A development of the Swearingen Excalibur, the the SA-26 Merlin first flew with a new pressurized fuselage and vertical fin powered by Lycoming turbo charged engines. To increase engine reliability and power, the Lycomings were replaced with Pratt & Whitney Canada PT-6 turboprops. Re-designated the Merlin IIA, 36 were built before the engines were changed again to Garrett AiResearch TPE-331 resulting in the Merlin IIB (87 built). Delivered in 1967, this Merlin was later registered N55JM and N55ZN. The last registration was cancelled in 1989.