δtpropR(k) is the sound propagation time for sound emission point k, such that:
δtpropR(k) = SRR(k) / cR tR(k) is the time of sound reception at the microphone for sound emitted at point k, such that:
tR(k) = tER(k) + δtpropR(k) Finally calculate δtR(k), the effective time duration for the sound received at the microphone at time tR(k), as specified in A36.9.4.2.1 of part 36 where:
tR(k) = [(tR(k) – tR(k-1)) + (tR(k+1) – tR(k))]/2 403(a)(3) Computation of EPNL by the simplified method of adjustment [ETM 4.3.1.3] Section A36.9.3 of the part 36 provides specifications for the simplified adjustment method. The following procedure illustrates one method for meeting the requirements of this section.
403(a)(3)(A) Inputs required for performing the simplified method [ETM 4.3.1.3.1] The following inputs are required for the simplified method:
a) The one-third octave band spectrum representing the measured test-day aircraft noise at the time of PNLTM, SPL(i, kM), plus the spectra representing the measured test-day aircraft noise for any PNLT(k) values within 2 dB of the level of PNLTM (secondary peaks), SPL(i,k), determined in accordance with A36.9.3.2.2 of part
36. Additional guidance is provided in 401(c);
b) The average atmospheri c absorption coefficients, α(i) for each one-third octave band, i, determined for testday conditions, in dB per 100 metres, as determined from measured test-day meteorological data in accordance with A36.2.2.3 of part 36. Additional gui dance is provided in 401(b)(2) (Calculation of sound attenuation coefficients for the effects of atmospheric absorption);
c) The atmospheric ab sorption coefficients, α(i)0 for each one-third octave band, i, determined for reference conditions in dB per 100 meters, as determined in accordance with A36.2.2.3 of part 36. Note that reference conditions for atmospheric absorption are specified in B36.7 of part 36 for airplanes being certified under Stage 3 or Stage 4 or Stage 5 requirements, and in H36.3(a) of part 36 for helicopters, as a homogenous atmosphere with temperature of 77°F (25°C) and relative humidity of 70%;
d) The sound propagation distance (in meters) between the aircraft and the microphone at the time of emission of the PNLTM noise data record, SR( kM), and for each secondary peak record, SR(k ), as determined in 403(a)(2);
e) The reference sound propagation distance (in meters) between the aircraft and the reference microphone at the time of emission of the PNLTMR noise data record, SRR(kM), and of each secondary peak record, SRR(k), as determined in 403(a)(2);
f) The test-day bandsharing adjustment, ΔB, as determined in A36.4.4.2 of part 36;
g) The test-day aircraft groundspeed, V G, as determined from th e measured aircraft tr acking TSPI data from 403(a)(2);
h) The reference aircraft groundspeed, V GR, as determined from 403(a)(2);
i) The test-day value for EPNL, as specified in A36.4 of part 36;
j) The test-day value fo r PNLTM, as specified in A36.4 of part 36; and
k) A source noise adjustment, Δ3, as determined in A36.9.3.4.2 of part 36.
403(a)(3)(B) Adjustmen t of sound pressure levels to reference conditions [ETM 4.3.1.3.2] Adjust each measured test-day one-third octave band SPL in the spectrum associated with PNLTM, and in the spectra associated with any secondary peaks, for spherical spreading (also known as “inverse square law”) and the effect of the change in sound attenuation due to atmospheric absorp tion for differences between th e test and reference flight paths, using the equation provided in A36.9.3.2.1 of part 36:
For the measured test-day acoustic data spectrum associated with PNLTM, kM:
For all one-third octave bands, i:
SPLR(i,kM) = SPL(i,kM) + 0.01 [α(i) – α(i)0] SR(kM) + 0.01 α(i)0 (SR(kM) – SRR(kM)) + 20 log (SR(kM)/ SRR(kM)) For each measured test-day acoustic data spectrum associated with a secondary peak, k:
For all one-third octave bands, i:
SPLR(i,k) = SPL(i,k) + 0.01 [α(i) – α(i)0] SR(k) + 0.01 α(i)0 (SR(k) – SRR(k)) + 20 log (SR(k)/ SRR(k)) 403(a)(3)(C) De termination of reference-condition tone-corrected perceived noise levels [ETM 4.3.1.3.3] Calculate the reference-condition tone-corrected perceived noise level, PNLT R(kM) for the adjusted spectrum associated with PNLTM, kM, and for each spectrum associated with a secondary peak, k, using the procedures specified in A36.4.6 of part 36, including calculation of perceived noise level, PNLR(k) and tone-correction factor, CR(k).
