Engine malfunction involving Hiller UH12-E, VH-FBQ, 10 km north-west of Quirindi, New South Wales, on 19 December 1990

The pilot reported that the helicopter was cruising normally at 2500 feet when there was a loud noise from the engine. He entered autorotation and landed but the helicopter rolled on its side on landing. Specialist examination of the engine revealed that the number four piston connecting rod failed as a result of fatigue cracking initiated by galling between the connecting rod and the crankshaft bearing. Galling is the deposition of metal from one surface on another when the two surfaces come into forceful contact. The galling was induced by continual over speeding of the engine. Other connecting rods from the engine also showed evidence of galling.

Significant Factors:

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

1. The engine had previously been subjected to over speeding.

2. The connecting rod suffered a fatigue failure as a result of galling.

3. Uncontained mechanical failure of the engine.

4. The pilot was forced to land the helicopter on unsuitable terrain. This accident was not the subject of an on-scene investigation.