While maneuvering at low level during a coyote hunting operation, a total loss of engine power occurred and the helicopter collided with trees during a forced landing to unsuitable terrain. Examination of the engine provided evidence of partial failure and/or total failure of the valve assemblies in all cylinders. Laboratory analysis revealed evidence of progressive failure in the valve seats. This was indicative of repeated overspeed of the engine.

The National Transportation Safety Board determines the probable cause(s) of this accident as follows:

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