 feet (500 meters)
from the center microphone location and 65 feet (20 meters) above
ground level) at a constant climb angle β defined by the
certificated best rate of climb and Vy for minimum engine
performance. The constant climb angle β is derived from the
manufacturer's data (approved by the FAA) to define the flight
profile for the reference conditions. The constant climb angle β is
drawn through Cr and continues, crossing over station A, to the
position corresponding to the end of the type certification takeoff
path represented by position Ir.
(d) Level flyover reference profile. The beginning of the
level flyover reference profile is represented by helicopter
position Dr (Figure H2). The helicopter approaches position Dr in
level flight 492 feet above ground level as measured at Station A.
Reference airspeed must be either 0.9VH; 0.9VNE; 0.45VH + 65 kts
(0.45VH + 120km/h); or 0.45VNE + 65kts (0.45VNE + 120 km/h),
whichever of the four speeds is least. The helicopter crosses
directly overhead station A in level flight and proceeds to
position Jr.
(e) For noise certification purposes, VH is defined as the
airspeed in level flight obtained using the minimum specified
engine torque 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 VNE is the never-exceed airspeed. The values of VH and VNE
that are used for noise certification must be listed in the
approved Rotorcraft Flight Manual.
(i) The beginning of the approach profile is represented by
helicopter position E. The position of the helicopter is recorded
for a sufficient distance (EK) to ensure recording of the entire
interval during which the measured helicopter noise level is within
10 dB of Maximum Tone Corrected Perceived Noise Level (PNLTM). The
reference flight path, ErKr represents a stable flight condition in
terms of torque, rpm, indicated airspeed, and rate of descent
resulting in a 6° approach angle.
(ii) The test approach profile is defined by the approach angle
η passing directly over the station A at a height of AH, to
position K, which terminates the approach noise certification
profile. The test approach angle η must be between 5.5° and
6.5°.
(2) The helicopter approaches position H along a constant 6°
approach slope throughout the 10 dB down time period. The
helicopter crosses position E and proceeds along the approach slope
crossing over station A until it reaches position K.
Section H36.5 Symbols and units. The following symbols
and units as used in this appendix for helicopter noise
certification have the following meanings.
Flight Profile Identification -
Positions
Position
Description
A
Location of the noise
measuring point at the flight-track noise measuring station
vertically below the reference (takeoff, flyover, or approach)
flight path.
C
Start of noise certification
takeoff flight path.
Cr
Start of noise certification
reference takeoff flight path.
D
Start of noise certification
flyover flight path.
Dr
Start of noise certification
reference flyover path.
E
Start of noise certification
approach flight path.
Er
Start of noise certification
reference approach flight path.
F
Position on takeoff flight
path directly above noise measuring station A.
Fr
Position on reference takeoff
path directly above noise measuring Station A.
G
Position on flyover flight
path directly above noise measuring station A.
Gr
Position on reference flyover
path directly above noise measuring Station A.
H
Position on approach flight
path directly above noise measuring station A.
Hr
Position on reference path
directly above noise measuring Station A.
I
End of noise type
certification takeoff flight path.
Ir
End of noise type
certification reference takeoff flight path.
J
End of noise type
certification flyover flight path.
Jr
End of noise type
certification reference flyover flight path.
K
End of noise certification
approach type flight path.
Kr
End of noise type
certification reference approach flight path.
L
Position on measured takeoff
flight path corresponding to PNLTM at station A.
Lr
Position on reference takeoff
flight path corresponding to PNLTM of station A.
M
Position on measured flyover
flight path corresponding to PNLTM of station A.
Mr
Position on reference flyover
flight path corresponding to PNLTM of station A.
N
Position on measured approach
flight path corresponding to PNLTM at station A.
Nr
Position on reference approach
flight path corresponding to PNLTM at station A.
S
Sideline noise measuring
station (note: a subscript denotes the aircraft orientation
relative to the direction of flight).
Flight Profile Distances
Distance
Unit
Meaning
AF
Feet
Takeoff Height. The vertical
distance between helicopter and station A.
AG
Feet
Flyover Height. The vertical
distance between the helicopter and station A.
AH
Feet
Approach Height. The vertical
distance between the helicopter and station A.
AL
Feet
Measured Takeoff Noise Path.
