On March 17, 2007, about 1420 central daylight time, an experimental amateur-built Haddan Sonerai IIL, N5200C, piloted by a private pilot, received substantial damage on impact with terrain during a forced landing on a field near Fort Atkinson Municipal Airport (61C), Fort Atkinson, Wisconsin. 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 minor injuries and the passenger received serious injuries. The flight originated from 61C about 1415, en route to Beloit Airport (44C), Beloit, Wisconsin. A witness stated that he was traveling along Highway 26 when he saw the airplane flying "erratically." He initially thought the airplane was going to cross over Highway 26 but instead it "went under [a] tree line" and then crashed. The witness arrived at the accident site and saw the pilot was already out of the airplane trying to get his son out of the wreckage. The pilot reported to police that he owned the airplane for approximately one week and accumulated about 10 hours of flight time in the airplane. He departed from 61C in a northerly direction when the engine sputtered and quit approximately 500 feet above ground level. The pilot stated that he checked his fuel mixture and was unable to detect anything in the cockpit that would cause the engine to quit. He then looked for a landing area and believes that the airplane stalled. The pilot stated that the airplane has a takeoff speed of 60 mph and the stall speed is 55 mph. The airplane was located in an upright position and was preceded by 60 foot long tire marks. There was usable fuel aboard. On-scene examination of the airplane revealed no anomalies that would have precluded normal operation. The airplane flight manual states that the airplane is equipped with seatbelts and shoulder harnesses and also states within the Before Starting Engine checklist that they are to be adjusted and locked. The rear seat, which was occupied by the pilot, had a lap belt and no shoulder harness installed. The front seat, which was occupied by the pilot's son, did not have a lap belt nor did it have a shoulder harness, which is cited in the airplane manual as being present. Advisory Circular, AC 91-65, Use of Shoulder Harness In Passenger Seats, states, in part: "The safety board found that 20 percent of the fatally-injured occupants in these accidents could have survived with shoulder harnesses (assuming the seat belt was fastened) and 88 percent of the seriously injured could have had significantly less severe injuries with the use of shoulder harnesses. Energy-absorbing seats could have benefited 34 percent of the seriously injured. The safety board concluded that shoulder harness use is the most effective way of reducing fatalities and serious injuries in general aviation accidents."