0 10 20 30 40 50 –7 kt +7 kt 60 70 80 90 100 –800 –600 –400 –200 0 200 400 600 Flight track position (m) Aispeed (kt) 10-dB down period V is the reference airspeed at X 0 0 Potential X d0 efinition points x = ½ at + V t + V = at + V 2 0 0 X0 Overhead of flight track microphone Figure 52. Example of a reference airspe ed profile versus flight track position for a constant deceleration from 80 kt to 50 kt at 1 kt/s Page 257
0 10 20 30 40 50 60 70 80 90 100 –20 –15 –10 –5 0 5 10 15 20 Time (s) [= 0 seconds at overhead] –7 kt +7 kt Aispeed (kt) Overhead of flight track microphone 10-dB down period Constant deceleration = linear airspeed profile Figure 53. Example of a reference airspeed profile versus time for a constant deceleration from 80 kt to 50 kt at 1 kt/s 801(c) Reference Conditions [ETM 8.1.3] 801(c)(1) General [ETM GM No. 1 ATT H 2.3] Flight procedures designed to represent normal or noise abatement operations can vary from simple fixed flight path and airspeed procedures similar to noise certification test conditions to complex non-constant flight path and/or nonconstant airspeed procedures. The resulting reference flight procedures and data adjustment procedures should be submitted to the FAA for approval.
The primary reference test conditions that affect adjustments to the noise data are the reference atmospheric conditions, the reference helicopter flight path, and the reference helicopter airspeed. For acquiring noise data for LUP purposes, the reference atmospheric conditions should be the same as those specified in H36.3(a) and J36.3(a) of part 36.
In the process of developing flight profiles for LUP and noise abatement procedures, a reference flight path and/or reference airspeed procedure may not have been determined prior to obtaining a set of noise data suitable for LUP purposes. In such cases, the flight path and airspeed test data may be used to derive appropriate reference values. The method used should be approved by the FAA.
801(c)(2) Predefined co nstant flight path and constant airspeed [ETM GM No. 2 ATT H 2.3] If a predefined reference constant flight path and constant speed conditions similar to, but different from, those defined for noise certification testing under Appendix H of part 36 are used, the same adjustment procedures defined in Appendix H can be used with the new reference conditions substituted in the adjustment procedures as appropriate and the adjustment procedures modified as necessary to give results in terms of adjusted sound exposure level, L AE, and any other metrics selected by the applicant.
801(c)(3) Derived cons tant flight path [ETM GM No. 3 ATT H 2.3] If a reference flight path is not predefined, a reference path needs to be derived or otherwise determined from the flight test data. One method to define the reference path is to determine the mean of the test runs by calculating the path of each test run using a least-squares linear fit of the aircraft position data, defined in terms of X, Y and Z coordinates, between the 10 dB-down points and averaging the calculated results.
An example is the case where, as a result of flight testing multiple glide slopes, a fixed glide slope approach is deemed appropriate for pilot acceptability. If the selected flight path is repeated as necessary to obtain a statistically valid set of noise levels, the flight path data can be averaged to define the reference flight path.
801(c)(4) Derived constant airspeed [ETM GM No. 4 ATT H 2.3] If the reference airspeed, V r, is not predefined, a value of V r needs to be derived or otherwise determined from the measured data. One method to define V r is to determine the mean of the test runs by averaging the true airspeeds (TAS) of each test run that meets the test window criteria.
An example of this is the case where the sensitivity of noise level with airspeed and rate of descent is of interest. The test program might incrementally test a range of fixed IAS for one or more rates of descent, with the reference airspeed for a LUP flight profile subsequently defined after the flight test program.
For the special case of determining Vr for the flyover condition when using the equivalent Mach number method (see section 10 of 401(h)(8), 402(c)(2)(B) and J36.105(c) of this AC) to adjust for source noise, a separate method is described in 801(c)(7).
Note.— The reference ground speed, VGr, can be derived from true airspeed data since, by definition, the true airspeed and ground speed are identical for the zero wind reference condition.
