The public standards, regulations and guidance this topic draws on. Every factual claim in the preceding chapters traces to one of these; the worked example's aircraft, failure conditions, classifications and numbers are illustrative teaching values and belong to no source.
Editions matter more here than anywhere else in this knowledgebase, because two of the primary documents were reissued in December 2023 and the American regulatory baseline moved in August 2024. Each entry below is dated for that reason.
Regulations and airworthiness guidance
- 14 CFR § 25.1309, Equipment, systems, and installations, as amended by Amendment 25-152, 89 FR 68706, 27 August 2024, effective 26 September 2024 (the rule itself: catastrophic failure conditions must be extremely improbable and must not result from a single failure, and the amendment that added the Hazardous classification to the US rule).
- FAA Advisory Circular 25.1309-1B, System Design and Analysis, 30 August 2024, cancelling AC 25.1309-1A of 21 June 1988 (the five failure condition classifications, the average probability per flight hour bands, at-risk time, and Appendix A on where the 10⁻⁹ figure came from).
- FAA Advisory Circular 25.1309-1A, System Design and Analysis, 21 June 1988 (of historical interest, and worth reading once: three severity classes, three probability terms, and the FHA described as an optional preliminary step).
- EASA Easy Access Rules for Large Aeroplanes (CS-25), AMC 25.1309 (the European statement of the same classifications and probability terms, and the lineage the ARP documents follow).
Industry standards
- SAE ARP4761, Guidelines and Methods for Conducting the Safety Assessment Process on Civil Airborne Systems and Equipment, 1996 (the FHA worksheet, the aircraft and system levels, PSSA and SSA, the common cause analyses, and the contiguous wheel brake example that most of the open literature is built on).
- SAE ARP4761A / EUROCAE ED-135, December 2023 (the current edition, which restructured the process and moved material between documents; cite by edition, because the 1996 numbering does not carry over).
- SAE ARP4754A / EUROCAE ED-79A, Guidelines for Development of Civil Aircraft and Systems, 2010 (development assurance levels, the functional failure set, and the assignment rules for independent and dependent members).
- SAE ARP4754B / EUROCAE ED-79B, December 2023 (the current edition; EASA states in Certification Memorandum CM-DASA-002, issue 1 of 17 December 2024, that ED-79B is the standard currently recognised for the development assurance process).
- MIL-STD-882E, System Safety, US Department of Defense, 11 May 2012 (the defence-sector equivalent: preliminary hazard analysis, severity and probability categories, and the risk matrix).
Cross-industry comparisons
- ISO 26262, Road vehicles, Functional safety, part 3 (hazard analysis and risk assessment: severity, exposure and controllability combined into an ASIL, which is the same idea anchored differently).
- EN 50126, Railway applications, The specification and demonstration of reliability, availability, maintainability and safety (hazard identification and tolerable hazard rates in the railway lifecycle).
For the vocabulary these classifications sit inside, and for how the aviation ladder compares with SILs, ASILs and tolerable hazard rates, see the safety concept pages. For what happens to each failure condition next, the fault tree analysis module.