Robinson Helicopter R44 N297SU accident near Cedar City, Utah

Probable cause

A partial loss of engine power due to a damaged cylinder intake valve and subsequent collision with terrain during an autorotation.

NTSB analysis

The flight instructor and student had just completed a series of uneventful practice maneuvers and decided to perform off-airport landings at a location that the instructor had used before. After a series of reconnaissance orbits, low passes, and power checks over the landing area and, with the helicopter operating normally, the instructor decided to proceed with a landing.

The student was maneuvering at low altitude while attempting to land when

they felt a jolt, and the helicopter yawed to the left. The instructor took over the controls, and attempted to maneuver away from trees but the helicopter began to vibrate and yawed aggressively to the left with an accompanying reduction in engine speed. The helicopter began to descend with the low rotor rpm horn sounding, and the instructor performed an autorotation, during which the main rotor blade cut through the tail.

Postaccident examination revealed a damaged engine intake valve that would have resulted in a partial loss of engine power. The helicopter’s response during the event was consistent with a loss of engine power, although due to the altitude and environmental conditions, the helicopter was being operated at the upper limits of its performance envelope.

Text from the NTSB. Open the NTSB docket for WPR22LA363 for the full record.