Background
On July 21, 2011, at approximately 1926 central daylight time, an Air Tractor Inc AT-502, registration N1516G, experienced a total loss of engine power following the completion of an aerial application of a field near Fergus Falls, Minnesota. The airplane was registered to and operated by Farmers Union Oil Co. (DBA Cenex Airspray) under 14 Code of Federal Regulations Part 137 as an aerial application flight. Visual meteorological conditions prevailed at the time. The flight originated from Fergus Falls Municipal Airport-Einar Mickelson Field (FFM) about 1810.
Accident Details
According to the pilot, the airplane was fueled from a 300-gallon tank used to shuttle fuel. At takeoff, there were 120 gallons of fuel aboard, and the fuel gauges indicated the tanks were one-third full. The pilot reported a fuel consumption rate of approximately 50 gallons per hour.
After departing FFM, the pilot performed two aerial applications on two different fields before returning to FFM. He noted that his cruise altitude was 600 feet above ground level during the return. About 4 to 5 miles south of FFM, the airplane began losing engine power. The pilot activated the fuel boost pump and igniters to continuous operation. Approximately 1 mile south of FFM, the engine power was lost entirely.
The pilot attempted a forced landing on a highway but aborted due to a vehicle turning onto the road. He then landed in an area of 2-foot-deep water east of the highway, as a powerline prevented landing on the west side. During the landing, the airplane nosed over and remained inverted until it was examined at FFM.
The pilot, a certificated commercial pilot, was uninjured. The airplane sustained substantial damage to the fuselage and wings.
Examination
On August 2, 2011, a Federal Aviation Administration airworthiness inspector from the Minneapolis Flight Standards District Office examined the airplane at FFM. Before the airplane was placed upright, the inspector removed the drain plugs from the firewall fuel filter. The main fuel supply line to the engine produced no fuel. Removal of the fuel line through the fuel/oil heat exchanger yielded less than half an ounce of fuel. When the engine was removed from the firewall, a mixture of water with some oil drained from the hot section, but no fuel was present. After the airplane was uprighted, water drained from the fuselage section.
The operator arranged for a repair station to examine the fuel control unit (FCU) and the fuel pump. The FCU exhibited corrosion damage on the drive section and main housing, and water beads were observed in the bellows (air) chamber. The fuel pump showed water contamination in the fuel bowl and drive spline.