True, and the Jetstar also had two rear mounted engines per side. In pretty much all these cases I would have to stick with the engines available at that time being of limited power for the size of the aircraft. The only alternative was four engines.<br /><br />Douglas built a prototype, that sta in ABQ for years, with four wing mounted engines to compete with the Jetstar for the initial government contract. The one advantage to rear mounting four engines rather then hanging them on the wings was the structural strengthening in the rear was not that much more then that in the center section and outer wing for four engines.<br /><br />If you look at the 737 wing, landing gear and engine loads are taken in one structure, in the DC-9 you have two separate load bearing structures which adds weight to the design. Advantages of rear mounted engines is a smaller and more efficient wing and better center of gravity control. <div class="Discussion_UserSignature"> </div>