Consideration Reference Notice of Proposed Change to FAA – FAR 25-1309

Sofema Online (SOL) www.sofemaonline.com considers the proposed action to improve aviation safety by making System Safety Assessment (SSA) Certification requirements more comprehensive and consistent.

Details of Proposed Change

The FAA proposes revised and new safety standards to reduce the likelihood of potentially catastrophic risks due to latent failures in critical systems.

>> The standards would require the elimination of such risks as far as practical. When it is not practical to eliminate such a risk, the standards would require the reduction and management of any remaining risk.
>> The proposed standards would also improve the likelihood that operators discover latent failures and address them before they become an unsafe condition, rather than discovering them after they occur and the FAA addressing them with airworthiness directives (ADs).

Because modern aircraft systems (for example, avionics and fly-by-wire systems) are much more integrated than they were when the current safety criteria in § 25.1309 and other system safety assessment rules were established in 1970, ⁽²⁾ the new standards proposed in this rule would be consistent for all systems of the aeroplane, reducing the chance of a hazard falling into a gap between the different regulatory requirements for different systems.

Consistent criteria for conducting SSAs would also provide predictability for applicants by reducing the number of issue papers and special conditions necessary for aeroplane certification projects. ⁽³⁾

Specifically, the proposed rule would:

>> Require that applicants limit the likelihood of a catastrophic failure condition that results from a combination of two failures, either of which could be latent.
>> In this proposal, the FAA refers to this particular failure condition as a Catastrophic Single Latent Failure Plus One (CSL+1) because it consists of the catastrophic condition that results from a single latent failure plus one additional failure. See proposed § 25.1309(b)(5).
>> Revise safety assessment regulations to eliminate ambiguity, and provide consistency between, the safety assessments that applicants must conduct for different types of aeroplane systems.
>> Section 25.1309 would continue to contain the safety assessment criteria applicable to most aeroplane systems. Sections 25.671(c) (flight control systems) and 25.901(c) (powerplant installations) would be amended to remove general system safety criteria. Instead, the systems covered in these sections would be required to comply with § 25.1309 (system safety criteria).
>> Section 25.933(a) (thrust reversing systems) would allow compliance with § 25.1309 as an option. Sections 25.671, 25.901, and 25.933 would continue to contain criteria for safety assessments specific to flight control systems, powerplant installations, and thrust reversing systems, respectively.
>> Require applicants to assess and account for any effect that the failure of a system could have on the structural performance of the aeroplane. See proposed § 25.302.
>> Define the different types of failure of flight control systems, including jams, and define the criteria for safety assessment of those types of failures. See proposed § 25.671.
Require applicants to include, in the Airworthiness Limitations Section (ALS) of the aeroplane's Instructions for Continued Airworthiness (ICA), necessary maintenance tasks that applicants identify during their SSAs. See proposed § 25.1309(d).

Remove the “function properly when installed” criterion in § 25.1301(a)(4) for installed equipment whose function is not needed for the safe operation of the aeroplane

Next Steps

Sofema Aviation Services (www.sassofia.com) offers training to cover CS 25 System Safety Assessments – please see the following link.

For additional questions or comments – please email team@sassofia.com