accordance with paragraph (b)(2) of this section, is an acceptable alternative in determining the lateral noise level.
a. Explanation
This section specifies criteria for an applicant to calculate lateral reference flight paths.
b. Supplemental Information
None
c. Procedures
None
303. Section B36.7(b)(4)
The takeoff reference speed is the all-engine operating takeoff climb speed selected by the applicant for use in normal operation; this speed must be at least V2+10kt (V2+19km/h) but may not be greater than V2+20kt (V2+37km/h). This speed must be attained as soon as practicable after lift-off and be maintained throughout the takeoff noise certification test. For Concorde airplanes, the test day speeds and the acoustic day reference speed are the minimum approved value of V2 +35 knots, or the all-engines-operating speed at 35 feet, whichever speed is greater as determined under the regulations constituting the type certification basis of the airplane; this reference speed may not exceed 250 knots. For all airplanes, noise values measured at the test day speeds must be corrected to the acoustic day reference speed.
a. Explanation
This section specifies airspeed criteria that an applicant must use to calculate the takeoff reference flight path of subsonic transport category large airplanes, jet airplanes and Concorde airplanes.
b. Supplemental Information
(1) Supersonic Airplanes: This AC does not address the noise certification requirements for supersonic transport category airplanes, other than Concorde (See section 1d).
c. Procedures
(1) V2 Takeoff Airspeed: Criteria for determining V2 takeoff airspeeds are specified in 14 CFR Part
25.107 “Takeoff Speeds”.
(2) Applicant's Responsibility: The applicant is responsible for determination of appropriate takeoff reference airspeeds for airplane maximum weights.
304. Section B36.7(b)(5)
The takeoff configuration selected by the applicant must be maintained constantly throughout the takeoff reference procedure, except that the landing gear may be retracted. Configuration means the center of gravity position, and the status of the airplane systems that can affect airplane performance or noise. Examples include, the position of lift augmentation devices, whether the APU is operating, and whether air bleeds and engine power take-offs are operating;
a. Explanation
None
b. Supplemental Information
(1) Applicant’s Options for Selection of Takeoff Configuration: The noise certification takeoff configuration that is selected by the applicant must be within the airworthiness approved configurations, as recorded in the AFM. Example: If the applicant has certificated flap settings 2, 5 and 10 and those settings are identified in the AFM, then they are valid options for noise measurements during takeoff. Flap setting 0 is not a valid option in this example. Noise certification compliance for a configuration that is different from the tested configuration may require re-testing or an equivalency finding by the FAA.
c. Procedure
(1) Applicant's Responsibility: An applicant is responsible for demonstrating that an appropriate airplane takeoff configuration is selected and maintained for the calculation of the reference takeoff procedure.
305. Section B36.7(b)(6)
The weight of the airplane at the brake release must be the maximum takeoff weight at which the noise certification is requested, which may result in an operating limitation as specified in § 36.1581(d); and
a. Explanation
This section specifies criteria for defining a reference maximum takeoff weight of an airplane.
b. Supplemental Information
(1) Part 36 section 36.1581 Requirements: An airplane reference maximum takeoff weight for noise certification which is less than the maximum weight established under applicable airworthiness requirements must be furnished as an operating limitation in the limitations section of the airplane flight manual.
c. Procedure
(1) Applicant’s Responsibility: An applicant must define and obtain FAA approval of an airplane maximum takeoff weight to calculate reference EPNL values.
306. Section B36.7(b)(7)
The average engine is defined as the average of all the certification compliant engines used during the airplane flight tests, up to and during certification, when operating within the limitations and according to the procedures given in the Flight Manual. This will determine the relationship of thrust/power to control parameters (e.g., N1 or EPR). Noise measurements made during certification tests must be corrected using this relationship.
a. Explanation
This section specifies criteria for defining an airplane’s average engine thrust (power) characteristics.
b. Supplemental Information
None
c. Procedure
(1) Applicant’s Responsibility: An applicant must define and obtain FAA approval of an airplane’s average engine thrust (power) characteristics to calculate reference EPNL values.