The distance from station A to the measured helicopter position
L.
ALr
Feet
Reference Takeoff Noise Path.
The distance from station A to the reference helicopter position
Lr.
AM
Feet
Measured Flyover Noise Path.
The distance from station A to the measured helicopter position
M.
AMr
Feet
Reference Flyover Noise Path.
The distance from station A to helicopter position Mr on the
reference flyover flight path.
AN
Feet
Measured Approach Noise Path.
The distance from station A to the measured helicopter noise
position N.
ANr
Feet
Reference Approach Noise Path.
The distance from station A to the reference helicopter position
Nr.
CI
Feet
Takeoff Flight Path Distance.
The distance from position C at which the helicopter establishes a
constant climb angle on the takeoff flight path passing over
station A and continuing to position I at which the position of the
helicopter need no longer be recorded.
DJ
Feet
Flyover Flight Path Distance.
The distance from position D at which the helicopter is established
on the flyover flight path passing over station A and continuing to
position J at which the position of the helicopter need no longer
be recorded.
EK
Feet
Approach Flight Path Distance.
The distance from position E at which the helicopter establishes a
constant angle on the approach flight path passing over station A
and continuing to position K at which the position of the
helicopter need no longer be recorded.
part b - noise measurement under § 36.801 Section H36.101 Noise
certification test and measurement conditions.
(a) General. This section prescribes the conditions under
which aircraft 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) 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 approach test includes
simultaneous measurements 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
measuring 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, flyover, 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 station, above the line of
sight between the microphone and the helicopter.
(6) If a takeoff or flyover test series is conducted at weights
other than the maximum takeoff weight for which noise certification
is requested, the following additional requirements 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 certification 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 conducted at a weight at,
or above, the maximum 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 humidity measured at a point 33 feet (10
meters) above the ground at the noise measuring station must be
used to adjust for propagation path absorption.
(3) Relative humidity and ambient temperature at a point 33 feet
(10 meters) above the ground at the noise measuring station and at
the aircraft, is such that the sound attenuation in the one-third
octave band centered 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 conditions (including
turbulence) that will significantly 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 meters above the ground.
The location of the meteorological measurements must be approved by
the FAA as representative of those atmospheric conditions existing
near the surface over the geographical area which aircraft 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 aircraft testing
procedures and noise measurements 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 position relative to the
reference flight track (which passes through the flight track noise
measuring station) must be determined using an FAA-approved method.
The equipment used to make the determination must be independent of
normal flight instrumentation. Applicable independent systems are
radar tracking, theodolite triangulation, laser trajectography,
photo scaling, or differential global positioning system.
(3) The helicopter position along the flight path must be
related to the noise recorded at the noise measuring stations by
means of synchronized signals recorded at an approved sampling
rate. The helicopter position must be recorded relative to the
reference flight track during the entire time interval in which the
recorded signal is within 10 dB of PNLTM. Measuring and sampling
equipment must be approved by the FAA before testing.
(4) Aircraft performance data sufficient to make the corrections
required under section H36.205 of this appendix must be recorded at
an FAA-approved sampling rate using FAA-approved equipment.
Section H36.103 Takeoff test conditions.
(a) This section, in addition to the applicable requirements of
sections H36.101 and H36.205(b) of this appendix, applies to all
takeoff noise tests conducted under this appendix to show
compliance with Part 36.
(b) A test series must consist of at least six flights over the
flight-track noise measuring station (with simultaneous
measurements at all three noise measuring stations) as follows:
(1) An airspeed of either Vy ±5 knots or the lowest approved
speed ±5 knots for the climb after takeoff, whichever speed is
greater, must be established and maintained throughout the 10
dB-down time interval.
(2) The horizontal portion of each test flight must be conducted
at an altitude of 65 feet (20 meters) above the ground level at the
flight-track noise measuring station.
(3) Upon reaching a point 1,640 feet (500 meters) from the noise
measuring station, the helicopter must be stabilized at the maximum
takeoff power that corresponds to minimum installed engine(s)
specification power available for the reference ambient conditions
or gearbox torque limit, whichever is lower.
(4) The helicopter must be maintained throughout the 10 dB-down
time interval at the best rate of climb speed Vy ±5 knots, or the
lowest approved speed for climb after takeoff, whichever is
greater, for an ambient temperature of 25 °C at sea level.
