NTSB Factual Report

On July 20, 2008, approximately 0830 central daylight time, an Air Tractor AT-402B, N61318, registered to and operated by Tri-Rotor Spray & Chemical and piloted by a commercial pilot, was destroyed when it struck a pivotal sprinkler and impacted terrain while maneuvering near Deerfield, Kansas. Visual meteorological conditions prevailed at the time of the accident. The local aerial application flight was being conducted under the provisions of Title 14 Code of Federal Regulations (CFR) Part 137 without a flight plan. The pilot, the sole occupant aboard, sustained minor injuries. The flight originated approximately 0800 from Lakin Municipal Airport (36K), Lakin, Kansas.

According to the pilot's accident report, he had noticed a fuel imbalance of almost a quarter of a tank after the previous spray flight. The airplane was then serviced with 40 gallons of Jet A fuel through a single point refueling port. The pilot checked the fuel level again and noted the right tank had approximately 1-1/2 inch more fuel than the left tank, or roughly 1/2 capacity in the left tank and between 1/2 and 2/3 capacity in the right tank.

The pilot took off with 375 gallons of chemical mix to spray two corn circular fields. He used a left hand reverse racetrack pattern to spray the two circles. Halfway through the application he checked the fuel gauges and noted both were reading between 1/4 and 1/2 tank. On his final swath of the field, the pilot climbed over a set of power lines. It was his intention to utilize the southerly wind to drift the spray under the power lines to the edge of the field. He performed a right side slip maneuver (right wing down, left rudder) to spray the west circle, leveled his wings, and repeated the maneuver to spray the east circle. He then initiated a 60-degree bank right climbing turn from a height of about 30 feet. The pilot said that during the climbing turn, "altitude and decrease in airspeed felt normal." He looked out the right side of the airplane to check the spray pattern. When he attempted to level the wings at an altitude between 100 and 150 feet, the right wing "continued to drop followed by the nose." He said the stall warning horn never sounded, and there was no aerodynamic buffet. He opened the throttle completely, but the engine did not respond. The airplane struck a pivotal sprinkler and impacted terrain.

The pilot said the airplane was destroyed "from the nose to the front of the cockpit, including the prop[eller], engine, hopper, wings, main landing gear, windshield, and spray gear. The right wing impacted a center pivot sprinkler, damaging the end three sections. The crash area damaged approximately 5 acres of alfalfa."

Asked how the accident could have been prevented, the pilot answered that he should have realized the engine had lost power "when I still had enough airspeed. Everything in the right hand turn felt normal with aircraft altitude and decreasing airspeed." The pilot also said it was his opinion that the engine lost power "due to unporting of fuel from the tank to the engine [induced] by the slip maneuver." The pilot said that although there are no placards in the airplane prohibiting slips, there is a placard that warns a pilot of skidding turns which may cause fuel migration between tanks."

NTSB Probable Cause

The pilot inadvertently stalling the airplane. Contributing factors in this accident were the pilot intentionally performing low altitude maneuvers (side slips), unporting and starving the engine of fuel, and his initiating a climb at low airspeed.