On September 27, 2019, about 1045 eastern daylight time, an Air Tractor AT802 airplane, N801BF, sustained substantial damage during an impact with terrain following a partial loss of engine power near Columbus, Mississippi. The airplane was registered to and operated by Brignac Flying Service as a Title 14 Code of Federal Regulations Part 137 aerial application flight. The commercial pilot sustained serious injuries. Visual meteorological conditions prevailed and no flight plan had been filed. According to the pilot, during a chemical application pass over a field from north to south, he noticed the engine torque "had crept up." As he departed the field to the south, he attempted to reduce engine torque, but noticed the power lever "felt stuck." Since there was more room on the north end of the field to maneuver, he left the power lever where it was and re-entered the field. Following the subsequent pass from south to north, he pulled up and again tried to move the power lever. When it would not move, he increased pressure and it "broke free." The engine then went uncommanded to idle power. He attempted to increase the power but moving the power lever had no effect on the engine. During the forced landing, the left wing impacted a tree and the airplane cartwheeled prior to coming to rest on its landing gear, upright. The airplane sustained substantial damage to both wings, the fuselage, and tail section. A post-accident examination of the airframe and engine found no mechanical malfunctions or anomalies that would have precluded normal operation. The engine was disassembled and contained signatures consistent with a low power setting. Engine control continuity was established from the cockpit to the engine with no binding. During the examination of the fuel control unit, the power lever and condition lever shaft could not be easily moved by hand as a result of damage sustained during the impact. The fuel control unit was disassembled; however, the cause of the binding was not found. No anomalies were observed.