On June 10, 2006, at 1332 mountain standard time, a Cessna 210B, N9666X, experienced a hard landing and porpoised down the runway at Flagstaff Pulliam Airport, Flagstaff, Arizona. The pilot/owner was operating the airplane under the provisions of 14 CFR Part 91. The private pilot and one passenger were not injured; the airplane sustained substantial damage. The personal cross-country flight departed from Phoenix Deer Valley Airport, Phoenix, Arizona, about 1240, with a planned destination of Flagstaff. Visual meteorological conditions prevailed and a flight plan had not been filed. In a written statement the pilot reported that he configured the airplane for landing at Flagstaff with 30 degrees of wing flaps while maintaining an airspeed of 90 miles per hour (mph). The airplane touched down on the runway identifier markings (numbers). Shortly thereafter, the airplane bounced off the runway surface and became airborne again. The airplane porpoised down the runway, collapsing the nose landing gear on the third contact. The airplane incurred damage to the firewall. The pilot reported no preimpact mechanical malfunctions or failures with the airplane that would have precluded normal operation. The mishap was upgraded to an accident on June 20th due to the damage found by a Federal Aviation Administration inspector.