On May 2, 2000, at 1913 eastern daylight time, a Cessna 501, Citation, N56LW, landed with the right main landing gear partially extended on runway 18 at the Orlando International Airport, in Orlando, Florida. The personal flight was operated by the pilot under the provisions of Title 14 CFR Part 91 with no flight plan filed. Visual weather conditions prevailed at the time of the accident. The airplane sustained substantial damage. The private pilot and his passenger were not injured. The flight departed Leesburg, Florida, at 1850. According to the pilot, while enroute to land he silenced the landing gear warning horn and forgot to lower the landing gear. Just prior to the touchdown, the pilot attempted to lower the landing gear. The airplane touched down with the landing gear in transit, and the right landing gear collapsed. The airplane skidded approximately 2500 feet on the runway surface before coming to a complete stop on the runway. The right wing assembly received structural damage, and leaked jet fuel from the bottom side of the right wing assembly. The examination and the functional check of the airplane failed to disclose a mechanical problem with the landing gear extension and retraction system. The pilot also did not report a mechanical problem with the airplane. Reportedly, the pilot stated that he forgot to lower the landing gear, as instructed in the normal pre-landing checklist.