On July 18, 2012, about 1100 central daylight time, an Air Tractor AT-502B, N205SK, impacted a bean field after takeoff from a private airstrip near Wisner, Louisiana. The pilot sustained a serious injury. The airplane was substantially damaged. The airplane was registered to and operated by Delta Dusters LLC under the provisions of 14 Code of Federal Regulations Part 137 as an agricultural application flight. Visual meteorological conditions prevailed for the flight, which was not operated on a flight plan. The flight was originating at the time of the accident.
The pilot reported that the airplane lifted off of the 2,500-foot long 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 located off the end of the runway, substantially damaging both wings. He noted that the engine seemed to be "making good power" and there did not seem to be any mechanical issues during the accident takeoff. The pilot commented that the runway was rough and "needed the grass cut." He reduced the chemical load to 375 gallons due to the runway length and ambient temperature. In addition, the pilot stated that he extended the wing flaps to about three-quarters of full deflection for takeoff. The wind was from the south at about 3 knots. The accident takeoff was to the east.
A postaccident examination conducted by a Federal Aviation Administration (FAA) inspector did not reveal any anomalies consistent with a preimpact failure or malfunction. At the time of the examination, the wing flap actuator extension corresponded to a full down (25 degrees) deflection. The airplane flight manual stated that takeoffs with a full chemical hopper load from a short field should be made with a 10-degree flap deflection. The manual also noted that the takeoff roll and acceleration will be adversely affected by grassy or soft runway surfaces. The flight manual did not authorize takeoffs with flaps extended in excess of 10 degrees.
The pilot reported an operating weight at the time of the accident of 10,100 lbs., with a maximum gross weight of 10,480 lbs. The airplane manufacturer's documentation specified a maximum certificated takeoff weight of 8,000 lbs. Regulations and FAA guidance allow agricultural operators of restricted category airplanes to operate at weights in excess of the maximum certificated weights. In accordance with Civil Aeronautics Manual (CAM) 8 and Advisory Circular 20-33B, the airplane manufacturer demonstrated operations at 9,400 lbs. However, the guidance allowed operations of the AT-502B at weights up to 31-percent above the certificated takeoff weight (10,480 lbs.) provided that the operator performed a flight check confirming safe flight characteristics at that weight.
The airplane flight manual noted a takeoff distance required to clear a 50-foot obstacle of about 2,600 feet. This distance was applicable to departure from a hard surface runway, at a gross weight of 8,000 lbs. with 10 degrees flaps, at a pressure altitude of 0 feet (sea level), and an ambient temperature of 30 degrees Celsius. The 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 did not recommend that takeoffs be attempted with more than 10 degrees of flap.
Federal Aviation Administration guidance contained in the Pilot's Handbook of Aeronautical Knowledge (FAA-H-8083-25A) stated that a 10-percent increase in gross weight will result in at least a 21-percent increase in the takeoff distance required. In addition, the handbook noted that operations on any surface that is not hard and smooth will increase the ground roll during takeoff. The handbook also noted that it is possible to fly an airplane just clear of the ground at a slightly slower airspeed than that required to sustain level flight at higher altitudes due to a phenomenon known as ground effect. An airplane leaving ground effect after takeoff will experience an increase in drag and thrust required to maintain flight.