Continental Copters Inc 47G N6356X accident near Sandy Hook, Kentucky

Probable cause

The in-flight disengagement of the tail rotor extension shaft from the tail rotor gearbox, resulting in a loss of tail rotor control.

NTSB analysis

The pilot reported that as he approached a pre-planned landing zone, he reduced engine power for landing. The helicopter yawed to the right, then back to the left. The helicopter yawed again, and the pilot felt unusual vibrations, so he decided to perform an autorotation. The helicopter landed hard on a gravel road and sustained substantial damage. Examination of the wreckage revealed impact damage to the aft tail boom from main rotor contact. The aft-most section of the tail rotor drive shaft was missing and was not recovered. It is likely that, during the hard landing, a main rotor blade struck the tail boom and liberated the drive shaft section. Manipulation of the tail rotor shaft input at the tail rotor gearbox revealed a lack of continuity to the tail rotor hub and blades. The tail rotor did not rotate when the universal joint, located at the forward end of the extension housing tube, was turned. Subsequent examination showed that the tail rotor gearbox was operational; however, the tail rotor extension shaft was found disconnected from the input coupling to the tail rotor gearbox. Rotational scoring inside the extension shaft housing indicated excessive play in the shaft that was present before the accident, which would have resulted in the loss of tail rotor control.

Text from the NTSB. Open the NTSB docket for ERA13LA390 for the full record.