ATL03LA059

During cruise flight a "bump" was felt under the pilot's seat, then the airplane pitched up erratically and became difficult to control. The pilot selected an open field and executed an emergency landing. The airplane came to rest in a pond. The pilot reported that the crankshaft sheared behind the propeller flange and in front of the crankcase. Examination of the airplane on site revealed that one of the propeller blades separated at the flange, there was substantial damage to the nose bowl cowling due to the airplane nosing over into the pond. The firewall was bent slightly rearward at the base and there was also water damage to the wing spar. Further examination of the partial crankshaft recovered, revealed that the separation had occurred between the oil slinger and the propeller mounting flanges leaving a fracture face. The fracture face displayed arced crack arrest marks, consistent with fatigue propagation. The arcing of the crack arrest marks indicated that the fatigue origin was located further forward, towards the propeller-mounting flange on the unrecovered portion of the crankshaft.

On March 7, 2003, at 1745 central standard time, an Aeronca 7AC, N1648E, registered to and operated by a private owner, propeller blade separated in-flight, and the pilot conducted an emergency landing near Gordo, Alabama. The personal flight was operated under the provisions of Title 14 CFR Part 91 with no flight plan filed. Visual meteorological conditions prevailed at the time of the accident. The airplane sustained substantial damage, and the pilot and passenger were not injured. The flight originated from Tuscaloosa Municipal Airport, Tuscaloosa, Alabama, at 1700 on March 7, 2003.

According to the pilot, during cruise flight a "bump" was felt under his seat, then the airplane pitched up erratically and became difficult to control. The pilot selected an open field and executed an emergency landing. The airplane came to rest in a feeder pond.

The pilot reported that the crankshaft sheared behind the propeller flange and in front of the crankcase. There was 2391 hours total time on the part and 2170 hours total time at overhaul. Examination of the airplane on site revealed one of the propeller blades separated at the flange, substantial damage to the nose bowl cowling due to aircraft nosing over into pond, firewall bent slightly rearward at base and water damage to wing spar. Further examination of the partial crankshaft recovered revealed that the separation had occurred between the oil slinger and the propeller mounting flanges leaving a fracture face inclined at approximately 45 degrees to the longitudinal axis of the crankshaft. The fracture face displayed arced crack arrest marks, consistent with fatigue propagation. The arcing of the crack arrest marks showed that the fatigue origin was located further forward, towards the propeller-mounting flange on the unrecovered portion of the crankshaft.