On July 02, 2014, about 1930 mountain standard time, a Rockwell International Aero Commander 500S, veered off the runway and collided with terrain at the Cochise County Airport, Willcox, Arizona. The airplane was being operated as an air-attack coordinator for aerial forest firefighting activity under a "call when needed" contract to the United States Forest Service (USFS) by American East Airways Corp., d.b.a. Houston Air as a public-use flight. The airline transport pilot and crew member were not injured; the airplane sustained substantial damage. The local area flight departed from Willcox about 1745. Visual meteorological conditions prevailed and a company flight plan had been filed.The pilot stated that as the airplane approached the vicinity of the airport, he was not able to see any wind indicators due to the low-light conditions at dusk. He contacted a fixed base operator (FBO) at the airport and was advised that the wind was light and variable. As he continued the approach, he noted that the tetrahedron was indicating a right quartering tailwind of an unknown strength. As the airplane touched down, the pilot immediately experienced a right drift which he attributed to a 15 knot right quartering tailwind and attempted to correct by applying right throttle. The airplane responded by drifting left and he retarded the right throttle and added left throttle in an attempt to regain directional control. The airplane veered off the runway surface at an estimated ground speed of about 120 mph and encountered soft sand in the area adjacent to the runway. The pilot was unable to steer and the left wing collided with terrain and incurred substantial damage. The pilot stated that there were no preimpact mechanical malfunctions or failures with the airplane that would have precluded normal operation.