On January 14, 1998, a Bell 47G-3B-2 (registration N1461W) was involved in an aviation accident near Spanish Fork, UT. Investigators recorded the probable cause as: Repeated overspeed of the engine leading to progressive failure of the valve seats and subsequent failure of the valve assemblies, resulting in total loss of engine power. This summary draws on records from the U.S. National Transportation Safety Board (NTSB) historical archive.
During a low-level coyote hunting flight, a helicopter suffered total engine power loss and collided with trees during a forced landing. Examination revealed progressive valve seat failure due to repeated overspeed.
Accident Overview
A helicopter executing a low-level coyote hunting operation experienced a total loss of engine power while maneuvering. The pilot performed a forced landing to unsuitable terrain, during which the helicopter collided with trees. The accident resulted in damage to the aircraft.
Engine Examination
Post-accident examination of the engine provided evidence of partial failure and/or total failure of the valve assemblies in all cylinders. Laboratory analysis revealed evidence of progressive failure in the valve seats. This condition was indicative of repeated overspeed of the engine.
Findings
The investigatory analysis determined that the progressive failure of the valve seats, consistent with repeated engine overspeed, led to the failure of the valve assemblies and subsequent total loss of engine power. No other contributing factors were identified in the source material.
Probable cause
Repeated overspeed of the engine leading to progressive failure of the valve seats and subsequent failure of the valve assemblies, resulting in total loss of engine power.