403(a)(3)(D) Application of test-day ba ndsharing adjustment to reference-condition maximum tone-corrected perceived noise level and determination o f t h e 1 simplified adjustment term [ETM 4.3.1.3.4] In order to account for the presence of bandsharing in the measured te st-day PNLTM and EPNL, the test-day bandsharing adjustment, Δ B, as determined in A36.4.4.2 of part 36, is applied to the adjusted reference-condition PNLTR(kM) value prior to determination of other adjustment factors, and subsequent calculation of the simplified reference-condition effective perceived noise level, EPNLR as specified in A36.9.3 of part 36:
PNLTMR = PNLTR(kM) + ΔB Page 206
The simplified adjustment term Δ1 is then calculated per A36.9.3.2.1 of part 36, by subtracting the test-day (bandsharing-adjusted) value for PNLTM (as determined in accordance with A36.4.4.2 of part 36) from the referencecondition (bandsharing-adjusted) value for PNLTMR obtained from the equation above:
Δ1 = PNLTMR – PNLTM 403(a)(3)(E) Det ermination of the ΔPeak simplified adjustment term to account for the effects of secondary peaks [ETM 4.3.1.3.5] Using the bandsharing-adjusted reference-condition PNLTM R value as determined in 4.3.1.3.4, and the referencecondition values of PNLTR for each of the secondary peaks, as determined in 4.3.1.3.3, calculate the secondary peak adjustment term, ΔPeak, specified in A36.9.3.3.2 of part 36 as follows:
a) Compare the PNLT R values for all of the secondary peaks to determine which has the maximum value of PNLTR, and identify this secondary peak value as PNLTR(MaxPeak).
b) If the value of PNLT R(MaxPeak) exceeds that of PNLTMR, then calculate the secondary peak adjustment term, ΔPeak, by subtracting PNLTMR from PNLTR(MaxPeak) such that:
ΔPeak = PNLTR(MaxPeak) – PNLTMR 403(a)(3)(F) Det ermination of the Δ2 simplified adjustment term to account for change in noise level [ETM 4.3.1.3.6] Section A36.9.3.3.1 of part 36 specifies that whenever the flight path and/or ground velocity of aircraft differ between test-day and reference conditions, then a duration adjustment should be determined and applied.
This duration adjustment term, Δ2, comprising two components, accounts for the effects on the EPNL noise duration of differences between the test and reference distance and speed. These components are determined as follows:
Δ2 [distance component] = -7.5 log (SR(kM) / SRR(kM)) where:
kM is the noise data point at which PNLTM occurred; and Δ2 [speed component] = +10 log (VG / VGR) where:
VG and VGR are the test and reference ground speeds of the aircra ft, determined from aircraft tracking TSPI data, as determined in 403(a)(2).
The complete equation for the simplified duration adjustment is:
Δ2 = -7.5 log (SR(kM) / SRR(kM)) + 10 log (VG / VGR) 403(a)(3)(G) Determination of the Δ3 simplified adjustment term to account for differences in source noise [ETM 4.3.1.3.7] Section A36.9.3.4.2 of part 36 defines and describes various means of determining a Δ3 adjustment term to be used in the calculation of reference-condition effective perceived noise level.
Determine the appropriate process, and calculate the value for Δ3 per A36.9.3.4.2 of part 36, to account for the effects of differences in source noise between test-day and reference conditions.
Application of this adjustment term, Δ3, is illustrated in 403(a)(3)(H).
