What happened
During an ignition fire control flight at 100 feet AGL, the helicopter suffered a complete loss of engine power. In response to the failure, the pilot entered an autorotation to reach the only available forced landing area. The aircraft made a hard touchdown, which resulted in structural damage to the airframe.
The investigation
Post-accident examination of the engine revealed that both connecting rod bolts in the #1 cylinder had fractured. A metallurgical examination conducted by the safety board determined that one of the connecting rod bolts failed because of a preexisting fatigue crack. This crack originated from the head-to-shoulder fillet radius of the bolt.
Records indicated the engine was last overhauled in 1970. According to a service instruction letter from the engine manufacturer dated July 1, 1992, engines that do not reach the recommended operating hours between overhauls within a twelve-year period must be overhauled during the twelfth year. Additionally, Textron Lycoming Mandatory Service Bulletin No. 240M requires the replacement of connecting rod bolts and nuts every time the engine undergoes an overhaul.