of the adjusted static engine conditions: 1.e., sound propagation distances, and the approved NPD airspeed. In normalizing to these conditions, the following effects should be accounted for:
- spherical divergence
- atmospheric absorption, and
- airspeed. Airframe noise for a given configuration varies with velocity as follows:
A SPLairframe = 50 Log - NPD TEST where: VIEST is model or measured airspeed 'NPD Is approved NPD airspeed This equation is also valid for adjustments to EPNL where an empirically derived coefficient replaces the coefficient 50 since this value may be somewhat configuration dependent. However, FAA approval should be obtained for values other than 50.
h. Extrapolation to Airplane Flight Path. When computing noise levels corresponding to the slant distance of the airplane in flight from the noise measuring point, the principal effects are spherical divergence (inverse square law adjustments from the nominal static distance) and atmospheric attenuation, as described in sections A36.9 and A36.11 of Part 36. Further, account should be taken of the difference between the static engine axis and that axis in flight relative to the reference noise measuring points. The adjustments should be applied to the component noise source levels that have been separately identified.
1. Total Noise Spectra. Both the engine tonal and broadband noise source components in flight, as discussed earlier, together with the airframe noise and any installation effects, are summed on a mean-square pressure basis to construct the spectra of total airplane noise levels.
(1) During the merging of broadband and tonal components consideration should be given to appropriate bandsharing of discrete frequency tones.
(2) The effects of ground reflections should be included in the estimate of freefield sound pressure levels to simulate the sound pressure levels that would be measured by a microphone at a height of 1.2 m above a natural terrain. Information in SAE AIR 1672B-1983 may be used to apply adjustments to the freefield spectra to allow for flight measurements being made 1.2 m (4 ft). Alternatively, the ground reflection correction can be derived from other approved analytical or empirically derived models. Note that the Doppler correction for a static source at frequency static applies Chap 3 36 Par 18
(3) With regard to lateral attenuation, information in SAE AIR 1751-1981 applicable to the computation of lateral noise may be applied.
The process in this section is repeated for each measurement angle and for each engine power setting.
For EPNL calculation, a time should be associated with each extrapolated spectrum along the flight path by adjusting the measured data to the approved NPD reference conditions and the distance to the flight path. (NOTE: A time should be derived from each measurement location with respect to engine centerline and the airplane's true airspeed along the reference flight path assuming zero wind.) For each power setting and array of minimum distances, an EPNL should be computed from the projected time history using the methods described in Part 36, Appendix B. To reduce the influence of random spectral irregularities the tone corrections provided in Appendix 4 of this AC may be used to meet the requirements of Part 36, Appendix B.
k. Noise Increment Computations. An NPD plot can be constructed from the projected static data for both the original and changed versions of the engine or nacelle tested. Comparisons of the noise vs. power relationships for the two configurations at equivalent minimum distances, should determine whether the changed configuration resulted in an acoustic change. If there is an acoustic change, or 1f a new NPD is requested, the data applicable to the changed configuration should be developed from the static data projected to flight conditions plus the approved residual. This residual can be developed from the difference between flight data and static data for the flight configuration projected to flight. This residual has been limited to 3 decibels.
19. SUPPLEMENTAL FLIGHT TESTS. Supplemental flight testing has been found adequate for some type changes. An acceptable compliance plan may be developed by considering the technical items of paragraph 15 in conjunction with the flight test procedures outlined in Chapter 2 of this AC.
Additionally, consideration should be given to the effects the change in type design will have on the noise level at each of the Part 36 reference locations. Data should be acquired, analyzed, and normalized using the procedures described in Chapter 2, Noise Demonstration Flight Tests. The computation of noise increments, the development of the changed version NPD, computation of confidence intervals, and evaluation of the changed version noise levels can be made using procedures similar to those outlined in paragraph 17 of this AC for static tests.
20. SUPPLEMENTAL ANALYSES. Approved analytical procedures may be acceptable for demonstrating compliance with Part 36 for airplanes resulting from a change in type design. Depending upon the effect the change in type design will have on the basic airplane noise source characteristics, certification noise levels may be derived directly from the existing NPD, from an analytical extension of the existing NPD, or by supplementing the existing NPD with noise data derived by analytical modeling of the noise components.
Chap 3 Par 18 37
AC 36~4B 3/23/88 Noise Increments Derived from an Approved NPD. For type changes which retain the same basic noise source characteristics, certification noise levels may be derived directly from the approved NPD using the methods in paragraph 14(e) (2) of this AC.
