Flight History
The pilot reported that before the accident, the flight had been uneventful. All flight instruments were reading normally except for the turbine outlet temperature (TOT) gauge. The TOT gauge indicated 750 degrees, approximately 100 degrees higher than normal for the power setting of 70% torque.
Accident Sequence
The pilot was flying at 70 knots when the helicopter began losing rotor RPM. A passenger stated that they were about 200 to 300 feet above a ridge while flying southwest. After crossing the ridge, the helicopter began losing altitude rapidly. The pilot reported that while approaching a ridge line, the RPM started dropping, and he was unable to decelerate enough to land on top of the ridge. The helicopter contacted the ground on the south-southwest side of the ridge line and crashed.
Engine Examination
Post-accident examination of the engine revealed that the air bleed valve was dirty and had a hole in its diaphragm. In this condition, the valve would close late.
Environmental Factors
The accident site elevation was about 12,000 feet above mean sea level. Wind was gusting to 30 knots.