NTSB Identification: NYC01LA088
14 CFR Part 91: General Aviation
Accident occurred Friday, March 23, 2001 in Seneca Falls, NY
Probable Cause Approval Date: 08/21/2001
Aircraft: Bell 206 L-1, registration: N2138Y
Injuries: 2 Serious.
NTSB investigators may have traveled in support of this investigation and used data provided by various sources to prepare this aircraft accident report.
The Bell 206 L-1 helicopter was on a positioning flight. While in cruise flight, the pilot added power for a slow climb, and experienced multiple "bangs" and yawing. He reduced power, determined that he had lost tail rotor thrust, and set up for a precautionary landing in a wooded area. Upon touchdown, the helicopter rolled over. A bolt was found missing from the Thomas coupling located between the aft end of the aft short shaft, and the foward segment of the tail rotor drive shaft. In addition, the bracket for the forward hanger bearing was fractured. Metallurgical examination of the flange from the Thomas coupling with the missing bolt, revealed thread imprint marks on the inside of the bolt hole bore, and lipped material at the edge of the bolt hole bore. The hanger bearing mount had failed in overstress with no evidence of progressive cracking. The helicopter had been operated for 15.2 hours since the Thomas coupling had been disassembled and put back together. The mechanic reported that he had reused the bolts and self-locking nuts, and tightened them to the proper torque. The missing nut and bolt were not recovered. A check of the FAA database for SDRs revealed no other occurrences in the preceding 5 years.
The National Transportation Safety Board determines the probable cause(s) of this accident to be: the loss of a bolt in a Thomas coupling on the tail rotor drive shaft, for undetermined reasons, during climb, while operating over unsuitable terrain. Full narrative available
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