One major advantage of the trijet design is that the wings can be located further aft on the fuselage, compared to twinjets and quadjets with all wing-mounted engines, allowing main cabin exit and entry doors to be more centrally located for quicker boarding and deplaning, ensuring shorter turnaround times. The rear-mounted engine and wings shift the aircraft's center of gravity rearwards, improving fuel efficiency, although this will also make the plane slightly less stable and more difficult to handle during takeoff and landing. (The McDonnell Douglas DC-9 twinjet and its derivatives, whose engines are mounted on pylons near the rear empennage, have similar advantages/disadvantages of the trijet design, such as the wings located further aft and a more rearward center of gravity.)