STCs

STCs, or Supplemental Type Certificates, are aviation engineering approvals that authorize a specific modification to an aircraft, engine, propeller, or other aeronautical product that has already received a type certificate. An STC modifies the original type design, allowing the alteration to be legally installed on aircraft within the scope of the certificate. STCs are issued by national aviation authorities, such as the Federal Aviation Administration (FAA) in the United States or the European Union Aviation Safety Agency (EASA) in Europe, and may be recognized or validated in other jurisdictions.

An STC package typically includes the technical data that defines the modification, installation instructions, release-to-service conditions, and evidence showing compliance with applicable airworthiness standards. This can involve engineering analyses, testing, and, in some cases, flight tests. The STC specifies the exact aircraft models, serial ranges, and configurations to which the modification applies, as well as any required equipment or procedures.

The holder of an STC has the right to install the modification on aircraft within the defined scope and is responsible for continued airworthiness related to the modification. STCs are distinct from field approvals or Parts Manufacturing Authority (PMA) parts; STCs involve approved design data and compliance evidence, whereas PMA covers the manufacturing of approved parts. International validation of STCs may be pursued to extend approval to other countries.

Common examples of STCs include avionics upgrades, performance or weight-and-balance changes, or the installation of new systems and equipment. They play a central role in safely incorporating approved modifications into certified aircraft.