NTSB Identification: LAX02LA257.
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Accident occurred Thursday, August 22, 2002 in DOS PALOS, CA
Probable Cause Approval Date: 12/28/2004
Aircraft: Air Tractor AT-301, registration: N8793S
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.

During cruise flight the engine started to vibrate and the pilot made a forced landing in a newly plowed field and the airplane nosed over after encountering soft soil. The pilot had been crop dusting for about 7.5 hours when the event occurred. The outboard portion of one of the propeller blades had separated. A review of the airframe records indicated that the propeller was overhauled about 10 months prior to the accident. A metallurgical examination of the failed blade revealed it had failed as a result of fatigue cracking that originated from a nick, located on the flat side of the blade's leading edge. Also observed were groove marks that were relatively uniform and consistent with tool marks left by a file. In accordance with the overhaul manual, a field repair can be done to grind or file out corrosion of the blade, with a dye penetrant inspection to detect any visible damage or cracks (Hamilton Standard 130B Blade Overhaul Manual). The overhaul manual notes that tool and file marks should be polished out as one of the final steps in the process. According to the FAA approved flight manual, during the preflight walk-around inspection, the pilot is to inspect the propeller blades for nicks and cracks.

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

the failure of the propeller blade due to fatigue. Factors in the accident were the inadequate maintenance-repair of the blade, and, inadequate pilot preflight inspections.

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