(5) The average rotor speed must not vary from the maximum
normal operating rotor RPM by more than ±1.0 percent during the 10
dB-down time interval.
(6) The helicopter must stay within ±10° or ±65 feet (±20
meters), whichever is greater, from the vertical above the
reference track throughout the 10dB-down time interval.
(7) A constant takeoff configuration selected by the applicant
must be maintained throughout the takeoff reference procedure with
the landing gear position consistent with the airworthiness
certification tests for establishing best rate-of-climb speed,
Vy.
Section H36.105 Flyover test conditions.
(a) This section, in addition to the applicable requirements of
sections H36.101 and H36.205(c) of this appendix, applies to all
flyover noise tests conducted under this appendix to show
compliance with Part 36.
(b) A test series consists 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 with
simultaneous measurements at all three noise measuring stations
-
(1) In level flight cruise configuration;
(2) At a height of 492 feet ±30 feet (150 ±9 meters) above the
ground level at the flight-track noise measuring station; and
(3) The helicopter must fly within ±10° or ±65 feet (±20
meters), whichever is greater, from the vertical above the
reference track throughout the 10 dB-down time interval.
(c) Each flyover noise test must be conducted -
(1) At a speed of 0.9VH; 0.9VNE; 0.45VH + 65 kts (0.45VH + 120
km/h); or 0.45VNE + 65 kts (0.45VNE + 120 km/h), whichever speed is
least, to be maintained throughout the measured portion of the
flyover;
(2) At average rotor speed, which must not vary from the maximum
normal operating rotor RPM by more than ±1.0 percent during the 10
dB-down time interval.
(3) With the power stabilized during the period when the
measured helicopter noise level is within 10 dB of PNLTM.
(d) The airspeed shall not vary from the reference airspeed by
more than ±5 knots (9 km/hr).
Section H36.107 Approach test conditions.
(a) This section, in addition to the requirements of sections
H36.101 and H36.205(d) of this appendix, applies to all approach
tests conducted under this appendix to show compliance with Part
36.
(b) A test series must consist of at least six flights over the
flight-track noise measuring station (with simultaneous
measurements at the three noise measuring stations) -
(1) On an approach slope of 6° ±0.5°;
(2) At a height of 394 ±33 feet (120 ±10 meters)
(3) The helicopter must fly within ±10° or ±65 feet (±20 meters)
lateral deviation tolerance, whichever is greater, from the
vertical above the reference track throughout the 10 dB-down time
interval;
(4) At stabilized airspeed equal to the certificated best rate
of climb Vy, or the lowest approved speed for approach, whichever
is greater, with power stabilized during the approach and over the
flight path reference point, and continued to a normal touchdown;
and
(5) At average rotor speed, which may not vary from the maximum
normal operating rotor RPM by more than ±1.0 percent during the 10
dB-down time interval; and
(6) The constant approach configuration used in airworthiness
certification tests, with the landing gear extended, must be
maintained throughout the approach reference procedure.
(c) The airspeed shall not vary from the reference airspeed by
more than ±5 knots (±9 km/hr).
Section H36.109 Measurement of Helicopter Noise Received on the
Ground.
The measurement system and the measurement, calibration and
general analysis procedures to be used are provided in Appendix A,
section A36.3 of this part.
Section H36.111 Reporting and correcting measured data.
(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 must be reported
and is subject to FAA approval. An estimate must be made of each
individual error inherent in each of the operations employed in
obtaining the final data.
(b) Data reporting. (1) Measured and corrected sound
pressure levels must be presented in one-third octave band levels
obtained with equipment conforming to the standards prescribed in
section H36.109 of this appendix.
(2) The type of equipment used for measurement and analysis of
all acoustic, aircraft performance, and meteorological data must be
reported.
(3) The atmospheric environmental data required to demonstrate
compliance with this appendix, measured throughout the test period,
must be reported.
(4) Conditions of local topography, ground cover, or events
which may interfere with sound recording must be reported.
(5) The following aircraft information must be reported:
(i) Type, model, and serial numbers, if any, of aircraft engines
and rotors.
(ii) Gross dimensions of aircraft and location of engines.
(iii) Aircraft gross weight for each test run.
(iv) Aircraft configuration, including landing gear
positions.
