On May 9, 1998, a Bell UH-1H (registration N345SC) was involved in an aviation accident near Naches, WA. Investigators recorded the probable cause as: Loss of engine power for undetermined reasons. This summary draws on records from the U.S. National Transportation Safety Board (NTSB) historical archive.
A pilot reported low RPM after takeoff and initiated an autorotation after controls failed to increase it. The helicopter landed hard and tipped forward. Post-accident engine testing found no anomalies.
Accident Sequence
The pilot reported that shortly after takeoff, he noticed that the rotor rpm was low, as if it were bleeding off. He attempted to increase the rpm using the increase/decrease button on the collective, but the input had no effect. The pilot opted to reverse direction to return for landing. As the rpm continued to decrease, he initiated an autorotation toward a field in a narrow valley. The rpm decayed to a point where the pilot could not perform a normal autorotation due to low airspeed and altitude. The helicopter landed hard and rocked forward onto its nose before settling back on the skids.
Post-Accident Investigation
The engine was removed and sent to a facility for a test run. During the engine run, no anomalies were found that affected engine operation.