307. Section B36.7(c) Approach reference procedure:
The approach reference flight path must be calculated using the following:
308. Section B36.7(c)(1)
The airplane is stabilized and following a 3° glide path;
a. Explanation
This section specifies the reference conditions that an applicant must use in calculating an approach reference flight path.
b. Supplemental Information
None
c. Procedures
None
309. Section B36.7(c)(2)
For subsonic airplanes, a steady approach speed of VREF + 10 kts (VREF + 19 km/h) with thrust and power stabilized must be established and maintained over the approach measuring point. VREF is the reference landing speed, which is defined as the speed of the airplane, in a specified landing configuration, at the point where it descends through the landing screen height in the determination of the landing distance for manual landings. For Concorde airplanes, a steady approach speed that is either the landing reference speed + 10 knots or the speed used in establishing the approved landing distance under the airworthiness regulations constituting the type certification basis of the airplane, whichever speed is greater. This speed must be established and maintained over the approach measuring point.
a. Explanation
This section specifies the criteria that an applicant must use to determine reference approach airspeeds for subsonic transport category large airplanes and jet airplanes.
b. Supplemental Information
None
c. Procedures
None
310. Section B36.7(c)(3)
The constant approach configuration used in the airworthiness certification tests, but with the landing gear down, must be maintained throughout the approach reference procedure;
a. Explanation
None
b. Supplemental Information
(1) Approach Airworthiness Certification: Under the airworthiness regulations, airplanes are frequently airworthiness-certificated for more than one approach configuration. Such configurations may include:
(i) Multiple approach/landing flap settings and landing weights;
(ii) In-flight operable APU;
(iii) Environmental Control system operational conditions;
(iv) Engine bleed valve operational conditions.
The configuration that is most critical from a noise standpoint is the configuration that must be used for determination of reference approach EPNL values.
(2) Emergency Approach Configuration: Some airplanes are equipped with emergency in-flight operable equipment such as emergency air-turbine driven generators and emergency air-turbine driven hydraulic pumps. Emergency equipment operation is not a part of normal approach airworthiness approved configurations that require part 36 compliance.
(3) Restricted Configurations: On some airplanes, flap settings may be limited in order to comply with part 36 maximum noise levels (See section B36.5). For Stage 3 airplanes that require a flap limitation in order to comply with part 36, the installation of soft-guards and incorporation of appropriate AFM limitations are required. In addition, placards may be installed to provide appropriate information to the flight crew. Soft-guards make it obvious that limited flap settings are not to be used for normal operation, and would indicate any use of the unapproved settings by deformation of the soft-guard. For safety purposes, at the discretion of the flight crew, soft-guards allow use of noise restricted flap settings (that are airworthiness approved) for emergency conditions.
c. Procedures
(1) Applicant’s Responsibility: An applicant is responsible for demonstrating that an appropriate airplane configuration is selected and maintained in determining a noise certification approach reference procedure. This includes evaluating which approach configuration is most critical for approach noise certification and identifying that critical configuration in a noise certification compliance demonstration plan.
311. Section B36.7(c)(4)
The weight of the airplane at touchdown must be the maximum landing weight permitted in the approach configuration defined in paragraph (c)(3) of this section at which noise certification is requested, except as provided in § 36.1581(d) of this part; and
a. Explanation
This section specifies criteria for defining the reference maximum landing weight of an airplane for noise certification.
b. Supplemental Information
None
c. Procedures
None
312. Section B36.7(c)(5)
The most critical configuration must be used; this configuration is defined as that which produces the highest noise level with normal deployment of aerodynamic control surfaces including lift and drag producing devices, at the weight at which certification is requested. This configuration includes all those items listed in section A36.5.2.5 of appendix A of this part that contribute to the noisiest continuous state at the maximum landing weight in normal operation.
a. Explanation
This section specifies criteria for defining the reference configuration of an airplane for noise certification.
b. Supplemental Information
None
c. Procedures
(1) Most Critical Approach Configuration: An applicant must determine the most noise-critical configuration at the airplane’s maximum landing weight by evaluation of appropriate measured noise data and/or experience, or similarity with other airplane models. The results of this evaluation must include the effects of items listed in section A36.5.2.5.
