Accident Overview
A helicopter was in cruise flight at about 1,400 feet above ground level when the flight instructor heard a rumbling from beneath and behind the cockpit. The noise grew louder, the oil temperature increased, and the oil pressure dropped to zero. The engine then stopped producing power. The flight instructor initiated an autorotation and selected a high school athletic field for the forced landing. While attempting to extend the glide to reach the field and maintain rotor rpm, the tail of the helicopter struck the athletic field's perimeter fence just before touchdown. This impact caused a loss of control, and the helicopter subsequently collided with terrain.
Engine Examination
Post-accident examination of the engine revealed that the oil suction screen was completely occluded by metal particles. The number 3 cylinder assembly was removed; the piston and connecting rod were found stuck in the cylinder bore. The connecting rod was fractured at the yoke and free from the crankshaft. The connecting rod cap was fragmented, with fragments scattered in the oil sump. The number 3 connecting rod bearing material was completely extruded and fragmented, and the mode of failure could not be determined.
Maintenance History
Engine maintenance records indicated that the engine had accumulated a total of 2,157 hours of operation, with 759 hours since overhaul and 90 hours since the number 1 cylinder assembly was replaced due to low compression and a broken piston ring.