Aircraft: A device that is used or intended to be used for flight in the air. (Ref: part 1) Aircraft engine: An engine that is used, or intended to be used, for propelling aircraft. It includes turbosuperchargers, appurtenances, and accessories necessary for its functioning, but does not include propellers. (Ref: part 1) Airplane: An engine-driven fixed-wing aircraft heavier than air that is supported in flight by the dynamic reaction of the air against its wings. (Ref: part 1) Airport: An area of land or water that is used or intended to be used for the landing and takeoff of aircraft, and includes its buildings and facilities, if any. (Ref: part 1) Civil aircraft: Aircraft other than a public aircraft. (Ref: part 1) Commuter category airplanes: The commuter category is limited to propeller-driven, multiengine airplanes that have a seating configuration, excluding pilot seats, of 19 or less, and a maximum certificated takeoff weight of 19,000 pounds or less, intended for non-acrobatic operations. Commuter category airplanes are required to show compliance with part 23.
Helicopter: A rotorcraft that, for its horizontal motion, depends principally on its engine-driven rotors. (Ref: part 1) Large aircraft: Large aircraft means aircraft of more than 12,500 pounds, maximum certificated takeoff weight. (Ref:
part 1) Normal category airplane: The normal category is limited to airplanes that have a seating configuration, excluding pilot seats, of nine or less, a maximum certificated ta keoff weight of 12,500 pounds or less, and intended for nonacrobatic operation. Normal category airplanes are required to show compliance with part 23.
Normal category rotorcraft: A normal category rotorcraft is a rotorcraft with a maximum weight of 7000 pounds or less and that meets the regulatory requirements of part 27.
Primary category aircraft: A primary category aircraft is an aircraft that (1) is unpowered, or is an airplane powered by a single, naturally aspirated engine with a 61-knot or less stall speed, or is a rotorcraft with a 6-pound per square foot main rotor disc loading limitations, and (2) weighs not more than 2700 pounds, and (3) has a maximum seating capacity of not more than four persons, including the pilot, and (4) has an unpressurized cabin. A primary category aircraft is required to meet the regulatory requirements of §21.24 of part 21.
Propeller: A device for propelling an aircraft that has blades on an engine-driven shaft and that, when rotated, produces by its action on the air, a thrust approximately perpendicular to its plane of rotation. It includes control components normally supplied by its manufacturer, but does not include main and auxiliary rotors or rotating airfoils of engines. (Ref: part 1).
Public aircraft: Aircraft used only in the service of a government, or a political subdivision. It does not include any government-owned aircraft engaged in carrying persons or property for commercial purposes. (Ref: part 1) Restricted aircraft: Used for special purpose operations as defined in §21.25 of part 21.
Rotorcraft: A heavier-than-air aircraft that depends principally for its support in flight on the lift generated by one or more rotors (Ref: part 1).
Small aircraft: Small aircraft means aircraft of 12,500 pounds or less, maximum certificated takeoff weight. (Ref:
part 1) Page 5
Subsonic airplane: A subsonic airplane means an airplane for which the maximum operating limit speed, MMO, does not exceed a Mach number of 1.
Supersonic airplane: A supersonic airplane means an airplane for which the maximum operating limit speed, M MO, exceeds a Mach number of 1.
Transport category aircraft: Those aircraft (large or small) that are demonstrated to meet and are certificated to the regulatory requirements of part 25 for transport category airplanes or part 29 for transport category rotorcraft.
Jet Airplane: Any fixed wing airplane that is powered by a turbojet or turbofan engine regardless of whether it is an airplane certificated to part 23 (small or commuter aircraft) or part 25 (transport category aircraft).
Turbo-propeller airplane: An airplane whose primary source of thrust is from a propeller driven by a gas turbine engine.
Utility category airplane: The utility category is limited to airplanes that have a seating configuration, excluding pilot seats, of nine or less, a maximum certificated takeoff weight of 12,500 pounds or less, and intended for limited acrobatic operation. Utility category airplanes are required to show compliance with part 23.
