Radio altimeters for rotorcraft operations

This regulation requires all rotorcraft operating under Part 135 (commercial operations like air taxi and commuter flights) to have a working FAA-approved radio altimeter installed, effective April 24, 2017. A radio altimeter measures precise height above the ground, which is critical for safe low-altitude operations, approaches, and landings—especially in poor visibility.

The only exception is if the aircraft's approved Minimum Equipment List (MEL) allows temporary operation without one, or if the FAA grants special deviation authority.

For smaller rotorcraft (maximum gross weight 2,950 pounds or less) that cannot physically accommodate a radio altimeter, operators may request a Letter of Deviation Authority from their local Flight Standards office. This request must explain why the installation is impossible and must be submitted at least 60 days before planned operations. The FAA can modify or cancel any granted deviation at any time.

*This is a plain-English summary for study only. The official 14 CFR text on this page is controlling — always read the current regulation and consult a CFI.*