On August 2, 1998, at 1130 central daylight time (cdt) , a North American SNJ-6B, N7983C, registered to SNJ, Inc., was substantially damaged when the left main gear collapsed on landing at the Quincy Municipal Airport, Quincy, Illinois. The airline transport rated pilot was not injured. The passenger received minor injuries. The 14 CFR Part 91 personal flight was operating in visual meteorological conditions without a flight plan. The flight originated at Oshkosh, Wisconsin, at 0830 cdt. The pilot reported, "At touchdown the right wing started down as though the right gear was not down. I lifted the wing with the controls and applied power. When the aircraft cleared the runway to the left I reduced power and the right wing fell and the aircraft slid to a stop." The landing was made on runway 04 (7,097' x 150'). Inspection of the airplane revealed the right main landing gear collapsed for undetermined reasons.