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Federal Register / Vol. 86, No. 164 / Friday, August 27, 2021 / Notices
to people, such as delivering packages in residential areas. These uses are expected to have an impact on persons and property from much closer distances than traditional piloted aircraft.
When tested under the current requirements of part 36 for manned aircraft, the noise generated by many UA could be lost in the ambient background noise at the reference altitude of 492 feet required in part 36
appendix J, while the noise in their proposed operating environments would be more apparent to persons near it.
The use of distributed electric propulsion and a high level of automated control at each rotor allow UA to operate with a variety of profiles, unlike those of larger manned aircraft.
The complex vortex field created by the interaction of the rotors, combined with the airframe, can cause such aircraft to exhibit highly tonal spectral content and unique noise directivity patterns that are often coupled with the vehicle flight dynamics and flight profiles. Such noise characteristics and flight profiles have not been considered previously under the standards and testing contained in part 36 and its appendices. These noise characteristics and flight profiles are examples of the factors that caused the FAA to test these aircraft and gather consistent data as a means to understand their relevance and eventual use in informing future standards generally applicable to UA.
Effective generally applicable noise rules require a base of data gathered from a test environment common for all aircraft, and certifications of unmanned aircraft such as this one represent the early stages of such data gathering. At present, the FAA does not have a sufficient database of information about the noise generated by most UA models to establish generally applicable noise standards, due to their novelty and variety. While small UA have operated under part 107 for several years, those aircraft do not have type or airworthiness certificates, and did not require noise testing; only limited noise data on those smaller models has been collected, and most of the collected data was acquired in a manner inconsistent with formal noise certification test conditions.
As industry seeks both type and airworthiness certification for UA to allow operation under part 91 or commercial operation under part 135, a commensurate shift in the noise certification paradigm is occurring as a means to capture new operational concepts that will be reflected in future regulations. While the FAA will
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continue to build a database of noise characteristics as it engages with certification applicants, such data gathering takes time and requires input about a number of models and designs before the influences of design on noise can be fully understood. FAA expects to use data collected through this proposed rule to inform future particularly and generally applicable standards.
Matternet applied for type certification of its aircraft on May 18, 2018. The aircraft is a quadcopter design UA with a maximum takeoff weight of 29 pounds including a 4-pound payload, and a proposed operating altitude of 400 feet or lower. Since the FAA has found that the current noise certification standards cannot be effectively applied to the Matternet Model M2 UA, in order to fulfill the statutory requirement under section 44715a3, the FAA is proposing a set of noise certification standards described in this Rule of Particular Applicability that would apply only to the Matternet model M2.
Without this proposed rule, Matternet would be unable to certificate its aircraft until such time as the FAA was able to establish a rule of general applicability for UA noise certification. The benefits of this proposal include establishing a noise certification basis for Matternet to seek type certification, the fulfillment of the FAAs obligation to provide noise standards under 49 U.S.C. 44715, and the collection of additional data that will be used to inform the development of a larger UA noise database from which future standards of general applicability may be developed.
III. Discussion of the Proposal This proposed rule presents only the noise certification basis for one new model of UA seeking type certification, the Matternet M2. Nothing in this proposed rule is intended to affect the airworthiness certification of this aircraft model or any operational approvals.1 Those findings are made separately by the FAA in accordance with the applicable aircraft certification and operating rules.
When an applicant presents an aircraft of any type for certification, the FAA must determine which among its many regulations apply to the aircraft presented. This is true for airworthiness standards and noise standards. This is an iterative process, during which the 1 In addition, this rule neither assesses the environmental impacts of any eventual operation of the subject aircraft, nor constitutes any environmental review that may be required by the FAA before granting operational approval. Any such environmental review would be completed in advance of granting operational approvals.

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FAA determines the standards and processes that apply, taking into account any new or novel features of the aircraft. The FAA works closely with the applicant to ensure that the applicant understands what standards apply, and what must be demonstrated during certification.
As previously discussed, in the case of the Matternet model M2 UA, the FAA
reviewed part 36, including its appendices, and determined that while the subject aircraft has some characteristics that are similar to a small helicopter that would be noise certificated under appendix J, the differences require noise certification test criteria and standards tailored to the size and features of the UA. The FAA
then worked with Matternet to understand the novel features and expected operating environment of the aircraft so that the FAA could determine the appropriate modifications and additions to the limits and procedures to develop a complete noise certification basis that would effectively profile the aircraft. The results of the agencys assessments are presented in this proposed rule. The proposed rule text is annotated at the beginning of each paragraph to indicate similar requirements in appendix J for those unfamiliar with noise certification requirements. The requirements presented in this proposal stand alone for certification of the M2 aircraft.
In addition to the data gathered for noise certification of the model M2, the applicant has agreed to conduct another test and give the resulting data to the FAA to inform the larger database of noise experience with UA. Data from the supplemental test are not part of the type or airworthiness certification basis of the aircraft and will not be evaluated against any noise limits or regulatory criteria for noise certification purposes.
The supplemental test is designed to gather further information on an aircraft that is capable of hovering. The FAA
developed the supplemental testing procedure with a consideration toward minimal test efforts; for example, no new or extra equipment is required.
Additionally, rather than placing microphones at different spatial locations, the microphone is placed at height 4 feet above the ground in accordance with paragraph 22 of this proposed rule and remains in place.
Differences From Generally Applicable Noise Regulations As stated above, the FAA began its determination of the noise certification basis for the Matternet M2 aircraft using the outline of standards and procedures for small helicopters. To compensate for
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