On June 5, 2004, approximately 0830 mountain daylight time, a Grumman G-164B agricultural airplane, N8440K, was destroyed after impacting high tension power lines while maneuvering near Midvale, Idaho. The commercial pilot, sole occupant of the airplane, sustained serious injuries. The airplane was registered to Weiser Air Service, Weiser, Idaho, and operated under 14 CFR Part 137. Visual meteorological conditions prevailed for the aerial application flight, and a flight plan was not filed. The flight departed the Lee Williams Memorial Airport, Midvale, Idaho, at approximately 0745. According to the Pilot/Operator Aircraft Accident Report (NTSB form 612.1/2), the pilot reported that he was dispensing his load in an east to west direction while working under high tension power lines which traversed the field diagonally. The pilot stated that he impacted one of the power lines, which was lower than the others while making a spray pass to the west. The aircraft subsequently impacted terrain where it came to rest in an upright position prior to being destroyed as it was consumed by fire. The pilot reported to the NTSB investigator-in-charge that no anomalies existed prior to or during the flight which would have precluded normal operations.