a) the level for band j, the highest frequency unmasked band in spectral record k, which has already been adjusted for measurement conditions, is adjusted for test-day propagation effects to obtain the source level and then adjusted using reference propagation effects to the197 ft (60 m) distance from the source;
b) this level is then assigned as the level for all high frequency masked bands (i.e., band i, band i + 1, etc.)
at a distance of 197 ft (60 m);
c) a new source level is determined for each masked high frequency band by removing the associated reference-day propagation effects; and
d) the extrapolated level that would have been measured on the ground, in the absence of background noise, is determined for each masked high frequency band by adding the test-day propagation effects to each of the source levels determined in c) above.
306(c)(2)(J)(ii) Time extrapolation method [ETM 3.6.3.2.10.2] For a spectrum where LGB occurs at or between the 630 Hz one-third octave band and the 1.6 kHz band, use the time extrapolation method. This method reconstructs a masked band in a spectrum from the closest spectral record (i.e., closest in time) for which that band is valid. The levels fo r all one-third octave bands with frequencies greater than that of LGB must be reconstructed using this time extr apolation method. Any time-extrapolated levels should be categorized as reconstructed. Reconstruct the levels for the masked bands by using the following equation:
ሾܴܵܮ, ൌܮ , ߙ 100ሿ 20݈݃ଵሾܴܵሿ100 െ ܴܵ ܴܵ where:
— L xi,k is the time-extrapolated level in dB for masked band i and spectral record k;
— Li,m is the adjusted level in dB for band i in spectral record m, which is the nearest record in time to record k in which band i contains a valid level;
— SRm is the slant range or acoustic propagation distance in meters at the time of sound emission for spectral record m, between the aircraft and the microphone;
— SRk is the slant range or acoustic propagation distance in meters at the time of sound emission for spectral record k, between the aircraft and the microphone; and — αiis the test-day sound attenuation coefficient (dB per 100 m) for band i.
This procedure is based on the assumption that the aircraft spectrum is omnidirectional during the aircraft pass-by.
306(c)(2)(K) Handling of spectra af ter reconstruction of masked bands [ETM 3.6.3.2.11] After reconstruction of masked data has been performed, the background noise adjustment procedure is complete. The adjusted as-measured data set, comprised of adjusted levels, reconstructed levels, and possibly some masked levels, is next used to obtain the test-day PNLT time history desc ribed in A36.4.3 of part 36. The identification of masked data should be kept accessible for use during the tone co rrection procedure, since any tone correction which results from the adjustment for background noise may be eliminated from the process of identifying the maximum tone within a spectrum. When this background noise adjustment procedure is used, the band identified as LGB should be treated Page 103
as the last band of the tone correction calculation in the manner prescribed for the 10 kHz band in A36.4.3.1 of part 36, including the calculation of a new slope for band LGB + 1 that equals the slope at LGB (i.e., s ′(LGB + 1, k) = s′(LGB,k)) in Step 5 of the tone correction procedure.
306(d) General Considerations [ETM 3.6.4] 306(d)(1) Limitations and requirements for an y background noise adjustment procedure [ETM 3.6.4.1] Any method of adjusting for the effects of background noise must be approved by the FAA before it is used. The adjustment procedure presented in 306(c)(2) includes applicable limitations and requirements. Those limitations and requirements which apply to all methodologies are described as follows.
The applicant must be able to demonstrate by means of narrow-band analysis or other methods that no significant aircraft-generated tones occur in the masked one-third octave bands during the EPNL duration.
Neither frequency-dependent adjustments nor energy-subtraction of pre-detection levels can be applied to masked data.
When consecutive one-third octave bands in the range of 2.5 kHz to 10 kHz inclusiv e are masked, and when no consecutive bands are masked in the region of 800 Hz to 2 kHz inclusive, frequency extrapolation, as described in 306(c)(2)(J)(i), must be performed on all consecutive masked bands with nominal frequencies greater than 2 kHz.
When consecutive one-third octave bands in the range of 800 Hz to 2 kHz inclusive are masked, time extrapolation, as described in 306(c)(2)(J)(ii), must be performed on all consecutive masked bands with nominal frequencies greater than 630 Hz.
In cases where a single masked one-third octave band occurs between two adjacent valid bands, the levels of the adjacent adjusted bands may be arithmetically averaged and the averaged level used in place of the masked level. If the masked level is retained it must be included when counting the masked levels in the procedure described in 306(d)(2) 306(d)(2) Rejection of spectra due to masking [ETM 3.6.4.2] A spectrum becomes invalid if the following conditions prevail:
a) if, after any reconstruction of masked bands, more than four one-third octave bands retain masked values;
b) for records within one second of the record associated with the PNLTmax spectrum (i.e., five half-second data records) if:
1) more than four high frequency bands require reconstruction; or
2) the LGB is located at or below the 3150 Hz one-third octave band when the example background noise adjustment procedure presented in 306(c)(2) is used.
Note.— If an invalid spectrum occurs within the 10 dB-down period, the aircraft test run is invalid and cannot be used for aircraft noise certification purposes.
305(d)(3) Special tone correction considerations due to masking [ETM 3.6.4.3] Page 104
307 When the maximum tone correction for a one-third octave band spectrum occurs at a masked or reconstructed band, the tone correction for that spectrum cannot simply be set to zero. The maximum tone correction for the spectrum must be computed, taking masked or reconstructed levels into consideration. Any tone correction resulting from the adjustment for background noise may be eliminated by either one of the following two methods, as appropriate:
a) when the example background noise adjustment proce dure presented in 306(c)(2) is used or, specifically, when all of the high frequency bands in a spectrum are masked for frequencies beyond a certain band (i.e., “LGB”) the band labeled as LGB should be treated as the last band of the tone correction calculation, in the manner prescribed for the 10 kHz band (band number 24) in A36.4.3.1 of part 36, including calculation of a new slope for the band above LGB that equals the slope of the band at LGB (i.e., s′(LGB + 1,k) = s′(LGB,k)) in Step 5 of the tone correction procedure; or
b) for tone corrections that occur at one-third octave bands that are masked or reconstructed, set F equal to zero in Step 9 of the tone correction procedure, and recalculate the maximum tone correction for that spectrum.
