747 Can not maintain speed at cruise altitude

[Guest D17S]

It would be really interesting to hear about how the model is setup (I'm coming to trust this darn thing). So, hey Vanglis, Is the Vnav calculated MAX altitude supposed to be maintainable with CRZ power. It seems that it won't . . . but should it?If not, what variables can we look for to help us determine what should be happening? It can be like fuel quantity. If "start" - "fuel used" does not = "remaining," it's time to start looking at something. Similarly, if the airplane will not maintain airspeed at MAX (and it should), it's time for someone to go back, look out the window and check to see if a spoiler (or two) isn't floppin' around out there or a canoe (Flap track faring) didn't depart the premises or a sailboat (pylon access panel) . . . . or something else isn't hanging off the airplane (Yes, it certainly happens IRL! I'm afraid to tell you how many times I've walked around an arrival to find some really big pieces missing.)A thrust v altitude number could be a very important piece of information for a pilot to be aware of.There's no thrust/speed disagree light. We just have to know how the airplane should perform.

[Guest diskus]

IM new here but I have had similar experiences. basically I find to stay near the optimum crz and stay away from the max. also the calculated step climbs are not always maintainable . IM not sure why but weather is a guess. Thanks for the wealth of infoMike