403(a)(3)(H) Determinati on of the simplified reference-condition effective perceived noise level [ETM 4.3.1.3.8] Compute the simplified reference-condition effective perceived noise level, EPNLR, as specified in A36.9.3.1 of part 36 as follows:
EPNL R = EPNL + Δ1 + ΔPeak + Δ2 + Δ3 where:
— EPNL is the test-day value for effective perceive d noise level, determined in accordance with A36.4.6 of part 36;
— Δ1 is the simplified adjustment term for the eff ects of adjusting the PNLTM spectrum to reference conditions as determined in 403(a)(3)(D);
— ΔPeak is the secondary peak adjustment term as determined in 403(a)(3)(E);
— Δ2 is the simplified adjustment term for duration effects as determined in 403(a)(3)(F); and — Δ3 is the adjustment term for source noise effects as described in 403(a)(3)(G).
403(a)(3)(I) Worked example calculat ions illustrating the simplified method [ETM 4.3.1.3.9]
4.3.1.3.9 Worked example calculations illustrating the simplified method [Reserved] 403(a)(4) Computation of EPNL by the integrated method of adjustment [ETM 4.3.1.4] Section A36.9.4 of part 36 provides specifications for the integrated method. The following procedure illustrates one method for meeting the requirements of A36.9.4.
403(a)(4)(A) Inputs required for performing the integrated method [ETM 4.3.1.4.1] The following inputs are required for the integrated method:
a) the one-third octave band spectral time-history repr esenting the measured test-day aircraft noise, SPL( i,k), encompassing at least the test-day EPNL noise duration as defined in A36.4.6 of part 36; additional guidance is provided in 401(c);
b) the average atmospheric absorption coefficients, α(i), for each one-third octave band, i, determined for testday conditions, in dB per 100 meters, as determined from measured test-day meteorological data in accordance with A36.7 of part 36; a dditional guidance is pr ovided in 401( b)(2) (Calculation of sound attenuation coefficients for the effects of atmospheric absorption);
c) the reference atmospheri c absorption coefficients, α (i)0 for each one-third octave band, i, in dB per 100 metres, as determined in accordance with A36.7 of part 36; note that reference conditions for atmospheric absorption are specified in B36.7 of part 36 for airplanes being certified under Stage 3, Stage 4 or 5 Page 208
requirements, and in H36.3(a) of Appendix H of part 36 for helicopters, as a homogenous atmosphere with temperature of 77°F (25°C), and relative humidity of 70%;
d) the series of sound propagation distances (in metres) between the aircraft and the microphone at the time of emission of each noise data record, SR(k), as determined in 403(a)(2);
e) the series of reference sound pr opagation distances (in meters) betw een the aircraft and the reference microphone at the time of emission of each reference-condition noise data record, SRR(k), as determined in 403(a)(2); and
f) the series of effective durations, δtR(k) for the series of reference-condition noise data records, k, as determined in 403(a)(2).
403(a)(4)(B) Adjustmen t of sound pressure levels to reference conditions [ETM 4.3.1.4.2] Adjust each measured test-day one-third octave band SPL in the spectral time history for the effect of spherical spreading (also known as “inverse square law”) and the effect of the change in sound attenuation due to atmospheric absorption for differences between the test and reference flight paths, using the equation provided in A36.9.3.2.1 of part 36:
For all of the one-third octave bands, i, in each of the measured test-day acoustic data records, k:
SPLR(i,k) = SPL(i,k) + 0.01 [α(i) – α(i)0] SR(k) + 0.01 α(i)0 (SR(k) – SRR(k)) + 20 log (SR(k) / SRR(k)) Note.— Sufficient spectra in the measured test-day spectral time history should be adjusted to encompass the integrated reference-condition EPNL noise duration, which may exceed the test-day EPNL noise duration due to adjustments to SPLs that may result in different first and last 10 dB-down points being selected.
403(a)(4)(C) Determi nation of reference-condition tone-corrected perceived noise level time history [ETM 4.3.1.4.3] Calculate the reference-condition tone-corrected perceived noise level, PNLTR(k) for each adjusted spectrum, k, in the spectral time history using the procedures specified in A36.4.6 of part 36, including calculation of perceived noise level, PNLR(k) and tone-correction factor, CR(k).
