c. Procedures
None
220. Section 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.
221. Section 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.
222. Section 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.
223. Section A36.5.2.4
The applicant must report conditions of local topography, ground cover, and events that might interfere with sound recordings.
224. Section 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;
(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.
a. Explanation
This section specifies the noise certification data-reporting requirements.
b. Supplemental Information
(1) Applicant's Reporting Requirements: Following are items that the applicant also must report in meeting the requirements of sections A36.5.2.1 through A36.5.2.5:
(i) Test conditions throughout the 10 dB-down period, including test airspeed, engine performance parameters, and airplane flight path position.
(ii) Recorder sampling rates.
(iii) Airplane and engine performance information, including airplane altitude and climb angle.
Any other parameters that may affect the measurement or adjustment of acoustical, airplane, or engine performance data must also be recorded throughout the 10 dB-down period (e.g., SBV position, CG position).
c. Procedures
None
225. Section A36.5.3 Reporting of noise certification reference conditions.
226. Section 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.
a. Explanation
This section specifies a requirement to report reference conditions, parameters, procedures, and configurations used for noise certification testing.
b. Supplemental Information
(1) Reference Conditions: Reference conditions are specified under section B36.7.
(2) Equivalent Procedures: FAA does not approve equivalent procedures for noise certification reference conditions.
(3) DER Information: Reference airplane performance is to be FAA approved based on approved data. This may require that a flight analyst DER with appropriate authority for part 36 reference airplane performance submit completed FAA Form 8110-3 for review by the approving FAA flight test branch of the ACO.
(See the DER Guidance Handbook, reference 10 for additional information.)
c. Procedures
None
227. Section A36.5.4 Validity of results.
228. Section A36.5.4.1
Three average reference EPNL values and their 90 per cent 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 per cent confidence limits.
229. Section 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 per cent 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 per cent confidence interval are shown in the current advisory circular for this part.
a. Explanation
Appendix 1 of the appended TM describes methods for calculating 90 per cent confidence intervals
b. Supplemental Information
None
c. Procedures
None
230. Section 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.
a. Explanation
This section specifies that average values of EPNLr (effective perceived noise level adjusted for reference conditions) for the flyover, lateral and approach noise measurement points are to be within a 90 percent confidence interval limit of ±1.5 dB. Both the mean EPNL levels and the associated confidence intervals are to be reported.
b. Supplemental Information
(1) Average EPNLr Levels: The average values of EPNLr are to be reported in a noise certification compliance document for flyover, lateral, and approach. The average value of EPNLr for n clustered data points, L1, L2, - - - -, Ln, is: Lmean = (L1 + L2 + - - - + Ln)(1/n). The average value of EPNLr from an NPD database is the noise level determined along the regression line through the adjusted data set at the appropriate thrust (power)
and distance values, including any other additional adjustments necessary (e.g., adjustment to the airplane reference speed).
(2) 90 Percent Confidence Interval (Clustered Data): The test methods described in part 36 are conducted for a minimum of six repeated (e.g., at identical configuration, target thrust (power), and speed conditions) noise measurements for each of the three noise measurement points (flyover, lateral and approach).
These repeated tests create three clusters of data for correction and evaluation. The 90 percent confidence interval validity evaluation of clusters of data can be easily determined. If n measurements of EPNLr, (L1, L2, . . . .
Ln,) are obtained under approximately the same conditions and it can be assumed that they constitute a random sample from a normal population, then the statistical 90 percent confidence interval value for each clustered group can be derived.
(3) 90 Percent Confidence Interval (NPD Database): Noise-Power-Distance (NPD) database confidence intervals are determined by using a more general formulation than that used for a normal cluster of data points. The confidence interval is to be calculated about each data regression line, whether it is generated for flight test data, a combination of flight test and static test data, or analytical results.
(4) Single Test Values: When more than one noise measurement system is used at any one noise measurement point, the resulting noise level is to be the average of the measured noise levels for each noise measurement point. Some applicants prefer to provide multiple microphones at each noise measurement point.
When multiple microphones are used during the noise testing, the average noise level is to be reported for each noise measurement.
(5) Valid Conditions: All valid noise measurements that are witnessed by an FAA observer or an appropriate designee and determined to be valid are to be included in the confidence interval calculations even when they produce results that are outside the 90 percent confidence limit of ± 1.5 dB. The cause of erratic or possibly invalid noise data may include: testing under different temperature and humidity extremes, anomalous winds aloft, changes in measuring and recording equipment, changes in airplane hardware, background noise, shift in instrument calibrations, not testing in accordance with the approved test plan, etc. The FAA observer is to make a determination, during the course of noise certification testing, as to the validity of all noise measurements.
A noise measurement may not be excluded from the confidence interval calculations at a later date without FAA approval. Noise measurements determined in the field to be invalid for any reason must be repeated.
c. Procedures
(1) Applicant's Responsibility: An applicant is responsible not only for the development of equivalent procedures but also for the development of procedures to quantify a 90 percent confidence interval determination when the approved equivalent procedures are used. The confidence interval procedures that are used in conjunction with approved equivalent procedures may be unique to each of the three measurement conditions (flyover, lateral and approach) and may be suitable for either simplified or integrated methods of evaluating the EPNLr levels.