Note.— All band levels within a spectru m, whether adjusted, reconstructed or masked, must be included in the computation of the PNL value for that spectrum.
306(d)(4) Handling of masked data in reference conditions data sets [ETM 3.6.4.4] For any one-third octave band spectrum adjusted to reference conditions, all bands, including those containing masked levels or reconstructed levels, includin g values less than 0 dB, must be adju sted for differences between test and reference conditions (i.e., atmospheric absorption and spherical spreading). The special tone correction considerations listed in 306(c)(2) apply both to test and reference data sets.
Noise Reduction Systems [ETM 3.7] An aircraft can employ noise reduction systems that chan ge its configuration or operating condition to reduce noise, or implement devices or subsystems that directly reduce or counteract noise emissions. Two categories, variable noise reduction systems (VNRS) and selectable noise reduction systems (SNRS), have been defined to address differences in activation/actuation for these systems. General guidan ce on noise certification of ai rcraft equipped with these systems is provided below.
307(a) Variable Noise Reduction Systems [ETM 3.7.1] A VNRS is an integral design feature, or subsystem, of an aircraft that automatically changes the configuration or operating condition of the aircraft to reduce noise.
Note 1.— If pilot action is necessary to activate, i.e., select the use of, an automatically controlled noise reduction system or if a pilot can deactivate (deselect) an automatically controlled noise reduction system, such a system is not considered a VNRS.
Note 2.— Aircraft can incorporate variable systems, primarily intended to improve performance, reduce engine emissions and/or increase safety, that may also affect noise. Such aircraft can be noise certificated using the guidance provided for aircraft with VNRS. For such changes to existing type designs, the guidelines provided in 101(d) for “no acoustical change” are applicable.
For a VNRS-equipped aircraft, the VNRS characteristics may prevent flight from being conducted in accordance with the associated reference procedure(s) in part 36. In such cases, the reference procedures for noise certification of an aircraft with a VNRS should depart from those specified in part 36 only to the extent required by those design Page 105
characteristics that cause the departure and should be approved by the FAA after the rulemaking process for an deviation from part 36 is completed (see 201(a)(10) paragraph 2 of this AC).
The impact of a VNRS on nois e certification of an aircraft can extend beyo nd deviations from the part 36 reference procedures. A plan for noise certificatio n of a VNRS-equipped aircraft should take into consideration three key elements, namely:
a) the necessity, if any, to depart from the part 36 procedures;
b) the adaptation/modification of test proced ures to ensure compliance with part 36; and
c) the applicability of existing procedures in part 36 for adjusting the measured data to reference conditions.
Experience to date has shown that one or more of these elements may be interrelated, requiring detailed consideration of all three elements in devising an acceptable plan for noise certification.
307(a)(1) Reference procedures [ETM 3.7.1.1] The part 36 reference procedures typically utilize consta nt flight path and operational parameters. A VNRS can, however, result in non-constant reference flight paths and/or non-constant operational parameters such as non-constant rates of climb and/or non-constant engine/propeller/rotor speeds, respectively, that compel departure from the reference procedures. In addition to reducing noise emissions, a VNRS may, and typically does, impact aircraft performance during a noise certification reference procedure. In some cases, this impact can be indirect via another affected performance parameter. Both direct and indirect impacts on aircraft performance should be addressed in defining any departure necessary from the reference procedures in part 36 to accommodate a VNRS.
Actuation of a VNRS can be a function of one or more ope rational conditions such as airspeed, ground speed, height above ground level, density altitude, pressure altitude and ambient temperature. Beginning and end points on the reference flight path for any transition triggered by a VNRS should be determined using the reference test and meteorological conditions.
307(a)(2) Test conditions and procedures [ETM 3.7.1.2] When a VNRS results in a non-constant reference flight path for the aircraft, the flight path tolerances (height and lateral deviation limits) specified in part 36 for the corresponding constant reference procedure should be applied, subject to approval by the FAA. Similarly, when a VNRS results in a non-constant operational parameter for the aircraft, a reference schedule for the affected operating parameter should be defined along the reference flight path, and the test tolerances permitted by part 36 for that parameter should be applied to the reference schedule, subject to approval by the FAA.
307(a)(3) Adjustments to measured noise data [ETM 3.7.1.3] Adjustments to measured data in part 36 are based on constant reference procedures. A VNRS can, however, result in a non-constant reference procedure(s) that in turn impacts the adjustments to measured data that account for test deviations from reference flight profiles and test conditions. The adjustments to measured data specified in part 36 should be modified only as necessary to account for any departures from the reference procedures in part 36. In many cases, only minor changes to data-processing software that do not affect the adjustment procedures will be needed.
Any modifications, including software revisions, of the adjustments to measured data specified in part 36 are subject to approval by the FAA.
307(a)(4) Guidance for specific VNRS [ETM 3.7.1.4] Specific guidance for VNRS technologies will typically be developed as these technologies are developed and implemented in aircraft designs. Cross references to the appropriate sections of this Advisory Circular for the VNRS technologies for which specific guidance has been generally accepted by FAA are provided in Table 8.
Table 8. Cross references to spec ific guidelines in this ACfor VNRS Variable noise reduction Specific guidelines provided in system (VNRS) this AC Variable rotor speed Chapter 4, 401(h), H36.3:
helicopters H36.103(b) [Takeoff flight test procedures], paragraph 8) 307(b) Selectable Noise Reduction Systems [ETM 3.7.2] (Reserved) Note.— The guidance provided in 307 addresses VNRS only and, by inference, defines as selectable all noise reduction systems that do not satisfy the requirements for classification as VNRS. Guidance specific to SNRS, including a definition specific to SNRS, is not yet provided.
308 CALCULATION OF THE SPEED OF SOUND [ETM 3.8] For the purposes of noise certification the value of the speed of sound, c, is calculated from the equation taken from ISO 9613-1:1993(E):
c = 1125.9 (T/T0)½ ft/s, or c = 343.2 (T/T0)½ m/s where T0 = 293.15 K and T is the absolute ambient air temperature in kelvins.
