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Federal Register / Vol. 86, No. 184 / Monday, September 27, 2021 / Rules and Regulations
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failure considerations that are normally addressed by Special Condition no. 17
Safety Analysis. The FAA made no changes to the special condition as a result of the comment.
Comment Summary: Textron recommended adding a requirement for bearing protection that states, Engine bearings must be protected from rotor voltage or a periodic replacement interval shall be determined as defined in Special Condition no. 13.
FAA Response: The FAA agrees with the technical content of this comment, but there is no requirement in these special conditions to add rotor shaft grounding technology in the magniX
engines. Bearings could experience accelerated wear-out from ungrounded shafts, but the failure should not present a safety issue because the failure is predictable with sufficient testing.
Requirements such as 33.4, Instructions for Continued Airworthiness, Special Condition no. 3
Materials, Special Condition no. 5
Durability, Special Condition no. 13
Critical and life-limited parts, and Special Condition no. 29 Teardown inspection will all have a role in managing the consequences of potential bearing wear from electrical effects.
magniX may assess the impact to product support at the predicted bearing replacement frequency and decide to include rotor shaft grounding technology.
Comment Summary: TCCA
recommended that the FAA add a requirement to this special condition, requiring the applicant to demonstrate that the engine mounts and mounting features are fireproof if flammable fluids are used within the engine.
FAA Response: The FAA does not agree with the comment. The fire protection requirements in 14 CFR 33.17
apply to the magniX engines. The FAA
made no changes to the special condition as a result of the comment.
Special Condition No. 8, Accessory Attachments The FAA received no comments for Special Condition no. 8, and it is adopted as proposed. It requires the engine to comply with 14 CFR 33.25, which sets certain design, operational, and maintenance requirements for the engines accessory drive and mounting attachments, and which would otherwise be applicable only to reciprocating and turbine aircraft engines.
Special Condition No. 9, Overspeed The FAA proposed that Special Condition no. 9 would require magniX
to establish by test, validated analysis,
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or a combination of both, that: 1 The rotor overspeed not result in a burst, rotor growth, or damage that results in a hazardous engine effect; 2 rotors possess sufficient strength margin to prevent burst; and 3 operating limits of the engine not be exceeded in-service.
Comment Summary: GE stated that proposed Special Condition no. 9c was duplicative of Special Condition no.
10b and h Engine control systems, and requested the special condition be removed.
FAA Response: The FAA does not agree with the comment. The special conditions referenced by GE accomplish different safety objectives. Special Condition no. 9c requires that the engine must not exceed the rotor speed operational limitations that could affect rotor structural integrity. This requirement results in an overspeed limit. Special Condition no. 10b requires the engine control system must ensure the engine does not experience any unacceptable operating characteristics or exceed its operating limits, including in failure conditions where the fault or failure results in a change from one control mode to another, from one channel to another, or from the primary system to the back-up system, if applicable. The FAA made no changes to the special condition as a result of the comment.
Comment Summary: Ampaire stated that Special Condition no. 9
Overspeed should include more information from ASTM F333818.
FAA Response: The FAA does not agree with the comment. ASTM F3338
18 section 5.9, EPU Rotor Overspeed, contains technical criteria that the FAA
used in developing these special conditions. It also contains information that the applicant can use to propose means of compliance to these special conditions. The FAA did not change this special condition as a result of this comment.
Comment Summary: Textron recommended that the FAA modify Special Condition no. 9, paragraphs a and c, replacing speed with RPM.
Textron reasoned that the term speed could be misleading.
FAA Response: The units used for rotational speed in the limitations section of the engine manual can be expressed using various units. The FAA
recognizes that rpm is used in 14 CFR
33.88, Engine overtemperature test and 33.201, Design and test requirements for Early ETOPS eligibility, but speed units are not specified in all regulations that mention engine rotor speed.
Therefore, the FAA will maintain the term speed in these special conditions. The FAA did not change
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this special condition as a result of this comment.
Comment Summary: TCCA stated that proposed Special Condition no. 9
suggested that the controller will provide the engine overspeed protection and commented that the FAA should ensure that the overspeed protection will function as intended when exposed to high-intensity radiated fields HIRF, lightning environments, and threats.
TCCA stated that verification of this protection might require the electric motor and engine control system to be included in the test setup when conducting the HIRF and lightning transient system tests and recommended that these special conditions clarify this topic in the discussion section of these special conditions.
FAA Response: This special condition is a performance-based requirement, and test details will be established as part of the demonstration of compliance. The FAA made no changes to the special condition as a result of the comment.
Comment Summary: TCCA
recommended that the FAA modify Rotors must possess as stated in Special Condition no. 9b, to Rotors, including any integral fan rotors used for cooling, must possess.
FAA Response: These special conditions are not generally applicable to all electric engines; they apply only to the applicants proposed engines. The magniX engines do not use integral fan rotors to cool the engine. The FAA did not change this special condition as a result of the comment.
Special Condition No. 10, Engine Control Systems The FAA proposed that Special Condition no. 10 would impose several requirements.
Special Condition no. 10a proposed that the requirements of that special condition apply to any engine system or device that controls, limits, monitors, or protects engine operation and is necessary for the continued airworthiness of the engine.
Special Condition no. 10b proposed to require that an engine control system ensure that the engine does not experience any unacceptable operating characteristics such as unstable speed or torque control or exceed any of its operating limits.
Special Condition no. 10c proposed to require magniX to systematically design, develop, and verify the software and complex electronic hardware, including programmable logic devices.
RTCA DO254, Design Assurance Guidance for Airborne Electronic
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