801(c)(5) Multi-segmented flight path conditions at constant airspeed [ETM GM No. 5 ATT H 2.3] This guidance applies to multi-segmented approach profiles at a single constant reference airspeed, with each segment having a different reference descent angle or level flight condition.
Note.—An alternative procedure for supplying LUP data for multi-segmented flight profiles at constant airspeed is possible by combining segm ents from constant profile data sets. The applicant should be aware, however, that directivity effects can be important in propagating acoustic data to the flight paths for each segment, necessitating the use of additional microphones to provide greater geometric resolution of the recorded noise data.
801(c)(6) Guidance for mult i-segmented flight paths with climb segments [ETM GM No. 6 ATT H 2.3] (Reserved) Page 259
801(c)(7) Non-constant airspeeds and/or flight path conditions [ETM GM No. 7 ATT H 2.3] (Reserved) 801(c)(8) Approaches with constant deceleration and flight path conditions [ETM GM No. 8 ATT H 2.3] The deceleration phase of the reference flight profile should span the entire 10 dB-down period for each of the noise certification measurement points as illustrated in Figure 52 and Figure 53. If not, the reference approach procedure should not be treated as a single flight segment. It is also advisable that the deceleration phase be initiated as close as possible to the start of the 10 dB-down period in order to ensure that the airspeed is as close as possible to the reference airspeed at the first 10 dB-down point. This will be useful in minimizing the potential effects of wind on meeting both airspeed tolerance requirements.
Note.— Practice flights may be advisable to establish and/o r confirm a reference flight profile that meets these criteria.
If a reference deceleration or airspeed schedule is not predefined, its value needs to be derived or otherwise determined from the measured data. One method to de fine reference deceleration or airspeed schedule is to determine the mean of the test runs by averaging the deceleration or airspeed profile of each test run that meets the test window criteria.
801(c)(9) Other non-constant airspeed s and/or flight path conditions [ETM GM No. 9 ATT H 2.3] (Reserved) 802 EQUIVALENT PROCEDURES INFORMATION [ETM 8.2] (Reserved) 803 TECHNICAL PROCEDURES INFORMATION [ETM 8.3] 803(a) Adjustments to Reference Conditions [ETM 8.3.1] 803(a)(1) Constant airspeed and flight path conditions [ETM GM No. 10 ATT H 2.3] Helicopter noise data acquired for constant airspeed and f light path conditions are typically adjusted to reference conditions using standardized procedures such as provided in Appendices H and J of part 36.
803(a)(2) [Measurements processed using th e procedures of Appendix J of part 36 [ETM GM No. 11 ATT H 2.3] The following adjustments to noise data assume corrected as-measured one-third octave and aircraft position time history data and are available in Appendix J of part 36.
Note.— Corrected as-measured noise data are data corrected as per the requirements of A36.3.9 and A36.3.10 of part 36.
If a reference flight condition with a fixed flight path and/ or fixed airspeed different from those defined for noise certification testing under Appendix H of part 36 is measured, the same data adjustment procedures defined in Appendix H of part 36 can be used with the new referenc e conditions substituted in the adjustment procedures as appropriate and the adjustment procedures modified as necessary to give results in terms of sound exposure level (LAE) and any other metrics selected by the applicant.
The adjustments to be applied to time-integrated noise metrics (e.g., LAE or EPNdB) should include:
a) band-sharing correction for tone corrected metrics such as EPNL;
b) 1 adjustment for sound attenuation;
c) 2 duration adjustment for time-integrated metrics; and
d) 3 source noise adjustment for Flyovers.
Note.— The band-sharing correction, the 1 adjustment and the 3 adjustment should also be applied, as appropriate, to the maximum noise level (e.g., PNLTM, LAmax) if the value is to be published.
1 can be calculated for LAE and LAmax as follows:
a) determine the aircraft position at the time that the noise at L Amax was emitted and the slant range to the microphone diaphragm;
b) determine the reference aircraft position based on the reference flight path and th e reference slant range to the microphone diaphragm;
c) calculate a new reference L Amax from the one-third octave spectrum as adjusted using the equation in H36.205(f) of part 36;
d) calculate 1 by subtracting the test LAmax from the reference LAmax as in H36.205(f) of part 36.
