What happened
During cruise flight, the pilot of the helicopter heard a very loud bang, after which the aircraft began to yaw. The pilot determined that the aircraft had lost all tail rotor authority. While attempting a run-on landing in a field, the pilot heard metal grinding and high-pitched squealing noises, prompting the initiation of an autorotation. During touchdown, the aircraft encountered a ditch, which caused the right skid to collapse. The pilot was not injured.
The investigation
The National Transportation Safety Board Materials Laboratory examined the tail rotor drive shaft and the cluster fitting. Findings showed that damage to the tail rotor drive shaft was consistent with an overstress failure, likely caused by rotational contact between the shaft and the forward tail boom closure fitting. The cluster fitting exhibited fracture markings indicative of fatigue, with localized fatigue origin areas found on the outer surfaces of each lug.
Upon exiting the aircraft, the pilot observed that the left main tail boom support cluster fitting had broken loose from the frame. Investigation into maintenance records showed that FAA Airworthiness Directive 2003-13-15 R1 was applicable to the aircraft. This directive required the modification or replacement of original cluster fittings (part numbers 269A2234 and 269A2235) or specific dye penetrant inspections. While the aircraft logbook indicated a 100-hour/annual inspection on May 23, 2005, which noted compliance with the AD via inspection, the failed lug did not appear to have been modified and was not in compliance with the directive.