5. ABBREVIATIONS AND ACRONYMS The following abbreviations and acronyms are used within the text of this AC AC = FAA advisory circular ACO = Local FAA aircra ft certification office AEE = FAA Office of En vironment and Energy AFM = Airplane Flight Manual AMC = Acceptable means of compliance APU = Auxiliary power unit C/A = Coarse/Acquisition CAEP = Committee on Aviation Environmental Protection CDI = Course deviation indicator CG = Center of gravity CFR = Code of Federal Regulations CPA = Closest point of approach DAT = Digital audiotape dB = Decibel DER = Designated Engineering Representative DGPS = Differential global positioning system DMU = Distance measuring unit EPNL = Effective perceived noise level ETM = Environmental Technical Manual (“ICAO Environmental Technical Manual. Volume 1, Procedures for the Noise Certification of Aircraft”) FAA = Federal Aviation Administration GDI = Glide-slope deviation indicator GM = Guidance material GPS = Global positioning system Hz = Oscillatory frequency, cycles per second IAS = Indicated airspeed ICD = Inflow control device INS = Inertial navigation system ICAO = International Civil Aviation Organization ILS = Instrument landing system IOD = Issue of data Page 6
IRIG = Inter-Range Instrumentation Group IRIG B = Inter-Range Instrumentation Group Standard Serial Time Code Format B ISA = International standard atmosphere LAAS = Local area augmentation system LAmax = Maximum A-weighted sound level log = Logarithmic value to base 10 LUP = Land-use planning MAP = Manifold air pressure MLW = Maximum landing weight MSL = Mean sea level altitude, feet MTOW = Maximum takeoff weight NAC = No acoustical change NCS = Noise Certification Specialist NIST = National Institute of Standards and Technology NMEA = National Marine Electronics Association NPD = Noise-power-distance OAT = Outside air temperature RFM = Rotorcraft Flight Manual RH = Relative humidity, % rms = Root-mean-square грт = revolutions per minute SAE = Society of Automotive Engineers SB V = Surge bleed valve (engine internal operating valves) SR = Slant range STC = Supplemental Type Certificate TIA = Type Inspection Authorization TC = Type Certificate TSPI = Time-space-position information UTC = Coordinated universal time VLA = Very Light Aircraft VNTSC = Volpe National Transportation System Center (DOT) VREF = Reference Landing Speed Curtis Ho sclax Acting Director of Environment and Energy Page 7
Table of Contents Page
1. PURPOSE1
2. CANCELLATION3
3. REFERENCES3
4. DEFINITIONS4
5. ABBREVIATIONS AND ACRONYMS6
6-7. RESERVED7
CHAPTER 1. CERTIFICATION PROCEDURES FOR PRODUCT AND PARTS 14 CFR PART 21
101 EXPLANATORY INFORMATION10
CHAPTER 2. NOISE STANDARDS: AIRCRAFT TYPE AND AIRWORTHINESS
201 EXPLANATORY INFORMATION32
CHAPTER 3. TECHNICAL PROCEDURES AP PLICABLE FOR NOISE CERTIFICATION
O F A L L A I R C R A F T T Y P E S
301 NOISE MEASUREMENT PROCEDURES58
302 FLIGHT PATH MEASUREMENT65
303 ON-BOARD FLIGHT DATA ACQUISITION80
304 TIME SYNCHRONIZATION OF MEASURED DATA82
305 CALCULATION OF CONFIDENCE INTERVALS84
306 ADJUSTMENT OF AIRCRAFT NOISE LEVELS FOR THE EFFECTS97
307 NOISE REDUCTION SYSTEMS105
308 CALCULATION OF THE SPEED OF SOUND107
309 REFERENCE TABLES USED IN THE MANUAL CALCULATION OF107
