Summary
During cruise at 600 feet above ground level, the aircraft experienced a loud bang and subsequent vibration. While turning toward a field for landing, a second bang was heard and the vibration ceased. However, the aircraft then experienced an uncommanded right yaw and the nose began to tuck under. Despite remedial action by the pilot, the aircraft contacted terrain.
Investigation Findings
Investigation revealed that the tail rotor assembly had separated from the aircraft in flight. Laboratory examination determined that the gear box attachment studs failed due to low cycle fatigue. The tail rotor blade, serial number TCT-7478, had approximately 60 percent of its phenolic tip block missing and three aluminum rivets missing from the titanium skin. No bonding material was visible on the interior blade skin. The aircraft was operated in a salt water environment.
Airworthiness Directives
On April 17, 1982, Airworthiness Directive (AD) 82-17-04 was issued, requiring inspection of the tail rotor assembly specifically for tip block security, void, and retention every 7 days. This AD was later revised (AD 82-17-04, R1) to require compliance at intervals not to exceed 25 hours. On September 3, 1984, Revision 2 reverted the inspection requirement back to a 7-day interval. The operator had not received Revision 2, and the last inspection was performed on October 4, 1984, approximately 21 hours prior to the accident.