Accident Description
On August 31, 2013, about 0950 eastern daylight time, a Continental Copters, Inc. 47G helicopter, registration N6356X, was substantially damaged during a forced landing near Sandy Hook, Kentucky. The commercial pilot and one passenger were not injured. The helicopter was registered to Sierra Aeronautics LLC and was operated by the pilot under 14 Code of Regulations Part 91 as a positioning flight. Day visual meteorological conditions prevailed, and no flight plan was filed. The flight originated at Morehead, Kentucky (M97) about 0930.
Sequence of Events
As the helicopter was established in the traffic pattern for landing at a pre-established landing zone, at 300 feet above ground level, the pilot turned onto final and made a power reduction. The helicopter began to yaw to the right, then back to the left. The pilot raised the collective, and the helicopter yawed again to the right, accompanied by unusual vibrations. The pilot then attempted an autorotation. He avoided a tree and a parked car, and the helicopter landed hard on a gravel road.
Wreckage Examination
An inspector with the Federal Aviation Administration examined the wreckage. Evidence of main rotor contact with the aft section of the tail boom was found. The tail boom and main rotor blades sustained structural damage. The most aft section of the tail rotor drive shaft was missing; a search of the area did not locate the missing component. Manipulation of the tail rotor shaft input at the tail rotor gearbox revealed a lack of continuity to the tail rotor hub and blades. When the universal joint at the forward end of the extension housing tube was turned, the tail rotor did not rotate.
Component Inspection
Disassembly of the tail rotor gearbox showed that the internal gears appeared normal and well lubricated. The tail rotor extension shaft was found disconnected from the input coupling to the tail rotor gearbox. The splined end on the aft section of the shaft displayed signatures of overheating and rotation while out of the input coupling. Scoring marks inside the extension housing tube indicated excessive play in the shaft and center bearing housing.