NTSB Identification: FTW97LA326.
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Accident occurred Saturday, August 23, 1997 in OAK GROVE, LA
Probable Cause Approval Date: 11/06/1998
Aircraft: Bell 206B, registration: N7929J
Injuries: 1 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.
During an external load operation, the pilot was hovering the helicopter at about 60 feet above the boat, when the helicopter began to 'spin' to the right. He 'rolled off the throttle' and the spin stopped. He then maneuvered the helicopter to the right as it descended in an effort to clear the boat; however, the main rotor blades struck the front of the boat. Subsequently, the helicopter settled into the water and sank. Examination of the tail rotor drive system revealed that the #5 tail rotor drive shaft segment P/N 206-040-931-9 had separated at the bonded joint between the shaft tube and the flange fitting. Examination of this tail rotor drive segment by a metallurgist revealed that the separated joint revealed evidence of pitting which was indicative of plastic blast media impingement and the remaining adhesive had the consistency of powder/talc with no apparent structural integrity. According to the metallurgist the 'blast media impingement may effectively compromise the moisture barrier at the joint and allow the moist chloride environment to invade the joint and chemically degrade the adhesive.' Blast media impingement is not approved by Bell Helicopter.
The National Transportation Safety Board determines the probable cause(s) of this accident to be: The disconnect of the #5 tail rotor drive segment due to the debonding of the joint between the shaft tube and the flange fitting. Factors were the improper bead blasting of the tail rotor drive segment by an unknown maintenance personnel, and the lack of altitude and suitable terrain for the forced landing. Full narrative available
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