(v) Airspeed in knots.
(vi) Helicopter engine performance as determined from aircraft
instruments and manufacturer's data.
(vii) Aircraft flight path, above ground level in feet,
determined by an FAA approved method which is independent of normal
flight instrumentation, such as radar tracking, theodolite
triangulation, laser trajectography, or photographic scaling
techniques.
(6) Aircraft speed, and position, and engine performance
parameters must be recorded at an approved sampling rate sufficient
to correct to the noise certification reference test conditions
prescribed in section H36.3 of this appendix. Lateral position
relative to the reference flight-track must be reported.
(c) Data corrections. (1) Aircraft position, performance
data and noise measurement must be corrected to the noise
certification reference conditions as prescribed in sections H36.3
and H36.205 of this appendix.
(2) The measured flight path must be corrected by an amount
equal to the difference between the applicant's predicted flight
path for the certification reference conditions and the measured
flight path at the test conditions. Necessary corrections relating
to helicopter flight path or performance may be derived from
FAA-approved data for the difference between measured and reference
conditions, together with appropriate allowances for sound
attenuation with distance. The Effective Perceived Noise Level
(EPNL) correction may not exceed 2.0 EPNdB except for takeoff
flight condition, where the correction may not exceed 4.0 EPNdB, of
which the arithmetic sum of Δ1 (described in section H36.205(f)(1))
and the term −7.5 log (AL/ALr) from Δ2 term (described in section
H36.205(g)(1)(i)) may not exceed 2.0 EPNdB, for any combination of
the following:
(i) The helicopter not passing vertically above the measuring
station.
(ii) Any difference between the reference flight track and the
actual test flight track; and
(iii) Detailed correction requirements prescribed in section
H36.205 of this appendix.
(3) Helicopter sound pressure levels within the 10 dB-down time
interval must exceed the mean background sound pressure levels
determined under section B36.3.9.11 by at least 3 dB in each
one-third octave band, or must be corrected under an FAA-approved
method.
(d) Validity of results. (1) The test results must
produce three average EPNL values within the 90 percent confidence
limits, each value consisting of the arithmetic average of the
corrected noise measurements for all valid test runs at the
takeoff, level flyovers, and approach conditions. The 90 percent
confidence limit applies separately to takeoff, flyover, and
approach.
(2) The minimum sample size acceptable for each takeoff,
approach, and flyover certification measurements is six. The number
of samples must be large enough to establish statistically for each
of the three average noise certification levels a 90 percent
confidence limit which does not exceed ±1.5 EPNdB. No test result
may be omitted from the averaging process, unless otherwise
specified by the FAA.
(3) To comply with this appendix, a minimum of six takeoffs, six
approaches, and six level flyovers is required. To be counted
toward this requirement, each flight event must be validly recorded
at all three noise measuring stations.
(4) The approved values of VH and Vy used in calculating test
and reference conditions and flight profiles must be reported along
with measured and corrected sound pressure levels.
Section H36.113 Atmospheric attenuation of sound.
(a) The values of the one-third octave band spectra measured
during helicopter noise certification tests under this appendix
must conform, or be corrected, to the reference conditions
prescribed in section H36.3(a). Each correction must account for
any differences in the atmospheric attenuation of sound between the
test-day conditions and the reference-day conditions along the
sound propagation path between the aircraft and the microphone.
Unless the meteorological conditions are within the test window
prescribed in this appendix, the test data are not acceptable.
(b) Attenuation rates. The procedure for determining the
atmospheric attenuation rates of sound with distance for each
one-third octave bands must be determined in accordance with SAE
ARP 866A (Incorporated by reference, see § 36.6). The atmospheric
attenuation equations are provided in both the International and
English systems of units in section A36.7 of appendix A to this
part.
(c) Correction for atmospheric attenuation. (1) EPNL
values calculated for measured data must be corrected whenever
-
(i) The ambient atmospheric conditions of temperature and
relative humidity do not conform to the reference conditions, 77 °F
and 70%, respectively, or
(ii) The measured flight paths do not conform to the reference
flight paths.
(iii) The temperature and relative humidity measured at 33 feet
(10 meters) above the ground must be used to adjust for propagation
path absorption.
(2) The mean attenuation rate over the complete sound
propagation path from the aircraft to the microphone must be
computed for each one-third octave band from 50 Hz to 10,000 Hz.
