Incident Overview
During an approach to land, the engine lost power at approximately 500 feet above ground level. The pilot reported that during the subsequent autorotative landing, he had to maneuver to avoid trees and a ridge in order to land in a suitable area. During this time, rotor RPM dropped, and a crash landing occurred.
Investigation Findings
A teardown of the engine revealed that the timing gear, part number 67687, had failed and a tooth had separated. Additionally, the woodruff key, part number STD-858, had failed. A metallurgical examination revealed evidence of fatigue on both parts. The failure of the timing gear originated at an inner corner of the gear keyway. The engine had accumulated 613 hours of flight time since major overhaul.