Invalid entry (legs - altitude/FL)

[Squishy 0]

Hi,I'm flying from LPPT Lisboa to LPPT Madeira (portugal). Yes I know not a 747 flight but w/e.I've set CRZ alt to 36000 according to my FP. However my 747 decides all my legs should be 43000. When I try to change it, it says invalid entry. Same goes for FL370-FL400. I can however enter FL350.Can anyone explain this to me? Is it because of AIRAC max FL or FL rules? Or because of payload?Thanks

[scandinavian13 5,192]

Set your STEP to 0 instead of ICAO.

[Squishy 0]

Set your STEP to 0 instead of ICAO.

Please eleborate?

[scandinavian13 5,192]

Chapter 12 - FMC User GuidePages 20 and 21, referring to the PERF INIT page.

[Squishy 0]

Chapter 12 - FMC User GuidePages 20 and 21, referring to the PERF INIT page.

I see.However the manual says ICAO means step size = 2000, but i couldn't enter FL360, FL370, FL380, FL390 and FL400.. So that can't be it?Also I was flying westbound so FL360 should be correct?

[scandinavian13 5,192]

Right, and I said set your STEP to 0. Based on your weight, I believe the 744 is calculating the altitude it should be at for the weight, based off of your initially set altitude, plus the ICAO steps.

[yos233 1]

Right, and I said set your STEP to 0. Based on your weight, I believe the 744 is calculating the altitude it should be at for the weight, based off of your initially set altitude, plus the ICAO steps.

No, he would have been told MAX ALT. The FMC isn't supposed to stop you from choosing any altitude unless you literally cannot reach it.

[scandinavian13 5,192]

However my 747 decides all my legs should be 43000.

No, he would have been told MAX ALT. The FMC isn't supposed to stop you from choosing any altitude unless you literally cannot reach it.

Explain the quote from the initial post, then.

[yos233 1]

Explain the quote from the initial post, then.

If I could've I would've, but I can't. Just narrowing stuff down. If it were weight, the FMC would have behaved normally, giving a MAX ALT warning. If it were step climbs, choosing a new altitude should alter the altitude markings for all the waypoints automatically, and certainly not prevented him from typing in a new altitude on the waypoints.

[El padrino 2]

Hi,I'm flying from LPPT Lisboa to LPPT Madeira (portugal). Yes I know not a 747 flight but w/e.I've set CRZ alt to 36000 according to my FP. However my 747 decides all my legs should be 43000. When I try to change it, it says invalid entry. Same goes for FL370-FL400. I can however enter FL350.Can anyone explain this to me? Is it because of AIRAC max FL or FL rules? Or because of payload?Thanks

It cannot be the payload as this would restrict you from going higher rather than lower.AIRAC I don't think neither, unless you plan to fly through airways that are higher than your Cruise Level and this somehow poses a restriction in the FMC. Don't know if that's true but I find it a bit unlikely.It is however very strange that it won't let you choose any FL you want as CRZ... Especially considering that it automatically aims for a higher FL! Very confusing indeed!!!Is it possible to post some screeenshots for us to have a look?

[Squishy 0]

I was just taking screenshots when I entered 0 into stepsize. The legs immediately changed from 430 to 360.So maybe there's some ICAO rule that prevents me from using FL360? I still cant enter above e.g. FL380. I can only get it changed by changing CRZ alt.

[scandinavian13 5,192]

haha...no, there's no ICAO rule against FL360.What happened, as I had expected, is computers took your initally entered altitude, and then calculated the optimal profile from that altitude to other altitudes, based on your weight. Since a higher altitude was more optimal, it expected you would follow that OPT ALTitude across the legs, and displayed that as the ALT for the legs. If you don't plan on using a stepped climb, you should set the STEP to 0 as I mentioned, which tells the computers that you're cruising at FL360 and remaining there; not following the optimal altitudes for your weight.Regarding the error (not the altitude shown on the legs), I suspect you're not entering the altitude into the right spot, somehow.

[Squishy 0]

Regarding the error (not the altitude shown on the legs), I suspect you're not entering the altitude into the right spot, somehow.

I am.. I enter FL380 (e.g.) or 38000 in the place where it says 315/43000

[scandinavian13 5,192]

That would be why. That's not where you enter the altitude, unless it's for a crossing restriction on ascent/descent. You either enter it on the PERF INIT or the CRZ page to update your CRZ ALT, not on the LEGS page.

[Squishy 0]

That would be why. That's not where you enter the altitude, unless it's for a crossing restriction on ascent/descent. You either enter it on the PERF INIT or the CRZ page to update your CRZ ALT, not on the LEGS page.

What do you mean? you can change the desired speed/altitude for each leg on the legs page. I know you wouldn't change the cruize alt here... but still