Note.— At the noise certification reference temperature of 25°C, T = 298.15 K, and c therefore equals 1135.5 ft/s
(346.1 m/s).
309 REFERENCE TABLES USED IN THE MANUAL CALCULATION OF
OF EFFECTIVE PERCEIVED NOISE LEVEL [ETM 3.9] Table 9 and Table 10 and Figure 7 contain information useful for the manual calculation of EPNL. Such manual calculations are often used to verify the accuracy of computer programs used for calculating certification noise levels.
5 10 15 20 25 30 35 40 45 50 55 10/12/2017 AC 36-4D Table 9. Perceived noisiness (noys) as a function of sound pressure level (One-third octave band center frequencies (Hz)) SPL 50 63 80 100 125 160 200 250 315 400 500 630 800 1000 1250 1600 2000 2500 3150 4000 5000 6300 8000 10000 4 0.10
0.10 0.11 0.10 6 0.11 0.12 0.11 0.10 7 0.12 0.14 0.13 0.11 8 0.14 0.16 0.14 0.13 9 0.10 0.16 0.17 0.16 0.14
0.11 0.17 0.19 0.18 0.16 0.10 11 0.13 0.19 0.22 0.21 0.18 0.12 12 0.10 0.14 0.22 0.24 0.24 0.21 0.14 13 0.11 0.16 0.24 0.27 0.27 0.24 0.16 14 0.13 0.18 0.27 0.30 0.30 0.27 0.19
0.10 0.14 0.21 0.30 0.33 0.33 0.30 0.22 16 0.10 0.10 0.10 0.10 0.10 0.11 0.16 0.24 0.33 0.35 0.35 0.33 0.26 17 0.11 0.11 0.11 0.11 0.11 0.13 0.18 0.27 0.35 0.38 0.38 0.35 0.30 0.10 18 0.10 0.13 0.13 0.13 0.13 0.13 0.15 0.21 0.30 0.38 0.41 0.41 0.38 0.33 0.12 19 0.11 0.14 0.14 0.14 0.14 0.14 0.17 0.24 0.33 0.41 0.45 0.45 0.41 0.36 0.14
0.13 0.16 0.16 0.16 0.16 0.16 0.20 0.27 0.36 0.45 0.49 0.49 0.45 0.39 0.17 21 0.10 0.14 0.18 0.18 0.18 0.18 0.18 0.23 0.30 0.39 0.49 0.53 0.53 0.49 0.42 0.21 0.10 22 0.11 0.16 0.21 0.21 0.21 0.21 0.21 0.26 0.33 0.42 0.53 0.57 0.57 0.53 0.46 0.25 0.11 23 0.13 0.18 0.24 0.24 0.24 0.24 0.24 0.30 0.36 0.46 0.57 0.62 0.62 0.57 0.50 0.30 0.13 24 0.10 0.14 0.21 0.27 0.27 0.27 0.27 0.27 0.33 0.40 0.50 0.62 0.67 0.67 0.62 0.55 0.33 0.15
0.11 0.16 0.24 0.30 0.30 0.30 0.30 0.30 0.35 0.43 0.55 0.67 0.73 0.73 0.67 0.60 0.36 0.17 26 0.13 0.18 0.27 0.33 0.33 0.33 0.33 0.33 0.38 0.48 0.60 0.73 0.79 0.79 0.73 0.65 0.39 0.20 27 0.10 0.14 0.21 0.30 0.35 0.35 0.35 0.35 0.35 0.41 0.52 0.65 0.79 0.85 0.85 0.79 0.71 0.42 0.23 28 0.11 0.16 0.24 0.33 0.38 0.38 0.38 0.38 0.38 0.45 0.57 0.71 0.85 0.92 0.92 0.85 0.77 0.46 0.26 29 0.13 0.18 0.27 0.35 0.41 0.41 0.41 0.41 0.41 0.49 0.63 0.77 0.92 1.00 1.00 0.92 0.84 0.50 0.30
0.10 0.14 0.21 0.30 0.38 0.45 0.45 0.45 0.45 0.45 0.53 0.69 0.84 1.00 1.07 1.07 1.00 0.92 0.55 0.33 31 0.11 0.16 0.24 0.33 0.41 0.49 0.49 0.49 0.49 0.49 0.57 0.76 0.93 1.07 1.15 1.15 1.07 1.00 0.60 0.37 32 0.13 0.18 0.27 0.36 0.45 0.53 0.53 0.53 0.53 0.53 0.62 0.83 1.00 1.15 1.23 1.23 1.15 1.07 0.65 0.41 33 0.14 0.21 0.30 0.39 0.49 0.57 0.57 0.57 0.57 0.57 0.67 0.91 1.07 1.23 1.32 1.32 1.23 1.15 0.71 0.45 34 0.10 0.16 0.24 0.33 0.42 0.53 0.62 0.62 0.62 0.62 0.62 0.73 1.00 1.15 1.32 1.41 1.41 1.32 1.23 0.77 0.50
0.11 0.18 0.27 0.36 0.46 0.57 0.67 0.67 0.67 0.67 0.67 0.79 1.07 1.23 1.41 1.51 1.51 1.41 1.32 0.84 0.55 36 0.13 0.21 0.30 0.40 0.50 0.62 0.73 0.73 0.73 0.73 0.73 0.85 1.15 1.32 1.51 1.62 1.62 1.51 1.41 0.92 0.61 37 0.15 0.24 0.33 0.43 0.55 0.67 0.79 0.79 0.79 0.79 0.79 0.92 1.23 1.41 1.62 1.74 1.74 1.62 1.51 1.00 0.67 38 0.17 0.27 0.37 0.48 0.60 0.73 0.85 0.85 0.85 0.85 0.85 1.00 1.32 1.51 1.74 1.86 1.86 1.74 1.62 1.10 0.74 39 0.10 0.20 0.30 0.41 0.52 0.65 0.79 0.92 0.92 0.92 0.92 0.92 1.07 1.41 1.62 1.86 1.99 1.99 1.86 1.74 1.21 0.82