403(a)(4)(D) Identification of integrated reference-condition maximum tone-corrected perceived noise level [ETM 4.3.1.4.4] Using the reference-condition time history of PNLT R(k) obtained in 403(a)(4)(C), identify the record at which the maximum level occurs, PNLT R(kM), and determine and apply the integrated reference-condition bandsharing adjustment, ΔBR, as described in A36.4.4.2 of part 36, to obtain the bandsharing-adjusted reference PNLTMR:
PNLTMR = PNLTR(kM) + ΔBR Note that due to adjustments for differences between test-day and reference conditions, it is possible that the acoustic data record at which PNLTM R occurs will be different from the record at which the measured test-day PNLTM occurred. It is also possible that the bandsharing adjustment determined from the integrated reference-condition data set. ΔBR, will be different from the bandsharing adjustment determined from the measured test-day data set, ΔB.
403(a)(4)(E) Identification of integrat ed reference-condition EPNL Noise Duration [ETM 4.3.1.4.5] Using the reference-condition time history of PNLT R(k) obtained in 403(a)(4)(C), but including the bandsharing - adjusted value for PNLTM R obtained in 403(a)(4)(D), identify the limits of the reference-condition EPNL noise duration in accordance with A36.9.4.3.1 of part 36.
Note that due to adjustments for diffe rences between test-day an d reference conditions, the first and last referencecondition 10 dB-down points, kFR and kLR will quite likely be different from the first and last 10 dB-down points for the measured test-day EPNL noise duration, kF and kL.
403(a)(4)(F) Summation of integrated reference-condition EPNL [ETM 4.3.1.4.6] Compute the integrated reference-conditi on effective perceived noise level, EPNL R, by summing the PNLT R(k) “energy” between the limits, kFR and k LR, of the integrated reference-conditio n EPNL noise duration, obtained in
4.3.1.4.5, as follows:
ܮܰܲܧோ ൌ 10logሾሺ ଵ ሻ ∑ಽೃಷೃሺ10.ଵே்ೃሺሻሻሺݐߜோሺ݇ሻሻ ሿ where:்బ — the series of PNLT R(k) values is obtained in 4.3.1.4.3 (substitu ting as necessary the bandsharing-adjusted value of PNLTMR in place of the value for PNLTR(kM)); and — the effective durations, δtR(k), is obtained in 4.3.1.2.
In practice the adjusted EPNL value takes into account the contributions of sound energy associated with each individual time increment (record), and is calculated from a summation from the first 10 dB-down point, kFR, to the last 10 dB-down point, kLR. Note that due to the effects of the adjustment for differences between test and reference conditions the effective duration, δtR(k), associated with each record, is not likely to be uniform. Table 14 provides an example of how this calculation may be performed.
403(a)(4)(G) Worked example calculat ions illustrating the integrated method [ETM 4.3.1.4.7] Table 14. Example calculation of adjusted EPNL value when using the integrated method of adjustment.
Labels PNLT R(k) δtR(k) s “Energy”= ሺ10.ଵே்ೃሺሻሻሺݐߜோሺ݇ሻ
- 84.62 0.3950 -
- 85.84 0.3950 -
- 85.37 0.3951 - kFR 88.57 0.3951 284254291.2
- 88.82 0.3952 301173624.8
- 88.03 0.3953 251146317.4
- 88.76 0.3954 297191692.3
- 87.06 0.3956 201027875.5
- 86.92 0.3957 194700044.3
- 90.39 0.3960 433206721.0 Page 210
“Energy”= Labels PNLT R(k) δtR(k) s ሺ10.ଵே்ೃሺሻሻሺݐߜோሺ݇ሻ
- 89.89 0.3963 386388393.4
- 91.00 0.3967 499415710.9
- 90.08 0.3973 404686358.5
- 89.71 0.3981 372384998.9
- 89.61 0.3992 364914006.0
- 90.21 0.4009 420761559.6
- 91.14 0.4033 524358390.8
- 92.10 0.4066 659427985.6
- 93.68 0.4108 958584572.0
- 94.89 0.4153 1280447955.7
- 95.87 0.4196 1621195835.7
- 97.06 0.4231 2150022601.5 PNLTM 97.40 0.4256 2338845959.1
- 96.23 0.4273 1793630138.6
- 94.73 0.4285 1273358894.6
- 92.30 0.4294 729225824.4
- 88.75 0.4299 322379520.6 kLR 86.96 0.4304 213733335.2
- 85.41 0.4307 -
- 83.88 0.4309 -
- 83.01 0.4311 -
- - Total energy 18276462607.5
- EPNL = 10 log (total energy) – 10 92.61892 403(b) Jet Airplanes [ETM 4.3.2] 403(b)(1) Control of nois e certification computer program software and documentation related to static-to-flight projection processes [ETM 4.3.2.1] 403(b)(1)(A) General [ETM 4.3.2.1.1] Procedures for computer program software control must be developed, approved by the FAA, and maintained and adhered to by each applicant utilizing static-to-flight equivalencies (SFEs).