Note: Example items warranting consideration are as follows:
(i) Flaps extended to the extreme approved landing flap position (e.g., 30º flaps) for turbojet airplanes and to the least approved landing flap position (e. g. 10° flaps) for turbo-propeller airplanes;
(ii) A/C (Environmental Control System) operating;
(iii) Landing gear extended;
(iv) Operation of an APU in-flight;
(v) Maximum approved landing gross weight, and
(vi) Inter-compressor bleed trimmed to maximum trim stop.
313. Section B36.8 Noise Certification Test Procedures
314. Section B36.8(a)
All test procedures must be approved by the FAA.
a. Explanation
This section specifies a requirement for FAA approval of an applicant’s proposals for airplane noise certification test procedures and noise measurements.
b. Supplemental Information
(1) Test Witnessing: An FAA observer, or appropriately delegated designee, must witness airplane noise certification tests to ensure compliance with a FAA approved noise certification compliance demonstration plan. (See paragraph 6-3(f) of reference 7 of this AC.)
c. Procedures
(1) Constant Configuration: A flight crew must not modify the takeoff or approach configurations during noise certification testing. They must set the airplane configuration (including engine thrust (power), flap position, APU and A/C operation, gear position, etc.) in sufficient time to stabilize all conditions prior to the initial 10 dB-down point, and maintain that configuration constantly until after the final 10 dB-down point.
Note: throttle movement during the noise measurement is not permitted, except as required by the pilot-in-command to ensure safety. If this occurs, the noise level certification test condition is invalid, and is to be repeated.
315. Section B36.8(b)
The test procedures and noise measurements must be conducted and processed in an approved manner to yield the noise evaluation metric EPNL, in units of EPNdB, as described in appendix A of this part.
316. Section B36.8(c)
Acoustic data must be adjusted to the reference conditions specified in this appendix using the methods described in appendix A of this part. Adjustments for speed and thrust must be made as described in section A36.9 of this part.
317. Section B36.8(d)
If the airplane’s weight during the test is different from the weight at which noise certification is requested, the required EPNL adjustment may not exceed 2 EPNdB for each takeoff and 1 EPNdB for each approach. Data approved by the FAA must be used to determine the variation of EPNL with weight for both takeoff and approach test conditions. The necessary EPNL adjustment for variations in approach flight path from the reference flight path must not exceed 2 EPNdB.
a. Explanation
This section specifies limits on EPNL adjustments due to differences between takeoff and approach test weight and the maximum weight at which noise certification is requested.
b. Supplemental Information
(1) Applicability of section B36.8(d): The requirements of section B36.8(d) do not apply when approved equivalent noise measurement and evaluation procedures are used to develop Noise-Power-Distance (NPD) data for airplane noise certification compliance. (See sections 2.1.2 and 3.1.2 of the appended ICAO TM).
c. Procedures
None
318. Section B36.8(e)
For approach, a steady glide path angle of 3° ± 0.5° is acceptable.
a. Explanation
This section specifies limits on airplane deviations from a 3° glide path during approach noise certification measurements.
b. Supplemental Information
(1) Applicability of section B36.8(e): The requirements of B36.8(e) regarding limits on glide path deviations do not apply when approved equivalent noise measurement and evaluation procedures are used to develop Noise-Power- Distance (NPD) data for airplane noise certification compliance (See sections 2.1.2,
2.1.1.3, 2.1.1.4, and 3.1.2(a) of the appended ICAO TM).
c. Procedures
(1) Applicant's Responsibility: The applicant is responsible either for ensuring that approach tests are conducted within specified glide path tolerances, or for obtaining approval for equivalent noise measurement and evaluation procedures if testing is not to be conducted within specified tolerances.
