At approximately 1210 Central time, the airplane was destroyed after impacting terrain while maneuvering. The airplane was registered to the United States Border Patrol Air Operations Unit and was engaged in a routine air patrol mission. The Airline Transport pilot, the sole occupant, sustained fatal injuries. Visual conditions prevailed. A border patrol agent who witnessed the accident reported that the airplane was circling left. The agent stated that while turning downwind from a heading of south to a heading of east the airplanes angle of bank steepened. Subsequently, the airplane banked to the right, nosed over and assumed a steep nose-down attitude before impacting terrain. The agent further reported the wind was out of the north and gusting.