Why Can't I Follow The Altitude Profile?

[Guest cliffie1931]

Before take off from Alicante bound for Heathrow I set the cruise altitude to 30,000 ft assuming that the altitude profile will be followed by the FMC.However in the attachment you'll see that we're approaching the waypoint of ALT/10A which, according to the Flight Plan, should be crossed at 8,282 ft. In fact we have been climbing ever since leaving the airport and are now at 18,800 ft.As this happens only occasionally I'm not sure of the cause of the problem.Any suggestions please?Cliff

[mburkhard 23]

Cliff,in the screenshot you show the ALT/10 is your FROM waypoint and the F-PLN page just tells you at what altitude you crossed that one. Prof seems to get followed just fine on this shot.Markus

[Guest]

From what I know (I've only done the tutorial twice... ;) ) you have to enter the altitude of the first constraint there is in (for instance) a SID. If your final cruise alt is 30.000 but you have a constraint of 7000 in your flightplan (if I am not mistaken your waypoint ALT should be taken at 7000), you have to set that altitude 7000 first. This altitude will be magenta on the PFD until you passed the restricted point: then it will turn white and you will be able to enter the next constraint or the final cruise altitude. All this time you will have PROF activated, but it will be constraint by your manual settings in the alt window.So, in this case (afaik) you should have entered 7000 before departure, because you have to pass ALT (the waypoint) at that height. Right now you are already way too high. After passing ALT you can enter 30000 into the altitude window and the computer will follow that (you will see that in magenta on the PFD).Things are different when you descent: in that case you can set the altitude you wish to intercept the LOC at immediately when you start the descent, but the FMC will automatically keep certain constraint it gets to. You would think this would be the same at the start of the flight but I am sure they had a good reason to do this. ;)Again, I've only done the tutorial twice so I'm no expert but the info is still quite fresh, so...BTW I suppose there could be two different constraints in a SID: one that wants you to pass a certain point not higher than, for instance, 7000 and another that wants you to pass a point at no lower than 7000. But I don't know how you can tell that...

[mburkhard 23]

Again, I've only done the tutorial twice so I'm no expert but the info is still quite fresh, so...BTW I suppose there could be two different constraints in a SID: one that wants you to pass a certain point not higher than, for instance, 7000 and another that wants you to pass a point at no lower than 7000. But I don't know how you can tell that...

I suggest you study the FMS manual section too where profile is explained in great detail. You CAN enter all constraints before departure, no problem at all.When you go to the VERT REV page of a fix you may also enter 'at or above' and 'at or below' constraints, you'll see the corresponding entry fields there.Regards,Markus

[Guest]

I suggest you study the FMS manual section too where profile is explained in great detail. You CAN enter all constraints before departure, no problem at all.When you go to the VERT REV page of a fix you may also enter 'at or above' and 'at or below' constraints, you'll see the corresponding entry fields there.Regards,Markus

I most certainly will study everything: I just bought the MD-11 yesterday, so... gimme some time. ;) But as far as the OP is concerned: the tutorial gives me the impression that you can indeed enter constraints before departure, but you need to dial in the constraint altitude yourself, otherwise the plane will fly directly to the cruise alt. Why else do I have to enter an alt of 6000 at first during the tutorial flight? And this also seems the reason why TS is having problems with going to high directly.

[Guest cliffie1931]

I suggest you study the FMS manual section too where profile is explained in great detail. You CAN enter all constraints before departure, no problem at all.When you go to the VERT REV page of a fix you may also enter 'at or above' and 'at or below' constraints, you'll see the corresponding entry fields there.Regards,Markus

Thanks fellers...your info makes sense.Regards................Cliff

[mburkhard 23]

I most certainly will study everything: I just bought the MD-11 yesterday, so... gimme some time. ;) But as far as the OP is concerned: the tutorial gives me the impression that you can indeed enter constraints before departure, but you need to dial in the constraint altitude yourself, otherwise the plane will fly directly to the cruise alt. Why else do I have to enter an alt of 6000 at first during the tutorial flight? And this also seems the reason why TS is having problems with going to high directly.

Sir, Madame, You don't need to adjust the FCP altitude to a constraint to maintain it. I did this in the tutorial since 6000ft is also the initial climb clearance given by ATC as standard. When under ATC control you would not fly along an SID constraint at 6000ft while having the FCP altitude set to 37'000ft, but the FCP would be set to 6000ft according the ATC assigned altitude.Descent works the same way. I chose to set 4000ft from the beginning because I wanted to demonstrate that the profile mode would maintain a constraint altitude if reaching it.Cliff's issue was something else, he just misinterpreted a FROM waypoint as the TO waypoint and did not realise that he'd already passed it. The profile in his example is being flown as put in on the F-PLN page, so everything is as it should be, assuming that the constraints are the correct ones.Regards,Markus

[Guest]

Okay, clear, thanks for the explanation, Markus. It must be very hard to write a tutorial while knowing a lot of what you say can be interpreted in various (and often wrong) ways. :( Sorry for making this all more confusing than is should have been...! (BTW I've flown the tutorial again today: didn't have much time (christmas...!), so I did it only once. I really like it, I have to say! It's the perfect length for me. B) All went well although I always have to press some unexpected buttons... Like when I press the Autoflight button when the tutorial says so, I turn it OFF...? Probably because NAV was armed and when it became active the autoflight becomes active too...? Well, never mind, I'll do the tutorial a dozen times or more until I get it right :( : the more you do it, the more you see and notice (things that happen when you press buttons). Luckily the basics of the plane are quite easy to understand so I never have a problem 'repairing the mistakes' anyway B) . I am having a great christmas thanks to the MD-11!!!).Edit:Made a sig because I always forget my name... :(

[mburkhard 23]

Jeroen,I'm glad you like the plane and the tutorial flight! Regarding the autopilot, you can't turn it off with the AUTO FLIGHT button. So if you hear an alert when pressing the button this would mean that the AP did not engage at that moment. Make sure that you have your FD centered when doing so and don't try to engage the AP below 400ft AGL.Regards,Markus

[Guest]

Ha, funny, I just read that in the systems manual, page 120 (AUTO.10.24). :( It just happened again and indeed I must have pressed the Autoflight button too soon: NAV was still armed! NAV is activated at 400 ft and I suppose I pressed Autoflight too soon. This also may be due to the fact that I just discovered I have to press B (or D, I always mix those two up) when I load a flight because the altitude on the ground wasn't right. So while I thought I was already at 400 ft, I simply wasn't. So the next time I will simply wait until NAV is activated and then I'll turn on Autoflight: I don't even have to watch the altitude in that case.Learning to fly the plane this way is great: everytime I find an explanation for something I didn't understand before I get such a nice YESSSSS feeling! :( P.S. Before taking off this flight (right now I am reading the Systems pdf during cruise) I set the alt to 37000 and indeed all constraints are kept. Just wanted to give it a try and it works like a charm. Of course. :(