On March 2, 2002, about 1140 eastern standard time, a Cessna 172P, N65021, was substantially damaged while landing at the Chester County Airport, Coatesville, Pennsylvania. The certified flight instructor (CFI) and student pilot were not injured. Visual meteorological conditions prevailed and no flight plan was filed for the instructional flight conducted under 14 CFR Part 91. According to the CFI, the student was landing on runway 11, a 5,400-foot long, 100-foot wide, asphalt runway. About 5 feet above the runway, a gust of wind was encountered, which lifted the right wing. The left main landing gear touched down, and the gear spring twisted. The airplane began to drift to the left, and after the CFI "gave the student a second or two to recover from this position," he took the controls. Continuing to veer, the airplane departed the left side of the runway, where the left main landing gear collapsed. The airplane came to rest in a grass area. The left main landing gear spring was retained for further examination at the Cessna Aircraft Company Materials Laboratory. According to the manufacturer's technical report of the examination, the tubular spring for the left main landing gear fractured at the inboard end. The inboard end of the spring contained a longitudinal oriented fracture that intersected a fastener hole. The fracture face contained chevron marks typical of an overstress fracture that pointed back to the hole, indicating that the fracture emanated from the fastener hole. The overstress fracture region extended for about 3.5 inches from the hole. No evidence of corrosion was noted on the fracture region. Further examination of the fastener hole revealed that it contained machining marks and fretting. The composition and hardness of the material use to produce the spring were within manufacturer specifications. Review of the airplane's maintenance records revealed that the landing gear struts were removed from the fuselage, and floats were installed, in 1992. After about 2,158 hours of service, the floats were removed, and the original landing gear struts were re-installed. The airplane had accumulated about 3,598 hours of total service. The winds recorded at a nearby airport, at 1154, were from 150 degrees at 10 knots. The CFI reported that the winds at 40N, about the time of the accident, were from 180 degrees at 8 knots, gusting to 17 knots.