(1) Example Applications.
(a) Weight increase or decrease from the originally certificated airplane weight, for both takeoff and approach.
(b) Engine power increase or decrease.
(c) Airplane changes that could indirectly affect noise levels because of an impact on airplane performance (increased drag for example).
(2) Extension of the Approved NPD. For the type change examples above, certification noise levels may be derived from the approved NPD provided the reference aerodynamic performance is within the limits of the approved NPD. For cases where the reference aerodynamic performance (e.g., engine power) is beyond the 11mits of the approved NPD, the NPD may be extended within approved limitations. Among the items which should be considered in extension of the NPD are:
(a) the 90 percent confidence interval at the extended power;
(b) airplane/engine noise source characteristics and behavior;
(c) engine cycle changes; and
(d) quality of data to be extrapolated.
Analytical Modeling of Noise Components. Analytical procedures may be considered when validated by test data to demonstrate limited changes to the basic airplane noise source characteristics or to demonstrate no acoustical change. For type design changes, such as engine or nacelle redesign and acoustic lining changes, a validated analytical noise model may be used to derive predictions of noise increments within approved limitations. The analysis may consist of modeling each airplane component noise source and projecting these to flight conditions in a manner similar to the static test procedures described in paragraph 18 of this AC.
(1) Airplane Noise Components. A model of detailed spectral and directivity characteristics for each airplane noise component may be developed by theoretical and/or empirical analysis. Each noise component should be correlated to the parameter (s) which relates to the physical behavior of the source mechanisms. The source mechanisms, and subsequently the correlating parameters, should be identified through use of other supplemental tests such as engine or component tests.
Chap 3 38 Par 20
AC 36—4B 3/23/88 Projection of Airplane Component Noise Sources to Flight As described in paragraph 18, an EPNL representative of flight conditions should be computed by adjusting the airplane component noise source for motion, number of engines and shielding, reconstructing the total noise spectra and projecting the total noise spectra to flight conditions by accounting for propagation effects. In some cases adjustments for additional effects on the component noise sources may be required. For example, the effect of changes in acoustic treatment, such as nacelle lining, may be modeled and applied to the appropriate component noise sources.
(3) Noise Increment Computations. The computation of noise increments, the development of the changed version NPD, and evaluation of the changed version certification noise levels should be made using the procedures in paragraph 18(k). The validity of the resulting data base should be determined using an approved methodology. Guidance on confidence interval computations is provided in Appendix 5 of this AC.
21. SUPPLEMENTAL COMPONENT TESTS. Full scale or scale models of components of production hardware can be acoustically tested in a controlled laboratory environment such as a flow duct transmission loss facility, an anechoic chamber or a wind tunnel. Results from scale model component tests should be adjusted to full scale conditions using approved procedures. An example use of approved laboratory facilities is the determination of noise increments, resulting from changes in nacelle acoustic lining, in flow duct transmission loss facilities. These noise increments should be determined by applying the laboratory measured attenuation spectral differences to the measured one-third octave band flight levels.
22. METHODS FOR DEMONSTRATING NO ACOUSTICAL CHANGE. Several noise demonstration methods have previously been limited to use in demonstration of no acoustical change (defined in FAR 21.93(b)). These methods include analytical noise component models and component tests, and the use of noise units other than EPNL, where appropriate, to determine relative differences.
Approval of these methods has previously been confined to no acoustical change demonstrations. For demonstration of no acoustical change, the applicant is not precluded from use of either a noise demonstration flight test or other supplemental noise demonstration methods described in this AC.
Chap 3 Par 20 39 (anđ 40)
CHAPTER 4. DOCUMENTATION REQUIREMENTS
23. GENERAL. Documentation 18 a vital part of the noise certification process. A clear and concise record is necessary detailing where, how, and what tests were conducted, the data analyzed, and the results obtained. Good communication between the applicant and the certificating authorities before, NOISE COMPLIANCE DEMONSTRATION PLAN. At a minimum, a typical noise certification compliance demonstration plan should contain the information shown in the outline below. While the outline covers all types of noise demonstration methods described in the AC, a particular plan should address only those items of interest to an applicant. The plan should list equivalencies anticipated to be needed along with supporting documentation.
NOTE: All plans must be FAA approved and all equivalencies must be identified and any new equivalency not addressed in this AC must be submitted for approval.
a. Introduction. Address planned certification action.
b. Test Item. Airplane, complete with engine and nacelle description, weights, flaps, etc.
c. Type of Noise Demonstration Method.
(1) Noise Demonstration Flight Test.