CHAPTER 4. GUIDELINES FOR TRANSPORT CATEGORY LARGE AIRPLANES,
SUBSONIC JET AIRPLANES, AND HELICOPTERS EVALUATED UNDER APPENDIX A OR H OF 14 CFR PART 36
401 EXPLANATORY INFORMATION116
402 EQUIVALENT PROCEDURES INFORMATION160
403 TECHNICAL PROCEDURES INFORMATION192
CHAPTER 5. GUIDELINES FOR PROP ELLER-DRIVEN SMALL AIRPLANES AND
PROPELLER-DRIVE COMMUTER CATEGORY AIRPLANES EVALUATED UNDER APPENDIX G OF 14 CFR PART 36
501 EXPLANATORY INFORMATION218
502 EQUIVALENT PROCEDURES INFORMATION226
503 TECHNICAL PROCEDURES INFORMATION232
CHAPTER 6. GUIDELINES FOR HELI COPTERS NOT EXCEEDING 7000 LB EVALUATED UNDER APPENDIX J OF 14 CFR PART 36
601 EXPLANATORY INFORMATION237
602 EQUIVALENT PROCEDURES INFORMATION245
CHAPTER 7. GUIDELINES FOR TILTRO TOR AIRCRAFT EVALUATED UNDER APPENDIX K OF 14 CFR PART 3 Page 8
701 EXPLANATORY INFORMATION247
CHAPTER 8. GUIDELINES ON FLIGHT TEST WINDOWS AND ADJUSTMENT OF
LAND-USE PLANNING NOISE DATA MEASURED IN ACCORDANCE WITH ATTACHMENT H TO ANNEX 16, VOLUME I
801 EXPLANATORY INFORMATION253
802 EQUIVALENT PROCEDURES INFORMATION260
803 TECHNICAL PROCEDURES INFORMATION260
CHAPTER 9. GUIDELINES FOR AIRCRAFT RECERTIFICATION
901 INTRODUCTION266
902 ASSESSMENT CRITERIA267
903 RECERTIFICATION GUIDELINES FOR “MODIFIED”AIRPLANES271
Appendix 1. GENERAL REFERENCES273
Appendix 2. TECHNICAL REFERENCES274
Appendix 3. BIBLIOGRAPHY276
Appendix 4. DOT/FAA ADDRESSES277
Chapter 1 CERTIFICATION PROCEDURES FOR PRODUCT AND PARTS 14 CFR PART 21
CHAPTER TABLE OF CONTENTS
101 EXPLANATORY INFORMATION10
101(a) Part 21 General10
101(b) Airworthiness Certification10
101(c) Changes in Type Design10
101(d) No acoustical changes (NAC)11
101(e) Methods for Demonstrating No Acoustical Change (NAC)14
101(f) Acquisition of In-duct and/or Near-field Data for Demonstration of NAC29
101 EXPLANATORY INFORMATION 101(a) Part 21 General As part of the overall aircraft certification requirements iden tified in part 21, applicants must comply with the noise certification requirements of part 36. Section 21.17 of part 21 specifies that an applicant for a type certificate must show that the aircraft meets the applicable requirements of part 36. In addition, §§21.21 and 21.25 of part 21 specify that an applicant is entitled to a type certificate for an aircraft if the applicant submits the type design, test reports, and computations necessary to show that th e product to be certificated meets the applicable airworthiness and aircraft noise requirements. Similar requirements are imposed for aircraft manufactured in a foreign country for import into the United States (§21.29 of part 21). Refer to the part 21 regulations for specific regulatory language.
101(b) Airworthin ess Certification All aircraft requiring noise certification by the FAA are required to meet the applicable airworthiness requirements of part 21, which identifies the specific airworthiness standards for each aircraft type and product, such as:
a) part 23 for normal, utility, acroba tic, and commuter category airplanes;
b) part 25 for transport category airplanes;
c) part 27 for normal category rotorcraft;
d) part 29 for transport category rotorcraft;
e) part 33 for aircraft engines;
f) part 35 for propellers;
g) primary category aircraft; and
h) JAR-VLA aircraft.
