On July 16, 1998, approximately 2300 mountain daylight time, a Grumman-Schweizer G-164A agricultural airplane, N7951, operated by Carol's Flying Service of Wilder, Idaho, struck power lines while conducting nighttime agricultural aerial application operations approximately 5 nautical miles south of Caldwell, Idaho. The power lines were cut in the strike. The pilot was able to return to his airstrip near Wilder (from which the flight originated) and land without further incident; he was not injured in the occurrence. Following the occurrence, the airplane was found to have sustained substantial damage. No flight plan was filed for the 14 CFR 137 agricultural aerial application flight. The pilot reported that while approaching a field for a spray run, he miscalculated wire height and struck the wire. He stated that no mechanical failure or malfunction was involved in the accident. The pilot's second class FAA medical certificate, dated January 6, 1998, carried a restriction that the pilot must possess glasses that correct for near and intermediate vision. The pilot reported in an August 10, 1998 telephone query that he was wearing his glasses at the time of the accident. The pilot reported that he had 55 hours of night time within the previous 30 days. Astronomical data computation indicated that at Caldwell, evening twilight on July 16 ended at 2245, and that there was no moon at the time of the accident. The pilot reported the weather as clear with unrestricted visibility.