0.12 0.23 0.33 0.45 0.57 0.71 0.85 1.00 1.00 1.00 1.00 1.00 1.15 1.51 1.74 1.99 2.14 2.14 1.99 1.86 1.34 0.90 41 0.14 0.26 0.37 0.50 0.63 0.77 0.92 1.07 1.07 1.07 1.07 1.07 1.23 1.62 1.86 2.14 2.29 2.29 2.14 1.99 1.48 1.00 42 0.16 0.30 0.41 0.55 0.69 0.84 1.00 1.15 1.15 1.15 1.15 1.15 1.32 1.74 1.99 2.29 2.45 2.45 2.29 2.14 1.63 1.10 43 0.19 0.33 0.45 0.61 0.76 0.92 1.07 1.23 1.23 1.23 1.23 1.23 1.41 1.86 2.14 2.45 2.63 2.63 2.45 2.29 1.79 1.21 44 0.10 0.22 0.37 0.50 0.67 0.83 1.00 1.15 1.32 1.32 1.32 1.32 1.32 1.52 1.99 2.29 2.63 2.81 2.81 2.63 2.45 1.99 1.34
0.12 0.26 0.42 0.55 0.74 0.91 1.08 1.24 1.41 1.41 1.41 1.41 1.41 1.62 2.14 2.45 2.81 3.02 3.02 2.81 2.63 2.14 1.48 46 0.14 0.30 0.46 0.61 0.82 1.00 1.16 1.33 1.52 1.52 1.52 1.52 1.52 1.74 2.29 2.63 3.02 3.23 3.23 3.02 2.81 2.29 1.63 47 0.16 0.34 0.52 0.67 0.90 1.08 1.25 1.42 1.62 1.62 1.62 1.62 1.62 1.87 2.45 2.81 3.23 3.46 3.46 3.23 3.02 2.45 1.79 48 0.19 0.38 0.58 0.74 1.00 1.17 1.34 1.53 1.74 1.74 1.74 1.74 1.74 2.00 2.63 3.02 3.46 3.71 3.71 3.46 3.23 2.63 1.98 49 0.10 0.22 0.43 0.65 0.82 1.08 1.26 1.45 1.64 1.87 1.87 1.87 1.87 1.87 2.14 2.81 3.23 3.71 3.97 3.97 3.71 3.46 2.81 2.18
0.12 0.26 0.49 0.72 0.90 1.17 1.36 1.56 1.76 2.00 2.00 2.00 2.00 2.00 2.30 3.02 3.46 3.97 4.26 4.26 3.97 3.71 3.02 2.40 51 0.14 0.30 0.55 0.80 1.00 1.26 1.47 1.68 1.89 2.14 2.14 2.14 2.14 2.14 2.46 3.23 3.71 4.26 4.56 4.56 4.26 3.97 3.23 2.63 52 0.17 0.34 0.62 0.90 1.08 1.36 1.58 1.80 2.03 2.30 2.30 2.30 2.30 2.30 2.64 3.46 3.97 4.56 4.89 4.89 4.56 4.26 3.46 2.81 53 0.21 0.39 0.70 1.00 1.18 1.47 1.71 1.94 2.17 2.46 2.46 2.46 2.46 2.46 2.83 3.71 4.26 4.89 5.24 5.24 4.89 4.56 3.71 3.02 54 0.25 0.45 0.79 1.09 1.28 1.58 1.85 2.09 2.33 2.64 2.64 2.64 2.64 2.64 3.03 3.97 4.56 5.24 5.61 5.61 5.24 4.89 3.97 3.23
0.30 0.51 0.89 1.15 1.35 1.71 2.00 2.25 2.50 2.83 2.83 2.83 2.83 2.83 3.25 4.26 4.89 5.61 6.01 6.01 5.61 5.24 4.26 3.46 56 0.34 0.59 1.00 1.29 1.50 1.85 2.15 2.42 2.69 3.03 3.03 3.03 3.03 3.03 3.48 4.56 5.24 6.01 6.44 6.44 6.01 5.61 4.56 3.71 57 0.39 0.67 1.09 1.40 1.63 2.00 2.33 2.61 2.88 3.25 3.25 3.25 3.25 3.25 3.73 4.89 5.61 6.44 6.90 6.90 6.44 6.01 4.89 3.97 58 0.45 0.77 1.18 1.53 1.77 2.15 2.51 2.81 3.10 3.48 3.48 3.48 3.48 3.48 4.00 5.24 6.01 6.90 7.39 7.39 6.90 6.44 5.24 4.26 59 0.51 0.87 1.29 1.66 1.92 2.33 2.71 3.03 3.32 3.73 3.73 3.73 3.73 3.73 4.29 5.61 6.44 7.39 7.92 7.92 7.39 6.90 5.61 4.56 Page 108
SPL 50 63 80 100 125 160 200 250 315 400 500 630 800 1000 1250 1600 2000 2500 3150 4000 5000 6300 8000 10000 60 0.59 1.00 1.40 1.81 2.08 2.51 2.93 3.26 3.57 4.00 4.00 4.00 4.00 4.00 4.59 6.01 6.90 7.92 8.49 8.49 7.92 7.39 6.01 4.89 61 0.67 1.10 1.53 1.97 2.26 2.71 3.16 3.51 3.83 4.29 4.29 4.29 4.29 4.29 4.92 6.44 7.39 8.49 9.09 9.09 8.49 7.92 6.44 5.24 62 0.77 1.21 1.66 2.15 2.45 2.93 3.41 3.78 4.11 4.59 4.59 4.59 4.59 4.59 5.28 6.90 7.92 9.09 9.74 9.74 9.09 8.49 6.90 5.61 63 0.87 1.32 1.81 2.34 2.65 3.16 3.69 4.06 4.41 4.92 4.92 4.92 4.92 4.92 5.66 7.39 8.49 9.74 10.4 10.4 9.74 9.09 7.39 6.01 64 1.00 1.45 1.97 2.54 2.88 3.41 3.98 4.38 4.73 5.28 5.28 5.28 5.28 5.28 6.06 7.92 9.09 10.4 11.2 11.2 10.4 9.74 7.92 6.44 65 1.11 1.60 2.15 2.77 3.12 3.69 4.30 4.71 5.08 5.66 5.66 5.66 5.66 5.66 6.50 8.49 9.74 11.2 12.0 12.0 11.2 10.4 8.49 6.90 66 1.22 1.75 2.34 3.01 3.39 3.98 4.64 5.07 5.45 6.06 6.06 6.06 6.06 6.06 6.96 9.09 10.4 12.0 12.8 12.8 12.0 11.2 9.09 7.39 67 1.35 1.92 2.54 3.28 3.68 4.30 5.01 5.46 5.85 6.50 6.50 6.50 6.50 6.50 7.46 9.74 11.2 12.8 13.8 13.8 12.8 12.0 9.74 7.92 68 1.49 2.11 2.77 3.57 3.99 4.64 5.41 5.88 6.27 6.96 6.96 6.96 6.96 6.96 8.00 10.4 12.0 