Note 1.— Use of the 1 adjustment derived for EPNL and PNLTM is acceptable for application to LAE and LAmax noise data.
Note 2.— If the temperature and humidity meteorological conditions are within the zero attenuation adjustment window, the reference and test slant ranges may be replaced by the reference and test distances to the helicopter when the helicopter is over the center noise measuring point (see 402(c)(2)(A) of this AC). This assumes that the measurement points are the same or close to the locations used for noise certification testing, and the aircraft slant ranges are similar to those seen during noise certification testing. If additional measurement points are used that are significantly further from the flight path, consideration should be given to the increased error that is inherently added by the increased distances.
The 2 adjustment is applied only to time-integrated noise metrics. The measured and reference distance values used in determining 1 adjustments to the test data may be used to determine the distance term of the 2 adjustment.
An example of calculating 2 for LAE is:
a) determine a mean ground speed, V G, for each test run;
b) if a reference ground speed, V Gr, has not been predefined, determine a reference ground speed from the test results to be used as VGr in the 2 adjustment; and Page 261
c) calculate 2 as in H36.205(g) of part 36 from the slant ranges determined from the 1 adjustment procedure, mean ground speed, VG, of the test run, and the reference ground speed, VGr.
During noise certification testing, an accepted source noise adjustment procedure for flyovers is the method described in H36.205(e) of part 36. This adjustment is normally made using a sensitivity curve of the maximum PNLTM versus main rotor advancing blade tip Mach number. For time-integrated metrics other than EPNL, the corresponding maximum noise metric should be used in place of PNLTM.
An alternative method, the equivalent Mach number test procedure, is to calculate an adjusted reference true airspeed based on the pre-selected reference airspeed and/or test airspeed and the test-day outside air temperature (see 401(h)(7), section 10 of 401 (h)(8), 402(c)(2)(B) and AMC J36.105(c) of this AC). Either method is acceptable for adjusting flyover data for LUP purposes at other speeds when the reference airspeed is known beforehand.
Note.— Use of the source noise adjustment derived for EPNL and PNLTM is acceptable for application to LAE and LAmax noise data.
For some flyover tests without a predefined reference airspeed, Vr, for which the equivalent Mach number method is intended to be used, test runs may be flown at selected airspeeds without first adjusting the airspeed for test-day outside air temperature. In this case, the reference airspeed, V r, may be derived from the test data so that it includes the adjustment for source noise. This can be achieved by the following process:
a) calculate a main rotor advancing tip Mach number, M T, for each test run from the test true airspeed, VT, the main rotor blade tip rotational speed, V TIP, and the speed of sound, c T, calculated from the on-board measurement of outside air temperature:
ܯ் ൌ ்ܸ ܸ ்ூ்ܿ
b) calculate the mean of the test Mach numbers;
c) set the reference Mach number, M R, equal to the mean of the test Mach numbers;
d) calculate V r from the reference Mach number, M R, the main rotor blade tip rotational speed, V TIP, and the speed of sound, c, at 25C (77F):
ܸ ൌܿ ሺܯோሻ െܸ ்ூ; and
e) calculate the adjusted reference airspeed V ar and 2 for each test run as in the normal manner (see 401(h), section 10 of 401(h)(8) of this AC of and H36.205(g) and J36.205(c) of part 36).
Note.— A value of Vr can be selected that is different from that calculated above, with Var adjusted accordingly, as long as each test run used to determine the mean noise level for the chosen Vr is within the test window for airspeed.
803(a)(3) Measurements processed using the procedures of Appendix J of part 36 [ETM GM No. 12 ATT H 2.3] Note 1.— Appendix J applicants are encouraged to record the sound pressure signals and/or one-third octave data and, if possible, aircraft position time-history data in addition to the requirements of Appendix 4 of the Annex.
This will enable additional analysis and provision of data, including additional sound metrics.
