FAA Part 25 Rewrite Targets Faster, Clearer Aircraft Certification
FAA started an extremely important review of a number of provisions of Part 25 regulation, the main airworthiness rule framework for transport category airplanes in the USA. First and foremost, it means updating the certification framework for large commercial airplanes taking into account the changes due to the modern engineering use of composites, fly-by-wire systems, increasing complexity of the airplane systems, changes in the cabin architecture, etc.
First of all, it is not deregulation. As per FAA, it is supposed to help to decrease the certification timeframes while keeping or even raising the current safety level. The difference is crucial because Part 25 is the rulebook for obtaining and modifying type certificates for the transport category airplanes covering a wide range of questions starting from the airplane structure, flight characteristics, systems, cabin safety, fire protection, operating limitations, etc. The new design cannot be covered by the old language of the rules and thus the manufacturers have to request special conditions, exemptions, or equivalent level of safety findings on case-by-case basis.
These findings can be requested in certain cases, but it is costly for both applicants and the regulator. Modernization should help to transform certain case-by-case decisions into the base rules. If it is done, then the certification process becomes less dependent on the need for project-specific workarounds and more dependent on the baseline which is more clear and predictable. It is not only about the convenience of the engineers, but about the planning discipline fewer compliance surprises later in the development process, more predictable test campaign and more predictable assumptions for the suppliers of the avionics, propulsion, structure, cabin and other systems.
The timing issue is crucial here. FAA’s U.S. certification policy has faced quite tough criticism following the 737 MAX crisis and Aircraft Certification, Safety, and Accountability Act which was signed in 2020 and introduced additional oversight of the delegation practices. Some of the criticism was not aimed at the inadequacy of the current rules, but rather at the delegation practices and the process of surfacing of the safety-critical information during the certification process. This is still a topical issue. Rewriting Part 25 will not solve all of the certification governance issues. However, it will deal with another and equally important problem rule structure which, according to the administration, does not evolve enough taking into account the recent technologies, manufacturing processes and design approaches.
This aspect may become particularly important concerning the software intensive airplanes. The current process of the certification of the transport airplanes presupposes demonstrating the compliance with the appropriate weight, center-of-gravity and operating conditions either through tests, calculations or their combination. Increasing dependence of the airplane functions on the automation, integrated avionics and interaction of the systems instead of independent hardware increases the risks of ambiguities in the baseline rules creating schedule risks. The clear rules in this area will not necessarily simplify the certification process, but will make it more legible. It is important for the applicants who try to develop certification plan early in the development process and for the FAA which has to evaluate the safety-critical assumptions of this plan.
Derivative airplanes may also be impacted by this process. One of the aspects of the proposed rewrite of the Part 25 is how the agency will evaluate the changes compared to the already certified airplane. This is the engineering and program management issue no less than the legal one. Codification of this area will allow having a more stable approach to the amended type certificates and related compliance findings. Suppliers will also benefit from it as usual delays in the aircraft certification process delay the engine delivery, avionics integration, manufacturing of the structural components and further maintenance plans.
Human factors may also become the pressure point here. The modern cockpit impacts the pilot workload, alerting logic and interaction with the automation. The update of the Part 25 reflecting the pilot interaction with the new cockpit systems will follow the general trend of making the safety assessment more explicit and less fragmented through the project-specific findings. For the systems engineer this is the reminder that the certification process is not only about checking whether the function works, but the ability of the crew to understand, manage and control the airplane in the operational conditions.
There is also the transatlantic angle of this update. FAA has shown its desire to harmonize the requirements with those of EASA and this proposed update will reduce the number of differences between the rules of the two agencies. This can sound as a purely administrative measure, but it is directly related to the engineering process. The different rules of FAA and EASA require the manufacturers to maintain parallel documentation and analysis, compliance negotiations for the same underlying design. Harmonization will help to reduce this friction without changing the safety target.
It does not mean that all of this will happen immediately. The process is still in the proposal phase and the FAA has not presented any clear timeline yet. Notice-and-comment rulemaking of such scale will take several years and the final text can change drastically during the public debate, the congressional consideration and the international coordination. It would be a mistake to treat the current proposal as some guarantee of the acceleration of the certification process for some specific aircraft.
However, the direction is clear the FAA tries to transform the certification process of the transport category airplanes from the case-by-case relief to the set of rules which would reflect the real design of the airplane now. For the US aerospace industry this is the governance process with engineering consequences not the lowering of the safety level, but the possible reduction of the certification uncertainty in the age of software, automation, advanced materials and derivative development.
This is the significance of the Part 25 update. In the certification system the clarity is not the bureaucracy for its own sake, but the element of the safety architecture. When the baseline rules correspond to the technology which is being certified, both the oversight and the design process become more disciplined.
By Thomas Caldwell – AMI’s senior editor for mechanical and mobility engineering, covering vehicle electronics, systems integration, electrification, chassis systems, propulsion, and safety policy.
