Accident Overview
A commercial pilot and two passengers were conducting a survey of a road route in mountainous terrain. During cruise flight, the pilot observed a drop in manifold pressure, followed by a loss of oil pressure. Subsequently, the pilot reported that the engine ceased operation.
Emergency Descent and Landing
The pilot executed an autorotation to a snow-covered road. The landing was hard, resulting in the main rotor blades severing the tail boom and the landing skids collapsing.
Investigation Findings
A post-accident teardown of the engine revealed evidence consistent with a connecting rod failure. Specifically, the number five rod bearing had disintegrated, and the rod end cap had broken in service. The damaged rod end cap and connecting rod were subjected to metallurgical examination to determine the failure mode. The metallurgist's factual report indicated that the rod exhibited fracture characteristics typical of high cycle fatigue.