Appendix A to Part 36 - Aircraft Noise Measurement and Evaluation Under § 36.101
14:1.0.1.3.20.14.283.1.36 : Appendix A
Appendix A to Part 36 - Aircraft Noise Measurement and Evaluation
Under § 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
§§ 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 § 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 §
36.6).
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 80° 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 °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;
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 ±0.9 °F (±0.5 °C) 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 one-third 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 ±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 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 to
compute equivalent weighted sound attenuations 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 attenuations in
each one-third octave band must be determined by averaging the
atmospheric 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 averaging 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 calculation is required by
section A36.2.2.2(c) or A36.2.2.2(d) the atmosphere between the
airplane 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 absorption 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 bottom of each layer may be used to characterize the absorption
properties of each layer.
A36.2.2.4 The airport control tower or another facility must be
aproved by the FAA for use as the central location at which
measurements of atmospheric parameters are representative of those
conditions existing over the geographical area in which noise
measurements are made.
A36.2.3 Flight path measurement.
A36.2.3.1 The airplane height and lateral position relative to
the flight track must be determined by a method independent of
normal flight instrumentation such as radar tracking, theodolite
triangulation, or photographic scaling techniques, to be approved
by the FAA.
A36.2.3.2 The airplane position along the flight path must be
related to the noise recorded at the noise measurement locations by
means of synchronizing signals over a distance sufficient to assure
adequate data during the period that the noise is within 10 dB of
the maximum value of PNLT.
A36.2.3.3 Position and performance data required to make the
adjustments referred to in section A36.9 of this appendix must be
automatically recorded at an approved sampling rate. Measuring
equipment must be approved by the FAA.
Section A36.3 Measurement of Airplane Noise Received on the Ground
A36.3.1 Definitions.
For the purposes of section A36.3 the following definitions
apply:
A36.3.1.1 Measurement system means the combination of
instruments used for the measurement of sound pressure levels,
including a sound calibrator, windscreen, microphone system, signal
recording and conditioning devices, and one-third octave band
analysis system.
Note:
Practical installations may include a number of microphone
systems, the outputs from which are recorded simultaneously by a
multi-channel recording/analysis device via signal conditioners, as
appropriate. For the purpose of this section, each complete
measurement channel is considered to be a measurement system to
which the requirements apply accordingly.
A36.3.1.2 Microphone system means the components of the
measurement system which produce an electrical output signal in
response to a sound pressure input signal, and which generally
include a microphone, a preamplifier, extension cables, and other
devices as necessary.
A36.3.1.3 Sound incidence angle means in degrees, an
angle between the principal axis of the microphone, as defined in
IEC 61094-3 and IEC 61094-4, as amended and a line from the sound
source to the center of the diaphragm of the microphone
(incorporated by reference, see § 36.6).
Note:
When the sound incidence angle is 0°, the sound is said to be
received at the microphone at “normal (perpendicular) incidence;”
when the sound incidence angle is 90°, the sound is said to be
received at “grazing incidence.”
A36.3.1.4 Reference direction means, in degrees, the
direction of sound incidence specified by the manufacturer of the
microphone, relative to a sound incidence angle of 0°, for which
the free-field sensitivity level of the microphone system is within
specified tolerance limits.
A36.3.1.5 Free-field sensitivity of a microphone system
means, in volts per Pascal, for a sinusoidal plane progressive
sound wave of specified frequency, at a specified sound incidence
angle, the quotient of the root mean square voltage at the output
of a microphone system and the root mean square sound pressure that
would exist at the position of the microphone in its absence.
A36.3.1.6 Free-field sensitivity level of a microphone
system means, in decibels, twenty times the logarithm to the
base ten of the ratio of the free-field sensitivity of a microphone
system and the reference sensitivity of one volt per Pascal.
Note:
The free-field sensitivity level of a microphone system may be
determined by subtracting the sound pressure level (in decibels re
20 µPa) of the sound incident on the microphone from the voltage
level (in decibels re 1 V) at the output of the microphone system,
and adding 93.98 dB to the result.
A36.3.1.7 Time-average band sound pressure level means in
decibels, ten times the logarithm to the base ten, of the ratio of
the time mean square of the instantaneous sound pressure during a
stated time interval and in a specified one-third octave band, to
the square of the reference sound pressure of 20 µPa.
A36.3.1.8 Level range means, in decibels, an operating
range determined by the setting of the controls that are provided
in a measurement system for the recording and one-third octave band
analysis of a sound pressure signal. The upper boundary associated
with any particular level range must be rounded to the nearest
decibel.
A36.3.1.9 Calibration sound pressure level means, in
decibels, the sound pressure level produced, under reference
environmental conditions, in the cavity of the coupler of the sound
calibrator that is used to determine the overall acoustical
sensitivity of a measurement system.
A36.3.1.10 Reference level range means, in decibels, the
level range for determining the acoustical sensitivity of the
measurement system and containing the calibration sound pressure
level.
A36.3.1.11 Calibration check frequency means, in hertz,
the nominal frequency of the sinusoidal sound pressure signal
produced by the sound calibrator.
A36.3.1.12 Level difference means, in decibels, for any
nominal one-third octave midband frequency, the output signal level
measured on any level range minus the level of the corresponding
electrical input signal.
A36.3.1.13 Reference level difference means, in decibels,
for a stated frequency, the level difference measured on a level
range for an electrical input signal corresponding to the
calibration sound pressure level, adjusted as appropriate, for the
level range.
A36.3.1.14 Level non-linearity means, in decibels, the
level difference measured on any level range, at a stated one-third
octave nominal midband frequency, minus the corresponding reference
level difference, all input and output signals being relative to
the same reference quantity.
A36.3.1.15 Linear operating range means, in decibels, for
a stated level range and frequency, the range of levels of steady
sinusoidal electrical signals applied to the input of the entire
measurement system, exclusive of the microphone but including the
microphone preamplifier and any other signal-conditioning elements
that are considered to be part of the microphone system, extending
from a lower to an upper boundary, over which the level
non-linearity is within specified tolerance limits.
Note:
Microphone extension cables as configured in the field need not
be included for the linear operating range determination.
A36.3.1.16 Windscreen insertion loss means, in decibels,
at a stated nominal one-third octave midband frequency, and for a
stated sound incidence angle on the inserted microphone, the
indicated sound pressure level without the windscreen installed
around the microphone minus the sound pressure level with the
windscreen installed.
A36.3.2 Reference environmental conditions.
A36.3.2.1 The reference environmental conditions for specifying
the performance of a measurement system are:
(a) Air temperature 73.4 °F (23 °C);
(b) Static air pressure 101.325 kPa; and
(c) Relative humidity 50%.
A36.3.3. General.
Note:
Measurements of aircraft noise that are made using instruments
that conform to the specifications of this section will yield
one-third octave band sound pressure levels as a function of time.
These one-third octave band levels are to be used for the
calculation of effective perceived noise level as described in
section A36.4.
A36.3.3.1 The measurement system must consist of equipment
approved by the FAA and equivalent to the following:
(a) A windscreen (See A36.3.4.);
(b) A microphone system (See A36.3.5):
(c) A recording and reproducing system to store the measured
aircraft noise signals for subsequent analysis (see A36.3.6);
(d) A one-third octave band analysis system (see A36.3.7);
and
(e) Calibration systems to maintain the acoustical sensitivity
of the above systems within specified tolerance limits (see
A36.3.8).
A36.3.3.2. For any component of the measurement system that
converts an analog signal to digital form, such conversion must be
performed so that the levels of any possible aliases or artifacts
of the digitization process will be less than the upper boundary of
the linear operating range by at least 50 dB at any frequency less
than 12.5 kHz. The sampling rate must be at least 28 kHz. An
anti-aliasing filter must be included before the digitization
process.
A36.3.4 Windscreen.
A36.3.4.1 In the absence of wind and for sinusoidal sounds at
grazing incidence, the insertion loss caused by the windscreen of a
stated type installed around the microphone must not exceed ±1.5 dB
at nominal one-third octave midband frequencies from 50 Hz to 10
kHz inclusive.
A36.3.5 Microphone system.
A36.3.5.1 The microphone system must meet the specifications in
sections A36.3.5.2 to A36.3.5.4. Various microphone systems may be
approved by the FAA on the basis of demonstrated equivalent overall
electroacoustical performance. Where two or more microphone systems
of the same type are used, demonstration that at least one system
conforms to the specifications in full is sufficient to demonstrate
conformance.
Note:
An applicant must still calibrate and check each system as
required in section A36.3.9.
A36.3.5.2 The microphone must be mounted with the sensing
element 4 ft (1.2 m) above the local ground surface and must be
oriented for grazing incidence, i.e., with the sensing
element substantially in the plane defined by the predicted
reference flight path of the aircraft and the measuring station.
The microphone mounting arrangement must minimize the interference
of the supports with the sound to be measured. Figure A36-1
illustrates sound incidence angles on a microphone.
A36.3.5.3 The free-field sensitivity level of the microphone and
preamplifier in the reference direction, at frequencies over at
least the range of one-third-octave nominal midband frequencies
from 50 Hz to 5 kHz inclusive, must be within ±1.0 dB of that at
the calibration check frequency, and within ±2.0 dB for nominal
midband frequencies of 6.3 kHz, 8 kHz and 10 kHz.
A36.3.5.4 For sinusoidal sound waves at each one-third octave
nominal midband frequency over the range from 50 Hz to 10 kHz
inclusive, the free-field sensitivity levels of the microphone
system at sound incidence angles of 30°, 60°, 90°, 120° and 150°,
must not differ from the free-field sensitivity level at a sound
incidence angle of 0° (“normal incidence”) by more than the values
shown in Table A36-1. The free-field sensitivity level differences
at sound incidence angles between any two adjacent sound incidence
angles in Table A36-1 must not exceed the tolerance limit for the
greater angle.
A36.3.6 Recording and reproducing systems.
A36.3.6.1 A recording and reproducing system, such as a digital
or analog magnetic tape recorder, a computer-based system or other
permanent data storage device, must be used to store sound pressure
signals for subsequent analysis. The sound produced by the aircraft
must be recorded in such a way that a record of the complete
acoustical signal is retained. The recording and reproducing
systems must meet the specifications in sections A36.3.6.2 to
A36.3.6.9 at the recording speeds and/or data sampling rates used
for the noise certification tests. Conformance must be demonstrated
for the frequency bandwidths and recording channels selected for
the tests.
A36.3.6.2 The recording and reproducing systems must be
calibrated as described in section A36.3.9.
(a) For aircraft noise signals for which the high frequency
spectral levels decrease rapidly with increasing frequency,
appropriate pre-emphasis and complementary de-emphasis networks may
be included in the measurement system. If pre-emphasis is included,
over the range of nominal one-third octave midband frequencies from
800 Hz to 10 kHz inclusive, the electrical gain provided by the
pre-emphasis network must not exceed 20 dB relative to the gain at
800 Hz.
A36.3.6.3 For steady sinusoidal electrical signals applied to
the input of the entire measurement system including all parts of
the microphone system except the microphone at a selected signal
level within 5 dB of that corresponding to the calibration sound
pressure level on the reference level range, the time-average
signal level indicated by the readout device at any one-third
octave nominal midband frequency from 50 Hz to 10 kHz inclusive
must be within ±1.5 dB of that at the calibration check frequency.
The frequency response of a measurement system, which includes
components that convert analog signals to digital form, must be
within ±0.3 dB of the response at 10 kHz over the frequency range
from 10 kHz to 11.2 kHz.
Note:
Microphone extension cables as configured in the field need not
be included for the frequency response determination. This
allowance does not eliminate the requirement of including
microphone extension cables when performing the pink noise
recording in section A36.3.9.5.
A36.3.6.4 For analog tape recordings, the amplitude fluctuations
of a 1 kHz sinusoidal signal recorded within 5 dB of the level
corresponding to the calibration sound pressure level must not vary
by more than ±0.5 dB throughout any reel of the type of magnetic
tape used. Conformance to this requirement must be demonstrated
using a device that has time-averaging properties equivalent to
those of the spectrum analyzer.
A36.3.6.5 For all appropriate level ranges and for steady
sinusoidal electrical signals applied to the input of the
measurement system, including all parts of the microphone system
except the microphone, at one-third-octave nominal midband
frequencies of 50 Hz, 1 kHz and 10 kHz, and the calibration check
frequency, if it is not one of these frequencies, the level
non-linearity must not exceed ±0.5 dB for a linear operating range
of at least 50 dB below the upper boundary of the level range.
Note 1:
Level linearity of measurement system components may be tested
according to the methods described in IEC 61265 as amended.
Note 2:
Microphone extension cables configured in the field need not be
included for the level linearity determination.
A36.3.6.6 On the reference level range, the level corresonding
to the calibration sound pressure level must be at least 5 dB, but
no more than 30 dB less than the upper boundary of the level
range.
A36.3.6.7 The linear operating ranges on adjacent level ranges
must overlap by at least 50 dB minus the change in attenuation
introduced by a change in the level range controls.
Note:
It is possible for a measurement system to have level range
controls that permit attenuation changes of either 10 dB or 1 dB,
for example. With 10 dB steps, the minimum overlap required would
be 40 dB, and with 1 dB steps the minimum overlap would be 49
dB.
A36.3.6.8 An overload indicator must be included in the
recording and reproducing systems so that an overload indication
will occur during an overload condition on any relevant level
range.
A36.3.6.9 Attenuators included in the measurement system to
permit range changes must operate in known intervals of decibel
steps.
A36.3.7 Analysis systems.
A36.3.7.1 The analysis system must conform to the specifications
in sections A36.3.7.2 to A36.3.7.7 for the frequency bandwidths,
channel configurations and gain settings used for analysis.
A36.3.7.2 The output of the analysis system must consist of
one-third octave band sound pressure levels as a function of time,
obtained by processing the noise signals (preferably recorded)
through an analysis system with the following characteristics:
(a) A set of 24 one-third octave band filters, or their
equivalent, having nominal midband frequencies from 50 Hz to 10 kHz
inclusive;
(b) Response and averaging properties in which, in principle,
the output from any one-third octave filter band is squared,
averaged and displayed or stored as time-averaged sound pressure
levels;
(c) The interval between successive sound pressure level samples
must be 500 ms ±5 milliseconds(ms) for spectral analysis with or
without slow time-weighting, as defined in section A36.3.7.4;
(d) For those analysis systems that do not process the sound
pressure signals during the period of time required for readout
and/or resetting of the analyzer, the loss of data must not exceed
a duration of 5 ms; and
(e) The analysis system must operate in real time from 50 Hz
through at least 12 kHz inclusive. This requirement applies to all
operating channels of a multi-channel spectral analysis system.