(2) Supplemental Methods.
(a) Static Test
(b) F11ght Test
(c) Analys1s
(d) Component Test
d. Test Description. Highlights of the planned test should be noted and any deviations from the procedures described in Part 36 should be identified.
Data Acquisition Systems. Type and model of hardware and any deviations from the hardware and procedures described in Part 36 and this AC should be noted.
f. Data Analyses and Normalization Procedures. Highlights of the hardware and methods to be used should be noted. Also any deviations from the procedures described in Part 36 and this AC should be identified. The applicant's reference conditions also should be identified.
Equivalencies. All "equivalent procedures" to be considered in this certification should be identified. Any new equivalencies submitted for FAA approval should be supported with adequate engineering analyses and/or test Chap 4 Par 23 41
data. Requests for approvals of equivalencies should be submitted in a timely manner to provide for review by both regional and AFE personnel. Generally, this takes 30 to 60 days, depending upon the engineering complexity of the proposal.
25. NOISE CERTIFICATION COMPLIANCE REPORT. At a minimum, typical noise certification reports should contain the information shown in the outline below (as applicable to the configuration being certified). It is likely that there will be more than one report for a basic airplane with several derivative configurations.
a. Introduction. Define applicable requirements of Part 36 under which noise certification 18 requested.
b. Airplane, Engine, and Nacelle Descriptions. Provide the gross dimensions of the airplane (including the engine locations), descriptions of the engine and nacelle acoustic treatments, landing and takeoff weights, thrusts, and flap settings.
c. Airplane Performance at Reference Conditions. For the reference aerodynamic configuration (e.g., airplane weight, flap setting, etc.) provide the aerodynamic performance necessary to derive the certification noise levels. At a minimum, this includes power, height, and airspeed.
d. Certification Noise Levels. For the reference aerodynamic configuration, provide the certification noise levels and the applicable noise limits for each of the three Part 36 measurement locations.
e. Noise Certification Test Results. Provide details on the results of tests and analyses which demonstrate compliance with the applicable requirements of Part 36. The following information should be reported.
(1) Noise Demonstration Method. A description of the type of noise certification demonstration method used.
and serial numbers of the airplane and engine used in the test. (2) Test Airplane, Engine and Nacelle Descriptions. The type, model
(3) Test Description and Resultant Measurements. A summary of the representative examples of the acquired data. the noise, airplane position and performance, and meteorological data, and conduct of test, the type of equipment used for measurement and analysis of ground cover description, microphone locations, and any events interfering with sound measurements. (a) Test Site Description - The test site location, terrain and temperature and relative humidity. (b) Meteorological Data - Wind speed and profiles of ambient air gross weight, airspeed, power, and the position over the test range. (c) Airplane Position and Performance - Airplane configuration, 42 Chap 4 Par 24
(d) Engine Performance - Engine power settings and thrust, rotor speeds, and engine spool down characteristics (if appropriate).
(4) Analysis Procedure. A summary of the procedures used in the normalization of the measured data to reference conditions for each of the three measurement locations.
(5) Airplane Flight Manual Page (example).
DER WITNESS INFORMAL REPORT. In those cases where the acoustic test 18 witnessed by a Designated Engineering Representative (DER) appointed and acting under the DER Handbook, Order 8110.37, the following information may be required by the FAA (as appropriate) to establish validity or invalidity of the testing in accordance with the test plan. This report should be submitted as soon as practical following the completion of the acoustic flight test or ground test program:
a. Copy of the FAA approved planned test sequence or test plan itemizing conditions that were tested.
b. DER recorded manual notes for each condition and daily test summary.
c. Weather information for each condition.
d. DER observed equipment description, by type, model, and serial number, as appropriate.
e. Recorded miscellaneous DER comments: (1) observed peak and/or average dB, (2) reasons for acceptability or unacceptability of test conditions, (3) observed narrow band analysis results, (4) etc..
f. Reported equipment calibration results.
g. Reported equipment failures, malfunctions, anomalous operation, spurious signals, etc., and corrective action taken.
h. Overall after-the-test summary by DER.
1. Summary of all meetings or negotiations between the applicant, the testing organization, and the DER.
reduction/analysis, and certification approval. i critication apron late of the teetie, data
k. Plotted examples of measured and corrected spectral values for each of the three measuring locations, together with appropriate time-related (computer) listings, may be necessary for complete data review.
