On May 19, 2005, at 1800 central daylight time, N8505F, a Bell 47G-3B-1, collided with power lines during an aerial application flight in Twin Brooks, South Dakota. The commercial pilot received minor injures. The helicopter was substantially damaged. The 14 Code of Federal Regulations Part 137 flight was operating in visual meteorological conditions without a flight plan. The local flight originated at Summit, South Dakota, at 1630. The pilot reported that he saw the power lines just prior to contacting them. He stated the lines hit the bubble then they traveled over the top of the helicopter contacting the main rotor shaft. He stated the helicopter then settled in a level attitude onto the tracks. The pilot stated he was spraying for the purpose of weed control along the Burlington Northern Santa Fe railroad when the accident occurred. The pilot stated he was about 2.75 miles into the 3 mile run when the helicopter contacted the lines. The pilot reported that he saw a pole to his left, but it was off in the distance. The pole on his right, which he did not see, was nestled in a group of trees. The pilot reported he was flying at an altitude of 15 to 20 feet above the tracks at an airspeed of 43 to 45 miles per hour. He stated the bubble was clean and the sun was to his back as he flew to the east.