319. Section B36.8(f)
If equivalent test procedures different from the reference procedures are used, the test procedures and all methods for adjusting the results to the reference procedures must be approved by the FAA. The adjustments may not exceed 16 EPNdB on takeoff and 8 EPNdB on approach. If the adjustment is more than 8 EPNdB on takeoff, or more than 4 EPNdB on approach, the resulting numbers must be more than 2 EPNdB below the limit noise specified in section B36.5.
a. Explanation
None
b. Supplemental Information
None
c. Procedures
(1) Integrated Method: An applicant must use the “integrated method”, specified in section A36.9.4, when approved equivalent noise measurement and evaluation procedures result in EPNdB adjustments greater than 8 EPNdB for takeoff and 4 EPNdB for approach (See requirements specified in section A36.9.1.2).
320. Section B36.8(g)
During takeoff, lateral, and approach tests, the airplane variation in instantaneous indicated airspeed must be maintained within +3% of the average airspeed between the 10 dB-down points. This airspeed is determined by the pilot’s airspeed indicator. However, if the instantaneous indicated airspeed exceeds +3 kt (+5.5 km/h) of the average airspeed over the 10 dB-down points, and is determined by the FAA representative on the flight deck to be due to atmospheric turbulence, then the flight so affected must be rejected for noise certification purposes.
Note: Guidance material on the use of equivalent procedures is provided in the current advisory circular for this part.
a. Explanation
None
b. Supplemental Information
(1) Airspeed Variations: Possible causes and potential effects of airspeed variations during noise certification measurements are discussed under section A36.2.2.2(f) of this AC.
c. Procedures
None
321. - 349. [RESERVED]
350. PART A - GENERAL
351. Section F36.1 Scope [To be completed later.]
352. PART B - NOISE MEASUREMENT
353. Section F36.101 General Test Conditions [To be completed later.]
354. Section F36.103 Acoustical Measurement System [To be completed later.]
355. Section F36.105 Sensing, Recording, and Reproducing Equipment
356. Section F36.107 Noise Measurement Procedures [To be completed later.]
357. Section F36.109 Data Recording, Reporting, and Approval [To be completed later.
358. Section F36.111 Flight Procedures [To be completed later.]
359. PART C - DATA CORRECTION
360. Section F36.201 Correction of Data [To be completed later.]
361. Section F36.203 Validity of Results [To be completed later.]
362. PART D - NOISE LIMITS
363. Section F36.301 Aircraft Noise Limits [To be completed later.]
364. - 374. [RESERVED]
XV. 14 CFR PART 36 APPENDIX F. FLYOVER NOISE REQUIREMENTS FOR PROPELLER - DRIVEN
SMALL AIRPLANE AND PROPELLER-DRIVEN, COMMUTER CATEGORY AIRPLANE CERTIFICATION TESTS PRIOR TO DECEMBER 22, 1988
375. PART A - GENERAL
376. Section G36.1 Scope
This appendix prescribes limiting noise levels and procedures for measuring noise and adjusting these data to standard conditions, for propeller driven small airplanes and propeller-driven, commuter category airplanes specified in Secs. 36.1 and 36.501(c).
a. Explanation
Appendix G applies to the take-off noise requirements for propeller-driven small airplanes and commuter category airplanes that are tested on or after December 22, 1988, and that do not exceed 19,000 lbs.
in maximum gross take-off weight. It is a self-contained document, that includes the procedures for testing, weather limitations, calculations of the reference performance, adjustments of measured noise level data to reference conditions, and noise level limits. It is organized in four sections:
Part A – General Part B – Noise Measurement Part C – Data Correction Part D – Noise Limits
b. Procedures
Noise certification of small propeller-driven and commuter category airplanes in its most basic form requires a minimum of three actions, namely—
(1) Noise measurements conducted during a succession of take-off tests of the airplane within prescribed flight and noise measurement conditions. These conditions are described in paragraphs 377 to 404.