A36.3.7.3 The minimum standard for the one-third octave band
analysis system is the class 2 electrical performance requirements
of IEC 61260 as amended, over the range of one-third octave nominal
midband frequencies from 50 Hz through 10 kHz inclusive
(incorporated by reference, see § 36.6).
Note:
IEC 61260 specifies procedures for testing of one-third octave
band analysis systems for relative attenuation, anti-aliasing
filters, real time operation, level linearity, and filter
integrated response (effective bandwidth).
A36.3.7.4 When slow time averaging is performed in the analyzer,
the response of the one-third octave band analysis system to a
sudden onset or interruption of a constant sinusoidal signal at the
respective one-third octave nominal midband frequency, must be
measured at sampling instants 0.5, 1, 1.5 and 2 seconds(s) after
the onset and 0.5 and 1s after interruption. The rising response
must be −4 ±1 dB at 0.5s, −1.75 ±0.75 dB at 1s, −1 ±0.5 dB at 1.5s
and −0.5 ±0.5 dB at 2s relative to the steady-state level. The
falling response must be such that the sum of the output signal
levels, relative to the initial steady-state level, and the
corresponding rising response reading is −6.5 ±1 dB, at both 0.5
and 1s. At subsequent times the sum of the rising and falling
responses must be −7.5 dB or less. This equates to an exponential
averaging process (slow time-weighting) with a nominal 1s time
constant (i.e., 2s averaging time).
A36.3.7.5 When the one-third octave band sound pressure levels
are determined from the output of the analyzer without slow
time-weighting, slow time-weighting must be simulated in the
subsequent processing. Simulated slow time-weighted sound pressure
levels can be obtained using a continuous exponential averaging
process by the following equation:
Ls (i,k) = 10 log [(0.60653) 100.1 Ls[i, (k−1)] + (0.39347) 100.1 L
(i, k)] where Ls(i,k) is the simulated slow time-weighted sound
pressure level and L(i,k) is the as-measured 0.5s time average
sound pressure level determined from the output of the analyzer for
the k-th instant of time and i-th one-third octave band. For k = 1,
the slow time-weighted sound pressure Ls[i, (k − 1 = 0)] on the
right hand side should be set to 0 dB. An approximation of the
continuous exponential averaging is represented by the following
equation for a four sample averaging process for k ≥4: Ls (i,k) =
10 log [(0.13) 100.1 L[i,(k−3)] + (0.21) 100.1 L[i, (k−2)] + (0.27)
100.1 L[i, (k−1)] + (0.39) 100.1 L[i, k]] where Ls (i, k) is the
simulated slow time-weighted sound pressure level and L (i, k) is
the as measured 0.5s time average sound pressure level determined
from the output of the analyzer for the k-th instant of time and
the i-th one-third octave band.
The sum of the weighting factors is 1.0 in the two equations.
Sound pressure levels calculated by means of either equation are
valid for the sixth and subsequent 0.5s data samples, or for times
greater than 2.5s after initiation of data analysis.
Note:
The coefficients in the two equations were calculated for use in
determining equivalent slow time-weighted sound pressure levels
from samples of 0.5s time average sound pressure levels. The
equations do not work with data samples where the averaging time
differs from 0.5s.
A36.3.7.6 The instant in time by which a slow time-weighted
sound pressure level is characterized must be 0.75s earlier than
the actual readout time.
Note:
The definition of this instant in time is needed to correlate
the recorded noise with the aircraft position when the noise was
emitted and takes into account the averaging period of the slow
time-weighting. For each 0.5 second data record this instant in
time may also be identified as 1.25 seconds after the start of the
associated 2 second averaging period.
A36.3.7.7 The resolution of the sound pressure levels, both
displayed and stored, must be 0.1 dB or finer.
A36.3.8 Calibration systems.
A36.3.8.1 The acoustical sensitivity of the measurement system
must be determined using a sound calibrator generating a known
sound pressure level at a known frequency. The minimum standard for
the sound calibrator is the class 1L requirements of IEC 60942 as
amended (incorporated by reference, see § 36.6).
A36.3.9 Calibration and checking of system.
A36.3.9.1 Calibration and checking of the measurement system and
its constituent components must be carried out to the satisfaction
of the FAA by the methods specified in sections A36.3.9.2 through
A36.3.9.10. The calibration adjustments, including those for
environmental effects on sound calibrator output level, must be
reported to the FAA and applied to the measured one-third-octave
sound pressure levels determined from the output of the analyzer.
Data collected during an overload indication are invalid and may
not be used. If the overload condition occurred during recording,
the associated test data are invalid, whereas if the overload
occurred during analysis, the analysis must be repeated with
reduced sensitivity to eliminate the overload.
A36.3.9.2 The free-field frequency response of the microphone
system may be determined by use of an electrostatic actuator in
combination with manufacturer's data or by tests in an anechoic
free-field facility. The correction for frequency response must be
determined within 90 days of each test series. The correction for
non-uniform frequency response of the microphone system must be
reported to the FAA and applied to the measured one-third octave
band sound pressure levels determined from the output of the
analyzer.
A36.3.9.3 When the angles of incidence of sound emitted from the
aircraft are within ±30° of grazing incidence at the microphone
(see Figure A36-1), a single set of free-field corrections based on
grazing incidence is considered sufficient for correction of
directional response effects. For other cases, the angle of
incidence for each 0.5 second sample must be determined and applied
for the correction of incidence effects.
A36.3.9.4 For analog magnetic tape recorders, each reel of
magnetic tape must carry at least 30 seconds of pink random or
pseudo-random noise at its beginning and end. Data obtained from
analog tape-recorded signals will be accepted as reliable only if
level differences in the 10 kHz one-third-octave-band are not more
than 0.75 dB for the signals recorded at the beginning and end.
A36.3.9.5 The frequency response of the entire measurement
system while deployed in the field during the test series,
exclusive of the microphone, must be determined at a level within 5
dB of the level corresponding to the calibration sound pressure
level on the level range used during the tests for each one-third
octave nominal midband frequency from 50 Hz to 10 kHz inclusive,
utilizing pink random or pseudo-random noise. Within six months of
each test series the output of the noise generator must be
determined by a method traceable to the U.S. National Institute of
Standards and Technology or to an equivalent national standards
laboratory as determined by the FAA. Changes in the relative output
from the previous calibration at each one-third octave band may not
exceed 0.2 dB. The correction for frequency response must be
reported to the FAA and applied to the measured one-third octave
sound pressure levels determined from the output of the
analyzer.
A36.3.9.6 The performance of switched attenuators in the
equipment used during noise certification measurements and
calibration must be checked within six months of each test series
to ensure that the maximum error does not exceed 0.1 dB.
A36.3.9.7 The sound pressure level produced in the cavity of the
coupler of the sound calibrator must be calculated for the test
environmental conditions using the manufacturer's supplied
information on the influence of atmospheric air pressure and
temperature. This sound pressure level is used to establish the
acoustical sensitivity of the measurement system. Within six months
of each test series the output of the sound calibrator must be
determined by a method traceable to the U.S. National Institute of
Standards and Technology or to an equivalent national standards
laboratory as determined by the FAA. Changes in output from the
previous calibration must not exceed 0.2 dB.
A36.3.9.8 Sufficient sound pressure level calibrations must be
made during each test day to ensure that the acoustical sensitivity
of the measurement system is known at the prevailing environmental
conditions corresponding with each test series. The difference
between the acoustical sensitivity levels recorded immediately
before and immediately after each test series on each day may not
exceed 0.5 dB. The 0.5 dB limit applies after any atmospheric
pressure corrections have been determined for the calibrator output
level. The arithmetic mean of the before and after measurements
must be used to represent the acoustical sensitivity level of the
measurement system for that test series. The calibration
corrections must be reported to the FAA and applied to the measured
one-third octave band sound pressure levels determined from the
output of the analyzer.
A36.3.9.9 Each recording medium, such as a reel, cartridge,
cassette, or diskette, must carry a sound pressure level
calibration of at least 10 seconds duration at its beginning and
end.
A36.3.9.10 The free-field insertion loss of the windscreen for
each one-third octave nominal midband frequency from 50 Hz to 10
kHz inclusive must be determined with sinusoidal sound signals at
the incidence angles determined to be applicable for correction of
directional response effects per section A36.3.9.3. The interval
between angles tested must not exceed 30 degrees. For a windscreen
that is undamaged and uncontaminated, the insertion loss may be
taken from manufacturer's data. Alternatively, within six months of
each test series the insertion loss of the windscreen may be
determined by a method traceable to the U.S. National Institute of
Standards and Technology or an equivalent national standards
laboratory as determined by the FAA. Changes in the insertion loss
from the previous calibration at each one-third-octave frequency
band must not exceed 0.4 dB. The correction for the free-field
insertion loss of the windscreen must be reported to the FAA and
applied to the measured one-third octave sound pressure levels
determined from the output of the analyzer.
A36.3.10 Adjustments for ambient noise.
A36.3.10.1 Ambient noise, including both an acoustical
background and electrical noise of the measurement system, must be
recorded for at least 10 seconds at the measurement points with the
system gain set at the levels used for the aircraft noise
measurements. Ambient noise must be representative of the
acoustical background that exists during the flyover test run. The
recorded aircraft noise data is acceptable only if the ambient
noise levels, when analyzed in the same way, and quoted in PNL (see
A36.4.1.3 (a)), are at least 20 dB below the maximum PNL of the
aircraft.
A36.3.10.2 Aircraft sound pressure levels within the 10 dB-down
points (see A36.4.5.1) must exceed the mean ambient noise levels
determined in section A36.3.10.1 by at least 3 dB in each one-third
octave band, or must be adjusted using a method approved by the
FAA; one method is described in the current advisory circular for
this part.
Section A36.4 Calculation of Effective Perceived Noise Level From
Measured Data
A36.4.1 General.
A36.4.1.1 The basic element for noise certification criteria is
the noise evaluation measure known as effective perceived noise
level, EPNL, in units of EPNdB, which is a single number evaluator
of the subjective effects of airplane noise on human beings. EPNL
consists of instantaneous perceived noise level, PNL, corrected for
spectral irregularities, and for duration. The spectral
irregularity correction, called “tone correction factor”, is made
at each time increment for only the maximum tone.
A36.4.1.2 Three basic physical properties of sound pressure must
be measured: level, frequency distribution, and time variation. To
determine EPNL, the instantaneous sound pressure level in each of
the 24 one-third octave bands is required for each 0.5 second
increment of time during the airplane noise measurement.
A36.4.1.3 The calculation procedure that uses physical
measurements of noise to derive the EPNL evaluation measure of
subjective response consists of the following five steps:
(a) The 24 one-third octave bands of sound pressure level are
converted to perceived noisiness (noy) using the method described
in section A36.4.2.1 (a). The noy values are combined and then
converted to instantaneous perceived noise levels, PNL(k).
(b) A tone correction factor C(k) is calculated for each
spectrum to account for the subjective response to the presence of
spectral irregularities.
(c) The tone correction factor is added to the perceived noise
level to obtain tone-corrected perceived noise levels PNLT(k), at
each one-half second increment:
PNLT(k) = PNL(k) + C(k) The instantaneous values of tone-corrected
perceived noise level are derived and the maximum value, PNLTM, is
determined.
(d) A duration correction factor, D, is computed by integration
under the curve of tone-corrected perceived noise level versus
time.
(e) Effective perceived noise level, EPNL, is determined by the
algebraic sum of the maximum tone-corrected perceived noise level
and the duration correction factor:
EPNL = PNLTM + D
A36.4.2 Perceived noise level.
A36.4.2.1 Instantaneous perceived noise levels, PNL(k), must be
calculated from instantaneous one-third octave band sound pressure
levels, SPL(i, k) as follows:
(a) Step 1: For each one-third octave band from 50 through
10,000 Hz, convert SPL(i, k) to perceived noisiness n(i, k), by
using the mathematical formulation of the noy table given in
section A36.4.7.
(b) Step 2: Combine the perceived noisiness values, n(i, k),
determined in step 1 by using the following formula:
where n(k) is the largest of the 24 values of
n(i, k) and N(k) is the total perceived noisiness.
(c) Step 3: Convert the total perceived noisiness, N(k),
determined in Step 2 into perceived noise level, PNL(k), using the
following formula:
Note:
PNL(k) is plotted in the current advisory circular for this
part.
A36.4.3 Correction for spectral irregularities.
A36.4.3.1 Noise having pronounced spectral irregularities (for
example, the maximum discrete frequency components or tones) must
be adjusted by the correction factor C(k) calculated as
follows:
(a) Step 1: After applying the corrections specified under
section A36.3.9, start with the sound pressure level in the 80 Hz
one-third octave band (band number 3), calculate the changes in
sound pressure level (or “slopes”) in the remainder of the
one-third octave bands as follows:
s(3,k) = no value s(4,k) =
SPL(4,k)−SPL(3,k) • • s(i,k) =
SPL(i,k)−SPL(i−1,k) • • s(24,k) =
SPL(24,k)−SPL(23,k)
(b) Step 2: Encircle the value of the slope, s(i, k), where the
absolute value of the change in slope is greater than five; that is
where:
|Δs(i,k)| =
|s(i,k)−s(i−1,k)|>5
(c) Step 3:
(1) If the encircled value of the slope s(i, k) is positive and
algebraically greater than the slope s(i−1, k) encircle SPL(i,
k).
(2) If the encircled value of the slope s(i, k) is zero or
negative and the slope s(i−1, k) is positive, encircle SPL(i−1,
k).
(3) For all other cases, no sound pressure level value is to be
encircled.
(d) Step 4: Compute new adjusted sound pressure levels SPL′(i,
k) as follows:
(1) For non-encircled sound pressure levels, set the new sound
pressure levels equal to the original sound pressure levels,
SPL′(i, k) = SPL(i, k).
(2) For encircled sound pressure levels in bands 1 through 23
inclusive, set the new sound pressure level equal to the arithmetic
average of the preceding and following sound pressure levels as
shown below:
SPL′(i,k) = 1/2[SPL(i−1,k) + SPL(i +
1,k)]
(3) If the sound pressure level in the highest frequency band (i
= 24) is encircled, set the new sound pressure level in that band
equal to:
SPL′(24,k) = SPL(23,k) + s(23,k)
(e) Step 5: Recompute new slope s′(i, k), including one for an
imaginary 25th band, as follows:
(g) Step 7: Compute final one-third octave-band sound pressure
levels, SPL′ (i,k), by beginning with band number 3 and proceeding
to band number 24 as follows:
SPL′(3,k) = SPL(3,k)
SPL′(4,k) = SPL′(3,k) + s (3,k)
•
•
SPL′(i,k) = SPL′(i−1,k) + s (i−1,k)
•
•
SPL′(24,k) = SPL′(23,k) + s (23,k)
(h) Setp 8: Calculate the differences, F (i,k), between the
original sound pressure level and the final background sound
pressure level as follows:
F(i,k) = SPL(i,k)-SPL′(i,k) and note
only values equal to or greater than 1.5.
