On October 9, 1996, at 1430 central daylight time, a Callair B1A, N6203X, sustained substantial damage when the landing gear collapsed during a forced landing near Nebraska City, Nebraska. The commercial pilot reported minor injuries. The 14 CFR Part 91, ferry flight was operating in visual meteorological conditions. No flight plan was on file. The flight departed Yankton, South Dakota, about 1240, with a planned destination of Shenandoah, Iowa. The pilot reported he was cruising at 3,300 feet mean sea level. All gauges were "normal." He heard a "loud back fire" and the engine lost power. He pushed the throttle, mixture and propeller control full forward. The engine continued to run at "idle speed." He initially attempted to land at the nearest airport, Grunman County Airport, but "it became evident" that he would not make it to the airport. He selected a field for a forced landing. He lowered the flaps, then noticed farm equipment in the field. He side stepped to a different field and landed with "low airspeed and high sink rate." He landed "flat" on the main landing gear. The gear collapsed and the engine was bent downward. He egressed the airplane with minor injury. The Federal Aviation Administration Inspector who examined the engine reported that several spark plugs and the top of the pistons were oil covered. Several spark plugs "appeared to have been running rich." There was "a lot of oil in the plenum chamber." The supercharger blades had "excessive rub on the rear face."