On September 8, 2009, approximately 0830 Mountain Daylight Time, a Grumman G-164A, N6761Q, was substantially damaged during a forced landing near Kimball, Nebraska. The commercial pilot was not injured. Visual meteorological conditions prevailed and no flight plan was filed for the Title 14 Code of Federal Regulations Part 137 aerial application flight. The local flight originated at Western Nebraska Regional Airport/William B. Heilig Field (KBFF), Scottsdale, Nebraska, at 0745. According to a statement provided by the pilot, the airplane was maneuvered for the last pass of aerial application when the turbo-prop engine lost power and "backfired" several times. He added, that engine power surged several times before he pulled the emergency fuel shut-off handle and set up for a forced landing. The airplane overshot the intended landing area and collided with a fence and terrain before coming to rest in the upright position. Substantial damage was sustained to the airplane's fuselage. An inspection of the engine by a Federal Aviation Administration inspector revealed that the engine oil supply line was disconnected. Further examination of the oil line fitting revealed signatures consistent with improper thread engagement during installation. An inspection of the airframe did not reveal any anomalies.