On August 16, 2004, about 0915 mountain standard time, a Rockwell Commander 112TC, N54RR, landed gear up at Laughlin/Bullhead International Airport, Bullhead City, Arizona. The pilot/owner was operating the airplane under the provisions of 14 CFR Part 91. The private pilot, the sole occupant, was not injured; the airplane sustained substantial damage. Visual meteorological conditions prevailed, and a flight plan had not been filed. The personal cross-country flight originated from Henderson Executive Airport, Las Vegas, Nevada, about 0835 Pacific daylight time, with a planned destination of Bullhead City. In a telephone conversation with a National Transporation Safety Board investigator, the pilot reported that he was attempting to land on runway 16. In an effort to make the approach faster, he opted to leave the landing gear retracted for the initial approach. He mentally preformed a prelanding checklist "GUMPS," which included checking the gas, undercarriage, mixture, and propeller. During the landing flare, the airplane touched down on the bottom of the fuselage, and the pilot realized that he had forgotten to extend the landing gear. The pilot further stated that he did not use a physical checklist prior to landing. He also noted that he did not hear the gear warning horn sound, which he thought was a result of using external noise cancellation headsets. The pilot reported no mechanical malfunctions or failures with the airplane prior to impact. The accident was upgraded from an incident on August 24, 2004. The airplane incurred damage to the wing carry-though spar and possibly the fuselage aft bulkhead.