and published in the FAA approved AFM or AFMS (e.g., improved climb rates, shorter takeoff distances, change in Vy, etc.). Additional airworthiness criteria may need to be reestablished.
(4.5) Increase in drag with no other changes Any modification to an airplane that increases its drag during takeoff and initial climb will increase the Appendix G noise level unless other changes are also introduced. If takeoff distance is increased, or rate-of-climb decreased, or both, the reference height will decrease. The change in level can be calculated from the adjustment equations provided previously if the change in performance can be determined. If an applicant wants to show compliance with the noise regulation via the NAC method, they will probably have to conduct takeoff distance and climb tests. If it looks as though the proposed modification will increase drag sufficiently to make a measurable performance change, then an offsetting change will be required. The amounts of increase or decrease in noise level involved can be calculated by the methods use in the previous examples.
(4.6) Acoustical effects of combined changes Many proposed airplane modifications involve several changes. Examples are replacing an engine and fixed pitch propeller with a higher power engine and a variable pitch propeller, or increasing engine power and takeoff weight at the same time. The acoustical consequences of thes e combined effects can be calculated by combining the methods used in the examples. The sequence for calculating these effects is as follows:
a) Determine the effect changes in takeoff distan ce and rate-of-climb will have on reference height.
b) Determine the effect of helical Mach number caused by any ch anges in airplane speed, propeller rotational speed, or change in speed of sound because of change in reference height.
Note.— The default value of 150 for “k” in the correction equations is only valid when used to determine an increase in helical mach number. It CANNOT be used to reduce the noise level. The 150 factor is a generalized conservative value for simplified calculations where the true “k” value is not determined. Thus it is inherently inaccurate.
c) Determine the effect of an y changes in engine power.
d) Determine any change in noise level due to change in airplane climb angle.
e) Obtain the algebraic sum of the four incremental changes in sound level.
f) If the sum is greater than zero, there are two choices:
— Conduct Appendix G tests as described in the regulation; or — Evaluate different operating conditions to obtain an incremental noise level that is not greater than that of the original airplane. This may be accomplished by derating the engine, reducing fuel/payload, and/or limiting maximum takeoff rpm. One or a combination of these modifications may be iterated until a negative noise increment is obtained by the methods used in the examples.
The cost of not performing an Appendix G noise test should be balanced against the loss of airplane performance or takeoff weight limitations during the lifetime of operation.
101(f) Acquisition of In-duct and/or Near -field Data for Demonstration of NAC
(1) General The FAA has found it acceptable for applicants to conduct engine or component only noise tests to evaluate minor engine changes. Frequently the objective for these tests is to provide evidence that the changes involved produce Page 29
negligible impact on EPNL noise values and may theref ore be categorized as NACs relative to the certificated aircraft configuration. Such testing includes component tests, static engine tests in a test cell, near-field microphone measurements, and in-duct dynamic pressure measurements.
(2) Guiding principles The overall guiding principles to be followed in providing acceptable evidence for substantiation of engine NACs are:
a) the measurements and analyses should adequately model the noise such that small changes in aircraft noise levels can be quantified; and
b) the noise measurement technique and the test e nvironment should not introduce changes to the noise sources that invalidate the predicted small changes in aircraft noise levels.
These guiding principles should be applied in all cases, with details of the approach being justified on a case-bycase basis as appropriate.
Note 1.— It is important that the near-field or in-duct measurements enable a sufficiently accurate prediction of the changes to engine noise in the far field.
Note 2.— It is important that the noise-generating mechanisms of interest are not significantly affected by the test cell environment. The test cell should have an exhaust collector to minimize re-circulation. There should be insignificant inlet distortion or inflow turbulence, or a turbulence control screen or ICD should be employed to minimize such distortions or turbulence. Test cell measurements might not be appropriate for assessing jet noise changes because of the influence of the test cell on the jet development.
Note 3.— Care must be taken to ensure the noise source under investigation is not masked by other unrepresentative noise components. While a reduced acoustic standard of components not under investigation might be acceptable in many cases, there are examples where such differences might invalidate the premise of an NAC (e.g., noise from the intake being masked by a hard-walled bypass duct, or significant noise from an overboard air dump contaminating the measured noise).