(2) Methods for Calculating 90 percent Confidence Interval: Calculation methods for determining 90 percent confidence interval values for clustered and some other approved test results are presented in Appendix 1 of the appended ICAO TM. The TM provides confidence interval calculation methods for: clustered measurements, regression mean line, static test-derived NPD curves, and analytically derived NPD curves, and provides working examples (clustered, first-order regression curve, second-order regression curve, and the pooled data set).
(3) Reporting Requirements: EPNLr levels for each of the three noise measurement points (flyover, lateral, and approach) and the associated values of the 90% confidence intervals are to be reported to the FAA in noise certification compliance documentation.
(4) Retest Requirements: The FAA may require an applicant to retest or provide additional test data for any of the three noise measurement points (flyover, lateral or approach) when the reported results indicate:
(i) A required measurement is reported to be invalid, or
(ii) An insufficient number of measurements were conducted by the applicant to determine a suitable data sample, or
(iii) Data scatter indicates that the data are not from a normal population or trend (e.g., a discontinuity due to low power SBV operation), or
(iv) The 90 percent confidence interval for a noise measuring condition exceeds the allowable ±1.5 dB, or
(v) The test was not conducted in accordance with an approved noise certification compliance demonstration plan.
231. 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 onethird 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 per cent 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 kth 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.
Ds(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 mPa Sound pressure level. The sound pressure level that occurs in a specified frequency range at any instant of time.
SPL(a) dB re 20 mPa 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 mPa 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 20mPa 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 20mPa 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 20mPa 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 20mPa 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 20mPa 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.
I 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.
Dt 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.
a(i) dB/100ft dB/100m Test atmospheric sound attenuation The atmospheric attenuation of sound that occurs in the i-th one-third octave band at the measured air temperature and relative humidity.
a(i)o dB/100ft dB/100m Reference atmospheric sound attenuation 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) d e degrees Thrust cutback angles. The angles defining the points on the takeoff flight path at which thrust reduction is started and ended respectively.
h degrees Approach angle.
hr degrees Reference approach angle.
q 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. .
m Engine noise emission parameter.
D1 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.
D2 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.
D3 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.
a. Explanation
This section contains standard noise symbols, their associated units, and the meaning of terms that are used during the testing, analysis, and evaluation of airplane noise certification.
b. Supplementary Information
(1) Common Symbols: Some of the airplane noise certification symbols identified in this section may also be common to other aircraft noise certification activities, such as the noise certification of small airplanes and rotorcraft.
c. Procedures
None.
232. Section A36.7 Sound Attenuation in Air
233. Section A36.7.1
The atmospheric sound attenuation of sound must be determined in accordance with the procedure presented in section A36.7.2.
234. Section A36.7.2
The relationship between atmospheric sound attenuation, frequency, temperature, and humidity is expressed by the following equations.
A36.7.2(a) For calculations using the English System of Units:
( ) ( ) 4215.23106833.40log10 45325.14-1033.610000log05.210 −−×+ ×+ −×+ = q dh q a f f i
and
( ) −×+−×− × −×+− = 37100.32510589.9 10 210288074.297274664.1log 1001010 qq q d H f
where
( )h d is listed in Table A36-4 and f0 in Table A36-5;
( )a i is the attenuation coefficient in dB/1000 ft;
q 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):
( ) ( ) a q h d q i f f = + × − + × + × − − 10 2 05 0 1000 11394 1916984 10 0 842994 10 3 2 755624 . log . .
log . .
10-3
and
d q q q = − + × − × − × − + × − 101010 1328924 3179768 10 2 10 2173716 10 4 2 17496 10 6 3 0f Hlog . .
. .
where
( )h d is listed in Table A36-4 and f0 in Table A36-5;
( )a i is the attenuation coefficient in dB/100 m;
q is the temperature in °C; and
H is the relative humidity, expressed as a percentage.
235. Section 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.
Table A36-4. Values of h(d)
d h(d) d h(d)
0.00 0.000 2.50 0.450
0.25 0.315 2.80 0.400
0.50 0.700 3.00 0.370
0.60 0.840 3.30 0.330
0.70 0.930 3.60 0.300
0.80 0.975 4.15 0.260
0.90 0.996 4.45 0.245
1.00 1.000 4.80 0.230
1.10 0.970 5.25 0.220
1.20 0.900 5.70 0.210
1.30 0.840 6.05 0.205
1.50 0.750 6.50 0.200
1.70 0.670 7.00 0.200
2.00 0.570 10.00 0.200
2.30 0.495
Table A36-5. Values of f0
one-third octave center frequency
f0 (Hz)
one-third octave center frequency
f0 (Hz) 50 50 800 800 63 63 1000 1000 80 80 1250 1250 100 100 1600 1600 125 125 2000 2000 160 160 2500 2500 200 200 3150 3150 250 250 4000 4000 315 315 5000 4500 400 400 6300 5600 500 500 8000 7100 630 630 10000 9000