The Learjet 40 is derived from the Learjet 45, but with a shorter fuselage (by 24.5 inches/60 cm), and is powered by two Honeywell TFE731-20AR engines. These are known as the "AR" engines.

The Learjet 55 "Longhorn" is a business jet manufactured by Gates Learjet. The introduction of the Learjet 50 series occurred at the 1977 Paris air show. The winglets on the Learjet 55 were developed by NASA. The winglets gave the 55 the nickname "longhorn." Construction of the Learjet 55 began in April 1978 after extensive testing and work on the wing design which came, initially, from the Learjet 25. The Learjet 55 first flew on 19 April 1979. The first production aircraft were produced starting 18 March 1981. 147 Learjet 55 aircraft were delivered.

The modifications that converted the Learjet Model 55 into a Model 60 resulted from an aerodynamics improvement program and a need to increase the capacity of the Learjet product line. Several of these modifications were a first for Learjet. They include an all new inboard wing cuff added to the inboard sections of the “Longhorn” wing and an all new wing-to-body fairing. By increasing the wing chord and the leading edge droop, the wing cuff improved handling during approach and landing while the wing-to-body fairing reduced the interference drag between the wing and the fuselage. Since the engines were new for this aircraft, a new engine pylon had to be designed.