The procedures must consist of four key elements which, when implemented by the noise certification applicant, will result in documentation which properly describes and valid ates the applicable SFE noise certification computer program and data output. Throughout the development of a given airplane type, adherence to these procedures will enable the tracking of critical computer programs in orde r to verify that the initial software design has not been changed without substantiation.
The four key elements of configuration index, software control plan, design description, and verification process are described in 403(b)(1)(ii).
403(b)(1)(B) Software control procedures — four key elements [ETM 4.3.2.1.2] 403(b)(1)(B)(i) Configuration index [ETM 4.3.2.1.2.1] A configuration index must be established for each unique SFE software system. It will include all applicable elements of the software system and provide historic tracking of documents and software under control. Where appropriate, the index may be maintained in a general database.
403(b)(1)(B)(ii) Software control plan [ETM 4.3.2.1.2.2] A procedure for SFE software change management must be established that includes the baseline design identification, a software change control system and a method of reviewing and auditing software changes and maintaining a status accounting of changes.
Control of software changes must be maintained by establishing baselines within the verification process described below and by documenting modifications to the baseline case that result from program coding changes. Review and auditing procedures will be established within the verificat ion process to allow the validity of the program coding changes for the “modified” configuration to be assessed relative to the “baseline” configuration.
The configuration index must be updated to reflect, historically, the changes made to the software system.
403(b)(1)(B)(iii) Design description [ETM 4.3.2.1.2.3] A technical description of the methods used to accomplish the SFE certification must be provided, including an overview and a description of the soft ware system design to accomplish the t echnical requirements. The software design description should include the program structure, usage of subroutines, program flow control and data flow.
403(b)(1)(B)(iv) Verification process [ETM 4.3.2.1.2.4] The validation process for the SFE software system, or modifications to it, must include a procedure to verify that the calculations described in the documentation are being performed properly by the software. The process may include manual calculations compared to computer output, stepwise graphical displays, software audits, diagnostic subroutines that generate output of all relevant variables associated with the modifications, or other methods to establish confidence in the integrity of the software. The process results must be monitored and tracked relative to software calculation changes.
403(b)(1)(C) Applicability [ETM 4.3.2.1.3] Although the software control plan is applicable to all SFE-specific computer program software and documentation established through the specific procedur es and processes of each applicant, it may not be necessary to review and audit ancillary software such as, but not limited to, subroutines dealing with the sound attenuation coefficients for the effects of atmospheric absorption, noy calculations and tone corrections for each main program source code change.
403(b)(2) Identification of spectral irregularities [ETM 4.3.2.2] Page 212
403(b)(2)(A) Introduction [ETM4.3.2.2.1] Spectral irregularities that are not produced by aircraft noise sources may cause tone corrections to be generated when the procedures of A36.4.3 of part 36 are used. These spectral irregularities may be caused by:
a) the reflected sound energy from th e ground plane beneath the microphone mounted at 4 ft (1.2 m) above it, interfering with the direct sound ener gy from the aircraft (The reinforcing and destructive effects of this interference are strongest at lower fre quencies, typically 100 Hz to 200 Hz and diminish with increasing frequency. The local peaks in the one-third octave spect ra of such signals are termed pseudo-tones; above 800 Hz this interference effect is usually insufficient to generate a tone correction when the part 36 tone correction procedure is used.);
b) small perturbations in the propagation of aircraft noise when analyzed with one-third octave bandwidth filters; or
c) the data processing adjustments such as the background noise adjustment method and the adjustment for sound attenuation due to atmospheric absorption. (In the case of the latter, the sound attenuation coefficients, a, given in Reference T16 ascribe values at 4 kHz to the center frequency of the one-third octave band whereas at 5 kHz the value of “a” is ascribed to the lower pass frequency of the one-third octave. This difference is sufficient in some cases to generate a tone correction).
