NTSB Identification: LAX91LA249.
The docket is stored on NTSB microfiche number 43700.
Accident occurred Thursday, June 06, 1991 in HURON, CA
Probable Cause Approval Date: 05/27/1993
Aircraft: HILLER UH-12E, registration: N507HA
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.

THE PILOT COMPLETED AN AERIAL APPLICATION FLIGHT AND WAS RETURNING TO THE LOADING AREA WHEN THE HELICOPTER SUSTAINED A TOTAL LOSS OF POWER. DURING THE SUBSEQUENT AUTOROTATION THE PILOT ATTEMPTED TO SIDESLIP THE HELICOPTER BETWEEN THE ALMOND TREES BUT WAS UNABLE TO DO SO. THE ENGINE AND SUBSEQUENT METALLURGICAL EXAMINATION DISCLOSED THE NO. 3 CYLINDER CONNECTING ROD BOLT FAILED DUE TO FATIGUE. COMPANY MAINTENANCE PERSONNEL REPORTED THAT THE FATIGUE WAS CAUSED BY CONSISTENT ENGINE OVERSPEED POWER SETTINGS BY THE PILOTS FLYING THE HELICOPTER.

The National Transportation Safety Board determines the probable cause(s) of this accident to be:

THAT UNKNOWN PILOT(S) IMPOPERLY USED THE THROTTLE CONTROL WHICH CAUSED AN OVERSPEED CONDITION. CONTRIBUTING TO THIS ACCIDENT WAS THE CONNECTING ROD BOLT FATIGUE FAILURE.

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