On October 14, 1993, a Piper PA-24-250 (registration N6846P) was involved in an aviation accident near Thief Rvr Falls, MN. Investigators recorded the probable cause as: The fatigue failure of the propeller blade, which originated from a corrosion pit on the camber surface measuring 0.012 inch wide and 0.0014 inch deep. This summary draws on records from the U.S. National Transportation Safety Board (NTSB) historical archive.
During cruise flight at 8500 feet, a propeller blade separated due to fatigue originating from a corrosion pit. The pilot executed an uneventful landing in a sunflower field.
What happened
The aircraft was operating in cruise flight at an altitude of 8500 feet mean sea level when a mechanical failure occurred. Approximately one foot of the outboard portion of one propeller blade separated from the assembly. Following the separation, the pilot shut down the affected engine and proceeded to make an uneventful landing in a nearby sunflower field.
The investigation
A post-accident examination of the failed propeller blade was conducted to determine the root cause of the failure. Analysis revealed that the blade had failed due to fatigue. Further inspection identified the origin of the fatigue fracture as a corrosion pit located on the camber surface of the blade. This defect measured 0.012 inch in width and 0.0014 inch in depth.
Findings
The investigation determined that the primary factor contributing to the incident was the fatigue failure of the propeller blade. The fracture initiated at a corrosion pit on the camber surface, which served as the stress concentration point leading to the eventual separation of the outboard portion of the blade during flight operations.
Probable cause
The fatigue failure of the propeller blade, which originated from a corrosion pit on the camber surface measuring 0.012 inch wide and 0.0014 inch deep.
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