The inclusion of a tone correction factor in the computa tion of EPNL accounts for the subjective response to the presence of pronounced spectral irre gularities. Tones generated by aircraft noise sources are those for which the application of tone correction factors is appropriate. Tone correction factors that result from spectral irregularities (i.e., false tones produced by any of the causes cited above) may be disregarded. This section describes methods which have been approved for detecting and removing the effects of such spectral irregularities. Approval of the use of any of these methods however remains with the FAA.
403(b)(2)(B) Methods for identifying false tones [ETM 4.3.2.2.2] 403(b)(2)(B)(i) Frequency tracking [ETM 4.3.2.2.2.1] Frequency tracking of flyover noise data is useful for th e frequency tracking of spectral irregularities. The observed frequency of airplane noise sources decreases continuousl y during the flyover due to Doppler frequency shift, fDOPP, where:
݂ை ൌ ଵିெ௦ఒ, where:
— f is the frequency of the noise at source;
— M is the Mach number of the airplane; and — λ is the angle between the flight path in the direc tion of flight and a line connecting the source and observer at the time of sound emission.
Reflection-related effects in the spectra (i.e., pseudo-tones) decrease in frequency prior to, and increase in frequency after, passing overhead or abeam the microphone. Spectral irregularities caused by perturbations during the Page 213
propagation of the noise from the airplane to the microphone tend to be random in nature , in contrast to the Doppler effect. These differing characteristics can be used to separate source tones from false tones.
403(b)(2)(B)(ii) Narrow-band analysis [ETM 4.3.2.2.2.2] Narrow-band analysis with filter bandwidths narrower than those of one-third octave is useful for identifying false tones. For example, when the analysis is produced such that the spectral noise levels at an instance are presented in terms of image intensity on a line, the overall flyover analysis clearly indicates the Doppler-shifted airplane tones and those due to reflection as described above.
403(b)(2)(B)(iii) Microphone mounting height [ETM 4.3.2.2.2.3] Comparison of one-third octave spectra of measurements taken using the 4 ft (1.2 m) high microphone and corresponding data obtained from a neighboring microphone mounted flush on a hard reflecting surface (a configuration similar to that described in A36.4.4 of part 36 or at a height substantially greater than 4 ft (1.2 m), such as 33 ft (10 m), may be used to identify false tones. Changes to the microphone height alter the interference spectra irregularities from the frequency range of data from the 4 ft (1.2 m) high microphone, and when a comparison is made between the two data sets collected at the same time, noise source tones can be separated from any false tones which may be present.
403(b)(2)(B)(iv) Inspection of noise time-histories [ETM 4.3.2.2.2.4] Spectral irregularities which arise following data adjustment as described in this section will occur in the frequency range of between 1 kHz to 10 kHz, and the resulting false t one corrections will normally vary in magnitude between
0.2 dB to 0.6 dB. Time-histories of PNLs and PNLTs, which exhibit constant level differences, are often indicative of the presence of false tone corrections. Supplementary narrow-band analysis is useful in demonstrating that such tone corrections are not due to airplane -generated noise.
403(b)(2)(C) Treatment of false tones [ETM 4.3.2.2.3] When spectral irregularities give rise to false tones that ar e identified by, for example, the methods described in this section their values, when computed according to Step 9 of the tone correction calculation described in A36.4.3 of part 36, may be set to zero.