13.8 14.7 14.7 13.8 12.8 10.4 8.49 69 1.65 2.32 3.01 3.88 4.33 5.01 5.84 6.33 6.73 7.46 7.46 7.46 7.46 7.46 8.57 11.2 12.8 14.7 15.8 15.8 14.7 13.8 11.2 9.09 70 1.82 2.55 3.28 4.23 4.69 5.41 6.31 6.81 7.23 8.00 8.00 8.00 8.00 8.00 9.19 12.0 13.8 15.8 16.9 16.9 15.8 14.7 12.0 9.74 71 2.02 2.79 3.57 4.60 5.09 5.84 6.81 7.33 7.75 8.57 8.57 8.57 8.57 8.57 9.85 12.8 14.7 16.9 18.1 18.1 16.9 15.8 12.8 10.4 72 2.23 3.07 3.88 5.01 5.52 6.31 7.36 7.90 8.32 9.19 9.19 9.19 9.19 9.19 10.6 13.8 15.8 18.1 19.4 19.4 18.1 16.9 13.8 11.2 73 2.46 3.37 4.23 5.45 5.99 6.81 7.94 8.50 8.93 9.85 9.85 9.85 9.85 9.85 11.3 14.7 16.9 19.4 20.8 20.8 19.4 18.1 14.7 12.0 74 2.72 3.70 4.60 5.94 6.50 7.36 8.57 9.15 9.59 10.6 10.6 10.6 10.6 10.6 12.1 15.8 18.1 20.8 22.3 22.3 20.8 19.4 15.8 12.8 75 3.01 4.06 5.01 6.46 7.05 7.94 9.19 9.85 10.3 11.3 11.3 11.3 11.3 11.3 13.0 16.9 19.4 22.3 23.9 23.9 22.3 20.8 16.9 13.8 76 3.32 4.46 5.45 7.03 7.65 8.57 9.85 10.6 11.0 12.1 12.1 12.1 12.1 12.1 13.9 18.1 20.8 23.9 25.6 25.6 23.9 22.3 18.1 14.7 77 3.67 4.89 5.94 7.66 8.29 9.19 10.6 11.3 11.8 13.0 13.0 13.0 13.0 13.0 14.9 19.4 22.3 25.6 27.4 27.4 25.6 23.9 19.4 15.8 78 4.06 5.37 6.46 8.33 9.00 9.85 11.3 12.1 12.7 13.9 13.9 13.9 13.9 13.9 16.0 20.8 23.9 27.4 29.4 29.4 27.4 25.6 20.8 16.9 79 4.49 5.90 7.03 9.07 9.76 10.6 12.1 13.0 13.6 14.9 14.9 14.9 14.9 14.9 17.1 22.3 25.6 29.4 31.5 31.5 29.4 27.4 22.3 18.1 80 4.96 6.48 7.66 9.85 10.6 11.3 13.0 13.9 14.6 16.0 16.0 16.0 16.0 16.0 18.4 23.9 27.4 31.5 33.7 33.7 31.5 29.4 23.9 19.4 81 5.48 7.11 8.33 10.6 11.3 12.1 13.9 14.9 15.7 17.1 17.1 17.1 17.1 17.1 19.7 25.6 29.4 33.7 36.1 36.1 33.7 31.5 25.6 20.8 82 6.06 7.81 9.07 11.3 12.1 13.0 14.9 16.0 16.9 18.4 18.4 18.4 18.4 18.4 21.1 27.4 31.5 36.1 38.7 38.7 36.1 33.7 27.4 22.3 83 6.70 8.57 9.87 12.1 13.0 13.9 16.0 17.1 18.1 19.7 19.7 19.7 19.7 19.7 22.6 29.4 33.7 38.7 41.5 41.5 38.7 36.1 29.4 23.9 84 7.41 9.41 10.7 13.0 13.9 14.9 17.1 18.4 19.4 21.1 21.1 21.1 21.1 21.1 24.3 31.5 36.1 41.5 44.4 44.4 41.5 38.7 31.5 25.6 85 8.19 10.3 11.7 13.9 14.9 16.0 18.4 19.7 20.8 22.6 22.6 22.6 22.6 22.6 26.0 33.7 38.7 44.4 47.6 47.6 44.4 41.5 33.7 27.4 86 9.95 11.3 12.7 14.9 16.0 17.1 19.7 21.1 22.4 24.3 24.3 24.3 24.3 24.3 27.9 36.1 41.5 47.6 51.0 51.0 47.6 44.4 36.1 29.4 87 10.0 12.1 13.9 16.0 17.1 18.4 21.1 22.6 24.0 26.0 26.0 26.0 26.0 26.0 29.0 38.7 44.4 51.0 54.7 54.7 51.0 47.6 38.7 31.5 88 11.1 13.0 14.9 17.1 18.4 19.7 22.6 24.3 25.8 27.9 27.9 27.9 27.9 27.9 32.0 41.5 47.6 54.7 58.6 58.6 54.7 51.0 41.5 33.7 89 12.2 13.9 16.0 18.4 19.7 21.1 24.3 26.0 27.7 29.9 29.9 29.9 29.9 29.9 34.3 44.4 51.0 58.6 62.7 62.7 58.6 54.7 44.4 36.1 90 13.5 14.9 17.1 19.7 21.1 22.6 26.0 27.9 29.7 32.0 32.0 32.0 32.0 32.0 36.8 47.6 54.7 62.7 67.2 67.2 62.7 58.6 47.6 38.7 91 14.9 16.0 18.4 21.1 22.6 24.3 27.9 29.9 31.8 34.3 34.3 34.3 34.3 34.3 39.4 51.0 58.6 67.2 72.0 72.0 67.2 62.7 51.0 41.5 92 16.0 17.1 19.7 22.6 24.3 26.0 29.9 32.0 34.2 36.8 36.8 36.8 36.8 36.8 42.2 54.7 62.7 72.0 77.2 77.2 72.0 67.2 54.7 44.4 93 17.1 18.4 21.1 24.3 26.0 27.9 32.0 34.3 36.7 39.4 39.4 39.4 39.4 39.4 45.3 58.6 67.2 77.2 82.7 82.7 77.2 72.0 58.6 47.6 94 18.4 19.7 22.6 26.0 27.9 29.9 34.3 36.8 39.4 42.2 42.2 42.2 42.2 42.2 48.5 62.7 72.0 82.7 88.6 88.6 82.7 77.2 62.7 51.0 95 19.7 21.1 24.3 27.9 29.9 32.0 36.8 39.4 42.2 45.3 45.3 45.3 45.3 45.3 52.0 67.2 77.2 88.6 94.9 94.9 88.6 82.7 67.2 54.7 96 21.1 22.6 26.0 29.9 32.0 34.3 39.4 42.2 45.3 48.5 48.5 48.5 48.5 48.5 55.7 72.0 82.7 94.9 102 