The Beechcraft King Air series has its roots in the Twin Bonanza of 1951. That aircraft model was enlarged and re-engined to become the Model 65 Queen Air. The Queen Air design changed to incorporate a swept tail and pressurization. With the addition of Pratt & Whitney turboprop engines, the Queen Air became the Model 90 King Air. The King Air 90 led to the stretched King Air 100, which in turn had a T-Tail added to become the King Air 200. Beech took the Model 200, stretched the fuselage and added two Pratt & Whitney PT6A-65B engines to create a 19-passenger commuter airliner, the 1900.
While profitable as an airliner, the 1900and 1900C suffered from its low cabin ceiling of less than 5 feet. This made embarking and disembarking very unpleasant for the passengers. With the 1900D, the fuselage was extended 14 inches, and over a foot was added to the cabin height, giving nearly 6 feet of stand-up room.
The added cabin room resulted in a number of aerodynamic protrusions making the 1900D the easiest King Air to identify. The 1900D was very successful with commuter airlines in the 1990s but its production was eventually ended due to changes in passenger attitude and regulatory environments. An executive version of the 1900D is also available.