Incident Details
The helicopter was conducting an ignition fire control flight when it suffered a complete loss of engine power at an altitude of 100 feet above ground level. The pilot executed an autorotation to the only viable forced landing area available. The aircraft touched down hard, resulting in structural damage.
Engine Examination
Postaccident inspection of the engine disclosed that both connecting rod bolts in the number one cylinder were fractured. A metallurgical examination by the safety board revealed that one of the bolts had failed due to a preexisting fatigue crack. This crack originated from the head-to-shoulder fillet radius of the bolt.
Maintenance History
The engine was last overhauled in 1970. The engine manufacturer's service instruction letter dated July 1, 1992, states that all engines failing to accumulate the recommended time between overhauls within a twelve-year period must be overhauled during the twelfth year. Additionally, Textron Lycoming Mandatory Service Bulletin No. 240M mandates the replacement of connecting rod bolts and nuts at each overhaul.