Supplemental_type_certificate
Supplemental type certificate
Document of approval for modifications or repairs to an aircraft
A supplemental type certificate (STC) is a civil aviation authority-approved major modification or repair to an existing type certified aircraft, engine or propeller. As it adds to the existing type certificate, it is deemed "supplemental". In the United States issuance of such certificates is under the purview of the Federal Aviation Administration (FAA).
The determination of whether a proposed change in design, power, thrust, or weight to an existing type certified aircraft, engine, or propeller is acceptable under a STC is proposed by the design holder, and subjected to the approval of the FAA. If the FAA finds that the proposed changes are too substantial, a new type certificate will be required under 14 CFR 21.19. In this case, a substantially complete investigation of compliance with the applicable regulations will be required.[1][2]