102 94.9 88.6 72.0 58.6 97 22.6 24.3 27.9 32.0 34.3 36.8 42.2 45.3 48.5 52.0 52.0 52.0 52.0 52.0 59.7 77.2 88.6 102 109 109 102 94.9 77.2 62.7 98 24.3 26.0 29.9 34.3 36.8 39.4 45.3 48.5 52.0 55.7 55.7 55.7 55.7 55.7 64.0 82.7 94.9 109 117 117 109 102 82.7 67.2 99 26.0 27.9 32.0 36.8 39.4 42.2 48.5 52.0 55.7 59.7 59.7 59.7 59.7 59.7 68.6 88.6 102 117 125 125 117 109 88.6 72.0 100 27.9 29.9 34.3 39.4 42.2 45.3 52.0 55.7 59.7 64.0 64.0 64.0 64.0 64.0 73.5 94.9 109 125 134 134 125 117 94.9 77.2 101 29.9 32.0 36.8 42.2 45.3 48.5 55.7 59.7 64.0 68.6 68.6 68.6 68.6 68.6 78.8 102 117 134 144 144 134 125 102 82.7 102 32.0 34.3 39.4 45.3 48.5 52.0 59.7 64.0 68.6 73.5 73.5 73.5 73.5 73.5 84.4 109 125 144 154 154 144 134 109 88.6 103 34.3 36.8 42.2 48.5 52.0 55.7 64.0 68.6 73.5 78.8 78.8 78.8 78.8 78.8 90.5 117 134 154 165 165 154 144 117 94.9 104 36.8 39.4 45.3 52.0 55.7 59.7 68.6 73.5 78.8 84.4 84.4 84.4 84.4 84.4 97.0 125 144 165 177 177 165 154 125 102 105 39.4 42.2 48.5 55.7 59.7 64.0 73.5 78.8 84.4 90.5 90.5 90.5 90.5 90.5 104 134 154 177 189 189 177 165 134 109 106 42.2 45.3 52.0 59.7 64.0 68.6 78.8 84.4 90.5 97.0 97.0 97.0 97.0 97.0 111 144 165 189 203 203 189 177 144 117 107 45.3 48.5 55.7 64.0 68.6 73.5 84.4 90.5 97.0 104 104 104 104 104 119 154 177 203 217 217 203 189 154 125 108 48.5 52.0 59.7 68.6 73.5 78.8 90.5 97.0 104 111 111 111 111 111 128 165 189 217 233 233 217 203 165 134 109 52.0 55.7 64.0 73.5 78.8 84.4 97.0 104 111 119 119 119 119 119 137 177 203 233 249 249 233 217 177 144 110 55.7 59.7 68.6 78.8 84.4 90.5 104 111 119 128 128 128 128 128 147 189 217 249 267 267 249 233 189 154 111 59.7 64.0 73.5 84.4 90.5 97.0 111 119 128 137 137 137 137 137 158 203 233 267 286 286 267 249 203 165 112 64.0 68.6 78.8 90.5 97.0 104 119 128 137 147 147 147 147 147 169 217 249 286 307 307 286 267 217 177 113 68.6 73.5 84.4 97.0 104 111 128 137 147 158 158 158 158 158 181 233 267 307 329 329 307 286 233 189 114 73.5 78.8 90.5 104 111 119 137 147 158 169 169 169 169 169 194 249 286 329 352 352 329 307 249 203 115 78.8 84.4 97.0 111 119 128 147 158 169 181 181 181 181 181 208 267 307 352 377 377 352 329 267 217 116 84.4 90.5 104 119 128 137 158 169 181 194 194 194 194 194 223 286 329 377 404 404 377 352 286 233 117 90.5 97.0 111 128 137 147 169 181 194 208 208 208 208 208 239 307 352 404 433 433 404 377 307 249 118 97.0 104 119 137 147 158 181 194 208 223 223 223 223 223 256 329 377 433 464 464 433 404 329 267 119 104 111 128 147 158 169 194 208 223 239 239 239 239 239 274 352 404 464 497 497 464 433 352 286 120 111 119 137 158 169 181 208 223 239 256 256 256 256 256 294 377 433 497 533 533 497 464 377 307 121 119 128 147 169 181 194 223 239 256 274 274 274 274 274 315 404 464 533 571 571 533 497 404 329 122 128 137 158 181 194 208 239 256 274 294 294 294 294 294 338 433 497 571 611 611 571 533 433 352 123 137 147 169 194 208 223 256 274 294 315 315 315 315 315 362 464 533 611 655 655 611 571 464 377 124 147 158 181 208 223 239 274 294 315 338 338 338 338 338 388 497 571 655 702 702 655 611 497 404 125 158 169 194 223 239 256 294 315 338 362 362 362 362 362 416 533 611 702 752 752 702 655 533 433 Page 109
