BFO96LA038

The pilot stated that the airplane was in cruise flight at 1,500 feet MSL when the propeller separated from the airplane. The pilot made an emergency landing in a snow covered field. Upon touchdown in 18-inch deep snow, the nose wheel collapsed. The separated propeller assembly and the attached forward portion of the crankshaft flange were located, and examined in the NTSB laboratory. Postaccident inspection of the crankshaft revealed a spiral crack that intersected the fracture at the bottom corner of a keyway. Further examination showed that the cracks were filled with a iron nitride white layer. Maintenance records indicated that the main journals and pins of the crankshaft were ground, nitrided, inspected, and returned for service, in October, 1994.

On January 14, 1996, at about 1600 eastern standard time, an Ercoupe 415-C, N87424, made an emergency landing in a snow covered field after the propeller separated from the airplane near Hurlock, Maryland. The flight originated at 1545 eastern standard time from Easton/Newnan Field, in Easton, Maryland, with an intended destination of Salisbury-Wicomico County Regional Airport, in Salisbury, Maryland. The pilot and the one passenger reported no injuries. The airplane sustained substantial damage. No flight plan had been filed and visual meteorological conditions prevailed at the time of the accident. The flight was conducted under 14 CFR Part 91.

The pilot stated that the airplane was in cruise flight at 1,500 feet mean sea level (MSL), when the propeller assembly separated. He reported that the propeller assembly impacted the airplanes left wing as it departed the aircraft.

The separated propeller assembly and the attached forward portion of the crankshaft flange were found in a field near the where the airplane impacted the snow. The crankshaft and the recovered forward fragment of the crankshaft flange were sent to the Office of Research and Engineering of the National Transportation Safety Board. An examination of the separated crankshaft P/N A5334, S/N 15C6 from the Continental C85-12 engine was conducted. The examination revealed that the crankshaft had separated at the propeller flange. The forward portion of the crankshaft contained a spiral crack that intersected the fracture at the bottom corner of the keyway. The scanning electron microscope examination of both halves of the mating fractures showed that original microscopic fracture features were mechanically damaged by relative movement between the mating fractures. The metallurgist's factual report stated: "No anomalies, such as corrosion pits or gouge marks were noted at the surface of the keyway."

Maintenance records indicate that in October, 1994, the main journals and pins of the crankshaft were ground 0.02 inch undersize, nitrided, inspected by visual and magnetic particle method, and installed with replacement main bearing and rod bearing set.

According to the metallurgist's report, a light colored layer extended approximately 0.06 inches deep from the bottom corner of the keyway. The metallurgist reported that further examination of this layer revealed a spectrum consistent with an iron nitride white layer.