During a practice low level circuit, the engine failed, accompanied by a loud bang. During the subsequent forced landing, the helicopter rolled on to its right side. Later examination of the engine revealed that the number three connecting rod had failed at the crankshaft and pierced the crankcase. The connecting rod showed signs of metal fatigue. However, no manufacturing defects were identified near the fracture surface nor was any assembly-related fault established. This accident was not the subject of an on-scene investigation.