(i) Step 9: For each of the relevant one-third octave bands (3
through 24), determine tone correction factors from the sound
pressure level differences F (i, k) and Table A36-2.
(j) Step 10: Designate the largest of the tone correction
factors, determined in Step 9, as C(k). (An example of the tone
correction procedure is given in the current advisory circular for
this part). Tone-corrected perceived noise levels PNLT(k) must be
determined by adding the C(k) values to corresponding PNL(k)
values, that is:
PNLT(k) = PNL(k) + C(k) For any i-th
one-third octave band, at any k-th increment of time, for which the
tone correction factor is suspected to result from something other
than (or in addition to) an actual tone (or any spectral
irregularity other than airplane noise), an additional analysis may
be made using a filter with a bandwidth narrower than one-third of
an octave. If the narrow band analysis corroborates these
suspicions, then a revised value for the background sound pressure
level SPL′(i,k), may be determined from the narrow band analysis
and used to compute a revised tone correction factor for that
particular one-third octave band. Other methods of rejecting
spurious tone corrections may be approved.
A36.4.3.2 The tone correction procedure will underestimate EPNL
if an important tone is of a frequency such that it is recorded in
two adjacent one-third octave bands. An applicant must demonstrate
that either:
(a) No important tones are recorded in two adjacent one-third
octave bands; or
(b) That if an important tone has occurred, the tone correction
has been adjusted to the value it would have had if the tone had
been recorded fully in a single one-third octave band.
A36.4.4 Maximum tone-corrected perceived noise level
A36.4.4.1 The maximum tone-corrected perceived noise level,
PNLTM, must be the maximum calculated value of the tone-corrected
perceived noise level PNLT(k). It must be calculated using the
procedure of section A36.4.3. To obtain a satisfactory noise time
history, measurements must be made at 0.5 second time
intervals.
Note 1:
Figure A36-2 is an example of a flyover noise time history where
the maximum value is clearly indicated.
Note 2:
In the absence of a tone correction factor, PNLTM would equal
PNLM.
A36.4.4.2 After the value of PNLTM is obtained, the frequency
band for the largest tone correction factor is identified for the
two preceding and two succeeding 500 ms data samples. This is
performed in order to identity the possibility of tone suppression
at PNLTM by one-third octave band sharing of that tone. If the
value of the tone correction factor C(k) for PNLTM is less than the
average value of C(k) for the five consecutive time intervals, the
average value of C(k) must be used to compute a new value for
PNLTM.
A36.4.5 Duration correction.
A36.4.5.1 The duration correction factor D determined by the
integration technique is defined by the expression:
where T
is a normalizing time constant, PNLTM is the maximum value of PNLT,
t(1) is the first point of time after which PNLT becomes greater
than PNLTM-10, and t(2) is the point of time after which PNLT
remains constantly less than PNLTM-10.
A36.4.5.2 Since PNLT is calculated from measured values of sound
pressure level (SPL), there is no obvious equation for PNLT as a
function of time. Consequently, the equation is to be rewritten
with a summation sign instead of an integral sign as follows:
where Δt
is the length of the equal increments of time for which PNLT(k) is
calculated and d is the time interval to the nearest 0.5s during
which PNLT(k) remains greater or equal to PNLTM-10.
A36.4.5.3 To obtain a satisfactory history of the perceived
noise level use one of the following:
(a) Half-Second time intervals for Δt; or
(b) A shorter time interval with approved limits and
constants.
A36.4.5.4 The following values for T and Δt must be used in
calculating D in the equation given in section A36.4.5.2:
T = 10 s, and Δt = 0.5s (or the approved sampling time interval).
Using these values, the equation for D becomes:
where d is the duration time defined by the points corresponding to
the values PNLTM-10.
A36.4.5.5 If in using the procedures given in section A36.4.5.2,
the limits of PNLTM-10 fall between the calculated PNLT(k) values
(the usual case), the PNLT(k) values defining the limits of the
duration interval must be chosen from the PNLT(k) values closest to
PNLTM-10. For those cases with more than one peak value of PNLT(k),
the applicable limits must be chosen to yield the largest possible
value for the duration time.
A36.4.6 Effective perceived noise level.
The total subjective effect of an airplane noise event,
designated effective perceived noise level, EPNL, is equal to the
algebraic sum of the maximum value of the tone-corrected perceived
noise level, PNLTM, and the duration correction D. That is:
EPNL = PNLTM + D where PNLTM and D are calculated using the
procedures given in sections A36.4.2, A36.4.3, A36.4.4. and
A36.4.5.
A36.4.7 Mathematical formulation of noy tables.
A36.4.7.1 The relationship between sound pressure level (SPL)
and the logarithm of perceived noisiness is illustrated in Figure
A36-3 and Table A36-3.
A36.4.7.2 The bases of the mathematical formulation are:
(a) The slopes (M(b), M(c), M(d) and M(e)) of the straight
lines;
(b) The intercepts (SPL(b) and SPL(c)) of the lines on the SPL
axis; and
(c) The coordinates of the discontinuities, SPL(a) and log n(a);
SPL(d) and log n = −1.0; and SPL(e) and log n = log (0.3).
A36.4.7.3 Calculate noy values using the following
equations:
(a)
SPL ≥SPL (a) n = antilog {(c)[SPL−SPL(c)]}
(b)
SPL(b) ≤SPL <SPL(a) n = antilog {M(b)[SPL−SPL(b)]}
(c)
SPL(e) ≤SPL <SPL(b) n = 0.3 antilog {M(e)[SPL−SPL(e)]}
(d)
SPL(d) ≤SPL <SPL(e) n = 0.1 antilog {M(d)[SPL−SPL(d)]}
A36.4.7.4 Table A36-3 lists the values of the constants
necessary to calculate perceived noisiness as a function of sound
pressure level.
Section A36.5
Reporting of Data to the FAA
A36.5.1 General.
A36.5.1.1 Data representing physical measurements and data used
to make corrections to physical measurements must be recorded in an
approved permanent form and appended to the record.
A36.5.1.2 All corrections must be reported to and approved by
the FAA, including corrections to measurements for equipment
response deviations.
A36.5.1.3 Applicants may be required to submit estimates of the
individual errors inherent in each of the operations employed in
obtaining the final data.
A36.5.2 Data reporting.
An applicant is required to submit a noise certification
compliance report that includes the following.
A36.5.2.1 The applicant must present measured and corrected
sound pressure levels in one-third octave band levels that are
obtained with equipment conforming to the standards described in
section A36.3 of this appendix.
A36.5.2.2 The applicant must report the make and model of
equipment used for measurement and analysis of all acoustic
performance and meteorological data.
A36.5.2.3 The applicant must report the following atmospheric
environmental data, as measured immediately before, after, or
during each test at the observation points prescribed in section
A36.2 of this appendix.
(a) Air temperature and relative humidity;
(b) Maximum, minimum and average wind velocities; and
(c) Atmospheric pressure.
A36.5.2.4 The applicant must report conditions of local
topography, ground cover, and events that might interfere with
sound recordings.
A36.5.2.5 The applicant must report the following:
(a) Type, model and serial numbers (if any) of airplane,
engine(s), or propeller(s) (as applicable);
(b) Gross dimensions of airplane and location of engines;
(c) Airplane gross weight for each test run and center of
gravity range for each series of test runs;
(d) Airplane configuration such as flap, airbrakes and landing
gear positions for each test run;
(e) Whether auxiliary power units (APU), when fitted, are
operating for each test run;
(f) Status of pneumatic engine bleeds and engine power take-offs
for each test run;
(g) Indicated airspeed in knots or kilometers per hour for each
test run;
(h) Engine performance data:
(1) For jet airplanes: engine performance in terms of net
thrust, engine pressure ratios, jet exhaust temperatures and fan or
compressor shaft rotational speeds as determined from airplane
instruments and manufacturer's data for each test run;
(2) For propeller-driven airplanes: engine performance in terms
of brake horsepower and residual thrust; or equivalent shaft
horsepower; or engine torque and propeller rotational speed; as
determined from airplane instruments and manufacturer's data for
each test run;
(i) Airplane flight path and ground speed during each test run;
and
(j) The applicant must report whether the airplane has any
modifications or non-standard equipment likely to affect the noise
characteristics of the airplane. The FAA must approve any such
modifications or non-standard equipment.
A36.5.3 Reporting of noise certification reference
conditions.
A36.5.3.1 Airplane position and performance data and the noise
measurements must be corrected to the noise certification reference
conditions specified in the relevant sections of appendix B of this
part. The applicant must report these conditions, including
reference parameters, procedures and configurations.
A36.5.4 Validity of results.
A36.5.4.1 Three average reference EPNL values and their 90
percent confidence limits must be produced from the test results
and reported, each such value being the arithmetical average of the
adjusted acoustical measurements for all valid test runs at each
measurement point (flyover, lateral, or approach). If more than one
acoustic measurement system is used at any single measurement
location, the resulting data for each test run must be averaged as
a single measurement. The calculation must be performed by:
(a) Computing the arithmetic average for each flight phase using
the values from each microphone point; and
(b) Computing the overall arithmetic average for each reference
condition (flyover, lateral or approach) using the values in
paragraph (a) of this section and the related 90 percent confidence
limits.
A36.5.4.2 For each of the three certification measuring points,
the minimum sample size is six. The sample size must be large
enough to establish statistically for each of the three average
noise certification levels a 90 percent confidence limit not
exceeding ±1.5 EPNdB. No test result may be omitted from the
averaging process unless approved by the FAA.
Note:
Permitted methods for calculating the 90 percent confidence
interval are shown in the current advisory circular for this
part.
A36.5.4.3 The average EPNL figures obtained by the process
described in section A36.5.4.1 must be those by which the noise
performance of the airplane is assessed against the noise
certification criteria.
Section A36.6 Nomenclature: Symbols and Units
Symbol
Unit
Meaning
antilog
Antilogarithm to the base
10.
C(k)
dB
Tone correction factor. The
factor to be added to PNL(k) to account for the presence of
spectral irregularities such as tones at the k-th increment of
time.
d
s
Duration time. The time
interval between the limits of t(1) and t(2) to the nearest 0.5
second.
D
dB
Duration correction. The
factor to be added to PNLTM to account for the duration of the
noise.
EPNL
EPNdB
Effective perceived noise
level. The value of PNL adjusted for both spectral irregularities
and duration of the noise. (The unit EPNdB is used instead of the
unit dB).
EPNLr
EPNdB
Effective perceived noise
level adjusted for reference conditions.
f(i)
Hz
Frequency. The geometrical
mean frequency for the i-th one-third octave band.
F (i, k)
dB
Delta-dB. The difference
between the original sound pressure level and the final background
sound pressure level in the i-th one-third octave band at the k-th
interval of time. In this case, background sound pressure level
means the broadband noise level that would be present in the
one-third octave band in the absence of the tone.
h
dB
dB-down. The value to be
subtracted from PNLTM that defines the duration of the noise.
H
Percent
Relative humidity. The ambient
atmospheric relative humidity.
i
Frequency band index. The
numerical indicator that denotes any one of the 24 one-third octave
bands with geometrical mean frequencies from 50 to 10,000 Hz.
k
Time increment index. The
numerical indicator that denotes the number of equal time
increments that have elapsed from a reference zero.
Log
Logarithm to the base 10.
log n(a)
Noy discontinuity coordinate.
The log n value of the intersection point of the straight lines
representing the variation of SPL with log n.
M(b), M(c),
etc
Noy inverse slope. The
reciprocals of the slopes of straight lines representing the
variation of SPL with log n.
n
noy
The perceived noisiness at any
instant of time that occurs in a specified frequency range.
n(i,k)
noy
The perceived noisiness at the
k-th instant of time that occurs in the i-th one-third octave
band.
n(k)
noy
Maximum perceived noisiness.
The maximum value of all of the 24 values of n(i) that occurs at
the k-th instant of time.
N(k)
noy
Total perceived noisiness. The
total perceived noisiness at the k-th instant of time calculated
from the 24-instantaneous values of n (i, k).
p(b), p(c),
etc
Noy slope. The slopes of
straight lines representing the variation of SPL with log n.
PNL
PNdB
The perceived noise level at
any instant of time. (The unit PNdB is used instead of the unit
dB).
PNL(k)
PNdB
The perceived noise level
calculated from the 24 values of SPL (i, k), at the k-th increment
of time. (The unit PNdB is used instead of the unit dB).
PNLM
PNdB
Maximum perceived noise level.
The maximum value of PNL(k). (The unit PNdB is used instead of the
unit dB).
PNLT
TPNdB
Tone-corrected perceived noise
level. The value of PNL adjusted for the spectral irregularities
that occur at any instant of time. (The unit TPNdB is used instead
of the unit dB).
PNLT(k)
TPNdB
The tone-corrected perceived
noise level that occurs at the k-th increment of time. PNLT(k) is
obtained by adjusting the value of PNL(k) for the spectral
irregularities that occur at the k-th increment of time. (The unit
TPNdB is used instead of the unit dB).
PNLTM
TPNdB
Maximum tone-corrected
perceived noise level. The maximum value of PNLT(k). (The unit
TPNdB is used instead of the unit dB).
PNLTr
TPNdB
Tone-corrected perceived noise
level adjusted for reference conditions.
s (i, k)
dB
Slope of sound pressure level.
The change in level between adjacent one-third octave band sound
pressure levels at the i-th band for the k-th instant of time.
Δs (i, k)
dB
Change in slope of sound
pressure level.
s′ (i, k)
dB
Adjusted slope of sound
pressure level. The change in level between adjacent adjusted
one-third octave band sound pressure levels at the i-th band for
the k-th instant of time.
s (i, k)
dB
Average slope of sound
pressure level.
SPL
dB re
20 µPa
Sound pressure level. The
sound pressure level that occurs in a specified frequency range at
any instant of time.
SPL(a)
dB re
20 µPa
Noy discontinuity coordinate.
The SPL value of the intersection point of the straight lines
representing the variation of SPL with log n.
SPL(b)
SPL (c)
dB re
20 µPa
Noy intercept. The intercepts
on the SPL-axis of the straight lines representing the variation of
SPL with log n.
SPL (i, k)
dB re
20 µPa
The sound pressure level at
the k-th instant of time that occurs in the i-th one-third octave
band.
SPL′ (i, k)
dB re
20 µPa
Adjusted sound pressure level.
The first approximation to background sound pressure level in the
i-th one-third octave band for the k-th instant of time.
SPL(i)
dB re
20 µPa
Maximum sound pressure level.
The sound pressure level that occurs in the i-th one-third octave
band of the spectrum for PNLTM.
