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h.uslar

FMC VNAV PROBLEM!!!

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HiJust took off from SFO heading to LFPG. VNAV doesn't work, says "unable crz alt". I've set everything correctly, I've already checked the forum for similar problems and checked evry page on the FMC. It seems to be a problem with the fmc, because as you can see on th pic below, FMC fuel predfiction is: -2,200,000 Lbs at LFPG!!!!! This is just imposible!! Any help?RegardsHuc

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Huh from the screenshot you got it pretty messed up.You have quite a heavy fuel load, as you should have for this kind of flight. Your MCP Alt is set to FL310 but in your FMC you have set FL290 as cruise level. Your step size is very strange! 1555? Try ICAO or 2000 feet there.Now what climb are you actually trying to achieve? FL290 or FL310 or ???The next thing: You are using derated CLB 1 Thrust. For the airplane being this heavy i would suggest using full CLB Thrust setting!

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Hi,Well it seemed o be a software problem as FMC calculation appeared to be assuming fuel to be zero (hence that absurd fuel prediction at destination). What I did, was sving the flight and the panel state, loading another flight, an then reloading the flight again. That solved the problem. The FMC started recogniing fuel and doing fare predictions and vnav was available. Don't kow hoever how to explain what happened! Anyway the flight went on nicely! I agree with you about the fuel load. I landed at LFPG with 58 klbs on board!! I don't have that much time to make fuel calculations manually so I use the fuel calculator utility by Pierre Chevallier. Do you recommend me another utility for this?Thanks and regards,Henrique

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>Hi,>Do you recommend me another utility for>this?Yes, what about the PMDG FMC itself? It's quite accurante most of the times. On long range flights it's ok to have a little extra fuel, almost 60k lbs can be ok if you stay at or below 630k landing weight.By the way: How did you load the fuel? I hope only with the PMDG menu!? Everything else will get you into trouble.

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