The Air Tractor series of agricultural aircraft was designed in the USA by Mr. Leland Snow. well-known designer of agricultural aircraft, with more than 20 years experience in the field.

By 1981 the advantages of turbine-powered aircraft in the agricultural field were being realised throughout the world. Companies producing large agricultural aircraft considered ways of fitting their designs with turbine power plants to take advantage of more economical operation.

The AT-401 series was a development of the piston-engined AT-301 series and was the smallest of the series.

On the drawing-board at Air Tractor at the same time as the 400 series was a new aircraft, which became known as the AT-503. The prototype (N7309X) first flew in April 1986 and had a wingspan of 14.6 m (48 ft), a 821-kw (1,100-shp) Pratt & Whitney PT6A-45R turboprop and

Another variation on the Air Tractor theme, the AT-602 was a single-seat low-wing agricultural aircraft, basically described as a 502A with a larger hopper, the prototype (N6084K – c/n 602-0337) flying for the first time on 1 December 1995, certification being completed in June the following year.

The AT-802 series was an enlarged AT-503, having a length of 11.27 m (37 ft) and a wingspan of 17.68 m (58 ft), a hopper of 3,028 litres (666 Imp gals), and computer controlled hopper doors to drop the load of fire retardant as required when used in that role.