SPL(i)r
dB re
20 µPa
Corrected maximum sound
pressure level. The sound pressure level that occurs in the i-th
one-third octave band of the spectrum for PNLTM corrected for
atmospheric sound absorption.
SPL′ (i, k)
dB re
20 µPa
Final background sound
pressure level. The second and final approximation to background
sound pressure level in the i-th one-third octave band for the k-th
instant of time.
t
s
Elapsed time. The length of
time measured from a reference zero.
t(1), t(2)
s
Time limit. The beginning and
end, respectively, of the noise time history defined by h.
Δt
s
Time increment. The equal
increments of time for which PNL(k) and PNLT(k) are
calculated.
T
s
Normalizing time constant. The
length of time used as a reference in the integration method for
computing duration corrections, where T = 10s.
t(°F) (°C)
°F, °C
Temperature. The ambient air
temperature.
α(i)
dB/1000ft db/100m
Test atmospheric absorption.
The atmospheric attenuation of sound that occurs in the i-th
one-third octave band at the measured air temperature and relative
humidity.
α(i)o
dB/1000ft db/100m
Reference atmospheric
absorption. The atmospheric attenuation of sound that occurs in the
i-th one-third octave band at a reference air temperature and
relative humidity.
A1
Degrees
First constant climb angle
(Gear up, speed of at least V2 + 10 kt (V2 + 19 km/h), takeoff
thrust).
A2
Degrees
Second constant climb angle
(Gear up, speed of at least V2 + 10 kt (V2 + 19 km/h), after
cut-back).
δ
ε
Degrees
Thrust cutback angles. The
angles defining the points on the takeoff flight path at which
thrust reduction is started and ended respectively.
η
Degrees
Approach angle.
ηr
Degrees
Reference approach angle.
θ
Degrees
Noise angle (relative to
flight path). The angle between the flight path and noise path. It
is identical for both measured and corrected flight paths.
ψ
Degrees
Noise angle (relative to
ground). The angle between the noise path and the ground. It is
identical for both measured and corrected flight paths.
μ
Engine noise emission
parameter.
μr
Reference engine noise
emission parameter.
Δ1
EPNdB
PNLT correction. The
correction to be added to the EPNL calculated from measured data to
account for noise level changes due to differences in atmospheric
absorption and noise path length between reference and test
conditions.
Δ2
EPNdB
Adjustment to duration
correction. The adjustment to be made to the EPNL calculated from
measured data to account for noise level changes due to the noise
duration between reference and test conditions.
Δ3
EPNdB
Source noise adjustment. The
adjustment to be made to the EPNL calculated from measured data to
account for noise level changes due to differences between
reference and test engine operating conditions.
Section A36.7 Sound Attenuation in Air
A36.7.1 The atmospheric attenuation of sound must be determined
in accordance with the procedure presented in section A36.7.2.
A36.7.2 The relationship between sound attenuation, frequency,
temperature, and humidity is expressed by the following
equations.
A36.7.2(a) For calculations using the English System of
Units:
and where η(δ) is listed in
Table A36-4 and f0 in Table A36-5; α(i) is the attenuation
coefficient in dB/1000 ft; θ is the temperature in °F; and H is the
relative humidity, expressed as a percentage.
A36.7.2(b) For calculations using the International System of
Units (SI):
and where η(δ) is listed in
Table A36-4 and f0 in Table A36-5; α(i) is the attenuation
coefficient in dB/100 m; θ is the temperature in °C; and H is the
relative humidity, expressed as a percentage.
A36.7.3 The values listed in table A36-4 are to be used when
calculating the equations listed in section A36.7.2. A term of
quadratic interpolation is to be used where necessary.
Section A36.8 [Reserved] Section A36.9
Adjustment of Airplane Flight Test Results.
A36.9.1 When certification test conditions are not identical to
reference conditions, appropriate adjustments must be made to the
measured noise data using the methods described in this
section.
A36.9.1.1 Adjustments to the measured noise values must be made
using one of the methods described in sections A36.9.3 and A36.9.4
for differences in the following:
(a) Attenuation of the noise along its path as affected by
“inverse square” and atmospheric attenuation
(b) Duration of the noise as affected by the distance and the
speed of the airplane relative to the measuring point
(c) Source noise emitted by the engine as affected by the
differences between test and reference engine operating
conditions
(d) Airplane/engine source noise as affected by differences
between test and reference airspeeds. In addition to the effect on
duration, the effects of airspeed on component noise sources must
be accounted for as follows: for conventional airplane
configurations, when differences between test and reference
airspeeds exceed 15 knots (28 km/h) true airspeed, test data and/or
analysis approved by the FAA must be used to quantify the effects
of the airspeed adjustment on resulting certification noise
levels.
A36.9.1.2 The “integrated” method of adjustment, described in
section A36.9.4, must be used on takeoff or approach under the
following conditions:
(a) When the amount of the adjustment (using the “simplified”
method) is greater than 8 dB on flyover, or 4 dB on approach;
or
(b) When the resulting final EPNL value on flyover or approach
(using the simplified method) is within 1 dB of the limiting noise
levels as prescribed in section B36.5 of this part.
A36.9.2 Flight profiles.
As described below, flight profiles for both test and reference
conditions are defined by their geometry relative to the ground,
together with the associated airplane speed relative to the ground,
and the associated engine control parameter(s) used for determining
the noise emission of the airplane.
A36.9.2.1 Takeoff Profile.
Note:
Figure A36-4 illustrates a typical takeoff profile.
(a) The airplane begins the takeoff roll at point A, lifts off
at point B and begins its first climb at a constant angle at point
C. Where thrust or power (as appropriate) cut-back is used, it is
started at point D and completed at point E. From here, the
airplane begins a second climb at a constant angle up to point F,
the end of the noise certification takeoff flight path.
(b) Position K1 is the takeoff noise measuring station and AK1
is the distance from start of roll to the flyover measuring point.
Position K2 is the lateral noise measuring station, which is
located on a line parallel to, and the specified distance from, the
runway center line where the noise level during takeoff is
greatest.
(c) The distance AF is the distance over which the airplane
position is measured and synchronized with the noise measurements,
as required by section A36.2.3.2 of this part.
A36.9.2.2 Approach Profile.
Note:
Figure A36-5 illustrates a typical approach profile.
(a) The airplane begins its noise certification approach flight
path at point G and touches down on the runway at point J, at a
distance OJ from the runway threshold.
(b) Position K3 is the approach noise measuring station and K3O
is the distance from the approach noise measurement point to the
runway threshold.
(c) The distance GI is the distance over which the airplane
position is measured and synchronized with the noise measurements,
as required by section A36.2.3.2 of this part.
The airplane reference point for approach
measurements is the instrument landing system (ILS) antenna. If no
ILS antenna is installed an alternative reference point must be
approved by the FAA.
A36.9.3 Simplified method of adjustment.
A36.9.3.1 General. As described below, the simplified
adjustment method consists of applying adjustments (to the EPNL,
which is calculated from the measured data) for the differences
between measured and reference conditions at the moment of
PNLTM.
A36.9.3.2 Adjustments to PNL and PNLT.
(a) The portions of the test flight path and the reference
flight path described below, and illustrated in Figure A36-6,
include the noise time history that is relevant to the calculation
of flyover and approach EPNL. In figure A36-6:
(1) XY represents the portion of the measured flight path that
includes the noise time history relevant to the calculation of
flyover and approach EPNL; XrYr represents the corresponding
portion of the reference flight path.
(2) Q represents the airplane's position on the measured flight
path at which the noise was emitted and observed as PNLTM at the
noise measuring station K. Qr is the corresponding position on the
reference flight path, and Kr the reference measuring station. QK
and QrKr are, respectively, the measured
and reference noise propagation paths, Qr being
determined from the assumption that QK and QrKr form the same angle
θ with their respective flight paths.
(b) The portions of the test flight path and the reference
flight path described in paragraph (b)(1) and (2), and illustrated
in Figure A36-7(a) and (b), include the noise time history that is
relevant to the calculation of lateral EPNL.
(1) In figure A36-7(a), XY represents the portion of the
measured flight path that includes the noise time history that is
relevant to the calculation of lateral EPNL; in figure A36-7(b),
XrYr represents the corresponding portion of the reference flight
path.
(2) Q represents the airplane position on the measured flight
path at which the noise was emitted and observed as PNLTM at the
noise measuring station K. Qr is the corresponding position on the
reference flight path, and Kr the reference measuring station. QK
and QrKr are, respectively, the measured and reference noise
propagation paths. In this case Kr is only specified as being on a
particular Lateral line; Kr and Qr are therefore determined from
the assumptions that QK and QrKr:
(i) Form the same angle θ with their respective flight paths;
and
(ii) Form the same angle ψ with the ground.
Note:
For the lateral noise measurement, sound propagation is affected
not only by inverse square and atmospheric attenuation, but also by
ground absorption and reflection effects which depend mainly on the
angle ψ.
A36.9.3.2.1 The one-third octave band levels SPL(i) comprising
PNL (the PNL at the moment of PNLTM observed at K) must be adjusted
to reference levels SPL(i)r as follows:
A36.9.3.2.1(a) For calculations using the English System of
Units:
(1) The term 0.001[α(i)−α(i)0]QK is the adjustment
for the effect of the change in sound attenuation coefficient, and
α(i) and α(i)0 are the coefficients for the test and reference
atmospheric conditions respectively, determined under section A36.7
of this appendix;
(2) The term 0.001α(i)0(QK − QrKr) is the adjustment for the
effect of the change in the noise path length on the sound
attenuation;
(3) The term 20 log(QK/QrKr) is the adjustment for the effect of
the change in the noise path length due to the “inverse square”
law;
(4) QK and QrKr are measured in feet and α(i) and α(i)0 are
expressed in dB/1000 ft.
A36.9.3.2.1(b) For calculations using the International System
of Units:
SPL(i)r = SPL(i) + 0.01[α(i)−α(i)0]QK + 0.01α(i)0 (QK − QrKr) + 20
log(QK/QrKr) In this expression,
(1) The term 0.01[α(i) − α(i)0]QK is the adjustment for the
effect of the change in sound attenuation coefficient, and α(i) and
α(i)0 are the coefficients for the test and reference atmospheric
conditions respectively, determined under section A36.7 of this
appendix;
(2) The term 0.01α(i)0(QK − QrKr) is the adjustment for the
effect of the change in the noise path length on the sound
attenuation;
(3) The term 20 log(QK/QrKr) is the adjustment for the effect of
the change in the noise path length due to the inverse square
law;
(4) QK and QrKr are measured in meters and α(i) and α(i)0 are
expressed in dB/100 m.
A36.9.3.2.1.1 PNLT Correction.
(a) Convert the corrected values, SPL(i)r, to PNLTr;
(b) Calculate the correction term Δ1 using the following
equation:
Δ1 = PNLTr − PNLTM
A36.9.3.2.1.2 Add Δ1 arithmetically to the EPNL calculated from
the measured data.
A36.9.3.2.2 If, during a test flight, several peak values of
PNLT that are within 2 dB of PNLTM are observed, the procedure
defined in section A36.9.3.2.1 must be applied at each peak, and
the adjustment term, calculated according to section A36.9.3.2.1,
must be added to each peak to give corresponding adjusted peak
values of PNLT. If these peak values exceed the value at the moment
of PNLTM, the maximum value of such exceedance must be added as a
further adjustment to the EPNL calculated from the measured
data.
A36.9.3.3 Adjustments to duration correction.
A36.9.3.3.1 Whenever the measured flight paths and/or the ground
velocities of the test conditions differ from the reference flight
paths and/or the ground velocities of the reference conditions,
duration adjustments must be applied to the EPNL values calculated
from the measured data. The adjustments must be calculated as
described below.
A36.9.3.3.2 For the flight path shown in Figure A36-6, the
adjustment term is calculated as follows:
Δ2 = −7.5 log(QK/QrKr) + 10 log(V/Vr)
(a) Add Δ2 arithmetically to the EPNL calculated from the
measured data.
A36.9.3.4 Source noise adjustments.
A36.9.3.4.1 To account for differences between the parameters
affecting engine noise as measured in the certification flight
tests, and those calculated or specified in the reference
conditions, the source noise adjustment must be calculated and
applied. The adjustment is determined from the manufacturer's data
approved by the FAA. Typical data used for this adjustment are
illustrated in Figure A36-8 that shows a curve of EPNL versus the
engine control parameter μ, with the EPNL data being corrected to
all the other relevant reference conditions (airplane mass, speed
and altitude, air temperature) and for the difference in noise
between the test engine and the average engine (as defined in
section B36.7(b)(7)). A sufficient number of data points over a
range of values of μr is required to calculate the source noise
adjustments for lateral, flyover and approach noise
measurements.
A36.9.3.4.2 Calculate adjustment term Δ3 by subtracting the EPNL
value corresponding to the parameter μ from the EPNL value
corresponding to the parameter μr. Add Δ3 arithmetically to the
EPNL value calculated from the measured data.
A36.9.3.5 Symmetry adjustments.
A36.9.3.5.1 A symmetry adjustment to each lateral noise value
(determined at the section B36.4(b) measurement points), is to be
made as follows:
(a) If the symmetrical measurement point is opposite the point
where the highest noise level is obtained on the main lateral
measurement line, the certification noise level is the arithmetic
mean of the noise levels measured at these two points (see Figure
A36-9(a));
(b) If the condition described in paragraph (a) of this section
is not met, then it is assumed that the variation of noise with the
altitude of the airplane is the same on both sides; there is a
constant difference between the lines of noise versus altitude on
both sides (see figure A36-9(b)). The certification noise level is
the maximum value of the mean between these lines.
A36.9.4 Integrated method of adjustment
A36.9.4.1 General. As described in this section, the
integrated adjustment method consists of recomputing under
reference conditions points on the PNLT time history corresponding
to measured points obtained during the tests, and computing EPNL
directly for the new time history obtained in this way. The main
principles are described in sections A36.9.4.2 through
A36.9.4.4.1.
A36.9.4.2 PNLT computations.
(a) The portions of the test flight path and the reference
flight path described in paragraph (a)(1) and (2), and illustrated
in Figure A36-10, include the noise time history that is relevant
to the calculation of flyover and approach EPNL. In figure
A36-10:
(1) XY represents the portion of the measured flight path that
includes the noise time history relevant to the calculation of
flyover and approach EPNL; XrYr represents the corresponding
reference flight path.
(2) The points Q0, Q1, Qn represent airplane positions on the
measured flight path at time t0, t1 and tn respectively. Point Q1
is the point at which the noise was emitted and observed as
one-third octave values SPL(i)1 at the noise measuring station K at
time t1. Point Qr1 represents the corresponding position on the
reference flight path for noise observed as SPL(i)r1 at the
reference measuring station Kr at time tr1. Q1K and Qr1Kr are
respectively the measured and reference noise propagation paths,
which in each case form the angle θ1 with their respective flight
paths. Qr0 and Qrn are similarly the points on the reference flight
path corresponding to Q0 and Qn on the measured flight path. Q0 and
Qn are chosen so that between Qr0 and Qrn all values of PNLTr
(computed as described in paragraphs A36.9.4.2.2 and A36.9.4.2.3)
within 10 dB of the peak value are included.
