The Learjet 55 and its followon successor, the Learjet 60, are the largest members of the Learjet family, and date back to development work undertaken in the late 1970s.
Development of the Learjet 55 led to a number of sub variants, including the Learjet 55B which introduced a digital flightdeck, modified wings, improved interior, and most importantly, the previous optional higher takeoff weights becoming standard. The Learjet 55C introduced `Delta Fins' which gave a number of performance and handling advantages, the Learjet 55C/ER is an extended range version with additional fuel in the tail cone (the additional tank can be retrofitted to earlier aircraft), while the Learjet 55C/LR introduced more fuel capacity.
The improved Learjet 60 first flew in its basic definitive form in June 1991 (the modified Learjet 55 prototype earlier served as a proof of concept aircraft for the Learjet 60 with Garrett engines). It differs from the Learjet 55 in having a 1.09m (43in) fuselage stretch and new Pratt & Whitney Canada PW305 turbofans. Certification of the Learjet 60 was awarded in January 1993, with first deliveries following shortly afterwards.