403(b)(3) Noise data adjustments for tests at high altitude test sites [ETM 4.3.2.3] 403(b)(3)(A) Introduction [ETM 4.3.2.3.1] Jet noise generation is somewhat suppressed at higher altitudes due to the difference in the engine jet velocity and jet velocity shear effects resulting from the change in air density. The use of a high altitude test site for the noise test of an airplane model that is primarily jet-noise dominated should include making the following adjustments. These jet source noise adjustments are in addition to the standard pistonphone barometric pressure adjustment of about 0.3 dB/1000 ft
(0.1 dB/100 m) which is normally used for test sites not approximately at sea level. The jet source noise adjustments are applicable to tests conducted at sites at or above 1200 ft (366 m) mean sea level (MSL).
403(b)(3)(B) Jet source noise adjustment [ETM 4.3.2.3.2] Flight test site locations at or above 1200 ft (366 m) MSL, but not above 4000 ft (1219 m) MSL, may be approved Page 214
provided certain criteria are met (see Figure 46) and the source noise adjustments are applied.
Alternative criteria or adjustments require the approval by the FAA.
403(b)(3)(B)(i) Criteria [ETM 4.3.2.3.2.1] Jet source noise altitude adjustments are required for each one-half-second spectrum when using the integrated procedure and, for the PNLTM spectrum, when using the simplified procedure (see A36.9.3 and A36.9.4 of part 36) and are to be applied in accordance with the criteria described in Figure 46.
B17 B23 B27 100% 100% 0% 0% Applied correction Applied correction 60 90 120 150 Acoustic angle — degrees Integrated method Simplified method One-third octave frequency band number Figure 46. Criteria for jet source noise correction 403(b)(3)(B)(ii) Adjustment procedures [ETM 4.3.2.3.2.2] An acceptable jet source noise adjustment is as follows:
a) adjust each one-half-second spect rum or PNLTM one-half-second spectru m, as appropriate, in accordance with the criteria of 403(b)(3)(ii)(A) by using the following equation:
ΔSPL = [10 log (dR/dT) + 50 log (cT/cR) + 10k log (uR/uT)] [F1] [F2] w h e r e :
— subscript T denotes conditions at the actual airplane test height above MSL under standard atmospheric conditions (i.e., ISA + 18°F (ISA + 10ºC) and 70 percent relative humidity);
— subscript R denotes conditions at the airplane refe rence height above MSL (i.e., airplane test height above MSL minus the test-site altitude) under standard atmospheric conditions (i.e., ISA + 18°F (ISA + 10ºC) and 70 percent relative humidity);
— SPL denotes sound pressure level;
— dR is the density for standard atmosphere at the airplane reference height in lb/ft3 (kg/m3) ;
— dT is the density for standard atmosphere at the airplane test height in lb/ft3 (kg/m3);
— cR is the speed of sound corresponding to the absolu te temperature for a standard atmosphere at the airplane reference height in ft/s (m/s) — cT is the speed of sound corresponding to the absolu te temperature for a standard atmosphere at the airplane test height in ft/s (m/s) Page 215
— k = 8, unless an otherwise empirically derived value is substantiated;
— u = (ve – va) is the equivalent relative jet velocity in ft/s (m/s);
w h e r e :
— ve is the equivalent jet velocity as defined in Appendix C of Reference T12 and obtained from the engine cycle deck in ft/s (m/s);
— va is the aircraft velocity in ft/s (m/s);
— uR is the equivalent relative jet velocity in ft/s (m/s) where ve is determined at N1C TEST for standard atmosphere at the airplane reference height;
— uT is the equivalent relative jet velocity in ft/s (m/s) where v e is determined at N1C TEST for standard atmosphere at the airplane test height;
— N1C is the corrected engine rpm ܰଵ/√ߠ௧ଶ;
— F1 is a factor corresponding to the percentage of applied adjustment related to acoustic angle in Figure 46 (values range from 0.00 to 1.00); and — F2 is a factor corresponding to the percentage of applied adjustment related to the one-third octave band in Figure 46 (values range from 0.00 to 1.00);
b) for each one-third octave band SPL, arithmetically add the height jet noise adjustment in 403(b)(3)(ii)(B)
a)to the measured SPLs to obtain the altitude jet source noise adjusted SPLs for the derivation of PNL described in A36.4.1.3 a) of part 36; and
c) the height adjustment is to be applied to all measured test data including approach conditions unless it can be substantiated that the jet noise during approach does not contribute significantly to the total aircraft noise.