FAR 91.527 — Operating in Icing Conditions
FAR 91.527 explains takeoff and flight rules for icing conditions, including contamination limits, required ice protection, and severe icing prohibitions.
FAR 91.527 governs when large and turbine-powered multiengine airplanes may take off and fly in icing conditions. It exists because even small amounts of ice can disrupt airflow, add weight, and disable critical instruments — turning a routine flight into an emergency.
Takeoff contamination (a): No pilot may take off with frost, ice, or snow adhering to any:
- Propeller, windshield, or powerplant installation
- Stabilizing or control surface
- Wing
- Airspeed, altimeter, rate of climb, or flight attitude instrument system
The only exception is frost under the wing in the fuel tank area, if authorized by the FAA.
Flight into known or forecast icing (b): You may not fly IFR into known or forecast light or moderate icing, or VFR into known light or moderate icing, unless the airplane has functioning deicing/anti-icing equipment protecting all listed surfaces and instruments, meets SFAR 23 section 34, or is transport category certified for icing.
Severe icing (c): No pilot may fly into known or forecast severe icing unless the airplane meets SFAR 23 section 34 or transport category icing certification.
Forecast relief (d): If updated weather shows the forecast icing won't actually be encountered, the forecast-based restrictions in (b) and (c) no longer apply.