Following a normal flight the aircraft was established on final approach for landing. At about 140 feet above the ground the approach angle flattened and the nose pitched up. The co-pilot who was flying the aircraft believed that a windshear situation had been encountered and he initiated a go around. As full power was applied the nose pitched up violently. The crew did not observe any cockpit indications as to the reason for this reaction. The pilot in command took control of the aircraft and initiated a rolling turn. This had the effect of reducing the pitch angle and by manipulating power levers and rolling the pilot was able to regain control of the aircraft at about 6500 feet. A safe landing was subsequently carried out. Witnesses later reported that they observed that the aircraft had reached pitch and bank angles of 60 and 80 degrees respectively. The investigation did not reveal any fault with the aircraft or its systems which might have accounted for the incident. An analysis of the Flight Data and Cockpit Voice recorders indicated that the stabiliser trim had been operated 11 times in the two minutes of flight leading to the call for full power. The trim had been operated in bursts of about one second except that just before full power was applied the trim was operated for almost 10 seconds. The co-pilot had indicated that he had used the trim to reduce the aircraft speed during the approach. It was considered likely that he had either inadvertently kept the trim switch depressed or had experienced a brief electrical relay fault which resulted in full nose-up trim being applied. Shortly after the pilot in command had assumed control the trim was operated for a further 12 seconds presumably as nose down-trim was applied. Neither crew member recalled hearing the trim "clacker" operating. The audio level of this was low and it was likely that the device may not have been heard above the ambient noise level. Because there had been no indication of the cause of the initial pitch-up the crew had difficulty in determining the appropriate course of action. Although the investigation revealed that the initiating factor was probably a full nose-up trim situation the crew believed the problem was caused by a structural failure or a thrust reverser malfunction.

The pilot was carrying out solo circuit training. On this landing the aircraft was reportedly affected by a strong crosswind gust and collided with the airfield boundary fence.

During the later stages of the approach the aircraft developed a higher rate of descent than desired. The right main gear subsequently struck a sand filled drum which was located just short of the threshold lip. The impact resulted in the right wing being buckled and one of the right engine mounts fracturing. The pilot reported that he did not believe that the landing was heavy and as a consequence did not discover the damage on a subsequent superficial inspection before continuing the flight. The approach was flatter than normal and into a 20 to 30 knot wind. On late final the aircraft encountered a downdraught and the pilot did not arrest the rate of descent, resulting in the touchdown occurring prior to the threshold.

The glider was winch launched to a height of 900 feet above the ground. The pilot was unable to find any strong lift, and when the glider had descended to 600 feet the pilot rejoined the circuit for landing. Some sink was experienced on the downwind leg and the glider was only about 200 feet above the ground when the base turn was made. During the turn onto final approach, the right wing of the glider struck the ground. The aircraft swung sharply to the right and subsequently landed heavily. There was no other traffic in the area and the pilot could have modified his circuit and landed on a cross-strip. It was likely that he had attempted to land the aircraft close to the winch launch cable to facilitate the next flight.

Circumstances:

The pilot reported that he had made a normal landing on the grass runway 14. The wind was a light crosswind from the left. During the ground roll the aircraft began to swing to the left. Application of right rudder was not effective, and the aircraft ground looped to the left. During the ground loop the right hand gear leg broke off and the right wing contacted the ground. At the time of the accident there was a thunderstorm developing nearby and strong thermal activity was reported in the circuit area by another pilot. The loss of directional control was probably caused by a sudden wind gust associated with the unstable local conditions.

During a landing on a golf course, an elderly lady passenger sustained a fractured leg as she had not taken up the correct landing position. The pilot reported the landing was conducted in suitable weather conditions and that the rate of descent was not excessive.

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.

Circumstances:

The glider was lined up short of the normal launch point. During the winch launch the wing-walker apparently released the into wind wing early. The wing dropped and the glider veered into the gusting crosswind. The pilot abandoned the launch however the glider continued to weathercock and ran into the retrieval vehicle before being brought to a halt.

It was reported that the pilot was confronted with bad weather and elected to land on a beach. The aircraft touched down in an area of soft sand and nosed over.

During the take off run, on the open sea and just prior to lift off, the right engine suffered a total failure. The pilot was unable to maintain directional control, due to the prevailing conditions, and the aircraft finally stopped on a sandbar. The left hand float, float pylon and outboard three metres of the left wing were torn off during the deceleration. A strip examination of the failed engine revealed that there had been a failure of the compressor turbine section following a sulphidation attack which initiated a fatigue failure of the compressor blades. The compressor turbine was inspected 279 hours prior to the failure and sulphidation was detected at that time, however, the damage was recorded as being within acceptable limits. The engine manufacturers recommend that the engine be washed daily and that 200 hourly borescope inspections be carried out for signs of sulphidation on the blades. The operator washed the engine daily, however, a borescope inspection was not carried out during the period between the compressor turbine inspection and the engine failure. A borescope inspection 79 hours prior to the engine failure would probably have disclosed the advanced state of blade corrosion.