nhraracer90 wrote on Jul 21^st, 2009 at 2:30am:

anything? I do not mess with the FMC, only thing I do is put in the IRS position. Today i had it set at 235 and it went right past that to 248-250 before it pulled back the throttle.

Not "messing with the FMC" is probably the source of your problem. Entering just your initial IRS position is not enough - you must enter additional information during your pre-flight setup, or the engine performance management system and autothrottle will not work properly.

At a minimum, you need to enter your departure and destination airports, and probably at least one waypoint linking them together - your departure airport takeoff runway, takeoff flap setting, your zero fuel weight, intended cruise altitude and (possibly) cost factor. Without that preliminary information the FMS cannot calculate engine EPR settings for takeoff, climb and cruise, which would most likely render your autothrottle inoperative - even if the A/T switch is "on".

This aircraft isn't bug-free, but I can tell you from personal experience that the speed management functions DO work very well... IF the preliminary FMS programming is done before takeoff. You really do need to read and follow the procedures in the manual if you want the 757 to work properly, which is why CS keeps telling you do so when you submit trouble tickets.

In a real 757, the autopilot's basic heading and altitude hold functions will still work if the FMS fails - but the autothrottle definitely will NOT.

Another user here as produced some very good video tutorials for setting up the aircraft and programming the FMS before flight. The links are posted elsewhere in the forum.

Another thing to check: go to the FSX "aircraft" menu, then select the "realism" sub-menu. be sure that FSX is set up to display "indicated airspeed" and NOT "true airspeed" - otherwise you would definitely see overspeed problems, which will get more and more serious as your altitude increases.