(2) Corrections and adjustments of the noise level data to account for deviations in test conditions relative to a prescribed reference condition. Corrections and adjustments are described in paragraphs 405 and
415.
(3) Demonstration, reporting, and approval that the adjusted noise levels for the airplane are within the noise limit appropriate to the airplane, which is based on the maximum certificated take-off weight of the airplane. Demonstration, reporting, and noise limits are described in paragraphs 416 to 417.
377. PART B - NOISE MEASUREMENT
378. Section G36.101 General test conditions
(a) The test area must be relatively flat terrain having no excessive sound absorption characteristics such as those caused by thick, matted, or tall grass, by shrubs, or by wooded areas.
No obstructions which significantly influence the sound field from the airplane may exist within a conical space above the measurement position, the cone being defined by an axis normal to the ground and by a half-angle 75 degrees from the normal ground axis.
a. Explanation
XVI. 14 CFR PART 36 APPENDIX G. TAKE-OFF NOISE REQUIREMENTS FOR PROPELLER-DRIVEN,
SMALL AIRPLANE AND PROPELLER-DRIVEN, COMMUTER CATEGORY AIRPLANE CERTIFICATION TESTS ON OR AFTER DECEMBER 22, 1988
It is necessary to specify test condition limits in order to avoid conditions that could affect the consistency of the sound levels at the measuring microphone. This regulation presents the requirements for the test site in order to uniformly measure noise levels. Uneven terrain having features such as mounds or furrows can result in reflections that could influence the measured sound levels. Vegetation can reduce the amount of sound that is reflected from the ground surface. In most cases this effect results in a reduced sound level, but under some circumstances the level may be higher. Similarly, testing over a smooth, hard surface, such as a paved area, will generally result in a higher sound level.
Obstructions in the vicinity of the microphone can also influence the measured levels. Objects such as buildings, walls, trees, vehicles, and, if close enough, test personnel, can constitute obstructions and/or cause reflections. The noise measure specified in Appendix G is based on the sound level at only one point in time, which for propeller-driven airplanes occurs when the airplane is near the overhead position. Unless the microphone is under a tree or overhang, it is unlikely that an obstruction would be between the sound source and the microphone. However, nearby objects can still affect the sound because of reflections.
b. Supplemental Information
(1) Obstructions: No obstructions are permitted within a cone-shaped space centered on the microphone position, having a half-angle of 75° from the vertical (or a horizontal angle of 15° from the ground surface). At a distance of 50 feet from the microphone, an object must be no taller than 13.4 feet above the ground at the microphone location in order to meet this requirement. At a distance of 25 feet from the microphone, an object on the ground must be no taller than 6.7 feet above the ground at the microphone location.
c. Procedures
(1) Test Site Selection: When selecting the test site, it is necessary to consider topography, the condition of the ground surface, and nearby obstructions. Vegetation, such as shrubs and thick grass, in the vicinity of the microphone is not permitted. It is not permissible to place "soft" material around the microphone. In this context, this includes materials that do not occur naturally at the test site, such as artificial materials or soil that is prepared in such a way to make it unusually absorptive. Wet soil is not specifically addressed in the regulation, but it is likely that wet soil would result in higher measured noise levels and would therefore not be favorable to the applicant.
(2) Snow: Snow-covered surfaces are not addressed in the regulation; however, measurements under these conditions could result in lower noise levels. Conditions are considered acceptable if the snow is cleared within a radius around the microphone of approximately 50 feet.
