On July 14, 2003, at 1500 central daylight time, a Cessna 172P, N98395, operated by Southern Illinois University as an instructional airplane, was substantially damaged during final approach to runway 18 (4,000 feet by 60 feet, asphalt) at Pinckneyville-Du Quoin Airport (PJY), Pinckneyville, Illinois. The airplane struck a runway threshold light at the approach end of the runway. Visual meteorological conditions prevailed at the time of the accident. The 14 CFR Part 141 instructional flight was not operating on a flight plan. The certified flight instructor (CFI), private pilot, and student pilot passenger were uninjured. The flight originated from Southern Illinois Airport, Murphysboro, Illinois, at an unknown time. According to the CFI, the private pilot was practicing short field landings, soft field landings, and slips during the flight. "After his third landing he (private pilot) was instructed to perform a forward slip (power off) landing. He was performing the maneuver with no instructional assistance require[d], when his approach became low." The CFI reported adding power but stated that the airplane was too low and it impacted a threshold light on runway 18. The CFI reported no mechanical malfunctions or failures associated with the airplane.