101(c) Changes in Type Design
(1) General Section 21.93(b) of part 21 requires compliance with th e appropriate part 36 “acoustic al change” requirements for a voluntary type design change of an aircraft that ma y increase the noise levels of that aircraft, regardless of whether the change in type design is classified as a minor or major change in §21.93(a) of part 21.
(2) Voluntary changes A general description of FAA handling of various forms of voluntary changes in the type design of an aircraft is addressed in 201(a)(3) of this AC. Procedures for demonstration of compliance with part 21 for specific types of “no acoustical change” (NAC) are presented in 101(d) & (e).
101(d) No acoustical changes (NAC)
(1) NAC definition Aircraft/engine model design changes and airframe/engine performance changes may result in very small changes in aircraft noise certification levels that are not acous tically significant. These cha nges are referred to as no acoustical changes (NACs). For this AC NACs, which do not result in modification of an aircraft’s noise certification levels, are defined as:
a) changes in airplane noise certification levels approved by the FAA which do not exceed 0.10 dB at any noise measurement point and which an applicant does not track;
b) cumulative changes in airplane noise certification le vels approved by the FAA whose sum is greater than
0.10 dB but not more than 0.30 dB at any noise measurement point and for which an applicant has an approved tracking procedure;
c) for helicopters certificated according to the standa rds of Appendix H, changes in any one of the noise certification levels approved by the FAA which do not exceed 0.30 EPNdB; and
d) for helicopters certificated according to the standa rds of Appendix J, changes in the noise certification level approved by the FAA which does not exceed 0.30 dB(A).
(2) Tracking procedures With respect to the tracking procedure referred to in 101(d)(1)(b), noise certification approval has been given based upon the following criteria:
a) ownership by the certification applicant of the noise certification database and tracking process on an aircraft/engine model basis;
b) when the 0.30 dB cumulative change in the airplane noise certif ication level is exceeded, compliance with the part 36 requirements is required; the airc raft noise certification levels may not be based upon summation of NAC noise increments;
c) decreases in noise levels should not be included in the tracking process unless the type design change will be retrofitted to all aircraft in service and included on newly produced aircraft;
d) aircraft/engine design changes resulting in nois e level increases should be included in the tracking process regardless of the extent of retrofit to aircraft in service;
e) tracking of an aircraft/engine model should, in ad dition to engine design changes, include airframe and performance changes;
f) tracked noise increments should be determined on the basis of the most noise-sensitive condition and be applied to all configurations of the aircraft/engine model;
g) the tracking should be revised to account for a tracked design change increment that is no longer Page 11
applicable;
h) changes should be tracked to two decimal places (i.e., 0.01 dB). Round-off should not be considered when judging an NAC (e.g., 0.29 dB = NAC; 0.30 dB = NAC; 0.31 dB = acoustical change); and
i) an applicant should maintain formal documentation of all NACs approved under a tracking process for an airframe/engine model; the tracking list will be reproduced in each noise certification demonstration document.
Due to the applicability dates, some light propeller-driven airplanes are not required to have noise certification levels. However some modifications to these aircraft can be applied which may impact the noise characteristics.
In this case, the NAC criteria application should be treated with a procedure approved by the FAA.
(3) Criteria for helicopter certification Noise certification approval of modified helicopters should be granted according to the following criteria:
a) an NAC approval for a derived version can be made only if the parent “flight datum” helicopter was flight tested to obtain the noise certification levels;
b) noise levels for a helicopter designated as an NAC design cannot be used as the “flight datum” for any subsequent design changes; and
c) for changes exceeding 0.30 dB, compliance with part 36 requirements may be achieved either by testing or, subject to approval of the FAA, by analytical means; if analy tical means are employed, the noise certification levels cannot be used as the “flight datum” for any subsequent design changes.
Note.— Definition for parent “flight datum” aircraft is shown in Table 1.
A flow chart illustrating the criteria for dealing with modified helicopters is presented in Figure 1.
Due to the applicability dates, some helicopters are not required to have noise certification levels. However some modifications to these helicopters can be applied which may impact the noise character istics. In this case, the NAC criteria application should be treated with a procedure approved by the FAA.
