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Federal Register / Vol. 86, No. 184 / Monday, September 27, 2021 / Rules and Regulations
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apply only to the magniX engine designs, which do not include the power systems addressed in 14 CFR
23.2525. These power systems are normally approved as part of the airplane. Therefore, any other relevant part 23 airplane requirements would also be addressed during the airplane certification program. The FAA did not change this special condition as a result of this comment.
Comment Summary: Wisk acknowledged that the high voltage and current electrical system is analogous to the traditional fuel system. As such, omitting regulations that are equivalent to all, or parts of 14 CFR 33.67 from these special conditions may result in a loss of a critical interface boundary, resulting in a lack of clear ownership between the airframe and engine OEM.
Wisk requested that the FAA clarify within the proposed SC the analogous aspects of 33.67 for the interface between the engine controller and the airframe electrical system as it relates to voltage and current.
FAA Response: 14 CFR 33.67 includes requirements for features that do not exist in the magniX engine electrical system. However, the analogous aspects of 33.67 are included Special Condition no. 2, which requires magniX
to establish and declare ratings and operating limits based on power-supply requirements for the engine. Therefore, Special Condition no. 2 addresses Wisks comment. The FAA did not change this special condition as a result of this comment.
Special Condition No. 2, Engine Ratings and Operating Limits The FAA proposed that Special Condition no. 2 would require magniX, in addition to compliance with 14 CFR
33.7a, to establish engine operating limits related to the shaft horsepower, torque, speed, and duty cycles. The duty cycle is an engine rating that declares a performance capability for the loads that will be imposed on the engine, including, if applicable, starting, no-load and rest, and de-energized periods, including their durations or cycles and sequence in time.
Comment Summary: Wisk recommended that the FAA expand the ratings and operating limits required by Special Condition no. 2 to include maximum temperature, maximum and minimum voltage, current, and power;
and, if applicable, coolant and/or lubrication temperatures & pressures for safe operation.
FAA Response: It is not necessary to impose voltage and current limits to ensure that these magniX engines achieve the same level of safety
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intended by 14 CFR part 33. The FAA
has changed final Special Condition no.
2 to add temperature and power powersupply requirements to the engine ratings and operating limits.
Comment Summary: Wisk stated that proposed Special Condition no. 2a1
Rated Maximum Continuous Power should not have a time limit as it is continuous. Wisk suggested deleting the word time from proposed Special Condition no. 2a.
FAA Response: The FAA agrees that the power at the Rated Maximum Continuous Power rating is not time limited. The FAA has modified final Special Condition no. 2 to remove the time constraint from the rating.
Comment Summary: Wisk suggested that the FAA specify coolant and lubrication temperatures and pressures for safe operation.
FAA Response: The FAA does not agree with Wisks suggestion. A special condition is not required for coolant and lubrication operating temperatures.
Special Condition nos. 6 Engine cooling and 14 Lubrication system address Wisks suggestion. No changes were made to this special condition as a result of Wisks comment.
Comment Summary: Rolls-Royce commented that, by placing a duty cycle on the engines type certificate data sheet, proposed Special Condition no. 2
would be overly prescriptive when compared to the FAAs requirements for aircraft engines that operate using aviation fuel. Rolls-Royce stated that Special Condition no. 2b should be removed, and the FAA should require the applicant to define a duty cycle in the Airworthiness Limitations Section of the Operating Manual.
FAA Response: The magni350 and magni650 electric engines have different operating characteristics than conventional reciprocating or turbine engines. The performance capability of electric engine designs is defined, in part, by a duty cycle. Therefore the FAA
did not change this special condition as a result of this comment.
Comment Summary: GE
recommended that the FAA modify Special Condition no. 2 to require the applicant to list the engines cooling fluid as an engine operating limitation, similar to 14 CFR 33.7b3, which requires, for reciprocating engines, established ratings and operating limitations related to oil grade or specification.
FAA Response: The FAA agrees with the comment and has modified final Special Condition no. 2 to require a cooling fluid grade or specification as an operating limit.

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Comment Summary: Ampaire commented that the term power, as used in proposed Special Condition no.
2, is not the most relevant metric for electric machinery and power electronics. Ampaire stated that it understood power, as used in that condition, to be the electrical power output delivered by the magniX engine.
Ampaire recommended that the FAA
change the requirement to specify current and voltage.
FAA Response: The FAA does not agree with the comment. As used in Special Condition no. 2, power describes the mechanical shaft horsepower supplied by the engine to propel the aircraft and not the electrical power delivered by the engine. The FAA made no changes to the special condition as a result of the comment.
Comment Summary: Ampaire asked that the FAA include more details from ASTM F333818, such as those listed in sections 5.3.15.3.8, EPU Operating Limitations and Ratings, in Special Condition no. 2.
FAA Response: The FAA does not agree with the comment. ASTM F3338
18 contains technical criteria that the FAA used in developing these special conditions. The airworthiness requirements for these engines include paragraphs from the ASTM specification and from 14 CFR part 33. The FAA
made no changes to the special condition as a result of this comment.
Comment Summary: Textron recommended that the FAA add engine temperature to the ratings and operating limits mandated by Special Condition no. 2.
FAA Response: The FAA agrees with the comment. The FAA has changed final Special Condition no. 2 to add temperature to the engine ratings and operating limits.
Comment Summary: Textron stated the term speed, as used in Special Condition no. 2a, could be misleading and mistaken for aircraft speed or gearbox output-shaft speed. Textron stated the term speed should instead be RPM.
FAA Response: The FAA does not agree with the comment. Engine speed is typically measured in units that describe a rate of mechanical rotation.
In Special Condition no. 2, the word speed, used in the context of rotational speed, applies to the output-shaft rotation rate. The applicant can express engine speed using various units, so the measurement unit of the engine shaft rotation does not need to be prescribed in Special Condition no. 2.
The FAA did not change the special condition based on the comment.

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