Note 2.— In addition to the center microphone required by Appendix J, applicants should give consideration to acquiring data using two additional measurement points symmetrically disposed at 492 ft (150 m). The adjustments Page 262
in this section can be applied to the noise levels measured at those locations. This requires the calculation of the slant range distance from the aircraft position at the overhead point to the sideline location.
The following adjustments assume corrected as-measured data obtained from an integrating sound level meter and aircraft position at the overhead point and are available in Appendix J of part 36. When as-measured one-third octave data are used to calculate LAE, the method described in 803(a)(2) can be used if aircraft time-history position data are also available.
Note.— Corrected as-measured noise data are data corrected as per the requirements of J36.109(d)(ii) of Appendix J of part 36.
The adjustments to be applied to time-integrated noise metrics (e.g., LAE) should include:
a) 1 adjustment separated into spherical spreading and duration terms (see example below); and
b) 2 adjustment.
Note 1.— The separation of the 1 adjustment into spherical spreading and duration terms is based on the terms specified in Appendix 2 of the Annex.
Note 2.— The spherical spreading term of the 1 adjustment should be applied to the maximum noise value (e.g., LAmax) if the value is also to be provided.
An example of calculating 1 is:
a) determine the slant range distance, SR , from the aircraft to the microphone using the measured aircraft height, H, when the helicopter is over the center noise measur ing point; for the flight track microphone, SR will equal H;
b) determine the reference slant range, SR REF, to the microphone using the reference flight path; and
c) calculate spherical spreading term of 1SS as follows:
1SS = 20 log (SR/SRREF) The duration term of the 1 adjustment need be applied only to the time-integrated metric and is calculated as follows:
1D = –7.5 log (SR/SRREF) The 2 adjustment need be applied only to the time-integrated noise metric. For flyovers, the equation described in J36.205(c) of part 36 for J3 and reproduced here should be used to calculate 2.
2 = 10 log (Var/Vr) where Var is the adjusted reference true airspeed.
To calculate the 2 adjustment for takeoff and approach flight conditions, the ground speed of each test run is required.
However, Appendix J of part 36 requires measurement of the ground speed, V G. If each test run is performed with a headwind component, then it is considered acceptable that a 2 adjustment need not be calculated. Note, however, that the resulting noise level will be higher than if adjusted. If ground speed is measured, then 2 should be calculated using the following equation:
2 = 10 log (VG/Vr) Page 263
where Vr is predefined or calculated as in 801(c)(7).
803(a)(4) Multi-segmented flight path conditions at constant airspeed [ETM GM No. 13 ATT H 2.3] Because of the multiple flight segments, determination of Q r to define a Q rKr distance may not be feasible.
Alternatively, if QrKr cannot be located on the reference flight profile, the minimum distances to the test and reference flight profiles can be used to approximate the ratio of Q rKr to QK in determining the 1 and 2 adjustments. The determination of minimum distances should be made to ensure that the adjustments to data are based on distances from the corresponding flight segment on both the test and reference profiles.
803(a)(5) Non-constant airspeed and flight path conditions [ETM GM No. 14 ATT H 2.3] (Reserved) 803(a)(6) Approaches with constant deceleration and flight path conditions [ETM GM No. 15 ATT H 2.3] If a predefined constant reference flight path equivalent to or similar to that defined for noise certification testing under Appendix H is used, the 1 adjustment and the first (distance) component of 2 adjustment defined in Appendix H of part 36, can be used with:
a) the new reference conditions substituted as appropriate; and
b) the adjustment procedures modified as necessary to give results in terms of adjusted sound exposure level, LAE, and any additional metrics selected by the applicant.
For the constant reference airspeed conditions of noise certification under Appendix H of part 36 the second term of the 2 adjustment uses a ground speed ratio to effect a duration adjustment to the measured noise levels. Because the reference airspeed is constant, this ground speed ratio is a time ratio. With a non-consta nt reference airspeed due to deceleration, however, a single reference ground speed is not available and the second term of the 2 duration adjustment is better determined directly from reference and test-time deltas defined for each test run. In this case, the 2 adjustment is modified to:
Δ2 = –7.5 log (QK/QrKr) + 10 log (Δtr,j / ΔtT,j) where tr,j is the reference flight path time interval between the test run 10 dB-down time points and tT,j is the test time interval of the 10 dB-down period for test run j.
