Primary finding
Probable cause
The failure of a tail rotor driveshaft coupling due to fatigue.
Investigator assessment
Analysis narrative
The pilot reported that while in cruise flight, the rear of the helicopter suddenly began to vibrate. He performed an autorotation to a field, and the helicopter landed hard. The tailboom and main transmission mounts were substantially damaged. The pilot reported that a tail rotor driveshaft coupling had split in half, which resulted in a loss of tail rotor drive. Postaccident examination of the tail rotor driveshaft coupling revealed that the coupling failure was initiated by fatigue cracking. A complete history of the part was not available; therefore, the total time in service of the part could not be determined.
Source record
Factual narrative
On July 31, 2012, about 0920 mountain daylight time, a Fairchild Hiller FH-1100 helicopter, N5038F, was substantially damaged following the failure of its tail rotor drive shaft and subsequent autorotation to a hard landing near Cody, Wyoming. The commercial pilot and his three passengers were not injured. The helicopter was being operated by the pilot, doing business as Eclipse Helicopter Services, Cody, under the provisions of 14 Code of Federal Regulations Part 91. No flight plan had been filed for the local personal flight, which had originated about 1 hour before the accident. Visual meteorological conditions prevailed at the time of the accident. The pilot reported that while in cruise flight, there was a sudden onset of a vibration coming from the rear of the helicopter. He performed an autorotation to a field straight ahead. During the landing sequence, the helicopter spun to the right 180 degrees. The landing skids, tail boom, and main transmission mounts were bent. The pilot reported that a tail rotor driveshaft coupling, identified as a Bendix 19E101-1D coupling, had split in half, which resulted in a loss of tail rotor drive. Postaccident examination of the tail rotor driveshaft coupling by the National Transportation Safety Board's Materials Laboratory in Washington, D.C., revealed that it failed due to fatigue cracking. A complete history of the part was not available; therefore, the total time in service of the part could not be determined.