On July 20, 2006, at 2006 central daylight time, an experimental amateur-built Schlei Avid Flyer Speed Wing, N507S, owned and piloted by a private pilot, received substantial damage on impact with terrain during an emergency landing. The pilot reported a loss of control. Visual meteorological conditions prevailed at the time of the accident. The 14 CFR Part 91 personal flight was not operating on a flight plan. The pilot received serious injuries. The flight departed from Henning, Minnesota, and was returning to Fergus Falls, Minnesota. The pilot stated that after he descended from a cruise altitude of 4,000 feet and "shortly" after leveling off at 3,000 feet, he felt the airplane "kind of shake." Following the shake, the airplane pitched down with a "slight" left bank. He thought he was in a spin so he reduced engine power to idle and applied right rudder but there was no effect on airplane control. Out of "desperation," he began to move the control stick "all over," looking for anything that would return control. He moved the control stick as far aft as and to the right as possible. The airplane began to level off. Hoping to level the attitude some more, he tried moving the control stick again but the airplane began "going down again." He then moved the control stick to its previous position but did not remember if it had an effect on airplane attitude. He knew that he was going to "crash," so he turned the fuel off and was going to turn the master switch off but did not remember if he did. Examination of the flight control system by the Federal Aviation Administration revealed a broken front aileron bell crank (part identification F-5). Additionally, there was a broken elevator clevis rod end (part identification F-43), which had a fracture that was more than half rusted.