The Learjet 60 is a Learjet 55, with a 3½-foot longer fuselage, Pratt & Whitney Canada PW305 engines, Collins Pro Line 4 avionics, and numerous other improvements. The Learjet 55 was Lear’s entry into the medium-sized business jet field. In designing the 55, Learjet utilizes the earlier Longhorn 28/29 wing with winglets and married it to a larger fuselage. The step-down aisle in the cabin has 5 ft 9 inches of headroom The Learjet 55B introduced a digital flight deck, modified wings, and an improved interior. The 55C comes equipped with Delta Fins that improve performance and handling. The improved Learjet 60 first flew in June 1991 and deliveries started after certification in 1993.