SPL 50 63 80 100 125 160 200 250 315 400 500 630 800 1000 1250 1600 2000 2500 3150 4000 5000 6300 8000 10000 126 169 181 208 239 256 274 315 338 362 388 388 388 388 388 446 571 655 752 806 806 752 702 571 464 127 181 194 223 256 274 294 338 362 388 416 416 416 416 416 478 611 702 806 863 863 806 752 611 497 128 194 208 239 274 294 315 362 388 416 446 446 446 446 446 512 655 752 863 925 925 863 806 655 533 129 208 223 256 294 315 338 388 416 446 478 478 478 478 478 549 702 806 925 991 991 925 863 702 571 130 223 239 274 315 338 362 416 446 478 512 512 512 512 512 588 752 863 991 1062 1062 991 925 752 611 131 239 256 294 338 362 388 446 478 512 549 549 549 549 549 630 806 925 1062 1137 1137 1062 991 806 655 132 256 274 315 362 388 416 478 512 549 588 588 588 588 588 676 863 991 1137 1219 1219 1137 1062 863 702 133 274 294 338 388 416 446 512 549 588 630 630 630 630 630 724 925 1062 1219 1306 1306 1219 1137 925 752 134 294 315 362 416 446 478 549 588 630 676 676 676 676 676 776 991 1137 1306 1399 1399 1306 1219 991 806 135 315 338 388 446 478 512 588 630 676 724 724 724 724 724 832 1062 1219 1399 1499 1499 1399 1306 1062 863 136 338 362 416 478 512 549 630 676 724 776 776 776 776 776 891 1137 1306 1499 1606 1606 1499 1399 1137 925 137 362 388 446 512 549 588 676 724 776 832 832 832 832 832 955 1219 1399 1606 1721 1721 1606 1499 1219 991 138 388 416 478 549 588 630 724 776 832 891 891 891 891 891 1024 1306 1499 1721 1844 1844 1721 1606 1306 1062 139 416 446 512 588 630 676 776 832 891 955 955 955 955 955 1098 1399 1606 1844 1975 1975 1844 1721 1399 1137 140 446 478 549 630 676 724 832 891 955 1024 1024 1024 1024 1024 1176 1499 1721 1975 1975 1844 1499 1219 141 478 512 588 676 724 776 891 955 1024 1098 1098 1098 1098 1098 1261 1606 1844 1975 1606 1306 142 512 549 630 724 776 832 955 1024 1098 1176 1176 1176 1176 1176 1351 1721 1975 1721 1399 143 549 588 676 776 832 891 1024 1098 1176 1261 1261 1261 1261 1261 1448 1844 1844 1499 144 588 630 724 832 891 955 1098 1176 1261 1351 1351 1351 1351 1351 1552 1975 1975 1606 145 630 676 776 891 955 1024 1176 1261 1351 1448 1448 1448 1448 1448 1664 1721 146 676 724 832 955 1024 1098 1261 1351 1448 1552 1552 1552 1552 1552 1783 1844 147 724 776 891 1024 1098 1176 1351 1448 1552 1664 1664 1664 1664 1664 1911 1975 148 776 832 955 1098 1176 1261 1448 1552 1664 1783 1783 1783 1783 1783 2048 149 832 891 1024 1176 1261 1351 1552 1664 1783 1911 1911 1911 1911 1911 150 891 955 1098 1261 1351 1448 1664 1783 1911 2048 2048 2048 2048 2048 Page 110
Table 10. Example of tone correction calculation for a turbotan engine SPL" dB dB dB Band SPL Step Step Step Step Step
(1) Hz dB 7 8 1 50 63 80 70 70 -8 —2⅓ 70 100 62 62 -8 +3·⅓ 67⅓ 125 16 71 +9 +6⅓ 71 6 160 80 +10 2 80 +9 +2⅓ 77⅓ 2⅓ 0.29 200 82 82 +2 -1⅓ 80⅓ 1⅓ 0.Õ6 250 +1 79 -3 —1 ⅕ 79 4 0.61 315 76 76 -3 77⅔ 10 400 11 78 +2 +1 78 2 0.17 11 500 80 4 80 +2 79 — 12 630 79 -1 79 -1 79 13 800 78 -1 78 —1 —⅓ 79 14 1 000 80 +2 80 +2 78⅔ 15 1 250 78 -2 4 78 -2 —⅓ 78 16 1 600 76 -2 76 -2 +⅓ 77% 17 2 000 79 +3 5 79 +3 +1 78 18 2 500 79 —·⅓ 79 2 19 3 150 79 12 79 -2⅓ 78⅔ 20 4 000 78 -1 5 78 -1 —6⅓ 76 2 0.33 21 5 000 71 6 71 -8 69⅔ 22 6 300 60 -11 4 60 -11 -8⅓ 61⅓ 23 8 000 54 54 -8 53 24 10 000 45 45 45 Step 1 ⅓)(-1) Step 6 Step 2 Step 7 Q(-1)+%(-1) Step 3 see instructions Step 8 Step 4 see instructions Step 9 see Table A36-2 Step 5 (a)(û(&) (-1) Note. — Steps 5 and 6 may be eliminated in the calculations if desired. In this case in the example shown, columns, and e should be removedand existing column (a) un) andy) become 2) • (a) and (a) coveringnew steps 5, 6 and 7 respectively. The existing steps5, 6,7, 8 and 9 in 4.3.1 of Appendix Aarethenreplacedby:
STEPS 6 (1- 1) + 1(0 (ı+1)]÷3 STEO (1) -Q (i) if>0 STEP 7 See Table A36-2.
