On April 21, 2000, at 1526 central daylight time (cdt), a Cessna 170A, N1233D, operated by a solo student pilot, was substantially damaged when the airplane sustained a hard landing on runway 16 (4001 feet by 100 feet, dry asphalt) at the South St. Paul Airport, St. Paul, Minnesota. Visual meteorological conditions prevailed at the time of the accident. The personal flight was being conducted under 14 CFR Part 91, and was not on a flight plan. The student pilot reported no injuries. The local flight originated at St. Paul, Minnesota, at 1400 cdt. In his written statement, the student pilot said that upon landing, the left axle broke causing the left wingtip to touch the runway. In his statement to a Federal Aviation Administration (FAA) inspector, the student pilot said that he landed hard on the airplane's left side. A FAA inspector examined the airplane at the South St. Paul Airport. The airplane's left main landing gear axle was broken at the gear leg mounting flange. The fracture ran around the circumference of the axle, flush against the flange, except for where it ran outside of a 7/16-inch wide spot weld observed on one side of the axle. The left landing gear box was pushed inward and aft. The airplane's left wing rear spar and left aileron were bent upward and cracked. Examination of the engine, engine controls, and other airplane systems revealed no anomalies. The airplane underwent an annual inspection on March 9, 2000. The airplane had logged 4 hours since the date of the annual inspection, to the time of the accident. The Cessna Aircraft Company, Wichita, Kansas, Product Support Division states that cracked landing gear axles should be replaced. The company provides no guidance regarding performing welds on their landing gear axles.