On June 2, 2011, about 2000 mountain standard time, a Scottish Aviation, Series 100 MDL 101, N101MY, experienced a partial loss of engine power during cruise flight about 4 miles east of Chandler, Arizona. The pilot made a forced landing in an open field. During rollout, the airplane's nose gear collapsed upon overrunning a ditch in the soft terrain, and the firewall was bent. The airplane was substantially damaged. Neither the airline transport pilot nor passenger was injured. The airplane was owned by the pilot, and it was operated under the provisions of 14 Code of Federal Regulations Part 91. Visual meteorological conditions prevailed. No flight plan was filed for the local area personal flight that originated from Chandler about 1915. The pilot reported to the National Transportation Safety Board investigator that the airplane was equipped with two interconnected fuel tanks in each wing. When the engine surged and power was lost, both of the wings' fuel tank gauges registered about 1/4-full. The pilot stated that he attempted to reacquire engine power, but he was not successful. As the airplane's altitude decreased, he redirected his attention to executing the forced landing. The pilot said that the entire flight was performed with the fuel selector on the “BOTH” position. Airplane recovery personnel reported to the Safety Board investigator that no fuel was found in the left wing tanks. About 8 gallons of fuel were found in the right wing tanks. According to the Pilot’s Operating Handbook, the fuel system consists of an inner and outer interconnected tank in each wing supplying fuel through a non-return valve to a fuel selector, a filter and a booster pump grouped together beneath the floor in front of the left hand front seat and thence through the engine-driven pump to the injector unit. The fuel selector is marked FUEL. OFF-L (ie, Left tank) - BOTH - R (ie, Right tank). Unusable fuel on either wing is 0.5 gallons. On June 15, the airplane was examined by Federal Aviation Administration inspectors, who reported that no fuel system discrepancies were found. The engine was test run in the airframe and it started and ran normally.