On July 31, 1983, a Bell 47G-3B-1 (registration N11102) was involved in an aviation accident near S. Lake Tahoe, CA. This summary draws on records from the U.S. National Transportation Safety Board (NTSB) historical archive.
During a takeoff over descending terrain in a mountainous area, a helicopter's rotor RPM decayed at 40 knots and 75 feet AGL. The helicopter settled to the ground and rolled onto its left side. Examination found no cause for the power loss.
Accident Narrative
During a takeoff over descending terrain in a mountainous area, the helicopter's rotor revolutions per minute (RPM) began to decay when the aircraft had accelerated to 40 knots and was approximately 75 feet above ground level (AGL). The pilot applied additional throttle and increased collective pitch in an effort to maintain rotor speed. However, the manifold pressure then decreased and the rotor RPM continued to decay. The helicopter subsequently settled to the ground, rolled onto its left side, and came to rest inverted.
Examination
A post-accident examination of the helicopter was conducted. The inspection focused on the engine, fuel system, ignition system, and other potential sources of power loss. No mechanical reason for the loss of power was identified. The density altitude at the time of the event was about 8,100 feet.