On July 25, 2005, about 1100 mountain daylight time, a Weatherly Aviation 620B, N2021V, sustained substantial damage after colliding with power transmission lines while maneuvering near Teton, Idaho. The airplane is owned by Teton River Flying Service, Inc, Teton, Idaho, and was being operated as an aerial application flight under the provisions of Title 14, CFR Part 137, when the accident occurred. The commercial pilot was not injured. Visual meteorological conditions prevailed for the local agricultural flight. In a telephone conversation with the National Transportation Safety Board (IIC), and subsequent written statement, the pilot reported that he inadvertently "stepped" on a power line just as was completing a low level turn during a spray run. After colliding with the power line, the airplane impacted terrain resulting in substantial damage to the airframe. The pilot reported that there was haze and smoke in the area on the morning of the accident.