FAR 91.135 — Class A Airspace Operations
FAR 91.135 requires IFR flight, ATC clearance, two-way radio, and transponder/ADS-B in Class A airspace. Study guide for pilot students and checkride prep.
FAR 91.135 governs how you operate in Class A airspace — generally from 18,000 feet MSL up to FL600 in the U.S. The rule is strict because Class A is a high-altitude, high-speed environment where everyone must be talking to ATC and flying on instruments.
To operate in Class A, you must:
- Fly under instrument flight rules (IFR) — VFR is not permitted.
- Receive an ATC clearance before entering the airspace.
- Carry a two-way radio and maintain continuous communication with ATC on an assigned frequency.
- Be equipped with the required transponder (§ 91.215) and, after January 1, 2020, ADS-B Out (§ 91.225).
Why it matters: traffic in Class A includes airliners moving at high speeds, so positive ATC control and standardized IFR procedures are the only safe way to mix traffic.
If something fails — like an inoperative transponder — ATC can authorize a deviation. Planned deviations from this section must be requested in writing at least 4 days in advance.