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chris41

oops, started my descent too early

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I was climbing to cruize altitude 330 and I made the mistake of changing my cruising altitude to 340 (per request of ATC) in the FMC. I now realize I should have instead changed the MCP altitude to 340 not the FMC. By doing so my aircraft went into descent mode and that is not what I wanted. Now I can't get the cruize or climb page. I do realize these become inoperable once cruize altitude is reached but that was not yet the case. My question is: is there anything I can do to correct my mistake or do I just have to live with it and continue the flight without the use of VNAV (at least until I reach the descent phase of the flight)? I don't wish to guess what the optimal cruize level should be and at what speed I should be at at the FL.Thanks,Chris Porter

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Why worry? I only use VNAV for the climb in the 737. I always use MCP SPD and VS for my descents.

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I know in the real Airbus you can trick the aircraft into getting back into the Crz phase by entering a lower Crz alt into the FMC. Once your back at your correct Crz alt then re-enter, eg FL370. Never tested it in the 737,744 or MD11The situation you found yourself in has happened a lot in the real world.Just reread your post, dont you have it the other way round?? You have FL330 in the FMC but climbed to FL340 in FLCH on the MCP?

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I was climbing to cruize altitude 330 and I made the mistake of changing my cruising altitude to 340 (per request of ATC) in the FMC. I now realize I should have instead changed the MCP altitude to 340 not the FMC. By doing so my aircraft went into descent mode and that is not what I wanted. Now I can't get the cruize or climb page.
I believe setting a higher CRZ ALT shouldn't put FMC into descent mode, regardless of where you put the altitude. Putting a lower CRZ ALT in the FMC or MCP shouldn't make it enter descent mode, either. . . As far as I know, it's how you tell it to go down. If you hit ALT INT to go higher, no prob. If you hit ALT INT to go lower than your current, then yes, it will go into descent mode.Did you get any "Unable Cruise Altitude" messages?

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I used to disconnect from VNAV during my initial descent but in using Radar Contact and usually getting crossing restrictions to be around FL110-120 at or around 240 knots within 40 NM of the arrival airport I would just program that into the FMC and let VNAV control the descent, not that I didn't handle it manually before I started programming the FMC to do it (it wasn't difficult, just a little tedious). I don't know, I just like to let VNAV control the cruise phase of the flight. That and I hadn't even arrived at cruise level before making the mistake. Don't like the FMC being in descent mode while still 1400nm out from the arrival airport.As for the other comment I will give it a try. Time to minipulate the FMCThanksChris Porter

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I believe setting a higher CRZ ALT shouldn't put FMC into descent mode, regardless of where you put the altitude. Putting a lower CRZ ALT in the FMC or MCP shouldn't make it enter descent mode, either. . . As far as I know, it's how you tell it to go down. If you hit ALT INT to go higher, no prob. If you hit ALT INT to go lower than your current, then yes, it will go into descent mode.Did you get any "Unable Cruise Altitude" messages?
Entering a higher cruise altitude using the MCP doesn't put the plane into descent mode but in my case by entering a higher cruise altitude in the Cruise page it did put the aircraft/FMC into descent mode. Then when I would reselect VNAV I would get a message but I can't remember what it said. Something about MCP cruise altitude which I checked several times to make sure I had the correct FL there. Thanks,Chris Porter

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I did another flight but there is no place to put the lower altitude to get the CRZ or cruise page to come back up. You can only look at the DES page not the CLB or CRZ pages.Thanks,Chris Porter

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Entering a higher cruise altitude using the MCP doesn't put the plane into descent mode but in my case by entering a higher cruise altitude in the Cruise page it did put the aircraft/FMC into descent mode. Then when I would reselect VNAV I would get a message but I can't remember what it said. Something about MCP cruise altitude which I checked several times to make sure I had the correct FL there. Thanks,Chris Porter
Hmm, that sounds like a "simism" to me.

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Sorry, a "simism"?Chris Porter
Sorry: Simism - something the sim does that the plane doesn't do in real life. I don't think the real plane would enter the descent mode in the way you're describing, so I don't have much advice.What mode are you climbing in? You should be in VNAV.

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I did another flight but there is no place to put the lower altitude to get the CRZ or cruise page to come back up. You can only look at the DES page not the CLB or CRZ pages.Thanks,Chris Porter
I have to go back to the original documentation to confirm how the real one works. I believe the only way to get the FMC reset the VNAV modes is to reenter the flight plan from the INIT page.

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I don't really know if I'm understanding well the problem in this case, but any cruise altitude change should be entered in three places (well, this is what i do, if i remember...),1.- In the PERF INIT page (push INIT REF key and then select PERF), (enter the new FL in the upper right line 1R) and activate the change.2.- In the MCP altitude selector (and get there in the way you prefer: FLCH, VNAV or VS).3.- In the pressurization panel in the overhead (update crz alt).

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