What happened
While operating in cruise flight at approximately 1,4 and00 feet above ground level, the flight instructor of the helicopter heard a rumbling noise originating from beneath and behind the cockpit. Shortly after this noise began, the oil temperature increased and the oil pressure dropped to zero, causing the engine to stop producing power.
The instructor adjusted the flight controls for autorotation and selected a high school athletic field for a forced landing. During the attempt to extend the glide to reach the field while maintaining rotor RPM, the tail of the aircraft struck a perimeter fence at the field. This impact caused a loss of control and subsequent collision with the terrain. There were no injuries reported.
The investigation
An examination of the engine revealed that the oil suction screen was completely occluded by metal particles. Upon removal of the number 3 cylinder, investigators found that the associated piston and connecting rod were stuck in the cylinder bore. The connecting rod had fractured at the yoke and was free of the crankshaft. Additionally, the connecting rod cap was fragmented, with pieces found scattered in the oil sump. The material from the number 3 connecting rod bearing was also completely extruded and fragmented.
Maintenance records indicated the engine had a total of 2,157 hours of operation, with 759 hours since the last overhaul. The records also showed that 90 hours had passed since the number 1 cylinder assembly was replaced due to low compression and a broken piston ring.