Md Helicopter 369D N124AL accident near Columbia, California

Probable cause

The loss of power transmission to the main rotor for reasons that could not be determined because postaccident examination of the airframe and engine did not reveal any anomalies that would have precluded normal operation of the helicopter.

NTSB analysis

The pilot reported that the helicopter was in cruise flight at 12,500 feet mean sea level over mountainous terrain when power stopped being transmitted to the main rotor system. He performed an autorotation to an open area. During the landing, the tail rotor sustained damage to both blades as they went through about 1 foot of snow. After landing, the engine was still running but was not spinning the main rotor blades. Postaccident examination of the airframe revealed no anomalies that would have precluded normal operation. The drive train was fully functional. The engine was run in a test cell, which confirmed that it met specifications for all parameters including performance. The reason for the loss of engine power could not be determined.

Text from the NTSB. Open the NTSB docket for WPR11LA220 for the full record.