On June 12, 2005, about 1130 Pacific daylight time, a Cessna 210, N9457T, landed gear up at the Watsonville Municipal Airport (WVI), Watsonville, California. The owner/pilot was operating the airplane under the provisions of 14 CFR Part 91. The private pilot and two passengers were not injured; the airplane sustained substantial damage. The personal cross-country flight departed the San Carlos Airport (SQL), San Carlos, California, about 1045. Visual meteorological conditions prevailed, and no flight plan had been filed. In a telephone conversation, the pilot reported that he put the gear position handle in the down position as he was crossing over the field to enter the downwind leg of the traffic pattern for runway 20. At this time he noticed that the green landing gear enunciator light had illuminated. Due to the high level of traffic in the pattern, the pilot did not look into the mirrors to visually check if the landing gear had deployed successfully like he usually does. During the landing flare, the airplane's tail impacted the runway causing the airplane to bounce. The tail came down and impacted the runway again. Shortly thereafter, the entire airplane spun off the runway to the left onto the grass separating the taxiway and the runway. The pilot stated that the main landing gear did not deploy. In a written statement, the pilot stated that the airplane was severely damaged. The prop bent, both of the wing tips bent, the elevator bent on both sides, the front wheel strut broke, the undercarriage was damaged, and the fuselage buckled. In a telephone conversation, a Federal Aviation Administration (FAA) inspector reported that he examined the airplane after the accident occurred. He stated that the main landing gear doors were closed, and the main gear was in the retracted position. The nose wheel had partially extended. In his interview, the FAA inspector stated that witnesses to the accident heard the airplane's engine increase in power just prior to the landing. According to the Cessna 210 Owners Manual, the landing gear and doors operate in a specific sequence. Once the pilot places the gear position handle out of the neutral position, the engine driven hydraulic pump begins to create hydraulic pressure and transfers it to the hydraulic actuators, which operate the landing gear doors and landing gear. When the gear position handle is placed in the down position, the hydraulic pump supplies pressure to the door's actuators first, allowing the doors to open. Then, the hydraulic pressure will switch to the landing gear actuators, and the gear will extend. Once the landing gear has completed the extension, the hydraulic pressure will switch back to the door's actuators, and the doors will close. When the doors have completely closed, the gear position handle will return to the neutral position, completing the process.