Gyrocopter (privately designed and built), Not registered, 8 km east of Euston, New South Wales, on 19 November 1989

Circumstances:

Seven days prior to the accident a new propeller was fitted to the aircraft after which two brief test flights were made. The aircraft was not flown again until the accident flight. Witnesses reported that on the day of the accident the pilot had been flying the aircraft for about 20 minutes. He was proceeding in a westerly direction at an altitude of about 100 feet above the ground when the rotor blades appeared to disintegrate. The propeller had in fact come off its mounting and hit one of the rotor blades. The rotor blade was destroyed and the aircraft dived to the ground. Subsequent investigation showed that the six bolts securing the propeller to the hub assembly had failed. The propeller was secured to the hub assembly with a compression plate on either side of the propeller hub to distribute the compression loads from bolt tension over a large area of the hub. The plates had been coated with black paint which had allowed slippage to occur between the propeller and the hub plates. This resulted in the inability of the hub assembly to achieve successful engine torque transfer through friction. The torque transfer was achieved through the bolts only which failed in bending.

Significant Factors:

The following factors were considered relevant to the development of the accident:

1. Inadequate engineering design in that the propeller was attached to its mounting in a manner that resulted in the drive being transferred to the mounting bolts.

2. Failure of the mounting bolts, which led to the separation of the propeller.

Recommendations:

1. It is recommended that the Australian Ultralight Federation and the Australian Sport Rotorcraft Association advise their members of the CAA Airworthiness Advisory Circular - May 1987, Item 187-1 addressing the basic principles and conditions of engine torque transmission to wooden propellers.