On May 18, 1994, a Bell 47G (registration N933B) was involved in an aviation accident near Sulphur, OK. Investigators recorded the probable cause as: The total loss of engine power caused by the failure of an engine accessory oil pump gear, which prevented the pilot from completing the autorotation due to trees, resulting in a bounce that severed the tailboom. This summary draws on records from the U.S. National Transportation Safety Board (NTSB) historical archive.
A helicopter lost engine power during a turn-around maneuver at low altitude. The pilot was unable to complete the autorotation due to trees, leading to a bounce that severed the tailboom.
What happened
The incident occurred when the aircraft experienced a total loss of engine power while flying approximately 50 feet above the ground. This failure took place during the initial phase of a turn-around maneuver. Following the power loss, the pilot initiated an autorotation to maintain control and attempt a landing. However, the presence of trees in the immediate vicinity hindered the pilot's ability to complete the autorotation successfully. The helicopter subsequently bounced upon contact with the ground. This impact caused the main rotor blade to flex excessively, which ultimately severed the tailboom.
The investigation
A mechanical examination of the aircraft was conducted by the operator to determine the root cause of the power loss. The inspection focused on the engine components responsible for maintaining proper lubrication and pressure. The examination revealed a specific mechanical failure within the engine assembly.
Probable cause
The total loss of engine power caused by the failure of an engine accessory oil pump gear, which prevented the pilot from completing the autorotation due to trees, resulting in a bounce that severed the tailboom.