On September 13, 2005, a Bell 47G-3B-1 (registration N24SD) was involved in an aviation accident near Rock Springs, WY. Investigators recorded the probable cause as: the pilot's failure to maintain control of the helicopter during the attempted autorotation after he experienced an engine overspeed that occurred for reasons undetermined. This summary draws on records from the U.S. National Transportation Safety Board (NTSB) historical archive.
A pilot reported a grinding noise and yaw, followed by an engine overspeed and autorotation. The helicopter impacted hard, resulting in substantial damage. Examination revealed all six shearbolts failed with shearing signatures.
Accident Details
According to the pilot, the helicopter was maneuvering at approximately 25 feet above ground level when he heard a grinding noise. The helicopter yawed to the right a couple of times. The pilot stated that the engine then began to overspeed, prompting him to initiate an autorotation. The helicopter impacted the ground hard, resulting in substantial damage.
Examination Findings
A post-accident examination revealed that all six shearbolts had failed. Fracture faces of the shear bolts showed signatures consistent with a shearing action. The examination of the helicopter airframe, engine, transmission, and remaining systems revealed no anomalies.