Accident Summary
A helicopter accident occurred during a takeoff attempt from a ski slope. The helicopter was heading north, down the slope. The pilot estimated a north wind of 5 knots and computed density altitude at 11,000 feet. During the hover preceding takeoff, rotor and engine RPM began to decrease. The pilot observed engine RPM at 2,700 just before the helicopter crashed 130 feet down slope from the lift-off point. The helicopter rolled over after impact.
Sequence of Events
The pilot initiated a takeoff from a ski slope with a northern heading, proceeding down slope. The prevailing wind was estimated from the north at 5 knots. Density altitude calculations indicated a value of 11,000 feet. While in a hover, the pilot noted a decay in both rotor and engine RPM. The engine RPM was observed to be at 2,700 before the helicopter contacted terrain. The helicopter came to rest 130 feet down slope from its liftoff point, having rolled over during the accident sequence.
Post-Accident Examination
Following the accident, an engine run was conducted on the helicopter's powerplant. This test did not reveal any evidence that could explain the reported loss of power. No mechanical anomalies were identified that would account for the RPM decay experienced by the pilot.
Conclusion
The accident investigation source did not specify a probable cause for the event. The reported loss of power remains unexplained after the post-accident engine examination.