Incident Details
During a turn-around, the pilot noticed an unusual pedal reaction but attributed it to gusty winds reaching 15 knots. Shortly after completing the turn, he experienced a complete loss of tail rotor control. The failure was indicated by a reduction in noise, an increase in rotor RPM, and a yaw to the right. At an altitude of approximately 300 feet above ground level, the pilot was unable to maintain directional control and initiated an autorotation toward a narrow logging road.
As the helicopter descended, the main rotor blades struck trees on both sides of the road. During touchdown, the main rotor contacted and severed the tail boom.
Mechanical Findings
An examination of the tail rotor drive system revealed that the teeth on the forward (short) tail rotor drive shaft (part number 47-644-180-9) were worn and showed signs of overheating. The matching splines on the front coupling (part number 47-620-494-3) were also overheated and stripped. Only a minimal amount of lubrication was found inside the front coupling.
Maintenance Recommendations
The Bell Maintenance & Overhaul Instructions for the helicopter specified that the tail rotor drive components should undergo daily inspections and be lubricated every 50 hours of operation.