CHI94IA017

In cruise flight at 8500 feet MSL, there was a separation of approximately one foot of the outboard portion of one propeller blade. The pilot shut down the engine and made an uneventful landing in a sunflower field. Examination of the failed propeller blade revealed it had failed due to fatigue. The origin of the fatigue fracture was at a corrosion pit on the camber surface of the blade measuring 0.012 inch wide and 0.0014 inch deep.

On October 13, 1993, at 1945 central daylight time, a Piper PA-24-250, N6846P, experienced a separation of approximately one foot of the outboard portion of one propeller blade while in cruise flight at 8,500 feet mean sea level. The private pilot made an uneventful forced landing near Thief River Falls, Minnesota. There was no damage to the airplane. The personal flight originated at Warroad, Minnesota, at 1900, with an intended destination of Arthur, North Dakota. No flight plan was filed, and visual meteorological conditions prevailed at the time.

The engine logbook indicated the propeller had been overhauled and reinstalled on April 1, 1986 at airframe total time of 2,942 hours. There were four annual inspection logbook entries stating the propeller had been "dressed and painted." The last inspection was an annual inspection completed on December 1, 1992. The airplane had flown 88 hours since inspection. The total time accumulated since the propeller had been overhauled was 1,000 hours.

The remaining portion of the failed propeller blade was sent to the National Transportation Safety Board Materials Laboratory, Washington D.C., for examination. The metallurgical report stated the fracture was typical of a fatigue separation. The fatigue origin was a corrosion pit on the camber surface of the blade measuring 0.012 inches wide and 0.0014 inches deep.