On August 9, 2001, at 0915 central daylight time, a Grumman-Schweizer G-164B agricultural airplane, N542KG, was substantially damaged during a forced landing following a loss of engine power while maneuvering near Bunkie, Louisiana. The commercial pilot, who was the sole occupant of the airplane, received minor injuries. The airplane was registered to and operated by APC, Inc., of Bunkie, Louisiana. Visual meteorological conditions prevailed and a flight plan was not filed for the 14 Code of Federal Regulations Part 137 aerial application flight. The pilot departed his private grass airstrip approximately 0900, and was returning at the time of the accident. The pilot reported that after he finished dispensing a chemical load, he climbed to 200 feet agl and reduced engine power to "slow the airplane [in order] to apply the dispersal pump brake." When he reapplied power, the engine "made popping and sputtering noises." The pilot initiated a forced landing to a clearing in a field; however, the airplane impacted trees approximately 30 feet prior to the clearing. According to the FAA inspector, who responded to the accident site, the wings and fuselage were substantially damaged, approximately half of the engine was found buried in the ground, and the fuel tanks were found compromised with fuel draining from them. On September 20, 2001, the engine was examined by the FAA inspector and the operator. The inspector stated that the propeller rotated, the spark plug leads were found broken, two cylinder heads were found separated, and an exhaust valve was found separated. It was not determined if the separation of the cylinder heads occurred prior to or during the impact sequence.