What happened
Shortly after takeoff, at an altitude of approximately 400 feet above the ground, the aircraft's engine produced a metallic noise. In response to the noise, the flight instructor initiated a turn back toward the runway. During this maneuver, the engine lost power and stopped running, leaving the propeller in a horizontal position.
As the aircraft continued its descent, the main wheels struck the bank of a pond located roughly 100 feet short of the runway. The impact caused the airplane to nose over. The pilot and passenger were able to exit the aircraft following the accident; both were not injured.
The investigation
Mechanical examination focused on the engine's crankshaft. Investigators discovered that the crankshaft had separated through the aft cheek of the #3 main bearing.
A magnified visual inspection of the fracture face identified characteristics of fatigue propagation. This fatigue began at the aft radius of the #3 main bearing and moved rearward through approximately 80% of the crankshaft cheek until the component failed due to overload. The investigation also located a single origin point on the surface of the radius within an area containing circumferential scratches. This origin was positioned on the journal, approximately 10 to 15 degrees before top center of the cylinders adjacent to #2 and #3.