Accident Overview
During a power line patrol flight over wooded terrain, a helicopter experienced a loss of tail rotor control at an altitude of approximately 60 to 85 feet above ground level. The helicopter began to spin to the right, prompting the pilot to attempt a hovering autorotation. However, the spin rate increased, and the helicopter subsequently settled onto the power line before crashing to the ground.
Examination Findings
A post-accident examination of the helicopter revealed that the tail rotor swashplate had failed due to fatigue. The swashplate's outer diameter was worn, with evidence of spalling. The bearing inner diameter was lightly scored. The swashplate threads were severely worn and showed spalling resulting from relative motion with the mating threads of the locknut. Additionally, the lockwasher tang had worn a significant pattern into the swashplate keyway.
Conclusion
The loss of tail rotor control was attributed to the fatigue failure of the tail rotor swashplate, which led to the inability to maintain directional control and subsequent crash.