What happened
The helicopter was in cruise flight at 4,700 feet, following a planned route along a ridgeline northwest of Lake Casitas. As the pilot approached the mountaintop, the aircraft nose suddenly veered to the left, accompanied by several coughing sounds from the engine. The pilot entered an autorotation in an attempt to reach a flat area on the mountaintop; however, the aircraft could not reach the intended landing site. The helicopter subsequently collided with the terrain and rolled over.
The investigation
Following recovery from the accident site, investigators examined the aircraft. They established control continuity for the cyclic, collective, throttle, and mixture control. An examination of the bottom spark plugs revealed a gray color, which indicated normal operation according to the Champion Aviation Check-A-Plug AV-27 Chart. During testing, investigators started the engine and observed that oil and fuel pressures remained within the green operating range on their respective instruments. The engine ran smoothly and was accelerated to 2,000 rpm. When each magneto was individually cycled, a smooth drop of 200 rpm was noted. The engine shutdown process was unremarkable.