On August 1, 1990, a Bell 47G-3B-1 (registration N34691) was involved in an aviation accident near Hanson, MA. Investigators recorded the probable cause as: The loss of tail rotor control due to the shearing of the tail rotor drive shaft between the number 5 and number 6 bearings. This summary draws on records from the U.S. National Transportation Safety Board (NTSB) historical archive.
A helicopter lost tail rotor control while flying at 100 feet during aerial application, resulting in a slow spin and ground impact due to a sheared drive shaft.
What happened
The pilot was conducting aerial application activities when the incident occurred. At the time of the event, the helicopter was operating approximately 100 feet above the ground. During this phase of flight, there was a sudden loss of tail rotor control. Following this mechanical failure, the aircraft entered a slow spin and subsequently descended into the ground.
The investigation
A post-accident examination of the wreckage revealed significant mechanical damage to the tail rotor system. The inspection determined that the tail rotor drive shaft had been sheared off. This structural failure occurred specifically between the number 5 and number 6 bearings within the assembly.
Probable cause
The loss of tail rotor control due to the shearing of the tail rotor drive shaft between the number 5 and number 6 bearings.