FTW94LA253

The helicopter experienced a complete loss of engine power during an ignition fire control flight at 100 feet AGL. The pilot entered autorotation to the only available forced landing area. The aircraft touched down hard and sustained structural damage. Postaccident examination of the engine realed that both connecting rod bolts in the #1 cylinder were fractured. A safety board metallurgical examination revealed that one of the connecting rod bolts had failed due to a preexisting fatigue crack that emanated from the head-to-shoulder fillet radius of the bolt. The engine was last overhauled in 1970. The engine manufacturer advises in their service instruction letter dated 7/1/92 that 'all engines that do not accumulate the recommended time operating hours between overhauls in a twelve year period, must be overhauled during the twelfth year.' Textron Lycoming mandatory service bulletin no. 240M requires replacement of the connecting rod bolts and nuts each time the engine is subject to overhaul.

On August 1, 1994, at 1345 central daylight time, a Hughes 269A helicopter, N9062G, was substantially damaged during a forced landing near Leander, Louisiana. The commercial pilot, sole occupant of the helicopter, was not injured. The helicopter, owned and operated by ARk-LA-TX Helicopters Inc., of Rodessa, Louisiana, was being operated under Title 14 CFR Part 137 at the time of the accident. Visual meteorological conditions prevailed for the aerial ignition fire control flight for which a flight plan was not filed. The flight originated from an airstrip near the accident site, approximately 15 minutes prior to the accident.

According to the operator, the helicopter was conducting aerial ignition fire control operations at altitudes below 100 feet AGL when the engine lost power without warning. The pilot stated that due to his low altitude, he lowered the collective and entered an autorotation as soon as he sensed the loss of power. The area that he was operating over was covered by stumps and downed trees, so he attempted to touchdown with minimal or no forward speed, and the helicopter landed hard.

Post accident examination of the wreckage by the operator and the FAA inspector revealed Structural damage to the airframe, tailboom, and main rotor blades. Post accident examination of the Lycoming HIO-360-B1A engine revealed that both connecting rod bolts for the number one cylinder failed while the engine was operating at 2,900 RPM.

According to the records, the engine had accumulated a total of 3,307 hours since new, with one engine overhaul performed in 1970, 936 hours prior to the accident. The recommended operating hours between overhauls for this engine is 1,500; however, the engine manufacturer advises on their Service Instruction Letter dated July 1, 1992, that "all engines that do not accumulate the recommended time operating hours between overhauls in a twelve year period, must be overhauled during the twelfth year."

Examination of the failed engine components was conducted by the Board's Materials Laboratory in Washington, D.C. The failure of the "trail" connecting rod bolts from the number one cylinder was a result of preexisting fatigue crack that initiated in the head-to-shoulder fillet radius of the bolt. See the enclosed Metallurgist's Factual Report for details of the examination.