(b) The portions of the test flight path and the reference
flight path described in paragraph (b)(1) and (2), and illustrated
in Figure A36-11(a) and (b), include the noise time history
that is relevant to the calculation of lateral EPNL.
(1) In figure A36-11(a) XY represents the portion of the
measured flight path that includes the noise time history that is
relevant to the calculation of lateral EPNL; in figure A36-11(b),
XrYr represents the corresponding portion of the reference flight
path.
(2) The points Q0, Q1 and Qn represent airplane positions on the
measured flight path at time t0, t1 and tn respectively. Point Q1
is the point at which the noise was emitted and observed as
one-third octave values SPL(i)1 at the noise measuring station K at
time t1. The point Qr1 represents the corresponding position on the
reference flight path for noise observed as SPL(i)r1 at the
measuring station Kr at time tr1. Q1K and Qr1Kr are respectively
the measured and reference noise propagation paths. Qr0 and Qrn are
similarly the points on the reference flight path corresponding to
Q0 and Qn on the measured flight path.
Q0 and Qn are chosen to that between Qro and Qrn all values of
PNLTr (computed as described in paragraphs A36.9.4.2.2 and
A36.9.4.2.3) within 10 dB of the peak value are included. In this
case Kr is only specified as being on a particular lateral line.
The position of Kr and Qr1 are determined from the following
requirements.
(i) Q1K and Qr1Kr form the same angle θ1 with their respective
flight paths; and
(ii) The differences between the angles 1 and r1 must be
minimized using a method, approved by the FAA. The differences
between the angles are minimized since, for geometrical reasons, it
is generally not possible to choose Kr so that the condition
described in paragraph A36.9.4.2(b)(2)(i) is met while at the same
time keeping 1 and r1 equal.
Note:
For the lateral noise measurement, sound propagation is affected
not only by “inverse square” and atmospheric attenuation, but also
by ground absorption and reflection effects which depend mainly on
the angle.
A36.9.4.2.1 In paragraphs A36.9.4.2(a)(2) and (b)(2) the time
tr1 is later (for Qr1Kr >Q1K) than t1 by two separate
amounts:
(1) The time taken for the airplane to travel the distance
Qr1Qr0 at a speed Vr less the time taken for it to travel Q1Q0 at
V;
(2) The time taken for sound to travel the distance
Qr1Kr-Q1K.
Note:
For the flight paths described in paragraphs A36.9.4.2(a) and
(b), the use of thrust or power cut-back will result in test and
reference flight paths at full thrust or power and at cut-back
thrust or power. Where the transient region between these thrust or
power levels affects the final result, an interpolation must be
made between them by an approved method such as that given in the
current advisory circular for this part.
A36.9.4.2.2 The measured values of SPL(i)1 must be adjusted to
the reference values SPL(i)r1 to account for the differences
between measured and reference noise path lengths and between
measured and reference atmospheric conditions, using the methods of
section A36.9.3.2.1 of this appendix. A corresponding value of
PNLr1 must be computed according to the method in section A36.4.2.
Values of PNLr must be computed for times t0 through tn.
A36.9.4.2.3 For each value of PNLr1, a tone correction factor C1
must be determined by analyzing the reference values SPL(i)r using
the methods of section A36.4.3 of this appendix, and added to PNLr1
to yield PNLTr1. Using the process described in this paragraph,
values of PNLTr must be computed for times t0 through tn.
A36.9.4.3 Duration correction.
A36.9.4.3.1 The values of PNLTr corresponding to those of PNLT
at each one-half second interval must be plotted against time
(PNLTr1 at time tr1). The duration correction must then be
determined using the method of section A36.4.5.1 of this appendix,
to yield EPNLr.
A36.9.4.4 Source Noise Adjustment.
A36.9.4.4.1 A source noise adjustment, Δ3, must be determined
using the methods of section A36.9.3.4 of this appendix.
A36.9.5 Flight Path Identification
Positions
Position
Description
A
Start of Takeoff roll.
B
Lift-off.
C
Start of first constant
climb.
D
Start of thrust
reduction.
E
Start of second constant
climb.
F
End of noise certification
Takeoff flight path.
G
Start of noise certification
Approach flight path.
H
Position on Approach path
directly above noise measuring station.
I
Start of level-off.
J
Touchdown.
K
Noise measurement point.
Kr
Reference measurement
point.
K1
Flyover noise measurement
point.
K2
Lateral noise measurement
point.
K3
Approach noise measurement
point.
M
End of noise certification
Takeoff flight track.
O
Threshold of Approach end of
runway.
P
Start of noise certification
Approach flight track.
Q
Position on measured Takeoff
flight path corresponding to apparent PNLTM at station K See
section A36.9.3.2.
Qr
Position on corrected Takeoff
flight path corresponding to PNLTM at station K. See section
A36.9.3.2.
V
Airplane test speed.
Vr
Airplane reference speed.
A36.9.6 Flight Path Distances
Distance
Unit
Meaning
AB
Feet (meters)
Length of takeoff roll. The
distance along the runway between the start of takeoff roll and
lift off.
AK
Feet (meters)
Takeoff measurement distance.
The distance from the start of roll to the takeoff noise
measurement station along the extended center line of the
runway.
AM
Feet (meters)
Takeoff flight track distance.
The distance from the start of roll to the takeoff flight track
position along the extended center line of the runway after which
the position of the airplane need no longer be recorded.
QK
Feet (meters)
Measured noise path. The
distance from the measured airplane position Q to station K.
QrKr
Feet (meters)
Reference noise path. The
distance from the reference airplane position Qr to station
Kr.
K3H
Feet (meters)
Airplane approach height. The
height of the airplane above the approach measuring station.
OK3
Feet (meters)
Approach measurement distance.
The distance from the runway threshold to the approach measurement
station along the extended center line of the runway.
OP
Feet (meters)
Approach flight track
distance. The distance from the runway threshold to the approach
flight track position along the extended center line of the runway
after which the position of the airplane need no longer be
recorded.
Appendix B to Part 36 - Noise Levels for Transport Category and Jet Airplanes Under § 36.103
14:1.0.1.3.20.14.283.1.37 : Appendix B
Appendix B to Part 36 - Noise Levels for Transport Category and Jet
Airplanes Under § 36.103 Sec. B36.1 Noise Measurement and
Evaluation. B36.2 Noise Evaluation Metric. B36.3
Reference Noise Measurement Points. B36.4 Test Noise
Measurement Points. B36.5 Maximum Noise Levels. B36.6
Trade-Offs. B36.7 Noise Certification Reference
Procedures and Conditions. B36.8 Noise Certification Test
Procedures. Section B36.1 Noise measurement and evaluation
(a) The procedures of Appendix A of this part, or approved
equivalent procedures, must be used to determine noise levels of an
airplane. These noise levels must be used to show compliance with
the requirements of this appendix.
(b) For Stage 4 airplanes, an acceptable alternative to
paragraph (a) of this section for noise measurement and evaluation
is Appendix 2 to ICAO Annex 16, Volume I, Amendment 7 (Incorporated
by reference, see § 36.6).
(c) For Stage 5 airplanes, an acceptable alternative to
paragraph (a) of this section for noise measurement and evaluation
is Appendix 2 to ICAO Annex 16, Volume 1, Amendment 11-B
(Incorporated by reference, see § 36.6).
Section B36.2 Noise Evaluation Metric
The noise evaluation metric is the effective perceived noise
level expressed in EPNdB, as calculated using the procedures of
appendix A of this part.
Section B36.3 Reference Noise Measurement Points
When tested using the procedures of this part, except as
provided in section B36.6, an airplane may not exceed the noise
levels specified in section B36.5 at the following points on level
terrain:
(1) For jet airplanes: The point on a line parallel to and 1,476
feet (450 m) from the runway centerline, or extended centerline,
where the noise level after lift-off is at a maximum during
takeoff. For the purpose of showing compliance with Stage 1 or
Stage 2 noise limits for an airplane powered by more than three jet
engines, the distance from the runway centerline must be 0.35
nautical miles (648 m). For jet airplanes, when approved by the
FAA, the maximum lateral noise at takeoff thrust may be assumed to
occur at the point (or its approved equivalent) along the extended
centerline of the runway where the airplane reaches 985 feet (300
meters) altitude above ground level. A height of 1427 feet (435
meters) may be assumed for Stage 1 or Stage 2 four engine
airplanes. The altitude of the airplane as it passes the noise
measurement points must be within + 328 to −164 feet (+100 to −50
meters) of the target altitude. For airplanes powered by other than
jet engines, the altitude for maximum lateral noise must be
determined experimentally.
(2) For propeller-driven airplanes: The point on the extended
centerline of the runway above which the airplane, at full takeoff
power, reaches a height of 2,133 feet (650 meters). For tests
conducted before August 7, 2002, an applicant may use the
measurement point specified in section B36.3(a)(1) as an
alternative.
(b) Flyover reference noise measurement point: The point on the
extended centerline of the runway that is 21,325 feet (6,500 m)
from the start of the takeoff roll;
(c) Approach reference noise measurement point: The point on the
extended centerline of the runway that is 6,562 feet (2,000 m) from
the runway threshold. On level ground, this corresponds to a
position that is 394 feet (120 m) vertically below the 3° descent
path, which originates at a point on the runway 984 feet (300 m)
beyond the threshold.
Section B36.4 Test noise measurement points.
(a) If the test noise measurement points are not located at the
reference noise measurement points, any corrections for the
difference in position are to be made using the same adjustment
procedures as for the differences between test and reference flight
paths.
(b) The applicant must use a sufficient number of lateral test
noise measurement points to demonstrate to the FAA that the maximum
noise level on the appropriate lateral line has been determined.
For jet airplanes, simultaneous measurements must be made at one
test noise measurement point at its symmetrical point on the other
side of the runway. Propeller-driven airplanes have an inherent
asymmetry in lateral noise. Therefore, simultaneous measurements
must be made at each and every test noise measurement point at its
symmetrical position on the opposite side of the runway. The
measurement points are considered to be symmetrical if they are
longitudinally within 33 feet (±10 meters) of each other.
Section B36.5 Maximum Noise Levels
Except as provided in section B36.6 of this appendix, maximum
noise levels, when determined in accordance with the noise
evaluation methods of appendix A of this part, may not exceed the
following:
(a) For acoustical changes to Stage 1 airplanes, regardless of
the number of engines, the noise levels prescribed under § 36.7(c)
of this part.
(b) For any Stage 2 airplane regardless of the number of
engines:
(1) Flyover: 108 EPNdB for maximum weight of 600,000 pounds or
more; for each halving of maximum weight (from 600,000 pounds),
reduce the limit by 5 EPNdB; the limit is 93 EPNdB for a maximum
weight of 75,000 pounds or less.
(2) Lateral and approach: 108 EPNdB for maximum weight of
600,000 pounds or more; for each halving of maximum weight (from
600,000 pounds), reduce the limit by 2 EPNdB; the limit is 102
EPNdB for a maximum weight of 75,000 pounds or less.
(c) For any Stage 3 airplane:
(1) Flyover.
(i) For airplanes with more than 3 engines: 106 EPNdB for
maximum weight of 850,000 pounds or more; for each halving of
maximum weight (from 850,000 pounds), reduce the limit by 4 EPNdB;
the limit is 89 EPNdB for a maximum weight of 44,673 pounds or
less;
(ii) For airplanes with 3 engines: 104 EPNdB for maximum weight
of 850,000 pounds or more; for each halving of maximum weight (from
850,000 pounds), reduce the limit by 4 EPNdB; the limit is 89 EPNdB
for a maximum weight of 63,177 pounds or less; and
(iii) For airplanes with fewer than 3 engines: 101 EPNdB for
maximum weight of 850,000 pounds or more; for each halving of
maximum weight (from 850,000 pounds), reduce the limit by 4 EPNdB;
the limit is 89 EPNdB for a maximum weight of 106,250 pounds or
less.
(2) Lateral, regardless of the number of engines: 103 EPNdB for
maximum weight of 882,000 pounds or more; for each halving of
maximum weight (from 882,000 pounds), reduce the limit by 2.56
EPNdB; the limit is 94 EPNdB for a maximum weight of 77,200 pounds
or less.
(3) Approach, regardless of the number of engines: 105 EPNdB for
maximum weight of 617,300 pounds or more; for each halving of
maximum weight (from 617,300 pounds), reduce the limit by 2.33
EPNdB; the limit is 98 EPNdB for a maximum weight of 77,200 pounds
or less.
(d) For any Stage 4 airplane, the flyover, lateral, and approach
maximum noise levels are prescribed in Chapter 4, Paragraph 4.4,
Maximum Noise Levels, and Chapter 3, Paragraph 3.4, Maximum Noise
Levels, of the International Civil Aviation Organization (ICAO)
Annex 16, Environmental Protection, Volume I, Aircraft Noise, Third
Edition, July 1993, Amendment 7, effective March 21, 2002.
[Incorporated by reference, see § 36.6].
(e) For any Stage 5 airplane, the flyover, lateral, and approach
maximum noise levels are prescribed in Chapter 14, Paragraph 14.4,
Maximum Noise Levels of ICAO Annex 16, Volume I, Amendment 11-B
(Incorporated by reference, see § 36.6).
Section B36.6 Trade-Offs
Except when prohibited by sections 36.7(c)(1) and
36.7(d)(1)(ii), if the maximum noise levels are exceeded at any one
or two measurement points, the following conditions must be
met:
(a) The sum of the exceedance(s) may not be greater than 3
EPNdB;
(b) Any exceedance at any single point may not be greater than 2
EPNdB, and
(c) Any exceedance(s) must be offset by a corresponding amount
at another point or points.
Section B36.7 Noise Certification Reference Procedures and
Conditions
(a) General conditions:
(1) All reference procedures must meet the requirements of
section 36.3 of this part.
(2) Calculations of airplane performance and flight path must be
made using the reference procedures and must be approved by the
FAA.
(3) Applicants must use the takeoff and approach reference
procedures prescribed in paragraphs (b) and (c) of this
section.
(4) [Reserved]
(5) The reference procedures must be determined for the
following reference conditions. The reference atmosphere is
homogeneous in terms of temperature and relative humidity when used
for the calculation of atmospheric absorption coefficients.
(i) Sea level atmospheric pressure of 2116 pounds per square
foot (psf) (1013.25 hPa);
(ii) Ambient sea-level air temperature of 77 °F (25 °C,
i.e., ISA + 10 °C);
(iii) Relative humidity of 70 per cent;
(iv) Zero wind.
