Further refinement of the 90 series resulted in the Model F90 and follow-on Model F90-1. The F-models featured the T-tail of the Super King Air mated to the fuselage and wings of the E90, with PT6A-135 engines of 560 kW driving four-bladed propellers. The F90 prototype flew on 16 January 1978 and 203 production versions followed between 1979 and 1983, when the F90 was superseded by the F90-1. The F90-1 was put into production with redesigned engine cowlings, upgraded PT6A-135A engines, hydraulic landing gear, and triple-fed electrical bus.