On August 4, 2009, approximately 1245 central daylight time, an Air Tractor AT-401B agricultural airplane, N60747, sustained substantial damage when it impacted terrain during a forced landing to a field near Waterloo, Iowa. The commercial pilot, who was the sole occupant, was not injured. The airplane was registered to and operated by Dakota Executive Flight, Inc., Miller, South Dakota. Visual meteorological conditions prevailed, and a flight plan was not filed for the Title 14 Code of Federal Regulations Part 137 aerial application flight. The flight departed Oelwein, Iowa, approximately 1215. According to the pilot's statement, he had just completed his first spray pass of the flight and was maneuvering for another pass when the airplane experienced an engine problem. He reported, "I was heading east while looking south at the auto traffic when I felt deceleration of the aircraft. During my instrument scan I noted that I had primary fuel pressure and the torque had decayed [from] approximately 70 percent to about 45 percent and was decaying rapidly. There was a [slight] hesitation in the decay at 40 percent then it decayed further. At this time, I executed my restart procedure, but was unable to get a relight." He elected to perform a forced landing to a corn field. The airplane impacted corn (approximately 9 feet tall) and terrain. The airplane contained approximately 140 gallons of fuel at the time of the accident. The pilot reported to local authorities that to his knowledge, the airplane had experienced a loss of engine power on four previous flights on unknown dates. Examination of the airplane revealed the wings were bent, the empennage was bent, and the main landing gear was folded underneath the fuselage. The airplane was recovered for further examination. A review of the maintenance records showed on March 16, 2009, the GE/Walter M601E-11 engine underwent a 300-hour inspection in accordance with the maintenance manual. At the time of the inspection, the engine had accumulated 810 total hours engine service time. The engine had accumulated 940 total hours engine service time at the time of the accident. On August 10, 2009, a Federal Aviation Administration inspector examined the airplane. According to the inspector, fuel was found at the fuel pump inlet, the oil filter was clear of contaminants, and the propeller rotated "smoothly" by hand. The compressor inlet showed no damage or foreign object debris. No anomalies with the engine were noted. The engine was removed and shipped to the factory in the Czech Republic for further examination. On November 18-19, 2009, at the GE Aircraft Engine (GEAC) facility in Prague, Czech Republic, the engine was examined under the supervision of the Czech Civil Aviation Authority. Examination of the engine showed no visible damage to the external cases, reduction gearbox, gas generator case, accessory gear box, and the fuel accessory components. All pneumatic lines were found secured. The engine was disassembled and no internal damage was noted in the compressor, combustion, and turbine sections, and gear boxes. According to the manufacturer, no failures or damage which could adversely affect the engine operation were found, and no evidence of a pre-impact mechanical anomaly was found. On November 20, 2009, the fuel distributor was bench tested and no anomalies were noted during the test. On November 26, 2009, the torque indicator was functionally tested and no anomalies were noted during the test. On November 30, 2009, the fuel control unit and fuel pump were tested on a slave Walter engine. No anomalies were noted during the test. The fuel control unit was sent to the manufacturer for further testing. All of the test results were acceptable except acceleration, which was found shorter than required in the technical specification. According to the engine manufacturer, "This anomaly should not have adverse effect on the situation related with this investigated case. In addition, this anomaly did not manifest during engine functional test at GEAC and engine parameters were found acceptable."