CEN12LA459 · Air Tractor Inc AT-502B

The pilot reported that the airplane lifted off of the 2,500-foot long, rough, turf airstrip about 100 feet before the end of the runway. However, the airplane did not climb out of ground effect, and it settled into a bean field. He stated that there were no mechanical issues with the airplane during the accident takeoff. The pilot had reduced the chemical load for the agricultural application flight due to the runway length and ambient temperature, and he had elected to conduct the accident takeoff with the wing flaps extended to about 25 degrees. He reported a gross weight for the accident takeoff of 10,100 lbs. Performance data indicated that a takeoff distance of about 2,600 feet was required to clear a 50-foot obstacle. However, that data was applicable to a hard surface runway at a maximum certificated gross takeoff weight of 8,000 lbs with 10 degrees of flaps. The airplane flight manual did not contain takeoff data for weights or flap settings in excess of 8,000 lbs and 10 degrees, respectively. The airplane manufacturer recommended that takeoffs not be attempted with more than 10 degrees of flap. Regulations and guidance related to agricultural application flights in restricted category airplanes allowed for operations up to 31 percent above the certificated gross takeoff weight. The pilot reported that the maximum gross weight for the airplane was 10,480 lbs, which corresponded to the 31 percent limit. FAA guidance suggested that an increase in takeoff gross weight of 31 percent will increase the required takeoff distance by about 90 percent. The reduced acceleration due to the rough, turf runway and the excess flap deflection selected by the pilot, combined with operating near the maximum permitted takeoff gross weight, resulted in the airplane's inability to attain a positive rate of climb after liftoff.

Verbatim NTSB analysis and probable cause from the NTSB dataset