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Federal Register / Vol. 86, No. 184 / Monday, September 27, 2021 / Rules and Regulations
from exceeding maximum limits and transients. Results from the safety analysis are used to decide how to manage the consequences of all failures that can reasonably be expected to occur.

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Special Condition No. 24, Temperature Limit The FAA proposed that Special Condition no. 24 would require magniX
to ensure the engine can endure operation at its temperature limits, plus an acceptable margin. An acceptable margin, as used in this special condition, is the amount of temperature above that required to prevent the leastcapable engine allowed by the type design from failing due to temperaturerelated causes when operating at the most extreme thermal conditions.
Comment Summary: Textron recommended that the FAA require the applicant to consider environmental conditions and that the engine temperature limit be substantiated at the worst-case environmental conditions to ensure the engine cooling system performance is adequate when the engine operates at the declared temperature limit.
FAA Response: The FAA has changed final Special Condition no. 24 with a requirement for magniX to account for operating environments when they establish a value for the engine temperature limit.
Comment Summary: TCCA
recommended that Special Condition no. 24 include the following footnote:
Acceptable margin, as used in the proposed special condition, is the amount of temperature above that required to prevent the least-capable engine allowed by the type design from failing due to temperature-related causes when operating at the most extreme thermal conditions. TCCA also recommended that Special Condition no. 24 includes: Upon completion of the demonstration, the engine must be within serviceable limits.
FAA Response: The FAA does not agree with this comment. The following special conditions already incorporate the technical criteria proposed by TCCA:
Special Condition no. 1 requires magniX to comply with 14 CFR 33.8, Selection of engine power and thrust ratings, for the proposed engines.
Section 33.8b requires that each selected rating must be for the lowest power or thrust that all engines of the same type may be expected to produce under the conditions used to determine that rating. This requirement will address the temperature margins
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required for the least thermally capable engine the type design allows.
Special Condition no. 32c General conduct of tests has provisions that require the engine and its components to be within serviceable limits, safe for continued operation, and capable of operating at the declared ratings without exceeding limits after completing the tests identified in these special conditions.
Special Condition no. 24 requires the engine design to demonstrate its capability to endure operation at its temperature limit plus an acceptable margin.
Special Condition no. 12 Stress analysis includes a requirement for a thermal stress analysis to show a sufficient design margin to prevent unacceptable operating characteristics and hazardous engine effects.
Therefore, Special Condition nos. 12, 24, 32c, and 33.8 address TCCAs recommendation. The FAA made no changes to the special condition as a result of the comment.
Comment Summary: EASA
commented that the temperature limit is a new requirement compared to the requirements in 14 CFR part 33, EASA
CSEs,11 and the technical criteria in ASTM F333818. EASA stated that the applicant demonstrates operation up to the limits as part of the endurance test.
EASA further commented that the engines serviceability after the endurance test is sufficient proof that the engine has been designed and manufactured with margins compared to the limits declared in the engine installation manual. Therefore EASA
recommended removing this requirement from this special condition.
FAA Response: The FAA does not agree with this comment. The FAA
included a temperature limit because it is directly related to a primary failure mechanism associated with the novel technology used in magniXs proposed electric engine designs. The FAA did not change this special condition as a result of this comment.
Special Condition No. 25, Operation Demonstration The FAA proposed that Special Condition no. 25 would require that the engine demonstrate safe operating characteristics throughout its declared flight envelope and operating range. The engine performance data magniX will use to certify each engine must account for installation loads and effects.
Comment Summary: Ampaire stated that the terminology used in the 11 https www.easa.europa.eu/certificationspecifications/cs-e-engines.

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proposed special condition uses the term demonstration, and the term used in the ASTM document refers to the requirement as a test ref. ASTM
F333818, section 5.20.8.
FAA Response: As used in these special conditions, a demonstration is a test, but the special condition also allows validated analysis to show compliance. A test is required to validate an analysis, so the requirement is always grounded in a test. The FAA
made no changes to the special condition as a result of this comment.
Comment Summary: Ampaire suggested that in-flight restart characteristics are a critical capability of electric engines and recommended that the FAA require this capability as part of the engine demonstration test. Airbus and TCCA also recommended that the FAA require a demonstration of in-flight restart capability. In addition, TCCA
recommended that the special conditions require these demonstrations to be conducted with a representative propeller.
FAA Response: The FAA does not agree with the comments. Engine inflight restart capabilities are established at the aircraft level in accordance with 14 CFR 23.2425b, 25.903e, 27.903d, and 29.903e. These regulations also require installed engines to have a restart capability within the aircrafts flight envelope. Therefore, a requirement for magniX to verify the inflight restart capability of their engines during the engine certification program is not within the bounds of these special conditions. No changes were made to final Special Condition no. 25 as a result of this comment.
Comment Summary: TCCA asked if a gearbox assembly is considered as a single part of the engine.
FAA Response: A gearbox assembly is not considered to be a single part of the magniX engine. Gearboxes used in the magniX engines are treated as an engine accessory. The 14 CFR part 33
requirements imposed by Special Condition no. 1 that address engines with gearboxes and apply to magniX
engines are 14 CFR 33.3, 33.5, 33.25, and Appendix A33.3. The special conditions that correspond to 14 CFR
part 33 requirements that address gearboxes used in the magniX engines are Special Condition nos. 2, 15, 20, 22, 23 and 26. No changes were made to these special conditions as a result of TCCAs comment.
Special Condition No. 26, Durability Demonstration The FAA proposed that Special Condition no. 26 would require magniX
to subject the engine to a durability
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