On August 17, 1999, at 0845 central daylight time, an Air Tractor AT-402 agricultural airplane, N4523L, was substantially damaged during a forced landing following a loss of engine power while maneuvering near Snyder, Texas. The non-instrument rated commercial pilot, sole occupant of the airplane, was not injured. The airplane was owned and operated by J.R. Davis Flying Service, of Seminole, Texas. Visual meteorological conditions prevailed for the Title 14 CFR Part 137 aerial application flight for which a flight plan was not filed. The local flight departed from the Winston Field Airport, near Snyder, Texas, approximately 2 hours prior to the accident. According to the operator, the aerial application flight was scheduled to spray cotton fields to the east and southeast of Snyder, as part of the federally sponsored boll weevil eradication program. In the narrative portion of the enclosed NTSB Form 6120.1/2, the pilot reported that the airplane was in a turn at approximately 500 feet agl when the engine lost power. The pilot added that he turned the airplane into the wind and lowered the flaps for a forced landing on a hay field. During the landing roll, the airplane impacted the top of a terrace on a heading of 241 degrees and then slid to a stop within 70 feet. Examination of the turbine powered airplane by the FAA inspector, who traveled to the accident site, revealed that the lower forward portion of the airframe, forward of the engine firewall, sustained structural damage. Both main landing gear assemblies "were knocked out." Approximately 25 gallons of Malathion pesticide remained in the hopper. A detailed examination of the aircraft fuel system revealed that fuel was present in both tanks, as well as in the fuel lines. The FAA inspector stated that the top right bolt securing the fuel control housing/assembly to the engine case was missing, and the remaining three bolts securing the fuel control were found loose. The missing bolt, with a piece of safety wire still attached to it, was found laying at the bottom of the engine cowling. The fuel control assembly was not mated to the gasket and evidence of a "severe fuel leak" was found at the base of the fuel control. According to the maintenance records, the Bendix fuel control, part number 2524439-4, serial number 194160, was last overhauled/installed on June 16, 1995. The last annual inspection was performed on April 1, 1999, at 12,493.9 hours, approximately 200 flight hours prior to the accident. No recent engine maintenance was reported by the operator.