On August 21, 1999, at 0905 hours Pacific daylight time, a Cessna TR182, N4809R, landed gear up at the South Lake Tahoe airport, Lake Tahoe, California. The airplane, owned and operated by the pilot under the provisions of 14 CFR Part 91, sustained substantial damage. The private pilot, the sole occupant, was not injured. Visual meteorological conditions existed for the personal flight that departed the Cameron Park, California, airport about 0800. The flight was scheduled to terminate at the Salt Lake City International Airport, Salt Lake City, Utah. No flight plan was filed. The pilot stated that after departure from Cameron Park, he climbed to 17,500 feet to maneuver around cloud buildups while crossing over the Sierra Nevada mountains. He noted the oxygen level had decreased to 400 pounds and was not sure he would have enough supplemental oxygen to complete the trip. He decided to land at the South Lake Tahoe airport to refill the oxygen system. The pilot reported that after reaching approach altitude he completed the "GUMP check" and came in for landing. During the landing flare he felt a slight bump, and realized that the horizon was lower than expected. The propeller struck the runway and the airplane skidded down the centerline of the runway. He stated that he was sure he put the landing gear down, but he also may have forgotten. The pilot further reported that the airplane had a history of problems with gear indication lights and warning horn. He said the airplane had been in and out of several repair shops in an attempt to resolve the discrepancies. During an interview with the Federal Aviation Administration (FAA), the pilot stated that he had become distracted by traffic on his approach path and did not verify that the green landing gear down indicator light was illuminated, or visually verify by looking out his side window to see whether the left main gear was extended. The landing gear system was inspected by an airframe and powerplant (A & P) mechanic from an FAA approved repair station. He stated that when the landing gear handle was placed in the up position the GEAR PUMP circuit breaker opened prior to the completion of the retraction cycle. The gear remained in a not stowed condition until the circuit breaker was reset. The landing gear then continued into the up and locked position. During manual and hydraulic extensions of the landing gear, the GEAR PUMP circuit breaker once again opened. The circuit breaker was reset and the landing gear continued down to the locked position. He noted that the landing gear down and locked light did not illuminate upon completion of the extension cycle, but rather it took 10 seconds after cycle completion for the green landing gear down indicator light to illuminate. He further reported that prior to the green landing gear down indication light illuminating, the aural gear warning horn would sound. The mechanic noted the warning horn was very faint and hard to hear in the quiet hangar where the inspection took place, and he opined that in a running aircraft it could not have been heard. The horn would silence as soon as the landing gear green safe light illuminated. The A & P mechanic tested the landing gear warning systems, which included the throttle position proximity switch; the circuit appeared to be functioning properly with the exception of the aural warning horn and the flap portion of the warning system, which was inoperative. He stated that when the landing gear handle was placed in the down position, whether the power was on or off, the landing gear would fall from the stowed position. Detailed examination of the landing gear struts, wheel rims, and tire sidewalls revealed no damage or scuff marks. A pattern of wrinkles was found on the fuselage aft of the entry door. The FAA airworthiness inspector who examined the airplane opined that the wrinkles were not related to the gear-up landing and that the fuselage appeared to be slightly distorted. Subsequent conversations with the airplane's owner established that it had been blown over in high winds while parked about 3 months prior to the accident. The discrepancies with the gear system began around this time.