Incident Overview
A helicopter, while being used to lift seismic materials on a 100-foot long line, had just brought the load to a hover at approximately 10 to 20 feet above ground. The pilot then heard a loud 'bang' and subsequently lost directional control. The helicopter began to spin uncontrollably and crashed moments later.
Witness Observations
Witnesses on the ground reported seeing the tail rotor blades stop rotating before the helicopter struck the ground.
Examination Findings
Post-crash examination of the helicopter revealed that the aft tail rotor driveshaft flexible coupling, identified as Bendix part number 369A5501, had failed. Due to damage sustained to the fracture surface during the accident, the mode of failure could not be determined.
Conclusion
The loss of directional control and subsequent crash were directly associated with the failure of the tail rotor driveshaft flexible coupling, which resulted in the cessation of tail rotor blade rotation.