These rates must be used in computing the corrections required in
section H36.111(d) of this appendix.
part c - noise evaluation and calculation under § 36.803 Section
H36.201 Noise Evaluation in EPNdB.
(a) Effective Perceived Noise Level (EPNL), in units of
effective perceived noise decibels (EPNdB), shall be used for
evaluating noise level values under § 36.803 of this part. Except
as provided in paragraph (b) of this section, the procedures in
appendix A of Part 36 must be used for computing EPNL. appendix A
includes requirements governing determination of noise values,
including calculations of:
(1) Perceived noise levels;
(2) Corrections for spectral irregularities;
(3) Tone corrections;
(4) Duration corrections;
(5) Effective perceived noise levels; and
(6) Mathematical formulation of noy tables.
(b) Notwithstanding the provisions of section A36.4.3.1(a), for
helicopter noise certification, corrections for spectral
irregularities shall start with the corrected sound pressure level
in the 50 Hz one-third octave band.
Section H36.203 Calculation of noise levels.
(a) To demonstrate compliance with the noise level limits of
section H36.305, the noise values measured simultaneously at the
three noise measuring points must be arithmetically averaged to
obtain a single EPNdB value for each flight.
(b) The calculated noise level for each noise test series,
i.e., takeoff, flyover, or approach must be the numerical
average of at least six separate flight EPNdB values. The 90
percent confidence limit for all valid test runs under section
H36.111(d) of this appendix applies separately to the EPNdB values
for each noise test series.
Section H36.205 Detailed data correction procedures.
(a) General. If the test conditions do not conform to
those prescribed as noise certification reference conditions under
section H36.305 of this appendix, the following correction
procedure shall apply:
(1) If there is any difference between measured test and
reference conditions, an appropriate correction must be made to the
EPNL calculated from the measured noise data. Conditions that can
result in a different value include:
(i) Atmospheric absorption of sound under measured test
conditions that are different from the reference test conditions;
or
(ii) Measured flight path that is different from the reference
flight path.
(2) The following correction procedures may produce one or more
possible correction values which must be added algebraically to the
calculated EPNL to bring it to reference conditions:
(i) The flight profiles must be determined for both reference
and test conditions. The procedures require noise and flight path
recording with a synchronized time signal from which the test
profile can be delineated, including the aircraft position for
which PNLTM is observed at the noise measuring station. For
takeoff, the flight profile corrected to reference conditions may
be derived from FAA approved manufacturer's data.
(ii) The sound propagation paths to the microphone from the
aircraft position corresponding to PNLTM must be determined for
both the test and reference profiles. The SPL values in the
spectrum of PNLTM must then be corrected for the effects of -
(A) Change in atmospheric sound absorption;
(B) Atmospheric sound absorption on the linear difference
between the two sound path lengths; and
(C) Inverse square law on the difference in sound propagation
path length. The corrected values of SPL must then be converted to
a reference condition PNLTM value from which PNLTM must be
subtracted. The resulting difference represents the correction
which must be added algebraically to the EPNL calculated from the
measured data.
(iii) As observed at the noise measuring station, the measured
PNLTM distance is different from the reference PNLTM distance and
therefore the ratio must be calculated and used to determine a
noise duration correction factor. Effective perceived noise level,
EPNL, is determined by the algebraic sum of the maximum tone
corrected perceived noise level (PNLTM) and the duration correction
factor.
(iv) For aircraft flyover, alternative source noise corrections
require FAA approval and must be determined and adjusted to account
for noise level changes caused by the differences between measured
test conditions and reference conditions.
(b) Takeoff profiles. (1) Figure H1 illustrates a typical
takeoff profile, including reference conditions.
(i) The reference takeoff flight path is described in section
H36.3(c).
(ii) The test parameters are functions of the helicopter's
performance and weight and the atmospheric conditions of
temperature, pressure, wind velocity and direction.
(2) For the actual takeoff, the helicopter approaches position C
in level flight at 65 feet (20 meters) above ground level at the
flight track noise measuring station and at either Vy ±5 knots or
the lowest approved speed for the climb after takeoff, whichever
speed is greater.