(v) In defining the reference takeoff flight path(s) for the
takeoff and lateral noise measurements, the runway gradient is
zero.
(b) Takeoff reference procedure:
The takeoff reference flight path is to be calculated using the
following:
(1) Average engine takeoff thrust or power must be used from the
start of takeoff to the point where at least the following height
above runway level is reached. The takeoff thrust/power used must
be the maximum available for normal operations given in the
performance section of the airplane flight manual under the
reference atmospheric conditions given in section B36.7(a)(5).
(i) For Stage 1 airplanes and for Stage 2 airplanes that do not
have jet engines with a bypass ratio of 2 or more, the following
apply:
(A): For airplanes with more than three jet engines - 700 feet
(214 meters).
(B): For all other airplanes - 1,000 feet (305 meters).
(ii) For Stage 2 airplanes that have jet engines with a bypass
ratio of 2 or more and for Stage 3 airplanes, the following
apply:
(A): For airplanes with more than three engines - 689 feet (210
meters).
(B): For airplanes with three engines - 853 feet (260
meters).
(C): For airplanes with fewer than three engines - 984 feet (300
meters).
(2) Upon reaching the height specified in paragraph (b)(1) of
this section, airplane thrust or power must not be reduced below
that required to maintain either of the following, whichever is
greater:
(i) A climb gradient of 4 per cent; or
(ii) In the case of multi-engine airplanes, level flight with
one engine inoperative.
(3) For the purpose of determining the lateral noise level, the
reference flight path must be calculated using full takeoff power
throughout the test run without a reduction in thrust or power. For
tests conducted before August 7, 2002, a single reference flight
path that includes thrust cutback in accordance with paragraph
(b)(2) of this section, is an acceptable alternative in determining
the lateral noise level.
(4) The takeoff reference speed is the all-engine operating
takeoff climb speed selected by the applicant for use in normal
operation; this speed must be at least V2 + 10kt (V2 + 19km/h) but
may not be greater than V2 + 20kt (V2 + 37km/h). This speed must be
attained as soon as practicable after lift-off and be maintained
throughout the takeoff noise certification test. For Concorde
airplanes, the test day speeds and the acoustic day reference speed
are the minimum approved value of V2 + 35 knots, or the
all-engines-operating speed at 35 feet, whichever speed is greater
as determined under the regulations constituting the type
certification basis of the airplane; this reference speed may not
exceed 250 knots. For all airplanes, noise values measured at the
test day speeds must be corrected to the acoustic day reference
speed.
(5) The takeoff configuration selected by the applicant must be
maintained constantly throughout the takeoff reference procedure,
except that the landing gear may be retracted. Configuration means
the center of gravity position, and the status of the airplane
systems that can affect airplane performance or noise. Examples
include, the position of lift augmentation devices, whether the APU
is operating, and whether air bleeds and engine power take-offs are
operating;
(6) The weight of the airplane at the brake release must be the
maximum takeoff weight at which the noise certification is
requested, which may result in an operating limitation as specified
in § 36.1581(d); and
(7) The average engine is defined as the average of all the
certification compliant engines used during the airplane flight
tests, up to and during certification, when operating within the
limitations and according to the procedures given in the Flight
Manual. This will determine the relationship of thrust/power to
control parameters (e.g., N1 or EPR). Noise measurements made
during certification tests must be corrected using this
relationship.
(c) Approach reference procedure:
The approach reference flight path must be calculated using the
following:
(1) The airplane is stabilized and following a 3° glide
path;
(2) For subsonic airplanes, a steady approach speed of Vref + 10
kts (Vref + 19 km/h) with thrust and power stabilized must be
established and maintained over the approach measuring point. Vref
is the reference landing speed, which is defined as the speed of
the airplane, in a specified landing configuration, at the point
where it descends through the landing screen height in the
determination of the landing distance for manual landings. For
Concorde airplanes, a steady approach speed that is either the
landing reference speed + 10 knots or the speed used in
establishing the approved landing distance under the airworthiness
regulations constituting the type certification basis of the
airplane, whichever speed is greater. This speed must be
established and maintained over the approach measuring point.
(3) The constant approach configuration used in the
airworthiness certification tests, but with the landing gear down,
must be maintained throughout the approach reference procedure;
(4) The weight of the airplane at touchdown must be the maximum
landing weight permitted in the approach configuration defined in
paragraph (c)(3) of this section at which noise certification is
requested, except as provided in § 36.1581(d) of this part; and
(5) The most critical configuration must be used; this
configuration is defined as that which produces the highest noise
level with normal deployment of aerodynamic control surfaces
including lift and drag producing devices, at the weight at which
certification is requested. This configuration includes all those
items listed in section A36.5.2.5 of appendix A of this part that
contribute to the noisiest continuous state at the maximum landing
weight in normal operation.
Section B36.8 Noise Certification Test Procedures
(a) All test procedures must be approved by the FAA.
(b) The test procedures and noise measurements must be conducted
and processed in an approved manner to yield the noise evaluation
metric EPNL, in units of EPNdB, as described in appendix A of this
part.
(c) Acoustic data must be adjusted to the reference conditions
specified in this appendix using the methods described in appendix
A of this part. Adjustments for speed and thrust must be made as
described in section A36.9 of this part.
(d) If the airplane's weight during the test is different from
the weight at which noise certification is requested, the required
EPNL adjustment may not exceed 2 EPNdB for each takeoff and 1 EPNdB
for each approach. Data approved by the FAA must be used to
determine the variation of EPNL with weight for both takeoff and
approach test conditions. The necessary EPNL adjustment for
variations in approach flight path from the reference flight path
must not exceed 2 EPNdB.
(e) For approach, a steady glide path angle of 3° ±0.5° is
acceptable.
(f) If equivalent test procedures different from the reference
procedures are used, the test procedures and all methods for
adjusting the results to the reference procedures must be approved
by the FAA. The adjustments may not exceed 16 EPNdB on takeoff and
8 EPNdB on approach. If the adjustment is more than 8 EPNdB on
takeoff, or more than 4 EPNdB on approach, the resulting numbers
must be more than 2 EPNdB below the limit noise levels specified in
section B36.5.
(g) During takeoff, lateral, and approach tests, the airplane
variation in instantaneous indicated airspeed must be maintained
within ±3% of the average airspeed between the 10 dB-down points.
This airspeed is determined by the pilot's airspeed indicator.
However, if the instantaneous indicated airspeed exceeds ±3 kt
(±5.5 km/h) of the average airspeed over the 10 dB-down points, and
is determined by the FAA representative on the flight deck to be
due to atmospheric turbulence, then the flight so affected must be
rejected for noise certification purposes.
Note:
Guidance material on the use of equivalent procedures is
provided in the current advisory circular for this part.
Appendix F to Part 36 - Flyover Noise Requirements for Propeller-Driven Small Airplane and Propeller-Driven, Commuter Category Airplane Certification Tests Prior to December 22, 1988
14:1.0.1.3.20.14.283.1.39 : Appendix F
Appendix F to Part 36 - Flyover Noise Requirements for
Propeller-Driven Small Airplane and Propeller-Driven, Commuter
Category Airplane Certification Tests Prior to December 22, 1988
part a - general Sec. F36.1 Scope. part b - noise
measurement F36.101 General test conditions. F36.103
Acoustical measurement system. F36.105 Sensing,
recording, and reproducing equipment. F36.107 Noise
measurement procedures. F36.109 Data recording, reporting,
and approval. F36.111 Flight procedures. part c - data
correction F36.201 Correction of data. F36.203 Validity
of results. part d - noise limits F36.301 Aircraft noise
limits. part a - general
Section F36.1 Scope. This appendix prescribes noise level
limits and procedures for measuring and correcting noise data for
the propeller driven small airplanes specified in §§ 36.1 and
36.501(b).
part b - noise measurement Sec. F36.101 General test conditions.
(a) The test area must be relatively flat terrain having no
excessive sound absorption characteristics such as those caused by
thick, matted, or tall grass, by shrubs, or by wooded areas. No
obstructions which significantly influence the sound field from the
airplane may exist within a conical space above the measurement
position, the cone being defined by an axis normal to the ground
and by a half-angle 75 degrees from this axis.
(b) The tests must be carried out under the following
conditions:
(1) There may be no precipitation.
(2) Relative humidity may not be higher than 90 percent or lower
than 30 percent.
(3) Ambient temperature may not be above 86 degrees F. or below
41 degrees F. at 33′ above ground. If the measurement site is
within 1 n.m. of an airport thermometer the airport reported
temperature may be used.
(4) Reported wind may not be above 10 knots at 33′ above ground.
If wind velocities of more than 4 knots are reported, the flight
direction must be aligned to within ±15 degrees of wind direction
and flights with tail wind and head wind must be made in equal
numbers. If the measurement site is within 1 n.m. of an airport
anemometer, the airport reported wind may be used.
(5) There may be no temperature inversion or anomalous wind
conditions that would significantly alter the noise level of the
airplane when the noise is recorded at the required measuring
point.
(6) The flight test procedures, measuring equipment, and noise
measurement procedures must be approved by the FAA.
(7) Sound pressure level data for noise evaluation purposes must
be obtained with acoustical equipment that complies with section
F36.103 of this appendix.
Sec. F36.103 Acoustical measurement system. The
acoustical measurement system must consist of approved equipment
equivalent to the following:
(a) A microphone system with frequency response compatible with
measurement and analysis system accuracy as prescribed in section
F36.105 of this appendix.
(b) Tripods or similar microphone mountings that minimize
interference with the sound being measured.
(c) Recording and reproducing equipment characteristics,
frequency response, and dynamic range compatible with the response
and accuracy requirements of section F36.105 of this appendix.
(d) Acoustic calibrators using sine wave or broadband noise of
known sound pressure level. If broadband noise is used, the signal
must be described in terms of its average and maximum
root-mean-square (rms) value for nonoverload signal level.
Sec. F36.105 Sensing, recording, and reproducing equipment.
(a) The noise produced by the airplane must be recorded. A
magnetic tape recorder is acceptable.
(b) The characteristics of the system must comply with the
recommendations in IEC 179 (incorporated by reference, see §
36.6).
(c) The response of the complete system to a sensibly plane
progressive sinusoidal wave of constant amplitude must lie within
the tolerance limits specified in IEC Publication No. 179, dated
1973, over the frequency range 45 to 11,200 Hz.
(d) If limitations of the dynamic range of the equipment make it
necessary, high frequency pre-emphasis must be added to the
recording channel with the converse de-emphasis on playback. The
pre-emphasis must be applied such that the instantaneous recorded
sound pressure level of the noise signal between 800 and 11,200 Hz
does not vary more than 20 dB between the maximum and minimum
one-third octave bands.
(e) If requested by the Administrator, the recorded noise signal
must be read through an “A” filter with dynamic characteristics
designated “slow,” as defined in IEC Publication No. 179, dated
1973. The output signal from the filter must be fed to a rectifying
circuit with square law rectification, integrated with time
constants for charge and discharge of about 1 second or 800
milliseconds.
(f) The equipment must be acoustically calibrated using
facilities for acoustic freefield calibration and if analysis of
the tape recording is requested by the Administrator, the analysis
equipment shall be electronically calibrated by a method approved
by the FAA.
(g) A windscreen must be employed with microphone during all
measurements of aircraft noise when the wind speed is in excess of
6 knots.
Sec. F36.107 Noise measurement procedures.
(a) The microphones must be oriented in a known direction so
that the maximum sound received arrives as nearly as possible in
the direction for which the microphones are calibrated. The
microphone sensing elements must be approximately 4′ above
ground.
(b) Immediately prior to and after each test; a recorded
acoustic calibration of the system must be made in the field with
an acoustic calibrator for the two purposes of checking system
sensitivity and providing an acoustic reference level for the
analysis of the sound level data.
(c) The ambient noise, including both acoustical background and
electrical noise of the measurement systems, must be recorded and
determined in the test area with the system gain set at levels that
will be used for aircraft noise measurements. If aircraft sound
pressure levels do not exceed the background sound pressure levels
by at least 10 dB(A), approved corrections for the contribution of
background sound pressure level to the observed sound pressure
level must be applied.
Sec. F36.109 Data recording, reporting, and approval.
(a) Data representing physical measurements or corrections to
measured data must be recorded in permanent form and appended to
the record except that corrections to measurements for normal
equipment response deviations need not be reported. All other
corrections must be approved. Estimates must be made of the
individual errors inherent in each of the operations employed in
obtaining the final data.
(b) Measured and corrected sound pressure levels obtained with
equipment conforming to the specifications described in section
F36.105 of this appendix must be reported.
(c) The type of equipment used for measurement and analysis of
all acoustic, airplane performance, and meteorological data must be
reported.
(d) The following atmospheric data, measured immediately before,
after, or during each test at the observation points prescribed in
section F36.101 of this appendix must be reported:
(1) Air temperature and relative humidity.
(2) Maximum, minimum, and average wind velocities.
(e) Comments on local topography, ground cover, and events that
might interfere with sound recordings must be reported.
(f) The following airplane information must be reported:
(1) Type, model and serial numbers (if any) of airplanes,
engines, and propellers.
(2) Any modifications or nonstandard equipment likely to affect
the noise characteristics of the airplane.
(3) Maximum certificated takeoff weights.
(4) Airspeed in knots for each overflight of the measuring
point.
(5) Engine performance in terms of revolutions per minute and
other relevant parameters for each overflight.
(6) Aircraft height in feet determined by a calibrated altimeter
in the aircraft, approved photographic techniques, or approved
tracking facilities.
(g) Aircraft speed and position and engine performance
parameters must be recorded at an approved sampling rate sufficient
to ensure compliance with the test procedures and conditions of
this appendix.
Sec. F36.111 Flight procedures.
(a) Tests to demonstrate compliance with the noise level
requirements of this appendix must include at least six level
flights over the measuring station at a height of 1,000′ ±30′ and
±10 degrees from the zenith when passing overhead.
(b) Each test over flight must be conducted:
(1) At not less than the highest power in the normal operating
range provided in an Airplane Flight Manual, or in any combination
of approved manual material, approved placard, or approved
instrument markings; and
(2) At stabilized speed with propellers synchronized and with
the airplane in cruise configuration, except that if the speed at
the power setting prescribed in this paragraph would exceed the
maximum speed authorized in level flight, accelerated flight is
acceptable.
part c - data correction Sec. F36.201 Correction of data.
(a) Noise data obtained when the temperature is outside the
range of 68 degrees F. ±9 degrees F., or the relative humidity is
below 40 percent, must be corrected to 77 degrees F. and 70 percent
relative humidity by a method approved by the FAA.