27. NOISE CONTROL ACT FINDINGS. The Noise Control Act of 1972 provides that the FAA, before issuing any original type certificate for any aircraft of any category (except experimental) and regardless of whether Part 36 applies to the aircraft, must determine whether (1) substantial noise abatement cannot be Chap 4 Par 25 43
Type App me A 3/23/88 AC 36-4B achieved for that aircraft by prescribing standards and regulations consistent with the limitations of section 611(d), or (2) substantial noise abatement may be so achieved in which case the regulatory process must be used to determine the extent of noise reduction to be required before an original type certificate may be issued. This finding must be made by FAA notwithstanding any delegation to companies or other private persons or procedures for type certificating foreign-manufactured aircraft. It is legally important that these findings be based on actual examination of each type design. This examination must be initiated as soon as possible after the application for type certificate in each original type certification process and reflect noise reduction potentials that become evident during the certification process.
The noise finding documentation is not 11mited to, but should include:
The sources of audible noise, aerodynamic or otherwise, in the particular type design, including any noise measurements made, who made them, whether witnessed by FAA or not, and an estimate as to their reliability.
b. The technical alternatives and means that may be available for reducing such noise, including appropriate recommendations regarding choices of practical technical alternatives which have a potential for reducing noise.
c. An estimate of the expected degree of potential noise reduction associated with each alternative identified in b. above.
d. Investigation and review of the manufacturer's design information, data, and tests.
e. For each noise reduction technical alternative identified in b. above, that is not incorporated in the type design, the economic and technical justification for not requiring that it be so incorporated.
28. AIRPLANE FLIGHT MANUALS. The Airplane F11ght Manual (AFM) aboard each airplane must contain (in addition to airworthiness required information) the certificated noise levels and the procedures used to demonstrate those levels. Further, the AFM must describe clearly the type certificate limits, 1f any, that are established as a result of Part 36 compliance when combined with the airworthiness limitations.
a. General Requirements for Limitation.
(1) An AFM may be issued for a single aircraft or a group of similar aircraft (including more than one series of a specific model). The AFM must clearly identify (by airplane serial number) the operating limitations, including the maximum weight limits, that apply to an airplane.
multiple configurations. (2) The AFM may address a single configuration (hardware build) or If an AFM Includes Information for more than one configuration (hardware build), the appropriate airplane operating limitations must be clearly identified for each configuration. Furthermore, if not all configurations are approved for the airplanes listed in the AFM, the AFM must airplane. clearly identify by serial number, the proper operating limits for each 44 Chap 4 Par 27
3/23/88 АС Зб-4B
(3) The operating limitations contained in the Limitations Section (including any noise limited weights) must be expressed in mandatory language, not permissive language. The terminology used in the AFM nust be consistent with the relevant regulatory language.
b. AFM Maximum Certificated Weight Limits. The takeoff and landing weight limits may be categorized (structural, customer option, noise-limited, etc.) provided that instructions in the Limitations Section clearly state that the most restrictive takeoff weight limit and landing weight limit of these categories are the maximum certificated weight limits. The Limitations Section may include more than one maximum landing weight limit if those landing weight limits are flap configuration dependent, based on structural, customer option, or noise certification considerations.
C. Multiple Noise Certifications.
(1) Multiple noise-limited gross weight pairs (takeoff and landing) for one configuration are not allowed. Only one set of gross weight limits that pertain to a particular configuration (hardware build) may be established under Part 36 for a particular airplane.
(2) An airplane configuration (hardware build) must be certificated to only a single "Stage" as appropriate under Part 36 (Stage 1, Stage 2, or Stage 3). The Limitations Section of the AFM for that airplane configuration shall not contain operating limits that do not meet the noise certification criteria for Part 36 for the "Stage." However, the Part 36 certification status of an airplane configuration may be amended to reflect another "Stage," if appropriate, provided the AFM is revised for that configuration to reflect this new "Stage" compliance status, and the previous "Stage" approval is deleted.
d. Landing Flap Restriction.
(1) An operating limitation preventing the use of an approved landing flap setting cannot be imposed under Part 36 and must be established under airworthiness requirements or a voluntary design change. If such a restriction 1s desired in order to comply with Part 36 certification requirements, that flap position is not approved for normal operation.
Reference to emergency use of the restricted flap may be incorporated in the Limitations Section and operational information may be included in the Emergency Procedures Section of the AFM.
For airworthiness purposes, some airplane models have a "softguard," which makes it obvious that the maximum flap setting is not to be used for normal operation and would indicate any use of the unapproved setting by its deformation. This policy 1s also required by the Transport Category Directorate on all Stage 3 airplanes that fail to comply with the provisions of Part 36 in the "noisiest" landing flap configuration. This 1s particularly important for STC projects where the basic AFM may not be modified, only supplemented, allowing the unapproved maximum flap performance information to remain intact and available.