1 10 100 1 000 10 000 Total perceived noisiness, , noys N Perceived noise level, PNL, PNdB 150 140 130 120 110 100 90 80 70 60 50 40 Figure 7. Perceived noise level as a function of total perceived noisiness Page 112
Chapter 4
GUIDELINES FOR TRANSPORT CATEGORY LARGE AIRPLANES, SUBSONIC JETAIRPLANES, AND HELICOPTERS EVALUATED UNDER APPENDIX A OR H OF 14 CFR PART 36
CHAPTER TABLE OF CONTENTS
401 EXPLANATORY INFORMATION116
401(a) Noise Measurements116
401(b) Noise Certification Test and Measurement Conditions116
401(b)(1) Ambient temperature116
401(b)(2) Calculation of sound attenuation coefficients for the effects of atmospheric absorption117
401(b)(3) Wind speed120
401(b)(4) Anomalous meteorological conditions121
401(b)(5) Time of meteorological measurements121
401(b)(6) Aircraft position measurement122
401(b)(7) Time space position information (TSPI) measurement system characteristics122
401(b)(8) Aircraft performance123
401(c) Measurement of Aircraft Noise Received on the Ground124
401(c)(1) Environmental specifications124
401(c)(2) Measurement system specification124
401(c)(3) Microphone orientation124
401(c)(4) Microphone specification124
401(c)(5) Recorder specifications125
401(c)(6) Pre-emphasis127
401(c)(7) Attenuator specifications127
401(c)(8) Linear integrating analyzer specifications127
401(c)(9) Analyzer performance specifications127
401(c)(10) Microphone incidence adjustments128
401(c)(11) Pink noise specification128
401(c)(12) Measurement system field calibration128
401(c)(13) Field acoustical calibrations128
401(c)(14) Windscreen loss adjustment129
401(c)(15) Measurement system background noise129
401(d) Calculation of EPNL from Measured Data129
401(d)(1) Instantaneous sound pressure levels129
401(d)(2) Tone correction calculation130
401(d)(3) Adjustments relating to background noise130
401(d)(4) Data resolution after tone correction calculation130
401(d)(5) Band sharing adjustment130
401(d)(6) Calculation of band sharing adjustment131
401(d)(7) Noise Duration131
401(d)(8) Equations for computing duration correction132
401(e) Reporting of Data to the FAA133
401(e)(1) Compliance records133
401(e)(2) EPNL average values133
401(e)(3) Calculation of 90 percent confidence intervals134
401(f) Nomenclature: Symbols and Units134
401(g) Sound Attenuation in Air135
401(h) Adjustment of Helicopter Flight Test Results135
401(h)(1) Adjustments to reference conditions135
401(h)(2) Reference data sources136
401(h)(3) Adjustments to measured noise data136
401(h)(4) Takeoff profile136
401(h)(5) Takeoff test conditions137
401(h)(6) Takeoff flight test procedures139
401(h)(7) Flyover configuration142
401(h)(8) Flyover test procedure144
401(h)(9) Approach configuration148
401(h)(10) Approach test condition149
401(h)(11) Approach test procedure150
401(h)(12) Adjustments of PNL and PNLT152
401(h)(13) Duration adjustment to EPNL152
401(i) Adjustment of Airplane Flight Test Results153
401(i)(1) Adjustments to reference conditions153
401(i)(1)(A) Origin of reference data154
401(i)(2) Takeoff configuration/profile154
401(i)(3) Takeoff test procedure157
401(i)(4) Approach test configuration157
401(i)(5) Approach test procedure159
401(i)(6) Lateral noise measurement160
401(i)(7) Integrated procedure adjustment160
401(i)(8) Acoustic emission angles160
402 EQUIVALENT PROCEDURES INFORMATION160
402(a) Subsonic Jet Airplanes160
402(a)(1) Flight test procedures161
402(a)(1)(A) Flight path intercepts161
402(a)(1)(A)(i) For takeoff161
402(a)(1)(A)(ii) For approach161
402(a)(1)(B) Generalized flight test procedures162
402(a)(1)(B)(i) For derivation of noise-power-distance (NPD) data162
402(a)(1)(B)(ii) For flight test procedures for determination of changes164
402(a)(1)(C) Determination of the lateral certification noise levels164
402(a)(1)(D) Takeoff flyover noise levels with thrust (power) reduction165
402(a)(1)(E) Measurements at non-reference points166
402(a)(1)(F) Atmospheric test conditions166
402(a)(1)(G) Layering equivalency166
402(a)(2) Analytical procedures167
402(a)(2)(A) Flyover noise levels with thrust (power) reduction167
402(a)(2)(B) Equivalent procedures based upon analytical methods168
402(a)(2)(C) Equivalent procedure for calculating the certification noise levels169
402(a)(3) Static engine noise tests and projections to flight noise levels170
402(a)(3)(A) General170
402(a)(3)(B) Limitation on the projection of static-to-flight data170
402(a)(3)(C) Static engine noise test procedures172
402(a)(3)(C)(i) General172
402(a)(3)(C)(ii) Test site characteristics172
402(a)(3)(C)(iii) Data acquisition and reduction systems173
402(a)(3)(C)(iv) Microphone types, locations and installations174
402(a)(3)(D) Projection of static engine data to airplane flight conditions174
402(a)(3)(D)(i) General174
402(a)(3)(D)(ii) Normalization to reference conditions176
402(a)(3)(D)(iii) Separation into broadband and tone noise177
402(a)(3)(D)(iv) Separation into contributing noise sources177
402(a)(3)(D)(v) Noise source position effects178
402(a)(3)(D)(vi) Engine flight conditions179
402(a)(3)(d)(vii) Noise source motion effects179
402(a)(3)(D)(viii) Airplane configuration effects180