FAR 21.111 — STC Applicability
FAR 21.111 sets the scope of Subpart E, covering procedural requirements for issuing supplemental type certificates (STCs) under Part 21.
FAR 21.111 is the opening section of Subpart E of Part 21 and simply tells you what that subpart is about. It states that the subpart prescribes the procedural requirements for the issue of supplemental type certificates (STCs).
Why does this matter to you as a pilot?
- An STC is the FAA approval mechanism used when someone modifies an aircraft, engine, or propeller in a way that changes its type design but doesn't warrant a brand-new type certificate. Think of items like an autopilot retrofit, a winglet kit, an engine conversion, or an avionics upgrade.
- Subpart E (which 21.111 introduces) is the rulebook for how applicants get those modifications approved.
- As a pilot, you'll see STCs referenced in the aircraft's records and supplements in the POH/AFM. Knowing where STC authority comes from in the regulations helps you understand why those supplements are legally part of the aircraft's approved data.
In short: 21.111 is a scope statement — it doesn't impose a duty on pilots, but it anchors the rest of Subpart E that governs STC issuance.
Five FAA-written-style questions. Instant explanations, every answer cites its source — no account needed.
You are flying VFR in Class E airspace at 8,500 feet MSL during the day. What are your minimum visibility and cloud clearance requirements?