What is a type certificate and why does every aircraft need one?

A type certificate (TC) is the formal approval issued by a civil aviation authority confirming that a specific aircraft design meets all applicable airworthiness standards. It is the foundational document of civil aviation safety — without a type certificate, an aircraft design cannot be legally manufactured or operated commercially. Every individual aircraft built to that design then receives its own airworthiness certificate confirming it conforms to the approved type design.

What is the fundamental difference between Part 23 and Part 25 aircraft?

FAR Part 23 covers normal category aircraft — generally smaller, simpler airplanes such as light singles, twins, and small commuter aircraft — while FAR Part 25 covers transport category aircraft, essentially airliners and large business jets. Part 25 imposes far more stringent requirements for structural safety factors, systems redundancy, occupant crashworthiness, and performance in engine-failure scenarios, reflecting the much larger number of passengers and higher operational complexity these aircraft carry.

What is an airworthiness directive and how is it different from a service bulletin?

An airworthiness directive (AD) is a legally mandatory corrective action issued by a civil aviation authority when an unsafe condition is found in a type-certificated product, and operators must comply with it within the specified timeframe or the aircraft cannot legally fly. A service bulletin, by contrast, is issued by the manufacturer and is typically advisory — recommended but not legally required — unless a regulator separately mandates compliance through an AD that references it.

What changed when the FAA rewrote Part 23 in 2017?

The 2017 rewrite replaced decades of prescriptive, one-size-fits-all design rules with performance-based safety objectives scaled to four certification levels based on seating capacity and speed, letting manufacturers use industry consensus standards (largely from ASTM) to show compliance. The goal was to cut certification cost and time for smaller aircraft — enabling faster adoption of new safety technology like angle-of-attack indicators and airframe parachutes — while keeping the underlying safety objectives the same or higher.

How do the FAA and EASA recognize each other's certifications?

The FAA and EASA operate under a Bilateral Aviation Safety Agreement (BASA) that allows each authority to validate, rather than fully re-certify, an aircraft already certified by the other, based on their shared confidence in each other's certification systems and the common baseline set by ICAO Annex 8. This validation process is still not automatic — it involves technical review and may require additional compliance findings for regional differences — but it avoids duplicating the entire certification effort for aircraft sold internationally.

Engineering·13 min read·July 12, 2026

📋 Aircraft Certification: FAR Part 23 vs Part 25 Explained

A guide to aircraft certification — the type certificate process, how FAR Part 23 (normal category) differs from Part 25 (transport category), airworthiness directives, and the roles of the FAA and EASA.

📖Aerospace Engineering Handbook (Full Access)

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Why Certification Exists

Every aircraft that carries passengers or cargo commercially has passed through a rigorous certification process designed to prove, before it ever flies a paying customer, that its design meets exacting safety standards. Certification is not a one-time checkbox — it is a comprehensive framework of design requirements, analysis, and testing administered by civil aviation authorities, chiefly the U.S. Federal Aviation Administration (FAA) and the European Union Aviation Safety Agency (EASA), that underpins the extraordinary safety record of modern air travel.

Topics covered

aircraft certificationFAR Part 23FAR Part 25type certificateairworthiness directiveFAA certificationEASA certificationsupplemental type certificatetransport category aircraftnormal category aircraftairworthinesscertification basis