On July 29, 2009, about 0415 Pacific daylight time, an Air Tractor Inc. AT-301, N23189, sustained substantial damage during a forced landing following a loss of engine power about 5 nautical miles northwest of Firebaugh, California. The commercial pilot was not injured. Visual meteorological conditions prevailed for the aerial application flight, which was conducted in accordance with 14 Code of Federal Regulations Part 137, and a flight plan was not filed. The flight departed from a private airstrip about 4 miles east of Dos Palos, California, at 0410. In a statement submitted to the Safety Board investigator-in-charge (IIC), the pilot reported that while approaching the field to be sprayed the airplane's engine lost power. The pilot stated that after making a forced landing the airplane impacted an angle ditch and nosed over, which resulted in substantial damage to the airplane's empennage. A Federal Aviation Administration (FAA) inspector, who responded to the accident site, reported that when he arrived he noted that no fuel was in either wing tank, and that no fuel was heard in the tanks, nor could he hear any sloshing of fuel in the tanks. The inspector further reported that when the fuel caps were opened no fuel exited and no fumes were present. When asked by the inspector who fueled the airplane, the pilot said that it was company personnel, that they always do both fuel and pesticide, and that they typically put 30 gallons of fuel in each tank. The pilot provided the IIC with a fuel load sheet, which indicated that the airplane was fueled prior to the 4th load after a change of airstrips took place at 0300; the accident occurred on the 4th load. A certificated FAA airframe and powerplant mechanic stated that an inspection of the engine revealed no abnormalities, either external or internal. The mechanic reported that a check of the opening and closing of the valves were normal with the rotation of the engine, that all 9 cylinders maintained adequate compression, that the blower impeller turned 10 to 1 with engine rotation, and that he dialed the crankshaft and found it within limits. The mechanic installed a serviceable propeller and conducted an engine run at full power, with normal manifold pressure and revolutions per minute (RPM) achieved; the magnetos checked normal. The mechanic stated that after the engine was shut down he removed the oil screen and found no foreign metal or debris. The mechanic reported that he found the engine to be airworthy for normal operation.