Hiller UH-12E, VH-FFU, 3 km west of Hay Point, Queensland, on 20 May 1990

Circumstances:

The helicopter was flying between two and three hundred feet above ground level when the pilot noticed severe oscillations of the rotor system, followed by engine stoppage a short time later. During the subsequent forced landing, the right skid contacted the ground at a significant forward speed and the helicopter rolled on to its right side. Examination of the rotor system indicated no apparent faults or failures prior to the accident. Fuel was drained from the fuel tank and the two carburettors (three points). The fuel tank and left carburettor showed clean fuel but the right carburettor contained a small but significant quantity of dirty water and solid debris. The fuel was also discoloured to a grey tone. The quantity of water was sufficient to cause engine rough running (which would induce rotor system oscillation) and engine stoppage. The pilot reported that he had conducted fuel checks before the flight from two drain points, one for the main fuel tank and one for the carburettors, both accessible from the left side of the helicopter. He was not aware that each carburettor had its own drain valve and that there was a total of three drain points.

Significant Factors:

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

1. The pilot was not aware of all the fuel drain points on the helicopter.

2. The engine failed due to water in a carburettor.

3. The pilot misjudged height and speed during the forced landing.