(3) Measurement systems Typical measurement systems used to acquire data for substantiation of an engine NAC include:
a) near-field microphones, either in test cells or outdoor facilities;
b) in-duct transducer measurements in the fan inlet or exhaust duct; and
c) core probes to assess combustor or low pressure turbine design changes.
4) Measurement and data analysis procedures The measurement and data analysis process should be accomplished on the basis of the following criteria:
a) an adequate array of transducers should be used to ensure that the measurements adequately model the noise (To determine overall changes in sound pressure level, the measured noise levels will typically need to be averaged azimuthally, radially and/or axially in order to avoid false conclusions being drawn from anomalous readings from single transducers.);
b) environmental conditions in the test setup should be monitored to demonstrate that the local environment
(e.g., test cell temperature) do not cause significant anomalies in the measured noise differences;
c) microphones should be mounted on the test cell wall or on the ground or floor but not in the shadow of any support structures or other test hardware;
d) in-duct transducers should be flush-mounted with minimal loss of area of acoustic treatment. Rakemounted transducers in the flow path should be avoided if they shed wakes that impinge on downstream structures and thereby create significant noise;
e) core probes should be fixed securely to the pylon, boat-tail fairing or other support and not be excessively buffeted by the flow;
f) the specifications of the measur ement system and calibration procedures for microphones, recording and reproducing systems should be in accordance with A36.3 of part 36 (Laboratory calibrations of in-duct transducers and core probes should be conducted be fore and, if possible, after each test. The dynamic range of the transducers should be sufficient to avoid overload.);
g) data should be acquired over the relevant engine operating speeds and for all relevant combinations of engine variables, as specified in the latest version of Reference T13;
h) the interpretation of in-duct meas urements should take into account the possibility that decaying or cutoff acoustic waves may be present that may mask ch anges sensed in the far field of the propagating wave; and
i) two alternative methods could be used in the subsequent analysis of the measured noise levels to demonstrate an NAC:
1) the measured component noise changes could be incorporated into a noise model that predicts the aircraft EPNL. This method has the added value of taking into account in-flight effects and the relative significance of the different noise sources; or
2) in some circumstances, it might be possible to reach the conclusion of an NAC without the need to incorporate the measured component noise changes into a noise model that predicts aircraft EPNL.
The measured noise changes could be examined to see if there is no increase in noise levels at any relevant frequency or engine condition.
Generally, noise models that predict the aircraft noise level expressed in EPNL are based on far-field static test data. Consequently, in either analysis it will be necessary to agree with the FAA on the method for calculating the impact on far-field static noise resulting from near -field microphone measurements or in-duct transducer measurements. This will normally require sound engine ering judgment, seeking out patterns in the data and technical explanations for any observed differences.
Furthermore the statistical uncertainty in the data should be considered. For example if statistical analysis shows that the uncertainty in the data is large and the differences are small, then no conclusions can be drawn from the data. On the other hand if the tests show large decreases in noise levels that outweigh the uncertainty in the data it may be possible to conclude, with reasonable certainty, that the changed engine is indeed quieter than the original engine.
Chapter 2 NOISE STANDARDS: AIRCRAFT TYPE AND AIRWORTHINESS
CHAPTER TABLE OF CONTENTS
201 EXPLANATORY INFORMATION32
201(a) Part 36 - Subpart A - General32
201(a)(1) Applicability and definitions32
201(a)(2) Aircraft configuration34
201(a)(3) Voluntary changes34
201(a)(4) Airworthiness certificates36
201(a)(5) Airworthiness certificates36
201(a)(6) One-Stage limit36
201(a)(7) Stage 1/ Stage 2 limits37
201(a)(8) Date of application37
201(a)(9) Airworthiness compatibility38
201(a)(10) Limitations of part38
201(a)(11) Configuration consistency39
201(a)(12) Dual stage certification39
201(a)(13) Exempt helicopter modifications39
201(a)(14) Helicopter compliance with part 3639
201(a)(15) Noise limits40
201(a)(16) Stage 2 helicopters40
201(b) Subpart B- Transport Category Large Airplanes and Jet Airplanes40
201(b)(1) Noise measurement and evaluation40
201(b)(2) Noise measurement constraints41
201(b)(3) Flight manual statement of Chapter 4 equivalency42
201(c) Subpart H – Helicopters42
201(c)(1) Noise limits42
201(d) Subpart 0 – Operating Limitations; and Information43
201(d)(1) Procedures, noise levels, and other information44
201(d)(2) Non-flight test data50
201(d)(3) Manuals, markings and placards50
201(d)(4) Supplemental information53
201(d)(5) Index of acceptability53
201(d)(6) Airplane limitations53
201(d)(7) Non-complying agricultural and fire fighting airplanes54
201(d)(8) Operating limitations54
201 EXPLANATORY INFORMATION 201(a) Part 36 - Subpart A - General 201(a)(1) Applicability and definitions §36.1(a)
(1) Applicable requirements Page 32
Unless otherwise specified, the date to be used for determining the applicability of the appropriate part 36 standards for an aircraft type design is the date on which application for a type certificate was made. An application for type certification is effective for the time periods specified in §21.17(c) of part 21.
