Originally Posted by
ghilis101
are you sure about that? we used to take a 1% fuel penalty for leaving the autothrottles on in the DC-10 during cruise. The reason for this is the autothrottles "hunt" for airspeed and are constantly moving the throttles back and forth, as opposed to manually setting power you leave the throttles where they are and its more efficient because the engines arent spooling up and down. however the PMS (performance managment system) equipped 747 didnt have this problem because it would actually allow the airplane to climb or descend up to 100 ft before it attempted to change the power setting. this was a huge fuel saver believe it or not.
Well, I will admit that I don't know regarding specific airplanes. But A/T were invented not only as a labor-saving device. They do have a function beyond that and I would say it must be fuel saving. Does the DC-10 have FADEC?
That combined with A/T should equate to significant savings. At least if, as you described, the system allows for most efficient altitude/speed tradeoffs.