MIA99LA152 · Christen Industries S-2B

After performing several aerobatic maneuvers at about 6,000 feet msl and 110 mph, the pilot noted that the engine rpm surged for about two seconds and then recovered to the previously set 2,500 rpm. He elected to return to the departure airport, which was about 17 miles from his location. About 1 minute later, at an altitude of 5,500 feet he said he '...noted the oil temperature started to climb.' At this point he was about 14 mile from the airport. He said, '...the engine vibrated severely with a loud metallic sound, oil poured onto the windscreen, and the cockpit filled with smoke...and the engine simultaneously seized, stopping the prop before I could feather it...I...determined that we could probably not clear the ridge line...the only practical place within gliding range to perform a forced landing was a small pasture about 1 mile behind us in the bottom of a valley alongside a small road...slowing to...90 mph...touched down about 150 feet past the fence...I had difficulty keeping the tailwheel from bouncing as we plowed through the high grass and had to make continuos rudder inputs to keep tracking straight. After approximately 300 feet of roll out, the aircraft yawed right, the left main collapsed under the aircraft, and we slid sideways onto the bottom left wing, which snapped off, taking the left upper wing with it...rotated about 180 degrees counterclockwise, and stopped in an upright position....' The engine teardown revealed that the No. 6 connecting rod had failed due to oil starvation. According to the FAA inspector, the cause of the oil starvation was 'undetermined.'

Verbatim NTSB analysis and probable cause from the NTSB dataset