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Guest AeroMan08

VNAV Problem!

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I'm currently enroute from KORD to VIDP in my B772LR. I have my VNAV button pressed on my autopilot but when I try to climb, it descends! In my attempt to investigate why it's refusing to climb, I went into my VNAV page on my FMC and discovered that the ECON DES page is activated even though I'm thousands of miles away from my destination. My ECON CRZ isn't activated.....but it should be. Does anyone know how to activate the ECON CRZ page? Please help me ASAP! Thank you.Ryan Cummins-AAL101

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Ryan,Check to ensure the CRZ ALT as seen in the PERF INIT page on the CDU is set to an altitude that is higher than your present altitude. Also check the LEGS page and make sure the next waypoint does not have an altitude restriction of some altitude lower than your present altitude.Jeff

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I have had this problem too - for some reason the aircraft wants to be @ 3000ft even though every page in the CDU had FL370 on it. There were no altitude restrictions on "legs" due for over 3000nm, and the MCP altitude was set to 37,000. The VNAV page on the CDU was stuck on ACT ECON DES also.The only way I could make the aircraft maintain altitude was to use FLCH and ALT HOLD. Moving from FLCH to VNAV resulted in an immediate descent back to low altitude.I managed to free up the problem somehow later in the flight (during the proper descent - had the aircraft holding @ 9000ft at LAM), but when setting the CDU up for the approach, I experienced the same sort of hang I sometimes get when altering the cost index, so wasn't able to test further.PSS - do you have any ideas/comments?Daniel Percy

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Daniel,Very strange, indeed. My suggestion to Ryan was based purely on speculation. I haven't actually experienced the problem you two have, so I'm not sure what the cause is. I'll defer to PSS' expert opinion.Jeff

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I had this problem when I accidentally lowered the flaps during a climb to cruise altitude (clumsy big fingers!!!!)the FMC changed to Econ Des mode & could only recover by using FLTCH & ALT Hold.!!!!:-doh

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