NTSB Identification: LAX99LA081.
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Accident occurred Sunday, January 24, 1999 in LEMOORE, CA
Probable Cause Approval Date: 11/30/2000
Aircraft: Hiller UH-12E, registration: N67064
Injuries: 1 Uninjured.
NTSB investigators may not have traveled in support of this investigation and used data provided by various sources to prepare this aircraft accident report.
While maneuvering during an aerial application flight at 15 feet above an alfalfa field, the pilot heard a noise emanating from the engine, and it seized. The pilot made a forced landing in the underlying soft field, and the helicopter rolled over after touching down on the uneven terrain. Maintenance records review disclosed that the helicopter's engine had operated about 482 hours since being overhauled. The engine examination revealed that the number two connecting rod was broken at its crankshaft end. Additionally, an inspection of the associated cylinder and piston revealed evidence of detonation. Similar excessive heat exposure signatures were observed with the other five piston heads. A small hole was found chaffed into the fuel primer line. Carbon deposits and burned rotor fingers were found in both magnetos.
The National Transportation Safety Board determines the probable cause(s) of this accident to be: The inadequate nature of the operator's maintenance, which failed to detect the primer and magneto discrepancies. An overly lean fuel mixture and/or magneto cross firing resulted in detonation, an ensuing connecting rod failure, and a total loss of engine power. Contributing factors were the helicopter's low altitude and the uneven, soft nature of the terrain. Full narrative available
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