On October 16, 2003, a Bell UH-1B (registration N234SJ) was involved in an aviation accident near Durham, CA. Investigators recorded the probable cause as: Failure of the power turbine shaft retaining bolt due to overload, which allowed the shaft to float and damage the power turbine disk blades. This summary draws on records from the U.S. National Transportation Safety Board (NTSB) historical archive.
A helicopter experienced a loss of engine power during a demonstration for school children, leading to a rapid descent, hard landing, and rollover. Investigation revealed a failed power turbine shaft retaining bolt.
Incident Overview
A helicopter conducting a demonstration flight for school children suffered a loss of engine power, resulting in a hard landing and rollover. The pilot had been performing simulated crop dusting turns and maneuvers over a field. After completing several simulated passes, the pilot returned to the middle of the field and turned into a light wind in preparation for landing. At that point, the helicopter lost power and entered an unexpectedly rapid descent. The pilot was unable to prevent the hard landing, and the helicopter rolled over.
Engine Examination
A teardown and examination of the engine revealed that the power turbine shaft retaining bolt had failed in overload. This failure allowed the shaft to float in a fore-and-aft manner, eventually damaging the blades on the power turbine disk. The type and degree of damage to the turbine section shafting and related components indicated that the bolt had separated at some undetermined point in time prior to the accident flight.
Probable cause
Failure of the power turbine shaft retaining bolt due to overload, which allowed the shaft to float and damage the power turbine disk blades.