Times for the first and last 10 dB-down points on the reference profile can be determined by the following procedure:
a) distance along the reference flight profile can be represented by:
Xr = ½ at2 + V0t + X0, where a is the reference deceleration, V0 is the reference airspeed at X0, and X0 is the selected reference flight track coordinate, typically at the initiation of the deceleration, overhead of the flight track microphone, or at the termination of the deceleration;
b) for each measurement point for each test run, j, time t can be incremented until the calculated X r coordinate agrees with the X T coordinates of the first and last 10 dB-down points to determine the corresponding times on the reference flight profile; alternatively, the solution to the quadratic equation Page 264
can be used to directly calculate tfirst and tlast as a function of x, i.e.:
ݐൌ െܸ √ ܸଶ െ4 ሺ 12ܽሻሺܺ െݔ ሻ 2ሺ 12ܽሻ
c) tr,j is then given by the difference between these two time values.
803(a)(7) Other non-constant airs peed and flight path conditions [ETM GM No. 16 ATT H 2.3] (Reserved) Page 265
Chapter 9 GUIDELINES FOR AIRCRAFT RECERTIFICATION TO STAGE 4 and 5
CHAPTER TABLE OF CONTENTS
901 INTRODUCTION266
902 ASSESSMENT CRITERIA267
902(a) General267
902(b) Recertification from Stage 3 to Stage 4 or Stage 5267
902(c) Recertification from Stage 2 to Stage 4 or Stage 5270
902(d) Recertification from Part 36, Stage 3 to Stage 4 or Stage 5270
903 RECERTIFICATION GUIDELINES FOR “MODIFIED”AIRPLANES271
903(a) Operational Limitations271
903(a)(1) Flap deflection271
903(a)(2) Propeller speed272
903(a)(3) Maximum authorized takeoff and landing weight272
903(a)(4) Takeoff thrust de-rate272
903(b) Demonstration Methods272
903(b)(1) Demonstration of lateral noise measured at 650 m272
903(b)(2) Center of gravity position during takeoff272
901 INTRODUCTION [ETM 9.1] Although the procedures described in this Chapter were developed for recertification to Stage 4 from its original certification, they are equally acceptable for recertification to Stage 5 from its original certification.
In other words recertification to Stage 4 also mean s recertification to Stage 5 if its noise limits and supplementary requirements are met. Recertification using the pro cedures in this Chapter is acceptable because there were no substantial procedural modifica tions to Part 36 between Stage 4 (Amendment 24) to Stage 5 (Amendement 31) that will influence the certification noise level.
Recertification is defined as the “Certification of an aircraft , with or without revision to noise levels, to a Standard different to that which it had been originally certificated”. The recertification of helicopters and light propeller-driven airplanes to a different Standard from that to which they were originally certificated is not considered.
In the case of an airplane being recer tificated to part 36, amendment 36-24 an d later, noise recertification should be granted on the basis that the evidence used to determine co mpliance is as satisfactory as the evidence expected of a new type design. In this respect the date used by the FAA to determine the recertification basis should be the date of acceptance of the first application for recertification.
Section 902 of this chapter addresses the assessment of existing approved noise levels associated with applications for the recertification of an airplane to Stage 4 or Stage 5. Section 903 includes guidelines for the recertification to Stage 4 of airplanes specially “modified” in order to achieve compliance with Stage 4 or Stage 5. The appropriate process for determining the compliance of a recertificated aircraft with a new standard should be determined by the aircraft’s certification noise levels and the associated substantiation documents. A flow chart describing the process for the recertification of subsonic jet airplanes from Stage 3 to Stage 4 or Stage 5 is presented in Figure 54. In the application of these recertification guidelines, existing arrangements be tween certificating authorities should be respected. It is expected that bilateral arrangements will facilitate the mutual recognition between authorities of approvals granted in accordance with the guidelines recommended in this AC.
