On July 1, 2002, approximately 0750 central daylight time, a Grumman-Schweizer G-164A agricultural airplane, N8917H, sustained substantial damage during a forced landing following a partial loss of engine power while maneuvering near Basile, Louisiana. The commercial pilot, sole occupant of the airplane, was not injured. The airplane was registered to B & S Flyers Inc. of Gueydan, Louisiana, and operated by Kib Aviation of Basile, Louisiana, under 14 Code of Federal Regulations Part 137. Visual meteorological conditions prevailed for the aerial application flight, and a flight plan was not filed. The airplane departed from a private airstrip near Basile, at 0730. In a telephone interview with the NTSB investigator-in-charge, the pilot reported that he had just completed his fourth spray load of the morning and was returning for the next load when the engine began running rough and started to backfire. The pilot stated "I checked the mags, propeller, and throttle lever, and found everything to be normal, but the engine continued to backfire." Not being able to maintain altitude, the pilot elected to make a forced landing in a rice field. After touchdown, the airplane nosed over and came to rest inverted. The pilot reported damage to the airplane included the vertical stabilizer, horizontal stabilizer, and rudder were destroyed, both propeller blades were bent, and the empennage was twisted and bent. During an engine examination by a certified mechanic, no mechanical failures or malfunctions were noted that would have prevented normal engine operation. The reason for the partial loss of engine power was undetermined.