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Federal Register / Vol. 86, No. 184 / Monday, September 27, 2021 / Rules and Regulations
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TCCA. In addition, design margins are also required by Special Condition nos.
9 Overspeed, 12 Stress Analysis, 19
Liquid Systems, 24 Temperature Limit, and 30 Containment. No changes have been made to this special condition as a result of this comment.
Special Condition No. 13, Critical and Life-Limited Parts The FAA proposed that Special Condition no. 13 would require magniX
to show whether rotating or moving components, bearings, shafts, static parts, and non-redundant mount components should be classified, designed, manufactured, and managed throughout their service life as critical or life-limited parts.
Special Condition no. 13 corresponds to 14 CFR 33.70, Engine life-limited parts, which is a complex requirement.
Accordingly, additional information is provided in this discussion. In this context, the engineering plan referenced in Special Condition no. 13b1
requires magniX to establish activities for managing documents, practices, and procedures that govern essential design criteria essential to part airworthiness.
The engineering plan contains methods for verifying the characteristics and qualities assumed in the design data.
The methods must be suitable for the part criticality. The engineering plan communicates information from engineering to manufacturing about the criticality of design features that affect airworthiness. In accordance with 14
CFR 21.137, Quality system, the plan must include a reporting system that flows problematic issues that develop while operating in-service so the applicants design process can address them. The engineering plan is established during pre-certification activities and executed during postcertification activities.
For example, the effect the environment has on engine performance might not be consistent with the design assumptions. The impact of ice slab ingestion on engine parts might not be fully understood until the engine response is evaluated during testing the specific ice quantities and shapes that the airplane sheds.
The term low-cycle fatigue, as referenced in Special Condition no.
13a2, is a decline in material strength from exposure to cyclic stress at levels beyond the stress threshold the material can sustain indefinitely. This threshold is known as the material endurance limit. Low-cycle fatigue typically causes a part to sustain plastic or permanent deformation during the cyclic loading and can lead to cracks, crack growth, and fracture. Engine parts that operate at
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high-temperatures and high-mechanical stresses simultaneously can experience low-cycle fatigue coupled with creep.
Creep is the tendency of a metallic material to permanently move or deform when exposed to the extreme thermal conditions created by hot combustion gasses and substantial physical loads such as high rotational speeds and maximum thrust. Conversely, high-cycle fatigue is caused by elastic deformation, small strains caused by alternating stress, and a much higher number of load cycles compared to the number of cycles that cause low-cycle fatigue.
The term manufacturing definition, as referenced in Special Condition no.
13b2, means the collection of data required to translate documented engineering-design criteria into physical parts and verify that the parts comply with the design data properties. Because FAA regulations do not require parts to fail during a certification program, the documents and processes have outcome expectations, required by 14 CFR
21.137, Quality system and 14 CFR
21.138, Quality manual, to result in parts with the integrity and reliability assumed in the design data. These production and quality systems limit the potential manufacturing outcomes to parts that are consistently produced within physical design constraints.
The manufacturing plan and service management plan ensure essential information from the engineering plan, such as the design characteristics that ensure the integrity of critical and lifelimited parts, is consistently produced and preserved over the lifetime of those parts. The manufacturing plan includes special processes and production controls to prevent manufacturinginduced anomalies, which can degrade the parts structural integrity. Examples of manufacturing-induced anomalies are material contamination, unacceptable grain growth, heat affected areas, and residual stresses. The service management plan has provisions for enhanced detection and reporting of service-induced anomalies that can cause the part to fail before reaching its life-limit or service limit. Abnormalities can develop in-service from improper handling, unforeseen operating conditions, and long-term environmental effects. The service management plan ensures important information that might affect the design processs assumptions is incorporated into the design process to remove unforeseen potential unsafe features from the engine.
Comment Summary: Wisk stated it is more appropriate to use The Applicant than the Company name magniX in Special Condition no.

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12b1. Wisk recommended changing the reference to the engine manufacturer reference from magniX to the applicant.
FAA Response: The FAA understands Wisks comment to be relevant to Special Condition no. 13b1 because Special Condition no. 12b1 does not exist. These special conditions are not applicable to all electric engine manufacturers. As stated in this preamble, these special conditions apply to the magniX magni350 and magni650 model engines. No change to this special condition is necessary as a result of this comment.
Comment Summary: Textron recommended that the post-certification activities described in the Discussion section of the proposed special conditions be included in the text of Special Condition no. 13.
FAA Response: The Discussion for this special condition is based on its similarity to 14 CFR 33.70, Engine lifelimited parts. No change to this special condition is necessary as a result of this comment.
Comment Summary: An individual commenter suggested there might be unique questions regarding low-cycle fatigue LCF of components used in electric engines. The commenter explained that if the core rotor speed is low, the risk of a rotor burst might not be significant. However, a core rotor assembly that uses windings or embedded permanent magnets if applicable may have some LCF/
thermal/electrical refer to corona effect on motor windings cycling challenges and the electrically powered electronics driving the motor. The individual also stated that they have learned through experience about the significance of thermal effects resulting from a broad range of operating conditions, especially during quick power transients.
FAA Response: Special Condition no.
13 requires magniX to determine the parts and components that should be classified designed, manufactured and managed throughout their service life as critical or life-limited parts. Therefore, Special Condition no. 13 provides the requirements for magniX to address the unique issues that arise when identifying and managing life-limited and critical electric engine parts. The FAA made no changes to these special conditions as a result of this comment.
Comment Summary: TCCA stated that 14 CFR 33.70 is similar enough to proposed Special Condition no. 13 that the FAA should replace the proposed special condition with reference to the 14 CFR part 33 requirement and modify it. EASA suggested the FAA remove the
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