Robinson Helicopter R44 N8325X accident near El Centro, California

Probable cause

A loss of main rotor rpm and airframe vibration for reasons that could not be determined based on the available information, which resulted in a forced landing to sloping terrain and the helicopter rolling over.

NTSB analysis

The helicopter pilot was performing an agricultural flight when he felt an airframe vibration, which was followed by the main rotor low rpm warning and a loss of rotor rpm. He reduced collective and the vibration and warning horn stopped. As he began to maneuver for a landing, he increased the collective and leveled the skids and again felt an airframe vibration and noted a loss of rotor rpm. During the landing on sloping terrain, the right front skid toe dug into the soft dirt and the helicopter came to rest on its side, resulting in substantial damage.

Examination of the helicopter revealed no mechanical anomalies that would have precluded normal operation, and the reason for the vibration and loss of rotor rpm could not be determined based on the available information.

Text from the NTSB. Open the NTSB docket for WPR16LA132 for the full record.