(2) Noise related type certification requirements See paragraph 7-8 of Reference G4.
(3) Supplemental type certificates See paragraph 7-8 of Reference G4.
(4) Definitions of terms Section 4 of the preamble of this AC provides definitions of terms (see Table 2) related to the aircraft types and categories within Items (1) – (4) of §36.1(a).
Table 2. Aircraft terminology and categories
AIRCRAFT TERMINOLOGY AIRCRAFT TERMINOLOGY Aircraft Large Aircraft Airplane Small Aircraft Jet Airplane Turboprop Airplane (Note 3) Propeller AIRCRAFT CATEGORIES (Note 1) AIRCRAFT CATEGORIES (Note 1) Airplane Helicopter Acrobatic Normal Commuter Transport Normal Primary Restricted (Note 2) Transport Utility Note 1.— Airplane Categories and Aircraft Classes: Part 1 recognizes a distinction between Airplane Categories (e.g., acrobatic , commuter, normal, primary, restricted , transport and utility) and Aircraft Classes
(e.g., Conventional Takeoff and Landing (CTOL), Vertical Takeoff and Landing (VTOL), Short Takeoff and Landing (STOL), Reduced Takeoff and Landing (RTO L), and Supersonic Transports (SST)). The noise certification requirements contained in part 36 are specified for several Airplane and Helicopter Categories but not for STOL, RTOL, SST (except for Concorde), or VTOL Aircraft Classes.
Note 2.— Restricted Category Propeller-Driven Large Airplanes: Propeller-driven large airplanes that have been type certificated in the restricted category (see §21.25 of part 21) are not required to demonstrate compliance with the requirements of part 36. In the absence of part 36 applicability, an Environmental Assessment is required (see paragraph 7-4 of Reference G4 for additional information).
Note 3.— Turboprop Airplanes: Turboprop-powered airplanes are included under the part 36 requirements applicable to propeller-driven airplanes (i.e., subsonic transport category large airplanes; propeller-driven small airplanes, including acrobatic, normal, restricted, and transport categories; or propeller-driven Page 33
201(a)(2) Aircraft configuration §36.1(b) An applicant’s proposal for an aircraft configuration to be certified under the requirements of part 36 must include any type design changes that may be a result of airworthiness standards testing and analysis, and which would result in acoustical changes. (See §36.1(c) for FAA criteria on when aircraft type design changes represent an acoustical change). If an applicant does not propose the appropriate ai rcraft configuration, additional noise certification testing and analysis may be required.
201(a)(3) Voluntary changes §36.1(c)
(1) Examples of voluntary changes in type design A voluntary change in the configuration of an aircraft means a change in the type design of that aircraft. Examples of voluntary changes in aircraft type design that may affect part 36 certificated noise levels are as follows:
a) increased engine thrust (powe r) to improve aircraft performance;
b) maximum gross weight changes;
c) limitations on operational flap settings related to noise;
d) hardware revisions (e.g., vortex generators, flap configuration, wing tip stabilizers, wing tip fuel tanks, etc.);
e) engine modifications to improve engine performance, accelera tion, deceleration, or surge margin protection;
f) addition of wing or body hardware to improve aerodynamics;
g) external nacelle changes to improve air flow patterns;
h) engine inlet changes to improve ice protection;
i) reduction of engine blade tip clearances to improve inlet flow characteristics, and;
j) modifications to engine /nacelle acoustic treatments.