(3) Figure H1 illustrates the significant geometrical
relationships influencing sound propagation. Position L represents
the helicopter location on the measured takeoff path from which
PNLTM is observed at station A, and Lr is the corresponding
position on the reference sound propagation path. Propagation paths
AL and ALr both form the same angle θ (theta) relative to their
respective flight paths.
(c) Level flyover profiles. (1) The noise type
certification level flyover profile is shown in Figure H2. Airspeed
must be stabilized within ±5 knots of the reference airspeed
determined using the procedures in section H36.3(d). The number of
level flights made with a headwind component must be equal to the
number of level flights made with a tailwind component.
(2) Figure H2 illustrates comparative flyover profiles when test
conditions do not conform to prescribed reference conditions. The
position of the helicopter shall be recorded for a distance (DJ)
sufficient to ensure recording of the entire interval during which
the measured helicopter noise level is within 10 dB of PNLTM, as
required. The flyover profile is defined by the height AG which is
a function of the operating conditions controlled by the pilot.
Position M represents the helicopter location on the measured
flyover flight path for which PNLTM is observed at station A, and
Mr is the corresponding position on the reference flight path.
(d) Approach profiles. (1) Figure H3 illustrates a
typical approach profile, including reference conditions.
(2) The helicopter approaches position H along a 6° (±0.5°)
average approach slope throughout the 10dB-down time interval.
Deviation from the 6° average approach slope must be approved by
the FAA before testing.
(3) Figure H3 illustrates portions of the measured and reference
approach flight paths including the significant geometrical
relationships influencing sound propagation. The measured approach
path is represented by segment EK with an approach allowable angle
θ. Reference positions, Er and Kr, define an idealized reference
approach angle of 6°. Position N represents the helicopter location
on the measured approach flight path for which PNLTM is observed at
measuring station A, and Nr is the corresponding position on the
reference approach flight path. The measured and reference noise
propagation paths are AN and ANr, respectively, both of which form
the same angle, θAPP, corresponding to PNLTM relative to their
approach flight paths.
(e) Correction of noise at source during level flyover.
(1) For level overflight, if any combination of the following three
factors, airspeed deviations from reference, rotor speed deviations
from reference, and temperature deviations from reference, results
in a noise correlating parameter whose value deviates from the
reference value of this parameter, then source noise adjustments
must be determined from the manufacturer's data that is approved by
the FAA.
(2) Off-reference tip Mach number adjustments must be based upon
a sensitivity curve of PNLTM versus advancing blade tip Mach
number, deduced from overflights performed at different airspeeds
surrounding the reference airspeed. If the test aircraft is unable
to attain the reference value, then an extrapolation of the
sensitivity curve is permitted if data cover at least a range of
0.03 Mach units. The advancing blade tip Mach number must be
computed using true airspeed, onboard outside air temperature, and
rotor speed. A separate PNLTM versus advancing blade tip Mach
number function must be derived for each of the three certification
microphone locations, i.e., centerline, sideline left, and
sideline right. Sideline left and right are defined relative to the
direction of flight for each run. PNLTM adjustments are to be
applied to each microphone datum using the appropriate PNLTM
function.
(f) PNLT corrections. If the measured ambient atmospheric
conditions of temperature and relative humidity differ from those
prescribed as reference conditions under this appendix (77 degrees
F and 70 percent, respectively), corrections to the EPNL values
must be calculated from the measured data under paragraph (a) of
this section as follows:
(1) Takeoff flight path. For the takeoff flight path
shown in Figure H1, the spectrum of PNLTM observed at station A for
the aircraft at position L is decomposed into its individual
SPL(i) values.
(i) Step 1. A set of corrected values are then computed as
follows:
SPL(i)r = SPL(i) + C[α(i) −
α(i)o]AL + Cα(i)o (AL − ALr) + 20 log (AL/ALr)
where SPL(i) and SPL(i)r are the measured and
corrected sound pressure levels, respectively, in the i-th
one-third octave band. The first correction term adjusts for the
effect of change in atmospheric sound absorption where α(i)
and α(i)o are the sound attenuation coefficients for the
test and reference atmospheric conditions, respectively, for the
i-th one-third octave band, and AL is the measured takeoff
sound propagation path. The conversion factor constant, C,
is 0.001 for English System of Units and is 0.01 for International
System of Units. The second correction term adjusts for the effects
of atmospheric attenuation due to the difference in the sound
propagation path length where ALr is the Reference takeoff sound
propagation path. The third correction term, known as the “inverse
square” law, adjusts for the effect of the difference in the sound
propagation path lengths.
