Incident Overview
While descending after completing a cross-country flight, the pilot of a helicopter heard a loud noise emanating from the rear of the aircraft. Immediately thereafter, control inputs via the tail rotor pedals became ineffective. The pilot executed an autorotation and landed in an open field. The landing site was characterized by a slope of approximately 6 degrees and uneven, rough terrain.
Landing Sequence
During the touchdown, the helicopter had about 5 knots of forward speed. The lower wire cutter contacted the ground, causing the skids to collapse and twisting the cross tubes aft. The main rotor blades sustained no damage. However, the tail booms buckled downward at the forward attachment point. The pilot performed a normal engine shutdown, and both he and the passenger exited the helicopter without any reported injuries.
Post-Event Examination
A detailed inspection of the helicopter after the event revealed that both tail rotor blades had separated approximately 9 inches outboard of the hub. Subsequent laboratory testing identified that one of the tail rotor blades failed due to fatigue. The fatigue crack originated at the protective strip trailing edge, inboard of the outboard tip of the blade doubler. Examination at the origin site determined that the fatigue was a result of chemical machining or etching that occurred during the manufacturing process.
Conclusion
The investigation concluded that the fatigue failure of a tail rotor blade led to the loss of tail rotor effectiveness, prompting the precautionary autorotation. The skid collapse and tail boom buckling were consequences of the uneven terrain during landing.