Transmission and gearbox involving a Hiller Aviation UH-12E, VH-FBV, Melrose Station, QLD on 12 December 1997

The pilot reported that while cruising at about 600 ft AGL, he heard a loud noise and the helicopter shook violently. He initiated autorotation and helicopter landed heavily a short time later. Both occupants escaped with minor injuries. Subsequent investigation revealed that the transmission torsion coupling had broken, and two steel back up pins had sheared. The transmission failure had caused complete loss of torque to the main rotor. The tail rotor and gear box showed no evidence of pre -impact damage.