Event Description
Shortly after takeoff, when the aircraft reached approximately 400 feet above ground level, the engine emitted a metallic noise. The flight instructor (CFI) initiated a turn back toward the runway. During the maneuver, the engine lost power and stopped, with the propeller coming to rest in a horizontal position. The airplane's main wheels struck the bank of a pond about 100 feet short of the runway. The impact caused the airplane to nose over. The pilot and passenger subsequently exited the aircraft.
Examination Findings
Post-accident examination of the engine's crankshaft revealed that it had separated through the aft cheek of the #3 main bearing. Magnified visual inspection of the fracture faces showed characteristics consistent with fatigue propagation. The fatigue crack initiated in the aft radius of the #3 main bearing and progressed rearward through approximately 80% of the crankshaft cheek before the remaining material failed in overload.
Further examination of the initiation area identified a single origin on the surface of the radius, located within an area that exhibited circumferential scratches. The origin point was situated on the journal approximately 10 to 15 degrees before top center of the adjacent #2 and #3 cylinders.