(2) Acoustical change criteria A voluntary change in the type design of an aircraft that may result in an increase in its certificated noise levels is defined as an “acoustical change.” A type design change that does no t result in an “acoustical change” as defined in section§21.93(b) of part 21 is referred to as a “no acoustical change” (NAC). The numerical criteria used by the FAA in defining an acoustical change for airplanes and helicopters are provided in 101(d) and (e) of this AC and are established to limit the cumulative effects of multiple small changes.
(3) NAC cumulative effects When type design changes result in reduced noise levels, an applicant may elect not to provide the full part 36 substantiation, but instead provide FAA with data a nd/or information to subs tantiate an NAC. However subsequent type design changes may require full part 36 certification because of cumulative acoustical effects.
Example: An applicant proposes a configuration change which will reduce the noise levels by approximately
2.1 dB for the flyover noise measurement point, 1.1 dB for the lateral noise measurement point, and with no Page 34
change in noise level at the approach noise measurement point. FAA verifies that the noise levels were reduced, and the applicant accepts the pre-change configuration certificated noise levels as published in the AFM to apply to this change in type design. The applicant may not make another type design change as an NAC that increases the flyover noise level and the lateral noise level without providing substantiation of the cumulative effects of this type design change on AFM noise certificated levels. Multiple type design changes must be evaluated on a cumulative basis (as a combined single configuration) for each noise measurement point for the purposes of determining whether there is an acoustical change.
(4) NAC approvals FAA may approve results of component laboratory demonstrations, back to-back noise comparisons from ground tests or flight tests of each configuration, acoustical analyses, etc as acceptable for substantiating that an applicant’s proposed changes to an aircraft type design is an NAC. The results from these evaluations must be applicable to an aircraft’s certificated noise levels at the part 36 reference noise measurement points.
(5) Non-standard jet airplane configurations Sections 21.93(b)(2)(i) and (ii) specify exceptions under which certain changes in jet airplane type design are not subject to compliance with part 36 requirements because such configurations are not intended for normal operations, but are typically required for maintenance ope rations (e.g., ferry flights, transporting engines to aircraft that cannot be ferried, etc.).
(6) Time-limited changes Time-Limited engine or nacelle chan ges on jet airplanes for periods of up to 90 days (as specified in §21.93(b)(2)(iii) of part 21) may be necessary for continued airplane operation until maintenance can be performed on the original engines or nacelles that were changed. These changes must comply with applicable airworthiness standards and the maintenance, preventa tive maintenance, rebuilding and alteration inspection requirements of part 43. Such changes do not require co mpliance with part 36 requirements even though they may result in an increase in airplane noise levels, relative to the certificated noise levels. FAA policy (see Federal Register Vol. 64, No. 225, Page 65655, dated November 23, 1999) permits the 90 day period allowed by §21.93(b)(2)(iii)of part 21 to continue to be used af ter December 31, 1999, but only for maintenance-related purposes. It cannot be used for meeting Stage 3 requirements due to lack of an adequate number of spare engines or nacelles, or insufficient number of engines or nace lles to operate a Stage 3 fleet at a given time. Section
21.93(b)(2)(iii) may only be us ed to intermix engines when maintenance is required and no conforming engine or nacelle for the configuration is available.
(7) Special purpose aircraft Type design changes to propeller-driven small airplanes and helicopters do not need to comply with the provisions of part 36 when they are operated for special purposes as specified in §§21.93(b)(3)(i-iv) and §21.93(b)(4) of part
21.
(8) Applicant’s responsibility Pursuant to §21.93(b), an applicant must identify type desi gn changes that affect an aircraft’s certificated noise levels by aircraft serial number and must demonstrat e part 36 compliance for those aircraft. The noise levels approved by the FAA for the modified aircraft must be documented in an FAA Approved AFM or RFM by either a revision to the AFM or RFM (typically an option only available to the aircraft manufacturer), an AFM or RFM Supplement (for Supplemental Type Certificates and Field Approvals), or a Supplemental AFM or RFM (for aircraft that do not have a FAA Approved AFM or RFM). Configurations and modifications for which noise approval is required must be found to comply with applicable airworthiness requirements specified in part 21 as well as the requirements of §36.3 of part 36.
