FAA Part 25 Rewrite Targets Certification Friction and Design Updates
The FAA is currently undertaking a large-scale overhaul of transport-airplane certification regulations in Part 25 of the Code of Federal Regulations through issuing a notice of proposed rulemaking published on June 26. The notice includes various provisions for transport category airplanes and propulsion systems; however, what is really important about it is that it addresses governance. In other words, the agency attempts to reduce the amount of applications seeking exemption, special conditions and equivalent level of safety findings in order to provide reasonable certificaion basis.
It is so because, first of all, Part 25 certification requirements serve as primary airworthiness regulations for transport category airplanes and their modifications. However, in some cases, new and modified designs do not comply with the language of outdated regulations and require additional data and analysis in order to set up a certification basis. As the FAA notes, this proposal is expected to eliminate repetitions of such cases while “maintaining or improving the level of safety provided by the current regulations.”
From the standpoint of engineering policy approach, it is not the case of diluting existing standards but incorporation of recurrent exceptions into primary regulation. According to the Department of Transportation, such a change was needed in order to simplify certification process for transport-category aviation products and update regulations in order to respond properly to technology proposals of the applicants. For U.S.-based developers, modifiers, and certification teams, it can mean transition from negotiation of individual regulation to compliance with established one.
One of the most evident objectives of the proposal is executive-interior design. The FAA seeks to withdraw Special Federal Aviation Regulation No. 109 from Part 25 and incorporate requirements of it into new sections of Part 25. Additionally, the agency will add definitions of low-occupancy and non-commercially operated airplanes. This is a clear example of systems integration as the agency intends to address the issue of such interior configuration not as a recurrence but as a primary transport airplane regulation.
Several changes that are covered by the proposed amendments involve various aspects that relate to cabin and onboard systems affecting the certification process of new and modified airplane designs. These aspects include such issues as marking and lighting of emergency exits, cabin configuration, lavatory fire protection, medical stretchers, passenger facilities, oxygen outlets, and operation without normal electrical power. Far from being merely cosmetic, these aspects involve such issues as intersection of human factors, emergency egress, fire protection, power architecture, and maintainability. Thus, it is quite common that such issues become problematic in case when outdated language of regulation does not cover non-standard interiors and equipment designs.
The issue of power loss becomes especially relevant today as operation without normal electrical power is primarily a systems issue rather than an equipment one. It not only covers power distribution and essential load but also such issues as crew procedures, preservation of safety functions in abnormal conditions, as well as emergency exit and evacuation logic and occupants’ usage.
Among other changes that are proposed by the FAA, there is also a specific provision for propeller-powered transport airplanes. The FAA will update the rules on power-lever movement by introducing a requirement to provide means for preventing flight crew from moving a power lever below flight idle position in flight unless the airplane is certified for such operations. On a high level, this is another example of certification control problem: to precisely determine allowable crew interfaces and system behavior for proper design operation.
Another important feature of this proposal is international alignment. The FAA has stated that several proposed changes will bring U.S. regulations closer to the European Aviation Safety Agency CS-25 standards. It does not mean equivalence, but it allows manufacturers and modifiers working in both FAA and EASA regulatory framework to reduce compliance duplications and associated efforts. For certification engineers, the harmonization is as important as text of technical regulation itself as mismatches lead to compliance duplications and associated schedule risks.
It should also be noted the scope of this proposal. It is not a finalized regulation but notice of the proposed rule-making. The commenting process is still open until Aug. 25. This means that the FAA does not claim that all certification challenges will disappear under the new Part 25. There will still be cases where application-specific compliance proving is required. Nonetheless, it is obvious that if the agency addresses recurrent exceptions and safety equivalencies, then it will make a decision to incorporate them into primary regulations.
This is the true importance of the NPRM for U.S. transport airplane sector. In solving the problem of certification delays, it recognizes not only paperwork issues but also governance problem generated by outdated regulations concerning new designs and systems. If the FAA will be able to reduce the number of repetitious exceptions while maintaining safety requirements, then it will mean the establishment of more reliable certification basis for aircraft developers, modifiers, and engineering teams responsible for implementation of the regulation text into certifiable hardware and cabin systems architecture.
Thomas Caldwell is AMI’s senior editor for mechanical and mobility engineering, covering vehicle electronics, systems integration, electrification, chassis systems, propulsion, and safety policy.
