Accident Overview
The accident occurred at the 5,500-foot level on Mount St. Helens. The density altitude at the time was 7,500 feet. While approximately 40 to 50 feet above ground level, the engine and rotor rpm began to decay rapidly. The helicopter touched down hard on a rock ledge, with one skid partially off the edge. As the rotor rpm continued to decrease, the rotor disc was no longer able to support the helicopter, and it rolled 100 feet down the mountain, resulting in substantial damage.
Maintenance Investigation
A post-accident maintenance inspection revealed that all spark plugs were severely worn. When tested, four out of eight plugs fired intermittently. Additionally, the left magneto had burned points. No other mechanical anomalies were reported.