On November 1, 1990, a Bell 47J-2 (registration N49DA) operated by Pigeon Forge Helicopters, Inc. was involved in an aviation accident near Gatlinburg, TN. Investigators recorded the probable cause as: THE ACCIDENT WAS INADEQUATE MAINTENANCE OF THE HELICOPTER, ALLOWING A TAIL ROTOR DRIVE SHAFT BEARING TO EXCEED WEAR LIMITS. THIS RESULTED IN HIGH LOADS ON THE TAIL ROTOR DRIVE SHAFT, AND THE RESULTING FATIGUE FAILURE OF THE DRIVE SHAFT. This summary draws on records from the U.S. National Transportation Safety Board (NTSB) historical archive.
Two passengers reported a pop sound followed by a clockwise spin and descent into trees. Investigation found tail rotor drive shaft failed due to fatigue cracking; worn components were beyond replacement limits.
Accident Description
Two passengers reported hearing a 'pop' sound, after which the helicopter began a clockwise spin to the right. The helicopter subsequently descended into trees on the side of a steep slope.
Investigation Findings
Examination revealed that the tail rotor drive shaft failed immediately forward of the tailboom extension tube. The failure was caused by fatigue cracking that propagated at a high rate, indicative of high loads. Additionally, the outer diameter of the tail rotor drive shaft forward bearing housing and the inner diameter of the tailboom extension tube were worn beyond replacement limits. According to the Bell Maintenance and Overhaul Manual, these components should have been replaced.
Seat Modification
Investigation also discovered that the passenger three-place bench seat had been altered. The individual seat belts were modified into a single long belt. This belt could be opened only on the left side; the buckle on the right side was taped closed with silver duct tape.
What happened in the 1 Nov 1990 Bell 47J-2 accident near Gatlinburg, TN?
Two passengers reported a pop sound followed by a clockwise spin and descent into trees. Investigation found tail rotor drive shaft failed due to fatigue cracking; worn components were beyond replacement limits.
What aircraft was involved and where did it happen?
The accident on 1 Nov 1990 involved a Bell 47J-2, registration N49DA, operated by Pigeon Forge Helicopters, Inc., at Gatlinburg, TN.
What was the probable cause of the accident?
THE ACCIDENT WAS INADEQUATE MAINTENANCE OF THE HELICOPTER, ALLOWING A TAIL ROTOR DRIVE SHAFT BEARING TO EXCEED WEAR LIMITS. THIS RESULTED IN HIGH LOADS ON THE TAIL ROTOR DRIVE SHAFT, AND THE RESULTING FATIGUE FAILURE OF THE DRIVE SHAFT.
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