On August 21, 2001, at 1503 Pacific daylight time, an Aero Commander 500S, N975AA, had both main landing gear collapse on landing at Elko, Nevada. Avcenter, Inc., was operating the airplane as a public-use fire command and control flight under the provisions of 14 CFR Part 91. The commercial pilot and two passengers were not injured; the airplane sustained substantial damage. The local flight departed Elko about 1330. Visual meteorological conditions prevailed, and a company VFR flight plan had been filed. The operator reported that the airplane touched down and began its landing roll. About 100 feet down the runway, both main landing gear collapsed. The resulting skid ground off the belly skin and damaged several structural airframe components. One of the observers in the airplane was also a pilot. He observed three green landing gear lights, and told the operator that he and the pilot both visually checked that the landing gear was down. He observed the pilot maintain one hand on the control yoke and the other on the throttle throughout the landing and landing roll. A Safety Board investigator interviewed a maintenance supervisor at Aero Air, Hillsboro, Oregon, who performed the tests on the landing gear after the accident. The supervisor stated that the plane was ferried to Aero Air with its landing gear in the locked position. Aero Air personnel physically checked the landing gear by putting the airplane on jacks and swinging the gear. The physical check was satisfactory, and everything worked normally. As a precaution, the operator asked them to check the actuators. The actuators were bench tested, and they functioned normally. Aero Air also resealed them, and tested them once more, and everything functioned normally. They did not perform any checks on the hydraulic system. In the same conversation the supervisor stated that the landing gear is held in place by hydraulic pressure, and when it passes center it uses elastic bungee cords. He also noted that the landing gear handle is a two-position handle, gear up, and gear down.