Type certification and continued airworthiness

A lifelong framework

Civil aviation safety relies on a continuous regulatory framework. It spans initial design approval, manufacturing oversight, operational maintenance, and mandatory safety actions issued throughout an airframe's operational life.

The three certification pillars

Airworthiness rests on three distinct certificates issued by civil aviation authorities such as the FAA or EASA:

• Type certificate (TC), for the design: approves the overall design, structural architecture and operating envelope against the certification basis, which is the airworthiness standards in effect at the time of application plus any special conditions. It is summarized in the type certificate data sheet (TCDS).
• Production certificate (PC), for manufacturing: approves the manufacturer's quality management system, facilities and processes to build products that conform to the approved type design.
• Airworthiness certificate, for each individual aircraft: issued to a specific airframe by registration and serial number. It confirms the aircraft conforms to its type design and is in a condition for safe operation. It remains effective only as long as maintenance, inspections and alterations are performed in accordance with the regulations.

Design change pathways

As aircraft evolve, structural or system modifications must follow formal approval pathways. The first question is whether a change is minor or major. A major change then follows a different path depending on whether the type certificate holder or a third party makes it.

• Minor changes: changes with no appreciable effect on weight, balance, structural strength, reliability, operational characteristics or other airworthiness factors. They are approved by the TC holder under a method acceptable to the authority.
• Major changes by the TC holder: approved through an amended type certificate or a major change approval.
• Major changes by third parties: approved through a supplemental type certificate (STC). This is the normal route when someone other than the original manufacturer designs a major change, for example retrofitting a new avionics suite, a cargo conversion or a winglet installation.

Parts and appliance approvals

• Parts manufacturer approval (PMA): allows a manufacturer to produce replacement or modification parts for installation on type-certificated products. The applicant must show the part meets the applicable airworthiness requirements, often by showing it is identical to the original part, or by test and analysis.
• Technical standard order authorization (TSOA): approves the design and production of articles that meet a technical standard order's minimum performance standard, such as flight recorders, seats and transponders. Installing a TSO article on a particular aircraft still needs its own installation approval.

Service bulletins

Once an aircraft enters commercial service, operating history across the global fleet drives continuous safety monitoring. A service bulletin (SB) is issued by the aircraft or component manufacturer to recommend modifications, inspections or component replacements.

Legal status: optional by default, unless it is mandated by an airworthiness directive or incorporated into an operator's mandatory maintenance program.

Airworthiness directives

An airworthiness directive (AD) is issued by the regulatory authority, for example under FAA Part 39, when an unsafe condition exists in a product and is likely to exist or develop in other products of the same design. ADs often require accomplishing a manufacturer's service bulletin by a set compliance time.

Legal status: legally mandatory. An aircraft that is not in compliance with an applicable AD is not airworthy and may not be operated.

Alternative method of compliance (AMOC)

If an operator cannot comply with an AD using the exact steps it specifies, for example because of alternative tooling, a different repair or parts availability, it must request and obtain approval of an alternative method of compliance (AMOC) from the authority before carrying out the work.

Key takeaways

• Three primary certificates: the TC approves the design, the PC approves manufacturing quality, and the airworthiness certificate covers each individual aircraft.
• STCs for outside modifications: major changes designed by a third party require a supplemental type certificate.
• ADs are legally mandatory: manufacturer service bulletins become binding only when required by an AD or an approved operator program.
• An AMOC is required for deviations: never depart from an AD's procedure without a prior approved AMOC.