(4) Helicopters modifications defined as NACs Changes in helicopter noise level(s) arising from modifi cations associated with the installation or removal of external equipment are defined as NACs and thus need not be determined. For the purposes of this section “external equipment” means any inst rument, mechanism, part, appurtenan ce, or necessary accessory that is attached to, or extends from, the helicopter exterior but is not used, nor is intended to be used, in operating or controlling the helicopter in flight and is not part of an airframe or engine.
The following examples are considered to be no acoustical changes:
a) the addition or removal of external equipment;
b) changes to the airframe made to accommodate the ad dition or removal of external equipment, to provide for an external load attaching means, to facilitate the use of external equipment or external loads, or to facilitate the safe operation of the helicopter with external equipment mounted to, or external loads carried by, the helicopter;
c) reconfiguration of the helicopter by the addition or removal of floats and skis;
d) flight with one or more doors and/or windows removed or in an open position; or
e) any changes in the operational limitations placed on the helicopter as a consequence of the addition or removal of external equipment, floats, skis, or flight operations with doors and/or windows removed or in an open position.
(5) Helicopters with variable noise reduction systems (VNRS) Aircraft can incorporate variable systems, primarily intended to reduce the takeoff/approach 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 for NAC are applicable.
Figure 1. “No-acoustical change” criteria for modifications to noise certificated helicopters Page 13
101(e) Methods for Demonstrating No Acoustical Change (NAC) for Propeller-Driven Small Airplanes and Commuter Category Airplanes
(1) Procedures The methods, as referred to in this section, are aircraft measurement, flight test, analytical or evaluation methods that differ from the methods specified in the text of Appendix G of part 36. The particular method(s) employed must be approved by the FAA. These methods differ from equivalent procedures in that they are used for a finding of NAC under §21.93(b) of part 21 and are not pertinent to part 36.
(2) Acoustical changes The regulatory need to evaluate all voluntary changes for acoustical change is found in §21.93(b) of part 21. An acoustical change in the type design of an airplane is defined in §21.93(b) as “…any voluntary change in the type design of an aircraft that may increase the noise levels of that aircraft is an acoustical change…”; note that a change in design that decreases the noise level is not an acoustical change in terms of the rule. There are four categories of small propeller-driven ai rplanes excluded from this evaluation of voluntary changes: 1) Airplanes designated for “agricultural aircraft operations” as defined in §137.3 of part 137; 2); Designated for dispensing firefighting materials; 3) U.S. registered and had flight time prior to January 1, 1955; and 4) Land configured airplanes reconfigured with floats or skis (non-permanent seasonal changes to the landing gear). The exclusions noted in §21.93(b) differ from an earlier definition that applied to propeller-driven small airplanes certificated under Appendix F of part 36. In the earlier definition, acoustical changes were restricted to (1) any change or removal of a muffler or other component of an exhaust system designed for noise control, or (2) any change to an engine or propeller installation which would increase maximum continuous power or propeller tip speed.
The current definition of acoustical change in §21.93(b ) for propeller-driven small airplanes and commuter category airplanes is more in line with that for all other aircraft categories. For example, an increase in takeoff weight without any change in engine/propeller installation would not be considered an acoustical change under the earlier definition. Now it would be, since the reference height for noise level measurement would be lower with the increased weight, which would result in a higher noise level.
Section 36.9 defines the noise comp liance requirements for propeller-driven small airplanes and commuter category airplanes for which an acoustical change approval is applied for under §21.93(b). Section 36.9 recognizes two airplane categories: those that have previously been shown to comply with part 36, and those that have not.
For the first group, any acoustical change must not incr ease noise levels beyond the limits stated in Part D of Appendix G. For the second group, noise levels may not exceed either these same limits, or "the noise level created prior to the change in type design, measured and corrected as prescribed in §36.501 of this part," whichever is greater. This may require that two noise certification tests need be run. The first is to establish the unmodified noise level standard and the second is to measure the modified noise level. Section 36.501(c) also requires that "compliance must be shown with noise le vels as measured and prescr ibed in Parts B and C of Appendix G, or under approved equivalent procedures."
