Plain English Meaning

An STC is an official FAA approval that lets someone change an aircraft from how it was originally built and certified — for example, installing a different engine, a new avionics package, or modified wingtips — and confirms the change is safe and legal.

Full Definition

Supplemental Type Certificates are FAA approvals authorizing a major modification or alteration to an aircraft, engine, or propeller from its original type-certificated design. An STC documents that the change has been engineered, tested, and approved as airworthy, and it identifies the specific product the modification applies to.

Context Anchor

Pilots encounter STCs in aircraft records, installed equipment paperwork, flight manual supplements, and discussions about whether a modified aircraft is legal to fly.