On June 29, 2000, at 1300 central daylight time, an Air Tractor AT-502, N91891, operated by a commercial pilot collided with the terrain following a loss of control during takeoff from a road in Portland, North Dakota. The pilot was not injured. The airplane was substantially damaged. The 14 CFR Part 137 flight was being operated in visual meteorological conditions prevailed and no flight plan was filed. The flight was originating at the time of the accident. The pilot reported that he made an emergency landing on the road following a loss of engine power. He stated that during the forced landing, the left wing of the airplane contacted a road sign. This resulted in damage to the leading edge of the wing and left aileron. The pilot reported that he had mechanics look at the airplane and it was determined that the loss of power was due to an "air lock." He stated they bled the fuel line and started the engine. The pilot reported that he determined that he could fly the airplane off the road and back to his private airstrip. The pilot stated that once airborne the airplane rolled to the left. He stated that he added right aileron control, however the airplane continued to roll until it struck the ground.