The Beech 400/400A evolved from the Mitsubishi Diamond 2 design that was bought by Beech in the mid-1980s. The original Mitsubishi MU300 Diamond 1 flew for the first time in August 1978. Only 11 Diamond 2s were built before Beech purchased the design and production rights. The Diamond 2 was renamed the Beech 400 and equipped with JT15D5 turbofan engines, a new interior and other minor changes.
The new Beech 400A has a higher maximum takeoff weight and greater operating ceiling along with improved performance. Moving the rear fuselage fuel tank increased cabin volume. The flight deck features a Collins Pro Line 4 electronic flight instrument system avionics suite. Raytheon introduced a new luxury standard interior for the Beech 400A in 1996.