(b) The performance correction prescribed in paragraph (c) of
this section must be used. It must be determined by the method
described in this appendix, and must be added algebraically to the
measured value. It is limited to 5dB(A).
(c) The performance correction must be computed by using the
following formula:
Where: D50 = Takeoff distance to 50 feet at
maximum certificated takeoff weight. R/C = Certificated best rate
of climb (fpm). Vy = Speed for best rate of climb in the
same units as rate of climb.
(d) When takeoff distance to 50′ is not listed as approved
performance information, the figures of 2000 for single-engine
airplanes and 1600′ for multi-engine airplanes must be used.
Sec. F36.203 Validity of results.
(a) The test results must produce an average dB(A) and its 90
percent confidence limits, the noise level being the arithmetic
average of the corrected acoustical measurements for all valid test
runs over the measuring point.
(b) The samples must be large enough to establish statistically
a 90 pecent confidence limit not to exceed ±1.5 dB(A). No test
result may be omitted from the averaging process, unless omission
is approved by the FAA.
part d - noise limits Sec. F36.301 Aircraft noise limits.
(a) Compliance with this section must be shown with noise data
measured and corrected as prescribed in Parts B and C of this
appendix.
(b) For airplanes for which application for a type certificate
is made on or after October 10, 1973, the noise level must not
exceed 68 dB(A) up to and including aircraft weights of 1,320
pounds (600 kg.). For weights greater than 1,320 pounds up to and
including 3,630 pounds (1.650 kg.) the limit increases at the rate
of 1 dB/165 pounds (1 dB/75 kg.) to 82 dB(A) at 3,630 pounds, after
which it is constant at 82 dB(A). However, airplanes produced under
type certificates covered by this paragraph must also meet
paragraph (d) of this section for the original issuance of standard
airworthiness certificates or restricted category airworthiness
certificates if those airplanes have not had flight time before the
date specified in that paragraph.
(c) For airplanes for which application for a type certificate
is made on or after January 1, 1975, the noise levels may not
exceed the noise limit curve prescribed in paragraph (b) of this
section, except that 80 dB(A) may not be exceeded.
(d) For airplanes for which application is made for a standard
airworthiness certificate or for a restricted category
airworthiness certificate, and that have not had any flight time
before January 1, 1980, the requirements of paragraph (c) of this
section apply, regardless of date of application, to the original
issuance of the certificate for that airplane.
Appendix G to Part 36 - Takeoff Noise Requirements for Propeller-Driven Small Airplane and Propeller-Driven, Commuter Category Airplane Certification Tests on or After December 22, 1988
14:1.0.1.3.20.14.283.1.40 : Appendix G
Appendix G to Part 36 - Takeoff Noise Requirements for
Propeller-Driven Small Airplane and Propeller-Driven, Commuter
Category Airplane Certification Tests on or After December 22, 1988
part a - general Sec. G36.1 Scope. part b - noise
measurement G36.101 General Test Conditions. G36.103
Acoustical measurement system. G36.105 Sensing,
recording, and reproducing equipment. G36.107 Noise
measurement procedures. G36.109 Data recording, reporting,
and approval. G36.111 Flight procedures. part c - data
corrections G36.201 Corrections to Test Results. G36.203
Validity of results. part d - noise limits G36.301
Aircraft Noise Limits. part a - general
Section G36.1 Scope. This appendix prescribes limiting
noise levels and procedures for measuring noise and adjusting these
data to standard conditions, for propeller driven small airplanes
and propeller-driven, commuter category airplanes specified in §§
36.1 and 36.501(c).
part b - noise measurement Sec. G36.101 General Test Conditions.
(a) The test area must be relatively flat terrain having no
excessive sound absorption characteristics such as those caused by
thick, matted, or tall grass, by shrubs, or by wooded areas. No
obstructions which significantly influence the sound field from the
airplane may exist within a conical space above the measurement
position, the cone being defined by an axis normal to the ground
and by a half-angle 75 degrees from the normal ground axis.
(b) The tests must be carried out under the following
conditions:
(1) No precipitation;
(2) Ambient air temperature between 36 and 95 degrees F (2.2 and
35 degrees C);
(3) Relative humidity between 20 percent and 95 percent,
inclusively;
(4) Wind speed may not exceed 10 knots (19 km/h) and cross wind
may not exceed 5 knots (9 km/h), using a 30-second average;
(5) No temperature inversion or anomalous wind condition that
would significantly alter the noise level of the airplane when the
nose is recorded at the required measuring point, and
(6) The meteorological measurements must be made between 4 ft.
(1.2 m) and 33 ft. (10 m) above ground level. If the measurement
site is within 1 n.m. of an airport meteorological station,
measurements from that station may be used.
(c) The flight test procedures, measuring equipment, and noise
measurement procedures must be approved by the FAA.
(d) Sound pressure level data for noise evaluation purposes must
be obtained with acoustical equipment that complies with section
G36.103 of this appendix.
Sec. G36.103 Acoustical Measurement System.
The acoustical measurement system must consist of approved
equipment with the following characteristics: (a) A microphone
system with frequency response compatible with measurement and
analysis system accuracy as prescribed in section G36.105 of this
appendix.
(b) Tripods or similar microphone mountings that minimize
interference with the sound being measured.
(c) Recording and reproducing equipment characteristics,
frequency response, and dynamic range compatible with the response
and accuracy requirements of section G36.105 of this appendix.
(d) Acoustic calibrators using sine wave or broadband noise of
known sound pressure level. If broadband noise is used, the signal
must be described in terms of its average and maximum
root-mean-square (rms) value for non-overload signal level.
Sec. G36.105 Sensing, Recording, and Reproducing Equipment.
(a) The noise produced by the airplane must be recorded. A
magnetic tape recorder, graphic level recorder, or sound level
meter is acceptable when approved by the regional certificating
authority.
(b) The characteristics of the complete system must comply with
the requirements in IEC 651 and IEC 561 (incorporated by reference,
see § 36.6). Sound level meters must comply with the requirements
for Type 1 sound level meters as specified in IEC 651.
(c) The response of the complete system to a sensibly plane
progressive sinusoidal wave of constant amplitude must be within
the tolerance limits specified in IEC 651, over the frequency range
45 to 11,200 Hz.
(d) If equipment dynamic range limitations make it necessary,
high frequency pre-emphasis must be added to the recording channel
with the converse de-emphasis on playback. The pre-emphasis must be
applied such that the instantaneous recorded sound pressure level
of the noise signal between 800 and 11,200 Hz does not vary more
than 20 dB between the maximum and minimum one-third octave
bands.
(e) The output noise signal must be read through an “A” filter
with dynamic characteristics designated “slow” as defined in IEC
651. A graphic recorder, sound level meter, or digital equipment
may be used.
(f) The equipment must be acoustically calibrated using
facilities for acoustic free-field calibration and if analysis of
the tape recording is requested by the Administrator, the analysis
equipment shall be electronically calibrated by a method approved
by the FAA. Calibrations shall be performed, as appropriate, in
accordance with paragraphs A36.3.8 and A36.3.9 of appendix A of
this part.
(g) A windscreen must be employed with the microphone during all
measurements of aircraft noise when the wind speed is in excess of
5 knots (9 km/hr).
Sec. G36.107 Noise Measurement Procedures.
(a) The microphone must be a pressure type, 12.7 mm in diameter,
with a protective grid, mounted in an inverted position such that
the microphone diaphragm is 7 mm above and parallel to a
white-painted metal circular plate. This white-painted metal plate
shall be 40 cm in diameter and at least 2.5 mm thick. The plate
shall be placed horizontally and flush with the surrounding ground
surface with no cavities below the plate. The microphone must be
located three-quarters of the distance from the center to the back
edge of the plate along a radius normal to the line of flight of
the test airplane.
(b) Immediately prior to and after each test, a recorded
acoustic calibration of the system must be made in the field with
an acoustic calibrator for the purposes of checking system
sensitivity and providing an acoustic reference level for the
analysis of the sound level data. If a tape recorder or graphic
level 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.
(c) The ambient noise, including both acoustic background and
electrical systems noise, must be recorded and determined in the
test area with the system gain set at levels which will be used for
aircraft noise measurements. If aircraft sound pressure levels do
not exceed the background sound pressure levels by at least 10
dB(A), a takeoff measurement point nearer to the start of the
takeoff roll must be used and the results must be adjusted to the
reference measurement point by an approved method.
Sec. G36.109 Data Recording, Reporting, and Approval.
(a) Data representing physical measurements and adjustments to
measured data must be recorded in permanent form and appended to
the record, except that corrections to measurements for normal
equipment response deviations need not be reported. All other
adjustments must be approved. Estimates must be made of the
individual errors inherent in each of the operations employed in
obtaining the final data.
(b) Measured and corrected sound pressure levels obtained with
equipment conforming to the specifications in section G36.105 of
this appendix must be reported.
(c) The type of equipment used for measurement and analysis of
all acoustical, airplane performance, and meteorological data must
be reported.
(d) The following atmospheric data, measured immediately before,
after, or during each test at the observation points prescribed in
section G36.101 of this appendix must be reported:
(1) Ambient temperature and relative humidity.
(2) Maximum and average wind speeds and directions for each
run.
(e) Comments on local topography, ground cover, and events that
might interfere with sound recordings must be reported.
(f) The aircraft position relative to the takeoff reference
flight path must be determined by an approved method independent of
normal flight instrumentation, such as radar tracking, theodolite
triangulation, or photographic scaling techniques.
(g) The following airplane information must be reported:
(1) Type, model, and serial numbers (if any) of airplanes,
engines, and propellers;
(2) Any modifications or nonstandard equipment likely to affect
the noise characteristics of the airplane;
(3) Maximum certificated takeoff weight;
(4) For each test flight, airspeed and ambient temperature at
the flyover altitude over the measuring site determined by properly
calibrated instruments;
(5) For each test flight, engine performance parameters, such as
manifold pressure or power, propeller speed (rpm) and other
relevant parameters. Each parameter must be determined by properly
calibrated instruments. For instance, propeller RPM must be
validated by an independent device accurate to within ±1 percent,
when the airplane is equipped with a mechanical tachometer.
(6) Airspeed, position, and performance data necessary to make
the corrections required in section G36.201 of this appendix must
be recorded by an approved method when the airplane is directly
over the measuring site.
Sec. G36.111 Flight Procedures.
(a) The noise measurement point is on the extended centerline of
the runway at a distance of 8200 ft (2500 m) from the start of
takeoff roll. The aircraft must pass over the measurement point
within ±10 degrees from the vertical and within 20% of the
reference altitude. The flight test program shall be initiated at
the maximum approved takeoff weight and the weight shall be
adjusted back to this maximum weight after each hour of flight
time. Each flight test must be conducted at the speed for the best
rate of climb (Vy) ±5 knots (±9 km/hour) indicated airspeed. All
test, measurement, and data correction procedures must be approved
by the FAA.
(b) The takeoff reference flight path must be calculated for the
following atmospheric conditions:
(1) Sea level atmospheric pressure of 1013.25 mb (013.25
hPa);
(2) Ambient air temperature of 59 °F (15 °C);
(3) Relative humidity of 70 percent; and
(4) Zero wind.
(c) The takeoff reference flight path must be calculated
assuming the following two segments:
(1) First segment.
(i) Takeoff power must be used from the brake release point to
the point at which the height of 50 ft (15m) above the runway is
reached.
(ii) A constant takeoff configuration selected by the applicant
must be maintained through this segment.
(iii) The maximum weight of the airplane at brake-release must
be the maximum for which noise certification is requested.
(iv) The length of this first segment must correspond to the
airworthiness approved value for a takeoff on a level paved runway
(or the corresponding value for seaplanes).
(2) Second segment.
(i) The beginning of the second segment corresponds to the end
of the first segment.
(ii) The airplane must be in the climb configuration with
landing gear up, if retractable, and flap setting corresponding to
normal climb position throughout this second segment.
(iii) The airplane speed must be the speed for the best rate of
climb (Vy).
(iv) For airplanes equipped with fixed pitch propellers, takeoff
power must be maintained throughout the second segment. For
airplanes equipped with variable pitch or constant speed
propellers, takeoff power and rpm must be maintained throughout the
second segment. If airworthiness limitations do not allow the
application of takeoff power and rpm up to the reference point,
then takeoff power and rpm must be maintained for as long as is
permitted by such limitations; thereafter, maximum continuous power
and rpm must be maintained. Maximum time allowed at takeoff power
under the airworthiness standards must be used in the second
segment. The reference height must be calculated assuming climb
gradients appropriate to each power setting used.
part c - data corrections Sec. G36.201 Corrections to Test Results.
(a) These corrections account for the effects of:
(1) Differences in atmospheric absorption of sound between
meteorological test conditions and reference conditions.
(2) Differences in the noise path length between the actual
airplane flight path and the reference flight path.
(3) The change in the helical tip Mach number between test and
reference conditions.
(4) The change in the engine power between test and reference
conditions.
(b) Atmospheric absorption correction is required for noise data
obtained when the test conditions are outside those specified in
Figure G1. Noise data outside the applicable range must be
corrected to 59 F and 70 percent relative humidity by an FAA
approved method.
(c) No corrections for helical tip Mach number variation need to
be made if the propeller helical tip Mach number is:
(1) At or below 0.70 and the test helical tip Mach number is
within 0.014 of the reference helical tip Mach number.
(2) Above 0.70 and at or below 0.80 and the test helical tip
Mach number is within 0.007 of the reference helical tip Mach
number.
(3) Above 0.80 and the test helical tip Mach number is within
0.005 of the reference helical tip Mach number. For mechanical
tachometers, if the helical tip Mach number is above 0.8 and the
test helical tip Mach number is within 0.008 of the reference
helical tip Mach number.
(d) When the test conditions are outside those specified,
corrections must be applied by an approved procedure or by the
following simplified procedure:
(1) Measured sound levels must be corrected from test day
meteorological conditions to reference conditions by adding an
increment equal to
Delta (M) = (HT α - 0.7 HR)/1000 where HT is the height in feet
under test conditions, HR is the height in feet under reference
conditions when the aircraft is directly over the noise measurement
point and α is the rate of absorption for the test day conditions
at 500 Hz as specified in SAE ARP 866A, entitled “Standard Values
of Atmospheric Absorption as a function of Temperature and Humidity
for use in Evaluating Aircraft Flyover Noise” as incorporated by
reference under § 36.6.
(2) Measured sound levels in decibels must be corrected for
height by algebraically adding an increment equal to Delta (1).
When test day conditions are within those specified in figure
G1:
Delta (1) = 22 log (HT/HR)
where HT is the height of the test aircraft when directly over the
noise measurement point and HR is the reference height.
