NTSB Identification: FTW98TA104.
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Accident occurred Thursday, January 22, 1998 in BRACKETTVILLE, TX
Probable Cause Approval Date: 10/30/1998
Aircraft: Hughes 269C, registration: N1093N
Injuries: 1 Minor,1 Uninjured.
NTSB investigators may not have traveled in support of this investigation and used data provided by various sources to prepare this public aircraft accident report.
The pilot and a crewmember/gunner of the public use helicopter reported hearing a loud squealing noise, emanating from the rear of the helicopter, while in flight at 75 feet AGL. Rotor RPM began decaying from 3,100 to approximately 2,000 RPM, and the pilot initiated an autorotation. During the landing, the main rotor blades contacted the ground, and helicopter came to rest in a rocky dry creek bed on its right side. The tension nut for the short shaft was found upstream from the point of impact. An examination revealed that splines for the drive shaft coupling were damaged, and the plating on the adapter was discolored as result of excessive heat. Further examination revealed that the damage sustained by the shaft and adapter were consistent with loss of grease and subsequent overheating and destruction of the drive splines. The forward rubber boot, used to retain the lubricant, had separated, resulting in the loss of lubrication.
The National Transportation Safety Board determines the probable cause(s) of this accident to be: failure of splines on the drive shaft coupling after separation of the forward bubber boot and loss of lubrication (grease), which resulted in a disconnect of the rotor drive system and an autorotation/forced landing. Lack of suitable terrain in the forced landing area was a related factor. Full narrative available
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