At 09:16 CDT, a Cessna 402C broke up during cruise flight, killing the pilot. The flight was operating as a Part 135 on-demand cargo flight from Dallas to Oklahoma City. The airplane was level at 6,000 feet msl and the pilot had visual contact with traffic that was going to pass him. He was cleared to descend from 6,000 feet msl to 4,000 feet msl. The pilot acknowledged the clearance and said he was beginning the descent. Witnesses reported that the airplane was level at approximately 1,000 feet agl, when the wing departed the aircraft. They also reported that they did not see any other airplanes in the area at the time of the wing separation.