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Federal Register / Vol. 86, No. 164 / Friday, August 27, 2021 / Notices
excessive sound absorption characteristics, such as might be caused by thick, matted, or tall grass, shrubs, wooded areas, or loose soil. Grass is acceptable if mowed to 3 inches or less in a 25 foot radius around any sound measuring stations.
b During the period when the flyover noise measurement is within 10
dB of the maximum A-weighted sound level, no obstruction that significantly influences the sound field from the aircraft may exist within a conical space above the noise measuring position the point on the ground vertically below the microphone. The cone is defined by an axis normal to the ground and by halfangle 80 degrees from this axis.
9 Weather restrictions Reference:
Part 36, appendix J, section J36.101c as modified: Each test must be conducted under the following atmospheric conditions:
a No rain or other precipitation.
b Ambient air temperature between 36 degrees and 95 degrees Fahrenheit 2
degrees and 35 degrees Celsius, inclusively, and relative humidity between 20 percent and 95 percent inclusively, except that testing may not take place where combinations of temperature and relative humidity result in a rate of atmospheric attenuation greater than 10 dB per 100
meters 30.5 dB per 1,000 feet in the one-third octave band centered at 8
kiloHertz.
c Wind velocity that does not exceed 10 knots 19 km/h and a crosswind component that does not exceed 5 knots 9 km/h. The wind must be determined using a continuous averaging process of no greater than 30 seconds.
d Measurements of ambient temperature, relative humidity, wind speed, and wind direction must be made between 4 feet 1.2 meters and 33
feet 10 meters above the ground.
Unless otherwise approved by the FAA, ambient temperature and relative humidity must be measured at the same height above the ground.
e No anomalous wind conditions including turbulence or other anomalous meteorological conditions that could significantly affect the noise level of the aircraft when the noise is recorded at the noise measuring station.
f If the measurement site is within 6,560 feet 2,000 meters of a fixed meteorological station such as those found at airports or other facilities, the weather measurements reported at that station may be used for temperature, relative humidity and wind velocity, when approved by the FAA before the test is conducted. The use of measurements reported at a fixed meteorological station, if not approved
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by the FAA before a test is performed, may cause the test to be disapproved and require that the aircraft be retested.
10 Aircraft test procedures Reference part 36, appendix J, section J36.101d, as modified:
a The aircraft test procedures and noise measurements must be conducted and processed in a manner that yields the noise evaluation measure designated LAE, as defined in paragraph 17 of this rule.
b The aircraft height relative to the noise measurement point sufficient to make corrections required in paragraph 26 of this rule must be determined by an FAA-approved method that is independent of normal flight instrumentation, such as a Differential Global Positioning System DGPS, or photographic scaling techniques. The aircraft position in three dimensions relative to the microphone must be monitored and recorded at all times during the test and data collection, with correlation via time synchronization to the acoustic noise data collection. The accuracy of the aircraft location system, and all sources of inaccuracy, along with possible error introduction when correlating to measured and recorded noise inaccuracies of timing devices and methods, must be determined and reported. A description of the aircraft location system and its accuracy must be included as part of the noise test plan required by paragraph 31 of this rule, and approved by the FAA before use.
c If an applicant demonstrates that the design characteristics of the aircraft would prevent flight from being conducted in accordance with the reference test conditions prescribed in paragraph 6 of this rule, then the applicant may request a variance in reference test conditions to be used.
Any variance from standard reference test conditions is limited to that required for the subject aircraft design characteristics that make compliance with the reference test conditions impossible.
11 Flyover Test Conditions Reference part 36, appendix J, section J36.105a, as modified: Paragraphs 12
through 15 of this rule prescribe the flight test conditions and allowable random deviations for flyover noise tests conducted to demonstrate compliance with this rule.
12 Level flight height and lateral path tolerances Reference part 36, appendix J, section J36.105b, as modified: A test series must consist of at least six flights. The number of level flights made with a headwind component must be equal to the number of level flights made with a tailwind
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component over the noise measurement station:
a In level flight and in cruise configuration;
b At the test height above the ground level over the noise measuring station as defined in paragraph 6 of this rule. For the selected height, the vertical tolerance of this height should be 10%
value; and c Within 10 degrees from the zenith.
13 Airspeed and Controls Reference part 36, appendix J, section J36.105c, as modified: Each flyover noise test flight must be conducted:
a At the reference airspeed specified in paragraph 6c of this rule; and b With the flight controls stabilized during the period when the measured aircraft noise level is within 10 dB of the maximum A-weighted sound level LAmax.
14 Aircraft weight Reference part 36, appendix J, section J36.105d, as modified: For the weight at which noise certification is requested, the aircraft test weight for each flyover test series must be specified for:
a MTOW inclusive of payload; and b Empty weight no payload.
15 Flyover height adjustment Reference part 36, appendix J, section J36.105e, as modified: If ambient noise at the measurement station, measured in accordance with paragraphs 17 through 21 of this rule, is found to be within 15 A-weighted decibels dBA of the A-weighted aircraft noise level LAmax, measured at the same location, the applicant may request the FAA approve an alternate flyover height. If an alternate flyover height is approved, the results must be adjusted to the reference flyover height specified in paragraph 6c of this rule using an FAA-approved method.
16 Supplemental hover test conditionsThis is a supplemental test to collect data for assessment of community noise impacts, and to inform later general noise and test standards for UA. This supplemental test does not require compliance with a noise limit and does not affect the noise certification findings for the subject aircraft.
The aircraft is required to hover at different spatial locations relative to the microphone in accordance with subparagraphs a through f of this paragraph.
a The aircraft must be at MTOW, inclusive of maximum payload weight of cargo.
b To ensure that the widest dimensional profile of the noise source is captured in the recordings, for each aircraft attitude heading 0, 90, 180 and
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