201(a)(4) Airworth iness certificates §36.1(d)
(1) Requirements for Issuance of Airworthiness Certificates An airworthiness certificate is issued for each airplane produced, and is a means of distinguishing (by date of issuance) airplanes within a production run that comply with the noise certification requirements of part 36. Prior to the original issuance of a standard airworthiness certificate (see §21.183 of part 21) and regardless of the date of application for certification, compliance with the regulatory requirements of part 36 (including Appendix B) is required for a transport category large airplane, or for a jet airplane regardless of category (see paragraph 7-11(a) of Reference G4). The following table summarizes the requirements of §36.1(d) of part 36.
Table 3. Requirements of §36.1(d) of part 36 Maximum Airplane Weight Airplane Type Engine Configuration Effective Date of Part 36 Compliance Date for Airplanes With Initial Flight Time on or After 75,000 pounds or less Subsonic All engines December 1, 1969 December 31, 1974 Greater than 75,000 Subsonic Without Pratt &Whitney JT3D engines December 1, 1969 December 1, 1973 Greater than 75,000 Subsonic With Pratt & Whitney JT3D engines December 1, 1969 December 31, 1974 Concorde – all weights Supersonic All engines October 13, 1977 January 1, 1980
(2) “Grandfathered” airplanes Airplane types not identified above are “grandfathered” airplanes and are permitted to continue normal operations without showing compliance with the requirements of part 36. For example, the twin-engine propeller-driven Convair 580 or Douglas DC-3 airplanes that first logged flight time before December 31, 1974, did not have to comply with the noise provisions of part 36 and may have received a standard airworthiness certificate under the provisions of §21.183 of part 21, or may have received a standa rd airworthiness certificate under the provisions of the regulations in effect at the time of certification without compliance with part 36.
201(a)(5) Airworth iness certificates §36.1(e)
(1) Requirements for issuance of airworthiness certificates:
An applicant must show compliance of individual airplanes with the requirements of part 36 prior to issuance of airworthiness certificates, as prescribed in §21.183 or 21.185 of part 21 (see paragraph 7-11 of Reference G4).
2) Commuter category airplanes:
Since airworthiness standards for commuter category airplanes became effective February 17, 1987, (under part 21, Amendment 21-59) there are no airplanes in this category with initial flight time before January 1, 1980. All commuter category airplanes are thus required to show compliance with the noise certification requirements of part 36.
201(a)(6) One-Stage limit §36.1(g) Page 36
(1) In-flight configuration changes:
In-flight changes in an airplane configuration (including changes in maximum gross weight) that could result in multiple certificated noise levels for a given noise meas urement point or stage classification are not permitted.
They are changes in the airplane type design and therefore require a change in operating limitations. A change in maximum gross weight requires an applicant to remove an airplane from service, and comply with the approval procedures of part 43.5 and 43.7. The type design approval procedures under part 21 must be followed if the change does not have prior certification approval.
201(a)(7) Stage 1/ Stage 2 limits §36.1(h)
(1) The Stage 1 noise limits apply to all helicopters for whic h application for a type certificate or a change in type design was made prior to March 6, 1986.
(2) The Stage 2 noise levels apply to all helicopters for which application for a type certificate or a change in type design is made on or after March 6, 1986, with the following exception. For helicopters for which application for issuance of an original type certificate in the normal, transport or restricted category is made on or after March 6, 1986, and which the FAA finds to be the first civil version of a helicopter which was designed and constructed for, and accepted for operational use by an Armed Force of the U.S. or the U.S. Coast Guard on or before March 6, 1986, it must be shown that the noise levels of the helicopter certificated under the provisions of Appendix H are no greater than Stage 2 levels pl us 2 EPNdB at each measuring point. There is no corresponding provision under Appendix J. The tradeoff provision of H36.305(b) of part 36 may not be used to show compliance with Stage 2 levels plus 2 EPNdB, nor may they be used to increase any noise level beyond these limits. Subsequent civil versions (acoustical changes) must meet the Stage 2 requirements without the extra 2 EPNdB at each measuring point. The tradeoff provisions of H36.305(b) of part 36 may be used in showing stage 2 compliance for these subsequent versions.
(3) Helicopters excepted Helicopters that are designated exclusively for agricultural aircraft operations, as defined in §137.3 of part 137, for dispensing firefighting materials, or for carrying external loads, as defined in §133.1(b) of part 133, are excluded from the noise certification requirements.
(4) Stage 1/Stage 2 A helicopter, with a maximum takeoff weight of 7000 lb (3175 kg) or less, that fails to comply with the Stage 2 noise limit prescribed in J36.305 of part 36 has the alternative to comply with the Stage 2 noise limit of H36.305 of part 36.