902 ASSESSMENT CRITERIA [ETM 9.2] 902(a) General Sections 902(b) and (d) are concerned with the assessment of existing approved noise levels associated with applications for the recertification of an airplane from Stage 3 to Stage 4 or 5 under part 36. Section 902(c) is concerned with the recertification of an airplane from Stage 2 to Stage 4 or 5 under part 36.
In applying the assessment criteria of each section, if the ap plicant is able to answer in the affirmative, to the satisfaction of FAA, all the questions that may be relevant then reassessment is not required. The existing approved Stage 3 noise levels of the airplane should be used to determine compliance with the new standard. Otherwise, in order to satisfy the requirements of FAA, the applicant may propose additional analysis or data. Such analysis may lead to an adjustment being applied to the existing approved Stage 3 noise levels. Applicants, at their discretion, may elect to provide new test data in place of, or in addition to, the analysis.
Note.— The FAA’s assessment of the suitability of the existing approved noise levels for compliance with the requirements of Stage 4 or Stage 5 will include a review of any equivalencies proposed by the applicant to meet the assessment criteria.
902(b) Recertification from Stage 3 to Stage 4 or Stage 5 [ETM 9.2.2] Noise levels already approved for compliance with Stage 3 and submitted in support of applications for recertification of existing aircraft should be assessed against the criteria presented in this section. These criteria have been developed to ensure satisfactory compliance with the new standard. The criteria consist of a list of simple questions concerning the manner in which the original Stage 3 data were obtained and subsequently processed. The questions are the result of a comparison of the various amendments and revisions to part 36, and to this AC to which an aircraft’s existing Stage 3 noise levels may have been approved.
For airplanes that were approved with Amendment 36-24 or later, a reassessment is not required. The airplane’s existing approved Stage 3 noise levels should be used to determine compliance with Stage 4 or Stage 5.
For airplanes that were approved in accordance with Amendment 36-23 or earlier, the applicant is required to show that the existing approved Stage 3 noise levels are equivalent to those approved to Amendment 36-24 by answering the following questions. Unless otherwise noted, section references refer to Amendment 36-24 to part 36.
For all airplanes:
a) Was full takeoff power used throughout the reference f light path in the determination of the lateral noise level? (See B36.3(a) of part 36, Amendment 36-24.)
b) Was the “average engine” rather than the “minimum engine” thrust or power used in the calculation of the takeoff reference flight path? (See B36.7(b)(1) of part 36, Amendment 36-24.)
Note.— The applicant may demonstrate compliance with Stage 4 or Stage 5 requirements by determining the lateral and flyover noise levels by adding a delta dB corresponding to the difference between the average and the minimum engine, as derived from approved NPD data based on the airplane performance changes due to this difference.
c) Was the “simplified” method of adjustment defined in A36.9.3 of part 36, used, and if so, was –7.5 used as the factor in the calculation of the noise propagation path duration correction term? (See A36.9.3.3.2 of part 36, Amendment 36-24.)
d) Was the takeoff reference speed between V 2 + 10 kt and V2 + 20 kt? (See B36.7(b)(4) of part 36, Amendment
36-24.)
Note.— The takeoff reference speed used to demonstrate compliance with Stage 4 requirements must meet the requirements of B36.7(b)(4) of part 36, Amendment 36-24.
e) Was the four half-second linear average approximati on to exponential averaging used and, if so, were the 100 percent weighting factors used? (See A36.3.7.5 of part 36, Amendment 36-24.)
Note.— The applicant is required to demonstrate compli ance with the requirements of A36.3.7.5 of part 36, through Amendment 36-24, which equates to an exponential averaging process for the determination of SLOW weighted sound pressure levels. Simulated SLOW weighted sound pressure levels may be obtained by using one of the two equations described in A36.3.7.5 of part 36 through Amendment 36-24, as appropriate, or by other methods as approved by the FAA.
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