On August 12, 2013, about 1322 central daylight time, a Rockwell International S-2R airplane, N5610X, was substantially damaged during a forced landing following a loss of engine power near Larchwood, Iowa. The pilot reported no injuries. The airplane was registered to Mitchell Aerial Application Inc. and operated by Crop Dusters LLC under the provisions of 14 Code of Federal Regulations Part 137 as an aerial application flight. Visual meteorological conditions prevailed for the flight, which was not operated on a flight plan. The local flight departed the Rock Rapids Municipal Airport (RRQ), Rock Rapids, Iowa, about 1200.The pilot reported that he experienced a complete loss of engine power during his third application flight of the day. He completed multiple spray passes at the first field designated for the flight, and then proceeded to the second field. The pilot stated that after spraying for about 10 minutes at the second field, the engine "flamed out." His attempts to restore engine power were not successful and he executed a forced landing to a gravel road. During the landing, he encountered a bridge, which he "crow hopped" over; however, the left wing subsequently struck a power line support pole. The airplane came to rest in a ditch along the side of the road. A postaccident examination of the airframe and engine did not reveal any anomalies consistent with a loss of engine power. After recovery, an examination of the airplane was conducted under the direct supervision of the NTSB investigator-in-charge. The airplane wings had been removed prior to the examination in order to facilitate the recovery. Continuity was confirmed between the engine and the cockpit engine controls. The cockpit fuel shutoff control was in the ON position at the time of the exam. The fuel lines from the wing roots to the engine appeared intact. The electrical fuel pump operated when power was applied, and residual fuel from the lines was observed to flow from the pump during operation. The insulation on the fuel shutoff valve wire harness was observed to be compromised at one location on the wire corresponding to pin A of the connector. Pin A was associated with opening the valve during engine starts. In the event of a short at Pin A, or a loss of electrical power to the valve, the valve is designed to remain open once the engine is operating. An electrical short (grounding) at Pin A would be expected to prevent starting of the engine; however, continued fuel flow to the engine would not be affected. Closing the valve required a separate electrical signal through Pin B to energize a separate solenoid and, thereby, closing the valve. Further examination of the engine was conducted at the engine manufacturer's facility under the direct supervision of the NTSB investigator-in-charge. Visual and borescope examinations were unremarkable. An engine test run was conducted. The engine started normally and stabilized at ground idle. The engine was operated at 2,005 rpm and 673 shaft horsepower with no anomalies observed. Exhaust gas and vibration parameters remained within limits during the test run. No anomalies related to an inability to produced rated power were observed.