379. Section G36.101(b)
The tests must be carried out under the following conditions:
(1) No precipitation;
(2) Ambient air temperature between 36 and 95 degrees F (2.2 and 35 degrees C);
(3) Relative humidity between 20 percent and 95 percent, inclusively;
(4) Wind speed may not exceed 10 knots (19 km/h) and cross wind may not exceed 5 knots (9 km/h), using a 30-second average;
(5) No temperature inversion or anomalous wind condition that would significantly alter the noise level of the airplane when the nose [noise] is recorded at the required measuring point, and
(6) The meteorological measurements must be made between 4 ft. (1.2 m) and 33 ft. (10 m) above ground level. If the measurement site is within 1 n.m. of an airport meteorological station, measurements from that station may be used.
a. Explanation
This section identifies the weather conditions under which noise measurements can be made. The regulatory limitations were created to provide the greatest flexibility for applicants, with minimum effect on measured or corrected noise, while providing good repeatability.
b. Supplemental Information
(1) Precipitation: Fog, rain, drizzle, and snow can have a number of adverse effects. Changes in sound generation and propagation under these conditions are not well documented. Most of the equipment used for measuring noise is not intended for use during conditions of precipitation, and the effects can range from changes in microphone and windscreen sensitivity or frequency response, to arcing of conventional condenser microphones, to possible failure of equipment because of electrical short circuits.
(2) Atmospheric Conditions: Atmospheric conditions can affect the generation and propagation of sound, for non-reference helical tip Mach numbers (see paragraph 413). Propellers generate higher noise levels at higher propeller helical tip Mach numbers. Usually the actual tip velocity is close to reference propeller tip velocity, but the speed of sound is a function of air temperature which is often different than the reference value.
Off-reference tip Mach numbers can occur because of off-reference air temperature. The regulation requires correction for non-reference tip Mach numbers under most circumstances. However, limiting the permissible test temperature range reduces the potential magnitude of this correction. Corrections are also required to account for non-reference atmospheric absorption of sound. The magnitude of this correction is also limited by restricting the range of permissible temperature and relative humidity.
(3) Nonuniform Atmosphere: The atmosphere between the source (airplane, propeller, and/or exhaust) and the microphone is not uniform. There can be strong temperature gradients (positive and negative), variations in relative humidity, and variation in wind. Turbulence is also associated with strong winds, which can cause irregular sound propagation. When there is a crosswind, it is necessary for the airplane to fly at an angle to maintain the required track over the ground. Corrections are not required to account for wind. The wind limits only provide a means of determining acceptability of the data.
(4) Weather Monitoring: Based on the above considerations, it is clearly necessary to monitor the weather conditions. Procedures used in the noise certification process for transport category airplanes and turbojet-powered airplanes call for measurement of the weather conditions between the ground and the height at which the airplane is flying (see section A36.2.2.2(b)). The absorption of sound in air can then be computed based on these measurements. This process requires an appreciable investment of time and resources. For propeller-driven airplanes, the magnitude of the adjustment for atmospheric absorption is less than that for turbojet airplanes. An adjustment procedure based on measurements of the weather near the surface is therefore considered sufficient and more appropriate for airplanes covered by this section.
c. Procedures
(1) General Weather Measurements: The applicant is required to measure weather conditions near the surface and in the vicinity of the noise measuring station. The acceptability of noise data is contingent on the conditions being within the specified limits of section G36.101(b). Under the requirements of the regulations, these measurements are to be made at a height between 4 feet (1.2 meters) and 33 feet (10 meters) above ground level. This allows the use of hand-held equipment but does not preclude the use of more complex equipment of the type identified in Appendix A of Part 36 and used during measurement of turbojet-powered airplanes if the applicant so chooses. The weather data may be recorded on a chart, or an FAA-witnessed record of the observations may be kept.
(2) Wind: Consistent with the less complex requirements for small propeller-driven airplanes, wind conditions can be measured at the time of the airplane overflight with a relatively simple anemometer with an appropriate calibration. If the device used does not provide enough information to compute the crosswind, then the wind in any direction is limited to the crosswind limit of 5 knots. The wind limits are based on a 30-second average.