When test day conditions are outside those specified in figure
G1:
Delta (1) = 20 log (HT/HR)
(3) Measured sound levels in decibels must be corrected for
helical tip Mach number by algebraically adding an increment equal
to:
Delta (2) = k log (MR/MT)
where MT and MR are the test and reference helical tip Mach
numbers, respectively. The constant “k” is equal to the slope of
the line obtained for measured values of the sound level in dB(A)
versus helical tip Mach number. The value of k may be determined
from approved data. A nominal value of k = 150 may be used when MT
is smaller than MR. No correction may be made using the nominal
value of k when MT is larger than MR. The reference helical tip
Mach number MR is the Mach number corresponding to the reference
conditions (RPM, airspeed, temperature) above the measurement
point.
(4) Measured sound levels in decibels must be corrected for
engine power by algebraically adding an increment equal to
Delta (3) = K3 log (PR/PT) where PR and PT are the test and
reference engine powers respectively obtained from the manifold
pressure/torque gauges and engine rpm. The value of K3 shall be
determined from approved data from the test airplane. In the
absence of flight test data and at the discretion of the
Administrator, a value of K3 = 17 may be used. Sec. G36.203
Validity of Results.
(a) The measuring point must be overflown at least six times.
The test results must produce an average noise level (LAmax) value
within a 90 percent confidence limit. The average noise level is
the arithmetic average of the corrected acoustical measurements for
all valid test runs over the measuring point.
(b) The samples must be large enough to establish statistically
a 90 percent confidence limit not exceeding ±1.5 dB(A). No test
results may be omitted from the averaging process unless omission
is approved by the FAA.
part d - noise limits Sec. G36.301 Aircraft noise limits.
(a) Compliance with this section must be shown with noise data
measured and corrected as prescribed in Parts B and C of this
appendix.
(b) For single-engine airplanes for which the original type
certification application is received before February 3, 2006 and
multi-engine airplanes, the noise level must not exceed 76 dB(A) up
to and including aircraft weights of 1,320 pounds (600 kg). For
aircraft weights greater than 1,320 pounds, the limit increases
from that point with the logarithm of airplane weight at the rate
of 9.83 dB (A) per doubling of weight, until the limit of 88 dB (A)
is reached, after which the limit is constant up to and including
19,000 pounds (8,618 kg). Figure G2 shows noise level limits vs
airplane weight.
(c) For single-engine airplanes for which the original type
certification application is received on or after February 3, 2006,
the noise level must not exceed 70dB(A) for aircraft having a
maximum certificated takeoff weight of 1,257 pounds (570 kg) or
less. For aircraft weights greater than 1,257 pounds, the noise
limit increases from that point with the logarithm of airplane
weight at the rate of 10.75dB(A) per doubling of weight, until the
limit of 85dB(A) is reached, after which the limit is constant up
to and including 19,000 pounds (8,618 kg). Figure G2 depicts noise
level limits for airplane weights for single-engine airplanes.
(Secs.
313(a), 603, and 611(b), Federal Aviation Act of 1958 as amended
(49 U.S.C. 1354(a), 1423, and 1431(b)); sec. 6(c), Department of
Transportation Act (49 U.S.C. 1655 (c)); Title I, National
Environmental Policy Act of 1969 (42 U.S.C. 4321 et seq.);
E. O. 11514, March 5, 1970 and 14 CFR 11.45). [Amdt. 36-16, 53 FR
47400, Nov. 22, 1988; 53 FR 50157, Dec. 13, 1988, as amended by
Amdt. 36-22, 64 FR 55602, Oct. 13, 1999; Amdt. 36-54, 67 FR 45236,
July 8, 2002; Amdt. 36-27, 70 FR 45504, Aug. 5, 2005; Amdt. 36-28,
71 FR 532, Jan. 4, 2006; FAA Doc. No. FAA-2015-3782, Amdt. No.
36-31, 82 FR 46131, Oct. 4, 2017]
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]
Appendix I to Part 36 [Reserved]
14:1.0.1.3.20.14.283.1.42 : Appendix I
Appendix I to Part 36 [Reserved]
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.
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.
Appendix K to Part 36 - Noise Requirements for Tiltrotors Under Subpart K
14:1.0.1.3.20.14.283.1.44 : Appendix K
Appendix K to Part 36 - Noise Requirements for Tiltrotors Under
Subpart K K1 General K2 Noise Evaluation Measure K3
Noise Measurement Reference Points K4 Noise Limits K5
Trade-offs K6 Noise Certification Reference
Procedures K7 Test Procedures Section K1 General
This appendix prescribes noise limits and procedures for
measuring noise and adjusting the data to standard conditions for
tiltrotors as specified in § 36.1 of this part.
Section K2 Noise Evaluation Measure
The noise evaluation measure is the effective perceived noise
level in EPNdB, to be calculated in accordance with section A36.4
of Appendix A to this part, except corrections for spectral
irregularities must be determined using the 50 Hz sound pressure
level found in section H36.201 of Appendix H to this part.
Section K3 Noise Measurement Reference Points
The following noise reference points must be used when
demonstrating tiltrotor compliance with section K6 (Noise
Certification Reference Procedures) and section K7 (Test
Procedures) of this appendix:
(a) Takeoff reference noise measurement points -
As shown in Figure K1 below:
(1) The centerline noise measurement flight path reference
point, designated A, is located on the ground vertically below the
reference takeoff flight path. The measurement point is located
1,640 feet (500 m) in the horizontal direction of flight from the
point Cr where transition to climbing flight is initiated, as
described in section K6.2 of this appendix;
(2) Two sideline noise measurement points, designated as
S(starboard) and S(port), are located on the ground perpendicular
to and symmetrically stationed at 492 feet (150 m) on each side of
the takeoff reference flight path. The measurement points bisect
the centerline flight path reference point A.
(b) Flyover reference noise measurement points -
As shown in Figure K2 below:
(1) The centerline noise measurement flight path reference
point, designated A, is located on the ground 492 feet (150 m)
vertically below the reference flyover flight path. The measurement
point is defined by the flyover reference procedure in section K6.3
of this appendix;
(2) Two sideline noise measurement points, designated as
S(sideline), are located on the ground perpendicular to and
symmetrically stationed at 492 feet (150 m) on each side of the
flyover reference flight path. The measurement points bisect the
centerline flight path reference point A.
(c) Approach reference noise measurement points -
As shown in Figure K3 below:
(1) The centerline noise measurement flight path reference
point, designated A, is located on the ground 394 feet (120 m)
vertically below the reference approach flight path. The
measurement point is defined by the approach reference procedure in
section K6.4 of this appendix. On level ground, the measurement
point corresponds to a position 3,740 feet (1,140 m) from the
intersection of the 6.0 degree approach path with the ground
plane;
(2) Two sideline noise measurement points, designated as
S(starboard) and S(port), are located on the ground perpendicular
to and symmetrically stationed at 492 feet (150 m) on each side of
the approach reference flight path. The measurement points bisect
the centerline flight path reference point A.
Section
K4 Noise Limits
For a tiltrotor, the maximum noise levels, as determined in
accordance with the noise evaluation in EPNdB and calculation
method described in section H36.201 of Appendix H of this part,
must not exceed the noise limits as follows:
(a) At the takeoff flight path reference point: For a
tiltrotor having a maximum certificated takeoff weight (mass) of
176,370 pounds (80,000 kg) or more, in VTOL/Conversion mode, 109
EPNdB, decreasing linearly with the logarithm of the tiltrotor
weight (mass) at a rate of 3.0 EPNdB per halving of weight (mass)
down to 89 EPNdB, after which the limit is constant. Figure K4
illustrates the takeoff noise limit as a solid line.
(b) At the Flyover path reference point: For a tiltrotor
having a maximum certificated takeoff weight (mass) of 176,370
pounds (80,000 kg) or more, in VTOL/Conversion mode, 108 EPNdB,
decreasing linearly with the logarithm of the tiltrotor weight
(mass) at a rate of 3.0 EPNdB per halving of weight (mass) down to
88 EPNdB, after which the limit is constant. Figure K4 illustrates
the flyover noise limit as a dashed line.
(c) At the approach flight path reference point: For a
tiltrotor having a maximum certificated takeoff weight (mass) of
176,370 pounds (80,000 kg) or more, in VTOL/Conversion mode, 110
EPNdB, decreasing linearly with the logarithm of the tiltrotors
weight (mass) at a rate of 3.0 EPNdB per halving of weight (mass)
down to 90 EPNdB, after which the limit is constant. Figure K4
illustrates the approach noise limit as a dash-dot line.
Section
K5 Trade-Offs
If the noise evaluation measurement exceeds the noise limits
described in K4 of this appendix at one or two measurement
points:
(a) The sum of excesses must not be greater than 4 EPNdB;
(b) The excess at any single point must not be greater than 3
EPNdB; and
(c) Any excess must be offset by the remaining noise margin at
the other point or points.
(c) The takeoff, flyover and approach reference procedures must
be established in accordance with sections K6.2, K6.3 and K6.4 of
this appendix, except as specified in section K6.1(d) of this
appendix.
(d) If the design characteristics of the tiltrotor prevent test
flights from being conducted in accordance with section K6.2, K6.3
or K6.4 of this appendix, the applicant must revise the test
procedures and resubmit the procedures for approval.
(e) The following reference atmospheric conditions must be used
to establish the reference procedures:
(1) Sea level atmospheric pressure of 2,116 pounds per square
foot (1,013.25 hPa);
(2) Ambient air temperature of 77 °Fahrenheit (25 °Celsius, i.e.
ISA + 10 °C);
(3) Relative humidity of 70 percent; and
(4) Zero wind.
(f) For tests conducted in accordance with sections K6.2, K6.3,
and K6.4 of this appendix, use the maximum normal operating RPM
corresponding to the airworthiness limit imposed by the
manufacturer. For configurations for which the rotor speed
automatically links with the flight condition, use the maximum
normal operating rotor speed corresponding with the reference
flight condition. For configurations for which the rotor speed can
change by pilot action, use the highest normal rotor speed
specified in the flight manual limitation section for the reference
conditions.
K6.2 Takeoff Reference Procedure. The takeoff reference
flight procedure is as follows:
(a) A constant takeoff configuration must be maintained,
including the nacelle angle selected by the applicant;
(b) The tiltrotor power must be stabilized at the maximum
takeoff power corresponding to the minimum installed engine(s)
specification power available for the reference ambient conditions
or gearbox torque limit, whichever is lower. The tiltrotor power
must also be stabilized along a path starting from a point located
1,640 feet (500 m) before the flight path reference point, at 65 ft
(20 m) above ground level;
(c) The nacelle angle and the corresponding best rate of climb
speed, or the lowest approved speed for the climb after takeoff,
whichever is the greater, must be maintained throughout the takeoff
reference procedure;
(d) The rotor speed must be stabilized at the maximum normal
operating RPM certificated for takeoff;
(e) The weight (mass) of the tiltrotors must be the maximum
takeoff weight (mass) as requested for noise certification; and
(f) The reference takeoff flight profile is a straight line
segment inclined from the starting point 1,640 feet (500 m) before
to the center noise measurement point and 65 ft (20 m) above ground
level at an angle defined by best rate of climb and the speed
corresponding to the selected nacelle angle and for minimum
specification engine performance.
K6.3 Flyover Reference Procedure. The flyover reference
flight procedure is as follows:
(a) The tiltrotor must be stabilized for level flight along the
centerline flyover flight path and over the noise measurement
reference point at an altitude of 492 ft (150 m) above ground
level;
(b) A constant flyover configuration selected by the applicant
must be maintained;
(c) The weight (mass) of the tiltrotor must be the maximum
takeoff weight (mass) as requested for noise certification;
(d) In the VTOL/Conversion mode:
(1) The nacelle angle must be at the authorized fixed operation
point that is closest to the shallow nacelle angle certificated for
zero airspeed;
(2) The airspeed must be 0.9VCON and
(3) The rotor speed must be stabilized at the maximum normal
operating RPM certificated for level flight.
K6.4 Approach Reference Procedure. The approach reference
procedure is as follows:
(a) The tiltrotor must be stabilized to follow a 6.0 degree
approach path;
(b) An approved airworthiness configuration in which maximum
noise occurs must be maintained;
(1) An airspeed equal to the best rate of climb speed
corresponding to the nacelle angle, or the lowest approved airspeed
for the approach, whichever is greater, must be stabilized and
maintained; and
(2) The tiltrotor power during the approach must be stabilized
over the flight path reference point, and continue as if
landing;
(c) The rotor speed must be stabilized at the maximum normal
operating RPM certificated for approach;
(d) The constant approach configuration used in airworthiness
certification tests, with the landing gear extended, must be
maintained; and
(e) The weight (mass) of the tiltrotor at landing must be the
maximum landing weight (mass) as requested for noise
certification.
Section K7 Test Procedures
K7.1 [Reserved]
K7.2 The test procedures and noise measurements must be
conducted and processed to yield the noise evaluation measure
designated in section K2 of this appendix.
K7.3 If either the test conditions or test procedures do
not comply to the applicable noise certification reference
conditions or procedures prescribed by this part, the applicant
must apply the correction methods described in section H36.205 of
Appendix H of this part to the acoustic test data measured.
K7.4 Adjustments for differences between test and
reference flight procedures must not exceed:
(a) For takeoff: 4.0 EPNdB, of which the arithmetic sum of delta
1 and the term −7.5 log (QK/QrKr) from delta 2 must not in total
exceed 2.0 EPNdB;
(b) For flyover or approach: 2.0 EPNdB.
K7.5 The average rotor RPM must not vary from the normal
maximum operating RPM by more than ±1.0 percent throughout the 10
dB-down time interval.
K7.6 The tiltrotor airspeed must not vary from the
reference airspeed appropriate to the flight demonstration by more
than ±5 kts (±9 km/h) throughout the 10 dB-down time interval.
K7.7 The number of level flyovers made with a head wind
component must be equal to the number of level flyovers made with a
tail wind component.
K7.8 The tiltrotor must operate between ±10 degrees from
the vertical or between ±65 feet (±20 m) lateral deviation
tolerance, whichever is greater, above the reference track and
throughout the 10 dB-down time interval.
K7.9 The tiltrotor altitude must not vary during each
flyover by more than ±30 ft (±9 m) from the reference altitude
throughout the 10 dB-down time interval.
K7.10 During the approach procedure, the tiltrotor must
establish a stabilized constant speed approach and fly between
approach angles of 5.5 degrees and 6.5 degrees throughout the 10
dB-down time interval.
K7.11 During all test procedures, the tiltrotor weight
(mass) must not be less than 90 percent and not more than 105
percent of the maximum certificated weight (mass). For each of the
test procedures, complete at least one test at or above this
maximum certificated weight (mass).
K7.12 A tiltrotor capable of carrying external loads or
external equipment must be noise certificated without such loads or
equipment fitted
K7.13 The value of VCON used for noise certification must
be included in the approved Flight Manual.