Robinson Helicopter R44 N94WC accident near Henderson, Texas

Probable cause

The partial loss of engine power in a hover due to a stuck exhaust valve.

NTSB analysis

The helicopter pilot was practicing hover takeoffs and landings in a crosswind. The passenger reported that, while hovering before a landing, the helicopter shuddered, and the left skid contacted the ground. The helicopter rolled onto its left side. The helicopter sustained substantial damage to the main rotor blades, fuselage, and tail boom.

Examination of the helicopter’s flight control systems and main and tail rotor drive systems did not show any preimpact anomalies that would have precluded normal operation. Examination of the No. 2 cylinder revealed that the exhaust push rod was bent and the exhaust valve was stuck. Borescope inspection of the No. 2 cylinder showed that the exhaust valve had contacted the piston and the intake valve appeared to be recessed in the No. 2 valve seat. The loss of engine power was most likely due to the stuck exhaust valve on the No. 2 cylinder.

Text from the NTSB. Open the NTSB docket for CEN22LA234 for the full record.