On August 9, 2013, about 1130 central daylight time, an Air Tractor Inc AT-400, N36538, impacted terrain when it veered off the runway during landing rollout at Billy Free Municipal Airport (0M0), near Dumas, Arkansas. The airplane received substantial damage to the fuselage near the tail wheel. The commercial pilot was uninjured. The airplane was registered to and operated by D & M Flying Service Inc under 14 Code of Federal Regulations Part 91 as a maintenance test flight that was not operating on a flight plan. The local flight originated at 1110. The pilot stated that he arrived at OMO at 1040 to pick up and fly the airplane home after it had undergone an annual inspection. The mechanic who performed the inspection requested the pilot perform a maintenance test flight of the airplane. At 1110, the pilot used runway 18 to depart on the flight and flew the airplane for about 5 minutes. The pilot stated that the airplane performed as expected, and the temperature and pressures were normal. The pilot then returned to the departure airport and landed on runway 36. As the tail wheel touched down onto the runway surface, the airplane veered to the left. The pilot attempted, but was unable, to regain control of the airplane. The airplane came to a stop on the west side of the runway, in a southerly direction. Examination of the tail wheel assembly by a Federal Aviation Administration inspector from the Little Rock Flight Standards District Office revealed that the tail wheel had been assembled correctly.