Incident Description
Shortly after takeoff at approximately 40 feet above ground level, the pilot observed that the high/low rotor/engine warning light was illuminated. The helicopter subsequently entered an uncommanded right yaw. The pilot initiated an autorotation. During the descent, the main rotor blades contacted trees. The pilot pulled collective pitch before impact with terrain.
Examination Findings
Post-incident examination of the helicopter revealed that the upper right tailboom attach bolt was stripped. This stripped bolt allowed the tailboom to shift, which resulted in the separation of the number 1 and number 2 tail rotor drive shaft sections at the coupling. Further examination of the stripped bolt by a qualified individual revealed that the bolt failed due to being overtorqued.
Maintenance History
According to the company mechanic, the tailboom attach bolts are checked for proper torque every 100 hours. The last such check had been accomplished approximately 55 hours prior to the incident.