On May 28, 1994, at 1905 central daylight time, a Beech 35, N3956N, was substantially damaged during descent near McKinney, Texas. The private pilot and his two passengers were not injured. Visual meteorological conditions prevailed for the personal flight. The pilot stated that the airplane was at approximately 300 feet AGL on final approach at the Aero-Country Airport, when the ailerons became locked. The pilot was not able to return the airplane to the level flight attitude. The pilot reported that the airplane entered a left 60 degree spiral, completing two 360 degree turns, until he was able to drag the left wing into a wheat field approximately a quarter of a mile west of the airport. At the time of ground impact, the airplane was configured with the landing gear and flaps retracted. The 1948 vintage airplane was equipped with a single throwover type control yoke, being operated from the left side. Examination of the control wheel, control wheel cast, chain and sprockets, revealed that a brass alloy foreign object, which was not recovered, became trapped between the sprocket and the chain, blocking the ailerons. The control wheel arm assembly has an open inspection window on its back side.