Incident Summary
At approximately 250 feet above ground level, the pilot-in-command heard a bang and observed the tail rotor gearbox pass the left side of the rotorcraft. The helicopter then nosed over and began turning to the right at a fast rate. The pilot-in-command entered an autorotation, and the aircraft subsequently impacted the ground.
Examination Findings
Investigators recovered several components, including the tail rotor gearbox, tail rotor output shaft, fork assembly, swash-plate with pitch links, tail-boom aft fitting, and tail rotor driveshaft flex-coupling. These parts were examined and tested at Boeing Helicopters in Mesa. Fractographic analysis indicated that all evaluated components failed in a ductile overload mode. The output shaft exhibited severe bending displacement of approximately 0.925 inches relative to a theoretical centerline, characteristic of a brief, unbalanced load. The conical bearing surfaces of the tail rotor fork assembly showed no heavy or unusual wear patterns. The tail rotor blades were not located during the investigation.