ERA17LA286 · Air Tractor Inc AT 402A

The pilot was departing on an agricultural application flight from a 2,300-ft-long runway. When the airplane reached the end of the runway, the pilot could "feel that the airplane did not want to fly." The pilot extended the flaps, then dumped the spray load that was in the airplane’s hopper tank in an attempt to become airborne; however, the airplane continued off the end of the runway, crossed a drainage ditch, and came to rest in a bean field, resulting in substantial damage.

The airplane’s hopper was loaded with about 3,400 lbs of a mixture of herbicide and other chemicals, which exceeded the hopper’s placarded limitation of 3,250 lbs. The airplane’s estimated weight at the time of the accident was 1,864 lbs higher than the manufacturer’s published gross weight and about 264 lbs more than field experience showed could be carried safely with adequate margins of performance and structural strength. Calculations by the airplane manufacturer using takeoff data of a similar airplane from a previous company test program indicated a takeoff ground roll distance of about 2,322 ft. Given the density altitude about the time of the accident, the airplane’s takeoff distance would have been increased by 24%, and there would have been an 18% decrease in its rate of climb. No preimpact failures or malfunctions were discovered that would have precluded normal operation. Despite the numerous indicators that the takeoff conditions were marginal, such as the high air temperature, high gross weight, and a short runway, the pilot failed to evaluate the conditions that existed in relation to the performance capability of the airplane.

Verbatim NTSB analysis and probable cause from the NTSB dataset