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Airbus MCDU questions

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Hello all!I have 3 questions regarding MCDU:1. How does the "Cost index (CI)" on init page optimize the Flight plan? In terms of optimal time, optimal fuel or optimal cost (balance between fuel/time)? Does this calculation affect the optimal suggested Cruise alt (FL opt)? 2. On itit page: why do the fields "Extra/Time" and "predicted Landing Weight (LW)" change during flight? The LW never matches the actual LW, what calculation is used here? What does "Extra/Time" mean, when to use these values?3. Is it realistic, that on FL410 the cabin altitude rises to 8700ft, wich gives me an amber warning?Once again I have to day, that the PSS Airbus series is, beside some minor weakpoints, great stuff!Hope someone can help,Greetings,Hakan

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Hey!as for the cost index, it tells the computer more or less the company policy for the flight that is done. low numbers result in lower speeds and a lower fuel consuption as high values will increase speed and fuel burn and therefor the flight gets more expensive for the company. To clarify the calculation, i have attached an extract from an Airbus manual on the issue.Apparently, to get back to your question, it is not directly affecting the calculated altitude.The Extra/Time value is according to manuals calculated like this: Taxi + Trip + Reserves + Alternate + Final and therefor equals to "block"From my experience, the LW prediction changes according to the current flight situation, meaning that when the engines are for some reason consuming more fuel it gets updated and the times change again once they are back to lower levels...i think i found out once when on cruising level and climbing/descending a little to test a few thingsno idea about the cabin warning, however hope i was of help,Salinawww.toomuchfs.com

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This answers all my questions perfectly, thank you, Salina!Greetings and Take care :) ,Hakan

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Hi Hakan,Which Airbus are you talking about? They heavies should be ok at thataltitude. I'm not sure that the A320's are certified to FL410?At least they usually fly somewhat lower. Have you looked at thePROG page and seen what OPT and MAX ALT is? Generally though,A320's operate in the lower to mid 30.000's.

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I am refering to the A330, I was step-climbing as recommended by the MCDU, but because of the FL-rules I was forced to go on FL410 instead onto recommended FL398 or something, and max FL was around 408. So indeed I went a bit to high! But FL410 should at least be ok as a maximum for A330, or do u have some hints on that?Thx for help,Greetings,Hakan

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SalinaMany thanks for the cost index pdf. I knew what, in principle, it was all about but your attachment makes it much clearer.RegardsTony

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