NTSB Identification: FTW98LA260.
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Nonscheduled 14 CFR
Accident occurred Sunday, June 07, 1998 in CORPUS CHRISTI, TX
Probable Cause Approval Date: 05/11/1999
Aircraft: Bell 206B, registration: N16814
Injuries: 4 Uninjured.
NTSB investigators may not have traveled in support of this investigation and used data provided by various sources to prepare this aircraft accident report.
The helicopter experienced a tail rotor drive shaft failure while on final approach to landing. Approximately 45 to 50 feet AGL, the pilot heard a 'loud snapping sound,' which was followed by a 'loss of tail rotor control.' An autorotation was initiated, and subsequently, the helicopter landed 'hard' on the grassy staging field and came to a stop upright. Examination of the helicopter revealed that two of the tail rotor drive shaft segments were fractured. Additionally, one of the two bolts connecting the aft end of one of the fractured segments to a disc coupling (Thomas Coupling) was missing. The missing bolt was not recovered, although a nut and two beveled washers were found on top of the tail boom beneath the driveshaft. An examination of the remaining bolt revealed that it exhibited fretting, wear and deformation to only the last two and one-half threads. Review of the maintenance records revealed no entries indicating that any of the tail rotor drive shaft segments were removed in the two years preceding the accident.
The National Transportation Safety Board determines the probable cause(s) of this accident to be: The failure of the tail rotor drive shaft due to the separation of a bolt at one of the drive shaft disc couplings for an undetermined reason, which resulted in the pilot's inability to maintain directional control during landing. Full narrative available
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