FAA 14 CFR Part 25 — Airworthiness Standards: Transport Category Airplanes
Issuing body / enforcer: Federal Aviation Administration (FAA), U.S. Department of Transportation. Jurisdiction: United States. Part 25 is the airworthiness code for type certification of transport-category airplanes; it is mirrored internationally (EASA CS-25) and accepted through bilateral validation.
What it is
Part 25 of Title 14, Code of Federal Regulations, sets the minimum airworthiness standards — structural, aerodynamic, systems, and performance — that a transport-category airplane must meet to earn an FAA Type Certificate. It is the rulebook behind every airliner certification: it defines how strong the wings must be, how the airplane must behave after an engine failure, what redundancy flight-control and electrical systems need, how evacuation must work, and how the manufacturer proves all of it by analysis and test.
Part 25 does not itself grant operating authority (that is Parts 91/121/135); it establishes the design standard the airplane is built and certified to. Once certified, the airplane is maintained under Part 43 and operated under the operating rules — but the Part 25 certification basis follows the airplane for life, governing every major change and supplemental type certificate.
Scope: who and what it applies to
- Applicability threshold: airplanes with a maximum takeoff weight over 12,500 lb (with certain exceptions), multi-engine turbine airplanes, and commuter-category airplanes above 19 seats — in practice, all airliners and large business jets.
- Applicants: airframe OEMs (Boeing, and foreign OEMs validating into the US system), STC holders making major changes, and modifiers (freighter conversions, winglets, avionics retrofits) whose changes touch the certification basis.
- Trigger: application for a new type certificate, an amended type certificate (derivative models), or a supplemental type certificate. The certification basis is fixed at the Part 25 amendment level in effect on the date of application (with a 5-year validity window for transport category, extendable).
Key requirements and compliance obligations
Part 25 is organised in subparts; the load-bearing ones for a compliance engineer:
- Subpart B — Flight. Performance requirements: takeoff, climb, landing distances; controllability and manoeuvrability; stability; stall characteristics; and operation with one engine inoperative (the famous "second-segment climb" gradients). High-speed characteristics including flutter-free operation up to V_D/M_D.
- Subpart C — Structure. Limit and ultimate loads (1.5× limit), fatigue and damage-tolerance evaluations, bird-strike resistance, discrete-source damage (uncontained engine failure, APU), emergency landing conditions (the 9g forward/3g upward static load cases for seats and attachments), and lightning/HIRF protection for structure and systems.
- Subpart D — Design and Construction. Materials and fabrication methods, flutter and vibration, control systems, landing gear, pressurisation, fire protection zones, and occupant protection.
- Subpart E — Powerplant. Engine installation, fuel systems, oil systems, thrust reversers, engine-control integration.
- Subpart F — Equipment. Electrical systems and equipment (including the 25.1353 battery and 25.1357 circuit-protection lineage), avionics installation, oxygen systems, emergency equipment.
- Subpart G — Operating Limitations and Information. The Airplane Flight Manual: limitations, procedures, and performance information the operator must have.
- Subpart H — Electrical Wiring Interconnection Systems (EWIS). Added after the TWA 800 and Swissair 111 investigations — design, installation, and Instructions for Continued Airworthiness for wiring.
- Appendices. Including Appendix H (Instructions for Continued Airworthiness), Appendix K (extended operations / ETOPS), and icing certification appendices (O for supercooled large droplets, added after Air France 447-era rulemaking).
Compliance method: for each requirement the applicant shows compliance by analysis, laboratory test, ground test, flight test, or similarity — documented in compliance checklists reviewed by the FAA (or by Organisation Designation Authorization holders — ODA — under FAA oversight). Key companion guidance: AC 25-series advisory circulars, and for systems/software the ARP4754/ARP4761/DO-178C/DO-254 chain (see sibling briefs).
Penalties and consequences of non-compliance
- Certification action: the FAA can deny, suspend, or revoke type certificates, amended TCs, and STCs; it can issue Airworthiness Directives mandating corrective action across fleets (non-compliance with an AD renders the aircraft unairworthy — it cannot legally fly).
- Civil penalties: under 49 U.S.C. § 46301, the FAA may assess civil penalties (currently up to roughly $25,000–$75,000+ per violation depending on entity type and inflation adjustments; each day of a continuing violation can be a separate violation). Manufacturing or installing non-conforming parts, or operating outside the type design, are classic enforcement targets.
- Certificate action against individuals and companies: suspension or revocation of production certificates, designee/ODA authority, and repair-station certificates.
- Criminal exposure: knowing falsification of certification records can be referred for criminal prosecution (18 U.S.C. § 1001 false statements; the 737 MAX cases demonstrated DOJ interest in certification fraud).
- Commercial: ADs and groundings impose fleet-wide costs; loss of a type certificate effectively kills the product line.
Version / edition status and live changes
- Part 25 is continuously amended; recent amendment activity continues to address icing (Appendix O implementation), EWIS, fuel-tank flammability (25.981 lineage), and crashworthiness. Flag (unverified detail): the exact current amendment number was not verified against the eCFR for this brief — practitioners should confirm the amendment level in effect on their application date via ecfr.gov.
- Ongoing: the FAA continues Part 25 rulemaking for new technologies — electric/hybrid propulsion integration, and special conditions for novel configurations (e.g., blended-wing-body, eVTOL-derived transport concepts) are being issued as special conditions under §21.16 where Part 25 does not yet address a novel feature.
- EASA CS-25 remains the harmonised counterpart; FAA-EASA differences are managed through the bilateral TIP.
Related certifications (from the engineering catalogue)
Flagship/license certifications in Aerospace: FAA Airframe and Powerplant (A&P) Mechanic Certificate — tangentially related: A&P mechanics maintain Part 25 airplanes under Parts 43/65/145, but the A&P exams do not test Part 25 design standards. CEng via RAeS — a professional registration; no direct Part 25 examination content. The credentials that truly require Part 25 mastery (FAA DER/ODA unit members, EASA CVE roles) are employer/designation-based, not catalogue credentials — flagged honestly here.
Honest flags
- Exact current amendment number and the penalty-dollar figures should be verified in the eCFR and 49 U.S.C. § 46301 inflation-adjustment rules before use in a compliance filing.
- Special conditions and exemptions (Part 11) are a live, case-by-case layer on top of Part 25 — this brief covers the standing rule, not active dockets.
Original ETS reference writing, verified against public sources on 2026-09-30. Thin sourcing is flagged inline. Not legal advice — confirm current editions with the issuing body.