DC-9 / US AirDC 9 airplane model US Air. No other airliner in history has undergone more development than the prolific DC 9 MD 80 MD 90 717 series, which started life with the 70 seat DC 9 10 of the early sixties. The DC 9 was developed as a short range airliner complementing the much larger DC 8. Development was launched on April 8, 1963, with a launch order from Delta following soon after. The DC 9 was an all new design, featuring rear fuselage mounted engines,