The FAA considers any change in type design that will increase the noise level by more than 0.10 dB(A) an acoustical change. However, no acoustical change results as long as any change that can be expected to increase the noise level is offset by other changes in design or performance that will decrease the noise level in such a way that the sum of the changes does not increase the expected noise level by more than 0.10 dB(A).
The purpose of this section is to examine methods for calculating changes in noise level introduced by common type design changes and methods for showing compensating noise level effects that will result in a demonstration of NAC.
(3) Factors that change noise level Page 14
Noise levels under Appendix G test procedures are affected by both the basic noise producing properties of the propeller/engine installation and by the takeoff and climb performance of the airplane. Regardless of what mechanical change is made to the airplane, noise levels can be expected to increas e if any of the following conditions results from a type design change (without compensating changes):
a) decrease in the height of the airplane at the refe rence distance of 8200 ft (2500 m) from brake release;
b) increase in engine horsepower;
c) removal or alteration of exhaust mufflers;
d) increase in propeller helical tip Mach number;
e) increase in propeller tip thickness;
f) decrease in airplane climb path angle;
g) increase in airplane drag;
h) increase in propeller inflow angle; or
i) change in the number of propeller blades.
Increases expected in the Appendix G noise levels cause d by any of the above changes must be offset by a compensating change to achieve NAC, a nd an appropriate analysis of the ef fects of such a change must be provided. Removal of exhaust mufflers or other changes in the exhaust system may require some form of testing to determine the acoustical effect. Similarly, increasing propeller tip thickness, such as by cutting the tips off an existing propeller to decrease its diamet er, may cause an increase in noise level (which might be offset by the decrease in the propeller rotational Mach number at the same rpm). In both the case of the altered exhaust system and that for the cut-down propeller, a comparison test, during which noise levels are measured for the modified and the unmodified airplanes utilizing part 36 Appendix G flyovers at the same height and airspeed, may be approved as a satisfactory method to determine whether an acoustical change has occurred.
Comparison tests are not generally cost saving methods since they may become as complex as a full part 36 Appendix G test.
(3.1) Parent aircraft definition Before making any analysis or conducting any test it is necessary to determine what defines the Parent (unmodified) airplane. The Parent airplane represents the noise characteristics existing prior to the change in type design. Table 1 will help identify the Parent aircraft for use in no-acoustical change evaluations.
Table 1. Definition for parent “flight datum” aircraft Modification Parent Aircraft STC/Field Approval/Type Design Change (All changes contained in the same approval).
Aircraft defined on the dataplate (Original T.C. configuration) Multiple STC’s/Field Approvals/Type Design Changes (None of which provided noise levels) Aircraft defined on the dataplate (Original T.C. configuration) Multiple STC’s/Field Approvals/Type Design Changes Aircraft defined on the (Where at least one* provides new noise levels and including any dataplate previously approved changes that provided noise levels). (Original T.C. configuration) * The approval that provides new noise values (STC, Service Bulletin, Field Approval, etc.) must be listed in the approval plus the modification that included noise value(s).
documentation as required to be previously or concurrently installed. [Should more than one of the included changes contain noise value(s), the approval that provides the lowest value(s), in all applicable reference profiles, will be used.
For approvals with more than one reference profile (e.g., Appendix B & H), when one modification does not provide lower, or equal, noise levels in all three profiles, then only one of the previously approved changes may be used as the acoustic parent definition. All other alterations are treated as acoustical changes.] Conversion from one aircraft model into another with no change to the aircraft dataplate.
Aircra ft defined on the dataplate (Original T.C. configuration) Conversion from one aircraft model into another with a new or additional dataplate being added.
Aircraft defined on the later installed dataplate.
(3.2) Definitions Following are definitions used in this section:
c = Speed of sound at reference height Page 16