N90805Air Tractor AT-502B · 2000

The pilot estimated that he had serviced the tailwheel-equipped airplane with about 400 gallons of water and an unknown additional quantity of sulfur in preparation for an aerial application flight. Additionally, the pilot had previously installed rotary atomizer chemical disbursement devices on the airplane and then performed two test flights, noting that with the devices installed the airplane performed "sluggishly." The pilot then taxied the airplane to the end of the 2,600-foot-long runway with the flaps set to three-fourths in preparation for takeoff. As the airplane accelerated down the runway, the tail of the airplane did not rise as the pilot expected, so he extended the flaps fully. As the airplane reached the end of the runway, the pilot felt that the airplane "did not want to fly." He elaborated that while the engine instruments indicated no abnormalities, the engine was not providing the amount of power he expected and that the airplane's performance was sluggish. He attempted to jettison the loaded chemical to reduce the airplane's weight, but when he attempted to actuate the load jettison handle, it would not move. As the airplane approached tall trees beyond the end of the runway, and with the airplane nearing a stalled condition, the pilot attempted to land the airplane in an agricultural field ahead. During the landing, the airplane nosed over resulting in substantial damage to the nose, empennage, and left wing. A Federal Aviation Administration inspector examined the airplane following the accident and found no evidence of any preimpact mechanical malfunctions or failures of the engine and that the load jettison mechanism functioned normally. An accurate account of the airplane's weight at the time of the accident could not be calculated due to variances in the values provided by the pilot and the operator.