Note.— The Appendix J noise limit us es a sound exposure level (SEL) that was defined more stringent by approximately 2 dB than the corresponding average of the three Appendix H noise limits in EPNL. However, this is no guarantee that subsequent Appendix H noise ce rtification testing will comply, especially for a military helicopter seeking civil certification.
201(a)(8) Date of application §36.2
(1) Requirements
a) Section 36.2 specifies the applicable part 36 requirements to be those in effect on the date of application for the a) aircraft type certificate or b) change in type design. If the time interval between application for the type certificate (or change in type design ) and the issuance of the type certif icate (or amended or supplemental Page 37
type certificate) exceeds 5 years, the applicable part 36 requirements are those in effect, on a date to be selected by the applicant, not earlier than 5 years before the date of issuance of the type certificate, amended type certificate, or supplemental type certificate.
b) Section 36.2(c) permits the applicant to elect to demonstrate compliance with a later part 36 standard than is required by §36.2(a) or (b). For the purposes of §36.2, “standard” refers to any of the requirements contained in part 36. As specified in §§36.2(c)(1) and (2), an applicant’s election of a later standard is subject to FAA approval, and the election must include standards adopted between the date of application and the effective date of the standard that the applicant has elected to comply with. Thus, an applicant’s election to demonstrate compliance with a particular later standard would also require that compliance be demonstrated with all other part 36 standards (applicable to the aircraft type) ad opted between the date of application and the effective date of the standard that the appli cant has elected to comply with. Furt her, in accordance with §36.2(c)(3), the FAA may require compliance with other standards that were adopted after the date of the elected standard.
For the purposes of §36.2(c)(3), “other standards” refers to other part 36 standards. For example, if the compliance standard elected under §36 .2(c)(3) had later been revised, the FAA may determine that it is appropriate for compliance to be demonstrated with the revised standard. Such a determination would also require that compliance be demonstrated with all other part 36 standards (applicable to the aircraft type) adopted between the date of application and the effective date of the standard that the FAA has determined to be the appropriate compliance basis.
201(a)(9) Airworth iness compatibility §36.3
(1) Requirements Aircraft certification tests and analyses must be conducted using configurations, procedures and information that are consistent with the airworthiness re gulations applicable to that aircraft. For example, noise tests or analyses may not be conducted with landing flap settings that could not meet the applicable airworthiness regulation requirements.
201(a)(10) Limitations of part §36.5
(1) Scope of part 36 regulation Part 36 requires compliance with U.S. Government noise standards for aircraft type and airworthiness certification but does not include noise standards related to aircraft operations, such as is provided in part 91. Part 36 certificated noise levels are achieved using procedures that can be duplicated practicably in normal operations by flight crews with safe reserves of thrust (power) and speed. Public Law 103-272 (Reference G2), mandates that the Administrator of the FAA prescribe standards to measure and evaluate aircraft noise. Under this law, an original type certificate may be issued for an aircraft for which substantial noise abatement can be achieved only after the FAA Administrator prescribes standards and regulations that apply to that aircraft. Consideration must be given to relevant information on aircraft noise, consultations with appropriate US and State authorities, whether the standards or regulations are consistent with the highest degree of safety and are economically reasonable, technologically practical, and appropriate for the type of aircraft to which they apply.
(2) Compatability with ICAO Annex 16 Standards Part 36 does not contain the Annex allowance to depart from the required reference procedures specified in Annex chapters. For example, §3.6.1.4 of Chapter 3 of Annex 16 permits the certificating authority to approve reference procedures that are different from those contained in §§ 3.6.2 and 3.6.3 of Annex 16, when design characteristics of an airplane would prevent flight from being conducted in accordance with §§ 3.6.2 and 3.6.3 of Annex 16. The FAA recognizes that there may be a need for changes to the specified reference procedures when part 36 may not be appropriate for a particular airplane when design characteristics of an airplane would prevent flight from being Page 38
conducted in accordance with the reference procedures described in part 36. In cases where part 36 is not appropriate, the rulemaking process, which includes a public comment period, would be followed to develop an appropriate noise certification standard . Thus, the main difference between th e U.S. and ICAO requirements is that under part 36, the reference procedures would be changed through the rulemaking process rather than solely at the discretion of the certificating authority.
