Accident Overview
On July 18, 2012, at approximately 1100 central daylight time, an Air Tractor AT-502B (registration N205SK) impacted a bean field after takeoff from a private airstrip near Wisner, Louisiana. The airplane, operated by Delta Dusters LLC under 14 Code of Federal Regulations Part 137 for agricultural application, sustained substantial damage. The pilot reported a serious injury. Visual meteorological conditions prevailed, and no flight plan was filed. The flight was originating at the time of the accident.
Pilot Report and Circumstances
The pilot stated that the airplane lifted off from the 2,500-foot long turf airstrip about 100 feet before the end of the runway. However, it did not climb out of ground effect and settled into a bean field beyond the runway, substantially damaging both wings. The pilot noted that the engine seemed to be "making good power" and no mechanical issues were apparent during the takeoff. The pilot commented that the runway was rough and "needed the grass cut." He had reduced the chemical load to 375 gallons due to the runway length and ambient temperature. The pilot extended the wing flaps to about three-quarters of full deflection for takeoff. Wind was from the south at about 3 knots, and the takeoff was to the east.
Postaccident Examination
A Federal Aviation Administration (FAA) inspector conducted a postaccident examination and did not find any anomalies consistent with a preimpact failure or malfunction. The wing flap actuator extension corresponded to a full down (25 degrees) deflection. The airplane flight manual specified that takeoffs with a full chemical hopper load from a short field should be made with a 10-degree flap deflection. It also noted that grassy or soft runway surfaces adversely affect takeoff roll and acceleration. The flight manual did not authorize takeoffs with flaps extended beyond 10 degrees.
Weight and Performance Considerations
The pilot reported an operating weight of 10,100 lbs.; the maximum gross weight was 10,480 lbs. The manufacturer's maximum certificated takeoff weight was 8,000 lbs. Regulations (Civil Aeronautics Manual 8 and Advisory Circular 20-33B) allow agricultural operators of restricted category airplanes to exceed maximum certificated weights. The manufacturer demonstrated operations at 9,400 lbs., and guidance permitted operations up to 31 percent above the certificated weight (10,480 lbs.) if the operator performed a flight check confirming safe flight characteristics at that weight.
The flight manual indicated a takeoff distance required to clear a 50-foot obstacle of about 2,600 feet for a hard surface runway at 8,000 lbs., with 10 degrees flaps, at sea level and 30°C. No takeoff data were provided for weights or flap settings exceeding 8,000 lbs. and 10 degrees. The manufacturer did not recommend takeoffs with more than 10 degrees of flap.
FAA Guidance on Weight and Surface Effects
According to the Pilot's Handbook of Aeronautical Knowledge (FAA-H-8083-25A), a 10-percent increase in gross weight results in at least a 21-percent increase in takeoff distance. Operations on surfaces that are not hard and smooth increase ground roll during takeoff. The handbook further explains that ground effect allows flight at a slightly slower airspeed just clear of the ground; leaving ground effect increases drag and thrust required to maintain flight.