Hiller UH12-E, VH-FBQ, 10km NW Quirindi NSW, 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 overspeeding of the engine. Other connecting rods from the engine also showed evidence of galling.