(ii) Step 2. The corrected values of the SPL(i)r are then
converted to reference condition PNLT and a correction term
calculated as follows:
Δ1 = PNLT − PNLTM which represents the correction to be added
algebraically to the EPNL calculated from the measured data.
(2) Level flyover flight path. (i) The procedure
described in paragraph (f)(1) of this section for takeoff paths is
also used for the level flyover paths, with the values of
SPL(i)r relating to the flyover sound propagation paths
shown in Figure H2 as follows:
SPL(i)r = SPL(i) + C[α(i) −
α(i)o]AM + Cα(i)o (AM − AMr) + 20 log (AM/AMr)
where the lines AM and AMr are the measured and reference level
flyover sound propagation paths, respectively.
(ii) The remainder of the procedure is the same for the flyover
condition as that prescribed in the paragraph (f)(1)(ii) of this
section regarding takeoff flight path.
(3) Approach flight path. (i) The procedure described in
paragraph (f)(1) of this section for takeoff paths is also used for
the approach paths, with the values of SPL(i)r relating to
the approach sound propagation paths shown in Figure H3 as
follows:
SPL(i)r = SPL(i) + C[α(i) −
α(i)o]AN + Cα(i)o (AN − ANr) + 20 log (AN/ANr)
where the lines AN and ANr are the measured and reference approach
sound propagation paths, respectively.
(ii) The remainder of the procedure is the same for the approach
condition as that prescribed in the paragraph (f)(1)(ii) of this
section regarding takeoff flight path.
(4) Sideline microphones. (i) The procedure prescribed in
paragraph (f)(1) of this section for takeoff paths is also used for
the propagation to the sideline locations, with the values of
SPL(i)r relating as follows to the measured sideline sound
propagation path shown in Figure H3 as follows:
SPL(i)r = SPL(i) + C[α(i) −
α(i)o]SX + Cα(i)o (SX − SXr) + 20 log (SX/SXr)
where S is the sideline measuring station and, based upon the
flight condition, the helicopter positions, X and Xr, correspond
to: X = L, and Xr = Lr for takeoff X = M, and Xr = Mr for flyover X
= N, and Xr = Nr for approach
(ii) The remainder of the procedure is the same for the sideline
paths as that prescribed in the paragraph (f)(1)(ii) of this
section regarding takeoff flight paths.
(g) Duration corrections. (1) If the measured takeoff and
approach flight paths do not conform to those prescribed as the
corrected and reference flight paths, respectively, under section
A36.5(d)(2) it will be necessary to apply duration corrections to
the EPNL values calculated from the measured data. Such corrections
must be calculated as follows:
(i) Takeoff flight path. For the takeoff path shown in
Figure H1, the correction term is calculated using the formula
-
Δ2 = −7.5 log (AL/ALr) + 10 log (V/Vr) which represents the
correction that must be added algebraically to the EPNL calculated
from the measured data. The lengths AL and ALr are the measured and
reference takeoff distances from the noise measuring station A to
the measured and the reference takeoff paths, respectively. A
negative sign indicates that, for the particular case of a duration
correction, the EPNL calculated from the measured data must be
reduced if the measured takeoff path is at greater altitude than
the reference takeoff path.
(ii) Level flyover flight paths. For the level flyover
flight path, the correction term is calculated using the formula
-
Δ2 = −7.5 log (AM/AMr) + 10 log (V/Vr) where AM is the measured
flyover distance from the noise measuring station A to the measured
flyover path, and AMr is the reference distance from station A to
the reference flyover path.
(iii) Approach flight path. For the approach path shown
in Figure H3, the correction term is calculated using the formula
-
Δ2 = −7.5 log (AN/ANr) + 10 log (V/Vr) where AN is the measured
approach distance from the noise measuring station A to the
measured approach path, and ANr is the reference distance from
station A to the reference approach path.
