Forced/precautionary landing involving a Robinson R22 Beta, VH-HVB, Wando Vale Station, Queensland, on 7 March 1996

The pilot reported that the helicopter was being used to muster cattle. While manoeuvering at about 30 ft AGL and a speed of 10 knots the pilot said he heard a loud bang. He was able to conducted an immediate autorotative landing.

Post flight inspection found that the main rotor drive shaft flex plate had separated at the gearbox end. The flailing end had then cut into the fuel tank, as well as causing other damage in the area.

Specialist examination concluded that the flexplate failure was caused by fatigue crack growth. The fatigue crack initiated at a region of intergranular corrosion at the edge of the plate. The pilot reported that the failure occurred some 40.8 hours after the previous 100 hourly inspection. Because of the type of flexplate in use, a dye penetrant inspection had been conducted on the flexplate during that previous inspection. This was required by an Airworthiness Directive, which subjected all such flexplates to a special inspection every 100 hours until they were replaced by a new version of flexplate. A similar directive issued by the United States FAA required an inspection every 50 hours.