On June 13, 2014, about 1100 Pacific daylight time, an Air Tractor AT-502B, N502JS, was substantially damaged during takeoff from a dirt airstrip near Princeton, California, following a reported partial loss of engine power. The airplane was registered to a private individual, and operated by Michaud Aviation, Willows, California, under the provisions of Title 14 Code of Federal Regulations Part 137. The commercial pilot, sole occupant of the airplane, was not injured. Visual meteorological conditions prevailed, and no flight plan was filed for the local aerial application flight, which was originating at the time of the accident.In a written statement to the National Transportation Safety Board (NTSB) investigator-in-charge (IIC), the pilot reported that the airplane was loaded with about 3,000 pounds of fertilizer in the hopper and had about 115 gallons of Jet A fuel on board prior to departure. During takeoff to the north from a dirt airstrip, the airplane lifted off about two-thirds down the runway. The pilot stated that as the airplane reached an altitude of about 10 to 15 feet above the ground, it felt like it [the engine] was experiencing a partial loss of power, and settled towards the ground. The pilot added full power, and it still felt as if the engine was only producing partial power. Subsequently, the airplane impacted the ground and came to rest upright. Post-accident examination of the airplane by local law enforcement revealed that the fuselage was displaced to the right forward of the vertical stabilizer, and the right aileron was partially separated. The airplane was recovered to a secure location for further examination. The recovered airframe and engine were examined by the NTSB IIC on July 31, 2014, at the facilities of Air Transport, Phoenix, Arizona. The engine remained attached via all mounts to the airframe. All fuel, oil, and pneumatic lines remained attached and secure to their respective fittings. Continuity was established from all engine cockpit controls forward to the engine. The engine was removed and shipped to the manufacturer's facility for further examination. The airframe was mostly intact. The fuel selector valve was found in the "OFF" position. The fuel selector valve was placed in the "on" position, and compressed air was applied to the right side fuel inlet port while the left fuel inlet port was blocked using a metal cap. Fuel was observed expelling from the engine supply fuel line. The fuel filter drain plug was removed, and a fuel sample was obtained. The fuel was found to be free of debris. Due to impact damage, airframe electrical power could not be obtained. An external battery was attached to the fuel pump positive and negative wires, and the fuel pump actuated normally. The left and right wings were examined, and the fuel vents were free of debris. The PT6A-34AG engine, serial number PCEPH0183, was examined at the facilities of Pratt & Whitney, Bridgeport, West Virginia, on December 3, 2014. The engine was installed on a test stand. All engine accessories remained intact. The chip plug detector was removed and found to be free of debris. The turbine blades and vanes were examined using a borescope, and exhibited normal operational signatures. The engine was installed within the engine run test cell using a slave starter and tach drive assembly. The engine was run for about 40 minutes at various power settings with no anomalies noted.