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Guest agentsmith

VNAV problems again

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Hi! i Have just installed the last patch with the VNAV update, but i'm still having problmes. When i go from CLB to CRZ(with VNAV), i can't open the "CLB" page on the fmc. same problem from CRZ to DES, as soon as the descent starts i can't open the "CRZ" page on the FMC. Are anyone else having this problems?Greetings, Roar Nicolaisen

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ok. it's just that i spoke to one i know and he said that he was able to open both the CRZ,CLB and DES page in any phases of flight. One more thing. If choose "DES NOW" with VNAV and start the descent, can you then go back to cruiz level again and continue as normal with VNAV? Like if you start a descent and than for one reason ore another change your mind and want to go back to cruiz level. Is it possible to then use LVL CHG to cruiz level again and then push VNAV to continue as normal? greetings, Roar

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I'll have to double check the page transitions. I think you are right but there could have been a FMC up date that changed this, not 100% sure. Your second question humm, I doubt that a pilot would fly in such a way, the fact is that he cannot descend without ATC clearance and they would not say "oops, go back to your crz alt" lol. It's possible if you are close to the path to resume a path descent, use the path deviation scale. If you go too much beyond the original TOD point you will not be able to resume a path descent with VNAV. Of course I am guessing here ;) [h4]Best Wishes,Randy J. Smithhttp://img.villagephotos.com/p/2003-8/196432/winglets_lg.jpg [h3] AMD XP 2200 |MUNCHKIN 512 DDR RAM |ECS[/b ][i] K7S5A MB[/i] |GF2 MX 32 MEG and still runs GOOD!|WIN XP PRO |MITSUBISHI DIAMOND PLUS 91 19"[/h3]

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agentsmith is correct. Think about it, how would you change your descent speed while in the cruise?Its a pretty unlikely scenario that you would have to climb back up to your cruising level after hitting descend now, cant answer your question on that one. However, what does occasionally happen is you get an early descent to a lower level, say FL350 to FL310, where you can use descend now and enter a new cruising altitude of FL310 on the cruise page and VNAV should sort itself out.

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Thank for joining in the discussion, you will need to sign your posts with your name thank you ;) I do recall a 737NG pilot saying this to be the case (access to pages) but what we need is some facts, reference to the AOM etc would do nicely ;) [h4]Best Wishes,Randy J. Smithhttp://img.villagephotos.com/p/2003-8/196432/winglets_lg.jpg [h3] AMD XP 2200 |MUNCHKIN 512 DDR RAM |ECS[/b ][i] K7S5A MB[/i] |GF2 MX 32 MEG and still runs GOOD!|WIN XP PRO |MITSUBISHI DIAMOND PLUS 91 19"[/h3]

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>agentsmith is correct. Think about it, how would you change>your descent speed while in the cruise?>>Its a pretty unlikely scenario that you would have to climb>back up to your cruising level after hitting descend now, cant>answer your question on that one. However, what does>occasionally happen is you get an early descent to a lower>level, say FL350 to FL310, where you can use descend now and>enter a new cruising altitude of FL310 on the cruise page and>VNAV should sort itself out.It's not uncommon at all to be temporarily given a higher or lower altitude for conflicting traffic. You may be cruising along at FL330 and get a temporary assignment to another altitude if you're overtaking someone (normally the aircraft that is not behaving as predicted gets the routing or altitude change).But if this were to happen I believe that the process would be to stay in LNAV, manually enter the new altitude and do a LVL change, and then LVL change back to your "normal" altitude and resume VNAV at that point.This happens much more frequently to airplanes flying in the mid 200s or high 300s where there may be conflict with turboprops or bizjets. In the mid 300s where most airliners are cruising is a pretty stable environment separation-wise.-Tim Metzinger

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The only time you would use descend now is to have an earlier top of descent, perhaps to get out of a bit of turbulence or have the aeroplane in a better position to handle loss of tailwind and avoid overspeed.As Tim says, in the cruise we would use LNAV, VNAV is also handy as it will do a cruise descent (not idle thrust descent) to a lower cruising altitude, V/S +/- 500 is a good idea for passenger comfort, you just have to keep an eye on your thrust required vs thrust available when near max altitude or risk speed loss.Tom Colton

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OK checking the AOM there are page transitions. But this does not answer the question on whether the pages can be accessed after passing (like CLIMB). Of course you can access the des page while in crz or climb, the question is if you should be able to access then in any en-route phase. Anthony?? Even if you use DES NOW, VNAV will start a shallow descent (app 1000 FPM) untill it merges with the orginal calculated path UNLESS you use a spd descent where it does not follow any path. DES NOW does not really change the TOD from a VNAV perspective as regards to the PATH. [h4]Best Wishes,Randy J. Smithhttp://img.villagephotos.com/p/2003-8/196432/winglets_lg.jpg [h3] AMD XP 2200 |MUNCHKIN 512 DDR RAM |ECS[/b ][i] K7S5A MB[/i] |GF2 MX 32 MEG and still runs GOOD!|WIN XP PRO |MITSUBISHI DIAMOND PLUS 91 19"[/h3]

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However, i tryed to go from FL330 to FL310 using the VNAV descent mode "DESCENT NOW". When i then went back to FL330 again using "LVL CHG" and tryed to activate VNAV again to continue with "VNAV PATH" and "FMC SPEED", the FMC gave the message "CHECK MCP ALT" and VNAV would not be activated.i Think that the stated happening along with the route transitions on the MCDU are related. For example if you use VNAV to descent in any way at all, the FMC completely forget about "CRUIZ" and you cannot go back to the CRZ page on the MCDU as well as use VNAV to keep CRUIZ. Same thing if you go from CLIMB to CRUIZ, when entering CRUIZ, FMC and VNAV forgets about CLB. This is why i think that all pilots use a "non VNAV mode"(LVL CHG ore V/S) when changing level to avoid traffic, forinstance. greetings, Roar

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Precisely (if I understand things correctly, lol). The FMC divides the flight path into three segments: CLB, CRZ and DES. The climb phase lasts until the T/C. The cruise phase is from the T/C until T/D and the descent phase is from T/D to the E/D. After the End of Descent there may be a section that covers a Missed Approach...As has been said it

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Roar,... when I see post titles like yours and then read the contents - the reasons of VNAV problems, AGAIN... I just feel suddenly soooooo tired.....anthonyAnthony MertonPrecision Manuals Developmenthttp://www.precisionmanuals.com

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