Hughes Lightwing, 25-0225, Cooranbong, New South Wales, on 19 December 1989

Circumstances:

The aircraft was being used for dual training and was operating in the circuit, having been airborne for about 45 minutes. During a turn onto the crosswind leg the engine partially lost power. The instructor immediately took control as the power was inadequate to maintain height and initiated a turn for landing on the reciprocal runway. On the approach, the aircraft struck trees bordering the edge of the strip and dived vertically to the ground. The instructor's seat attachment was damaged during the collision with the trees, prior to ground impact. Examination of the engine's spark plugs indicated the front cylinder had ceased to deliver power. The partial loss of power was the result of dirty fuel. Contamination was found in the float bowl of the front cylinder carburettor, in the fuel filter, and in the fuel line between the fuel tank and filter. The contaminated motor vehicle fuel was purchased from a nearby service station on the day prior to the accident. Two stroke oil was mixed with the fuel by the aircraft operator and not adequately filtered before being added to the aircraft fuel tanks.

Significant Factors:

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

1. The engine suffered a partial loss of power during the crosswind turn in the circuit.

2. The engine power output was insufficient to enable to the aircraft to reach the airstrip.

3. The partial power loss was due to fuel starvation as a result of contaminated fuel.

4. The fuel was not adequately filtered before it was added to the aircraft fuel tanks.

Recommendations:

It is recommended that the Australian Ultralight Federation remind all pilots and operators, of the requirements and procedures to maintain stringent fuel quality control.