Accident Sequence
A helicopter experienced a loss of engine power while in cruise flight at an altitude of 4,700 feet. The pilot had planned to fly along a ridgeline northwest of Lake Casitas. As the helicopter approached a mountaintop, the nose suddenly veered to the left. The pilot heard several coughing sounds emanating from the engine. Subsequently, the pilot entered an autorotation, but was unable to reach the flat mountaintop. The helicopter then collided with the terrain and rolled over.
Post-Accident Examination
Following recovery of the helicopter from the accident site, investigators conducted an examination. Control continuity was established for the throttle, mixture control, collective, and cyclic systems. The bottom spark plugs exhibited a gray coloration, which corresponded to normal operation according to the Champion Aviation Check-A-Plug AV-27 Chart.
Engine Testing
The engine was started and operated smoothly. Oil and fuel pressures indicated within the green operating range on their respective instruments. The engine was accelerated to 2,000 rpm; when each magneto was individually cycled, a smooth drop of 200 rpm was observed. The engine shutdown was unremarkable.