On December 12, 2016, about 1505 eastern standard time, a Piper PA-31-350 airplane, N27405, landed gear-up during the touchdown at Clearwater Air Park, Clearwater, Florida. The commercial pilot and two passengers were not injured. The airplane was registered to and operated by Creative Marketing Associates Incorporated, Saint Petersburg, Florida, under the provisions of 14 Code of Federal Regulations (CFR) Part 91 as a day, visual flight rules passenger flight. Visual meteorological conditions prevailed. The flight originated from the Peter O Knight Airport, Tampa, Florida, about 1455 EST. The pilot reported that after a cross-country flight in a retractable, tricycle landing gear-equipped airplane, he entered the traffic pattern at the destination airport. He recalled that on the downwind leg of the traffic pattern, he applied flaps, pushed the landing gear lever down and performed his GGUMPS checklist. He reported that, "I saw the landing gear down lights lighting up after I pushed the landing gear lever completely down." He reported that on short final, as the airplane passed through 500 feet above ground level, "I verified three green landing gear down indicator lights and applied full flaps for landing." He recalled that the airplane landed hard on the runway and skidded to a stop on the runway. The pilot held a Commercial Pilot Certificate, and has reported the accumulation of 4,664 total flight hours, of which 860 hours were accumulated in the accident airplane. He reported that he had accumulated 5 hours in the accident airplane the day before the accident. The accident airplane had flown 9.6 hours since a 100 hour inspection was completed two months prior to the accident. A post-accident inspection of the airplane by FAA Airworthiness Inspectors noted substantial damage to the fuselage keel beams, stringers and formers. Photographs of the left and right landing gear, leg and wheel doors provided by the FAA Airworthiness Inspector, reveal that no damage existed to the either leg or wheel doors, consistent with the landing gear being retracted during landing. Following the accident, a landing gear extension and retraction check was completed under the supervision of an FAA Aviation Safety Inspector, and a separate inspection was conducted by an FAA Airworthiness Inspector; both inspections confirmed that there were no faults, malfunctions or anomalies with the landing gear extension or retraction system, including indicator lights and warning horn.