On May 3, 1994, at 1200 eastern daylight time, a Cessna P210N, N7588K, registered to Paul Naz of Harper Woods, Michigan, and piloted by a private pilot, was substantially damaged during landing with a partially extended landing gear on Runway 18 (3,800' X 75' dry asphalt) at the James Clements Airport, Bay City, Michigan. Visual meteorological conditions prevailed at the time of the accident. The 14 CFR Part 91 flight had been operating on an instrument flight plan. The pilot reported no injuries. The flight departed Detroit, Michigan, at 1055 EDT. According to the pilot's written statement on NTSB Form 6120.1/2, the landing gear was extended while on the downwind leg for the landing runway. He said he confirmed the landing gear was down by visually checking the left main landing gear leg's position. Upon touchdown, the airplane "...acted very 'squirrelly' and then gently started veering to the right..." according to the pilot. He stated the airplane's left wing began to rise as it was veering to the right and decelerating. During a telephone interview the pilot stated, he added that he heard a "clunk" from the main landing gear when the airplane touched down. The pilot was asked to describe how he conducts the final phase of the landing approach. He stated the final approach speed is about 90 knots with full flaps. The pilot said he crossed the runway threshold and retarded the power to idle. He said the gear warning horn did not sound. Tire skid marks were approximately 1,100 feet long, according to the pilot. He said the skid marks were not the same distance apart as the landing gear normally would make and both marks started at the same point. A Federal Aviation Administration Principal Maintenance Inspector (PMI) inspected the accident site and airplane and reported parallel tire skid marks approximately four feet apart from beginning to end. Scuffing was observed on the main landing gear tires outside edge and sidewall. The landing gear pump's circuit breaker was found in the "OPEN" position during the cockpit inspection. The landing gear extension handle was found in the "DOWN" position. The PMI said the airplane's landing gear was cycled four times using its normal system. Each time the landing gear was extended the main gear legs had an aft and upward force applied to them. According to the PMI, the landing gear legs did not move from their extended position. The landing gear leg extension cycles were timed. The nose gear extended in three seconds and the main landing gear extended in seven seconds. One emergency extension exercise was conducted. The results were in accordance with the manufacturer's performance standards. Cessna Aircraft Corporation was contacted regarding inadvertent retraction of the main landing gear once the airplane touches down. The representative said the weight of the airplane will keep the landing gear extended, or drive it into the latched position if it had not been latched before touchdown. A weak landing gear pump motor would continuously run because it would not produce the required pressure to fully extend the landing gear according to the representative. He said this condition would eventually cause the pump's circuit breaker to open, shutting the pump off. He said pressure relief valve will automatically shut the pump off when a 1,650 pound per square inch pressure level is reached.