Incident Overview
A pilot conducting crop dusting operations experienced engine vibrations while in cruise flight, necessitating a forced landing. The aircraft touched down in a newly plowed field, but encountered soft soil causing it to nose over. The pilot had been engaged in crop dusting for approximately 7.5 hours at the time of the event.
Propeller Examination
Post-incident inspection revealed that the outboard portion of one propeller blade had separated. Airframe records showed the propeller had been overhauled about 10 months prior to the accident. A metallurgical examination of the failed blade determined that the separation resulted from fatigue cracking. The cracks originated from a nick located on the flat side of the blade's leading edge. Additionally, groove marks were observed on the blade, described as relatively uniform and consistent with tool marks left by a file.
Maintenance Manual Provisions
According to the Hamilton Standard 130B Blade Overhaul Manual, field repairs may include grinding or filing out corrosion on the blade, followed by a dye penetrant inspection to detect visible damage or cracks. The manual further notes that tool and file marks should be polished out as one of the final steps in the repair process.
Preflight Inspection Requirements
The FAA-approved flight manual for the aircraft specifies that during the preflight walk-around inspection, the pilot is required to inspect the propeller blades for nicks and cracks.