201(a)(11) Configuration consistency §36.7(c)
(1) Quietest airworthiness approved configuration This requirement was established to show that an acoustical change resulting from an approved type design change must be determined consistently. The FAA policy does not require an applicant to determine the quietest airworthiness approved configuration at the flyover or lateral noise measurement points by noise measurement and evaluation. However, FAA requires consistent evaluations between derivative and originally certificated configurations. For example, an applicant might choose an approved takeoff flap setting of 5 degrees. Later a type design change may be requested that would increase the flyover and lateral noise levels (an acoustical change).
The FAA may not require the applicant to measure and evaluate all airworthiness approved takeoff flap settings
(e.g., 0, 1, 2, 5, 10 degrees) to determine the quietest configuration, but may, in this example, require appropriate evaluations for a flap setting of 5 degrees.
201(a)(12) Dual stage certification §36.7(e)
(1) “Dual-Stage” certificated airplanes Some older airplane models have been certificated to Stage 2 for one configuration and to Stage 3 for another configuration (e.g., airplane takeoff flap setting or maximum allowable gross weights). These airplanes are classified as “Dual-Stage” certificated airplanes. No new dual certifications will be considered.
201(a)(13) Exempt helic opter modifications §36.11 Modifications excluded from compliance with part 36, as listed in part 21, §21.93(b)(4)(ii) “Classification of Changes in Type Design” include:
a) addition or removal of external equipment (This means any instrument, mechanism, part, apparatus, appurtenance, or accessory that is att ached to or extends from the helicopter exterior but is not used nor is intended to be used in operating or controlling a helicopter in flight and is not part of an airframe or engine.);
b) changes in the airframe made to accommodate the addition or removal to fac ilitate the use of external equipment, to provide for an external load attaching m eans, 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 on the helicopter as a consequence of the addition or removal of external equipment, floats, and skis, or flight operations with doors and/or windows removed or in an open position.
201(a)(14) Helicopter compliance with part 36 §36.11(a) Page 39
(1) Equivalent procedures Subject to prior approval by the FAA, equivalent procedures may be used to measure, evaluate and calculate noise levels (see 1(c) of the preamble of this AC). Some commonly used equivalent procedures relating to helicopter noise certification are included in Chapters 4 and 6 of this AC.
(2) Noise level tradeoffs Tradeoffs between the adjusted noise levels for flyover, takeoff and approach defined in H36.305(b) of part 36 may be used to show compliance with the maximum noise levels (noise limits) of Appendix H of part 36. Since Appendix J of part 36 only includes a flyover procedure, no tradeoff is possible.
(3) Compliance The procedure used to show compliance under Appendix H or Appendix J of part 36 must follow the applicable parts of the regulation. Compliance with the maximum noise levels (noise limits) prescribed in H36.305 or J36.305 of part 36 must be shown.
201(a)(15) Noise limits §36.11(b)
(1) Stage 1 helicopters The maximum noise levels (noise limits) associated with a Stage 1 helicopter certificated under Appendix H of part 36 after a change in type design are dependent on the noise levels of the original Stage 1 helicopter. Unless the Stage 1 helicopter after the change meets the Stage 2 maximum noise levels (noise limits), or Stage 2+ 2 EPNdB levels at each measurement point, it will be necessary to show that the helicopter has no increase in the noise levels at any of the measurement points. This will require determination of the noise levels associated with the original Stage 1 helicopter using Appendix H procedures. If this is not possible an applicant must obtain FAA approval for another procedure.
201(a)(16) Stage 2 helicopters §36.11(c)
(1) Helicopter under 7000 lb (3175 kg) If after a change in type design a helicopter previously certificated under Appendix J of part 36, fails to meet the Appendix J Stage 2 maximum noise levels (noise limits) prescribed in J36.305 of part 36 an applicant may attempt to show compliance by electing the use of Appendix H procedures and the Appendix H Stage 2 maximum noise levels (noise limits) specified in H36.305 of part 36.
(2) Noise levels Section 36.11 requirements apply to helicopters certificated under both Appendix H and Appendix J of part 36.
201(b) Subpart B- Transport Category Large Airplanes and Jet Airplanes 201(b)(1) Noise measur ement and evaluation §36.101
(1) Appendix A Page 40