(iv) Sideline microphones. For the sideline flight path,
the correction term is calculated using the formula -
Δ2 = −7.5 log (SX/SXr) + 10 log (V/Vr) where S is the sideline
measuring station and based upon the flight condition, the
helicopter positions, X and Xr, correspond to: X = L, and Xr = Lr
for takeoff X = M, and Xr = Mr for flyover X = N, and Xr = Nr for
approach
(2) The adjustment procedure described in this section shall
apply to the sideline microphones in the take-off, overflight, and
approach cases. Although the noise emission is strongly dependent
on the directivity pattern, variable from one helicopter type to
another, the propagation angle θ shall be the same for test and
reference flight paths. The elevation angle ψ shall not be
constrained but must be determined and reported. The certification
authority shall specify the acceptable limitations on ψ.
Corrections to data obtained when these limits are exceeded shall
be applied using FAA approved procedures.
part d - noise limits under § 36.805 Section H36.301 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.
(a) Limits. For compliance with this appendix, the
applicant must show by flight test that the calculated noise levels
of the helicopter, at the measuring points described in section
H36.305(a) of this appendix, do not exceed the following, (with
appropriate interpolation between weights):
(1) Stage 1 noise limits for acoustical changes for
helicopters are as follows:
(i) For takeoff, flyover, and approach calculated noise levels,
the noise levels of each Stage 1 helicopter that exceed the Stage 2
noise limits plus 2 EPNdB may not, after a change in type design,
exceed the noise levels created prior to the change in type
design.
(ii) For takeoff, flyover, and approach calculated noise levels,
the noise levels of each Stage 1 helicopter that do not exceed the
Stage 2 noise limits plus 2 EPNdB may not, after the change in type
design, exceed the Stage 2 noise limits plus 2 EPNdB.
(2) Stage 2 noise limits are as follows:
(i) For takeoff calculated noise levels - 109 EPNdB for
maximum takeoff weights of 176,370 pounds (80,000 kg) or more,
reduced by 3.01 EPNdB per halving of the weight down to 89 EPNdB,
after which the limit is constant.
(ii) For flyover calculated noise levels - 108 EPNdB for
maximum weights of 176,370 pounds (80,000 kg) or more, reduced by
3.01 EPNdB per halving of the weight down to 88 EPNdB, after which
the limit is constant.
(iii) For approach calculated noise levels - 110 EPNdB
for maximum weights of 176,370 pounds (80,000 kg) or more, reduced
by 3.01 EPNdB per halving of the weight down to 90 EPNdB, after
which the limit is constant.
(3) Stage 3 noise limits are as follows:
(i) For takeoff - For a helicopter having a maximum certificated
takeoff weight of 176,370 pounds (80,000 kg) or more, the noise
limit is 106 EPNdB, which decreases linearly with the logarithm of
the helicopter weight (mass) at a rate of 3.0 EPNdB per halving of
the weight (mass) down to 86 EPNdB, after which the limit is
constant.
(ii) For flyover - For a helicopter having a maximum
certificated takeoff weight of 176,370 pounds (80,000 kg) or more,
the noise limit is 104 EPNdB, which decreases linearly with the
logarithm of the helicopter weight (mass) at a rate of 3.0 EPNdB
per halving of the weight (mass) down to 84 EPNdB, after which the
limit is constant.
(iii) For approach - For a helicopter having a maximum
certificated takeoff weight of 176,370 pounds (80,000 kg) or more,
the noise limit is 109 EPNdB, which decreases linearly with the
logarithm of the helicopter weight (mass) at a rate of 3.0 EPNdB
per halving of the weight (mass) down to 89 EPNdB, after which the
limit is constant.
(b) Tradeoffs. Except to the extent limited under §
36.11(b) of this part, the noise limits prescribed in paragraph (a)
of this section may be exceeded by one or two of the takeoff,
flyover, or approach calculated noise levels determined under
section H36.203 of this appendix if
(1) The sum of the exceedances is not greater than 4 EPNdB;
(2) No exceedance is greater than 3 EPNdB; and
(3) The exceedances are completely offset by reduction in the
other required calculated noise levels.
[Amdt. 36-14, 53 FR 3541, Feb. 5, 1988; 53 FR 4099, Feb. 11, 1988;
53 FR 7728, Mar. 10, 1988, as amended by Amdt. 36-54, 67 FR 45237,
July 8, 2002; Amdt. 36-25, 69 FR 31234, June 2, 2004; Amdt. 36-25,
69 FR 41573, July 9, 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]