Chap 4 Par 28 45
3/23/88 AC 36-4B
(3) In order to approve a design that involves the restriction of the original landing flap settings, it is recommended that the following steps be taken in addition to any other requirements:
(a) Where permitted, remove the performance information that is relevant to the unapproved flap setting from the Performance Section of the AFM. (Note that supplemental type certificate (STC) applicants are not authorized to modify the basic AFM.)
(b) If the "unapproved" flap setting remains selectable:
(1) State in the Limitations Section of the AFM that the unapproved flap setting cannot be used except for emergencies.
(11) Place appropriate placards in the cockpit to prevent use of the restricted flap setting.
(111) For Stage 3 airplanes, provide a "softguard," such as a crushable cover plate, over the slot in which the flap selector handle travels, to restrain normal use of the unapproved flap setting.
e. Optional Engine Thrust Ratings (Derated and Reduced Thrust).
Compliance with Part 36 is only required at full rated takeoff thrust.
acceptable to establish through the type certification process a derated/reduced thrust that is less than the full rated takeoff thrust. The derated/reduced thrust 1s not an acoustical change under section 21.93(b) provided that the full rated takeoff thrust remains approved for that airplane. (Nothing herein precludes the use of the Part 36 thrust cutback procedure.)
certification hustle included in the Al and consist of only one takeoff, one The noise levels achieved during the type each airplane. The Part 36 "Stage" number should accompany the noise level information to indicate the compliance status. Supplementary information (labeled as such) may be added to the AFM concerning noise levels for other configurations and/or conditions not included in the certification summary.
29. ICAO CERTIFICATIONS.
of Part 36. However, some applicants require certification to the Annex 16 requirements published by the International Civil Aviation Organization (ICAO). Unless there is an in-force bilateral agreement which specifically includes noise and emissions certification, FAA participation is dependent upon management determination of the availability of resources. In any event, the FAA does not grant final approval of Annex 16 noise levels. This is the responsibility of the foreign airworthiness authority involved. FAA participation is limited to witnessing the tests and reviewing the data for In those cases where Stage 3 has been demonstrated, it 1s 46 Chap 4 Par 28
CERTIFICATION NOISE LEVELS The following noise levels comply with FAR Part 36, Appendix C, Stage 3 noise level requirements and were obtained by analysis of approved data from noise tests conducted under the provisions of FAR Part 36, Amendment 36-12. The test and analysis procedures used to obtain these noise levels are essentially equivalent to those required by the International Civil Aviation Organization (ICAO) in Annex 16, Volume I, Chapter 3.
ICAO Annex 16, Volume I, Chapter 3 approval 1s applicable only after endorsement by the Civil Aviation Authority of the country of airplane registration."
Chap 4 Par 29 47 (and 48)
Appendix 1 APPENDIX 1. NOISE DATA CORRECTIONS
FOR TESTS AT HIGH ALTITUDE TEST SITES INTRODUCTION. Jet noise generation 1s 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. Use of a high altitude test site for the noise test of a model that is primarily jet noise dominated should include making the following corrections. The following source jet noise corrections are in addition to the standard pistonphone barometric pressure correction (about 0.3 dB/1000 feet pressure attitude) which is normally used for test sites not approximately at sea level, and applies to tests conducted at sites at or above 1200 feet mean sea level (MSL) .
JET NOISE SOURCE CORRECTION. Flight test site locations at or above 1200 feet MSL, but not above 4000 feet MSL, may be approved provided the following criteria and source noise corrections are included in the requirements. Alternative criteria or corrections require the approval of AEE.
a. Criteria. Source jet noise altitude corrections from Figure l-l are required for each one-half second spectrum when using the integrated procedure and at PNLT section A36"17(f)) applied per the following criteria:
Figure 1-1 100% 100% - _ simplified method Applied Correction •Integrated method 0% ฿23 B27 0% 60 90 120 150 1/3 Octave Frequency Band Number Acoustic Angle - Degrees
b. Correction Procedure: An acceptable jet noise source correction is as follows:
(1) Correct each one-half second spectrum (or PNLT one-half second spectrum, as appropriate) for the test airport altitude using the criteria of para. (a) above and, ASPL = 10 108 (dr/dr) + 50 108 (Cp/CR) + 10k 108 (Up/Up) Par 1 1