Steve Bentley MD of Sofema Aviation Services www.sassofia.com – explains

A type certificate holder (TCH) can produce parts for its airplanes through the process of the manufacturer's authorisation FAR Part 21 / EASA Part 21 Subpart G has the authorization to manufacture those parts based on its type certificate, and production certificate.

However, organisation who are authorised as PMA-holding manufacturers are permitted to make replacement parts for aircraft, even though they are not the original manufacturer of the aircraft. An applicant for a PMA applies for approval from the FAA.

An STC is a certificate. It defines the product design change, states how the modification affects the existing type design, and lists serial number effectivity. It also identifies the certification basis, listing specific regulatory compliance for the design change. Information contained in the certification basis is helpful for those applicants proposing subsequent product modifications and evaluating certification basis compatibility with other STC modifications.

Both STC and PMA Parts are required to go through a certification process including Material Testing, Documentation development, Engineering Analysis, manufacturing the prototype, demonstrating compliance, and showing conformity to the required procedures.

An STC is a supplemental type certificate, which authorizes the installation of something on an aircraft that was not included in the original type certificate.

A supplemental type certificate (STC) is a design approval only. It does not provide any inherent production approval. An STC is usually developed when no product meets a required need. An STC holder who wants to produce articles for use on aircraft will need some other production arrangements (in addition to the STC). For example, STC holders may use production approval holders or parts manufacturer approval (PMA) to obtain FAA production approval for parts where the design has been approved under an STC.

PMA — Parts Manufacturer Approval “is an approval granted by the FAA to a manufacturer of aircraft parts. PMA-holding manufacturers are permitted to make replacement parts for aircraft, even though they may not have been the original manufacturer of the aircraft.”  Parts produced under an FAA PMA are approved parts.

PMA and STC (supplemental type certificate) parts comply with all regulatory obligations, particularly concerning any changes they introduce and their effect on the original type design.

The need for supplemental instructions for continued airworthiness, new airworthiness limitations, and other conditions will be established as part of the certification process.

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