VNAV Disconnect Question

[Guest Segwin]

Hello All:After changing some speeds and alt. for crossing restrictions in the CDU VNAV disconnects, although it is still lit, and the ALT HOLD indicator turns on. The IAS/MACH indicator also becomes active.How do I return it to VNAV operation and release it from the ALT HOLD?Tried pressing the ALT HOLD button, tried switching to VS, tried disengaging the AP. At a loss on what could be wrong.TIA.

[Guest Segwin]

bump

[baw716 0]

Reset your MCP Altitude then hit VNAV. Once the system is disconnected, you have to "tell" it what to do. By resetting the MCP Altitude, confirming it on the PFD, then hit VNAV, you should get VNAV SPD back in the FMA.Give it a try and let me know how you fare.Best,Dave Lamb

[Guest Segwin]

>Reset your MCP Altitude then hit VNAV. Once the system is>disconnected, you have to "tell" it what to do. By resetting>the MCP Altitude, confirming it on the PFD, then hit VNAV, you>should get VNAV SPD back in the FMA.>>Give it a try and let me know how you fare.>Best,>Dave Lamb>Hello Dave:Tried this, re-set it for 2k less however, VNAV still wouldn't take over.

[baw716 0]

This may sound like a dumb question, but where did you set it up? Did you reset the step size in the FMC or did your reset the altitude to 2000 on the MCP. Also, I don't recall if you were climbing or descending. If descending, my recommendation is not to be on VNAV; since unless you have programmed it exactly correct in the FMC and have the correct altitude dialed into the MCP, it won't work...and you won't even know it.If you are climbing, my recommendation is NOT to use VNAV below clean speed and/or 5000ft. Below these altitudes, you need the precision of V/S + SPD (and tightly controlling both) or FLCH if you are making a small altitude change and want to stay at the same speed. Remember too, that on the 777, the engines have to spool up or down, and that can take between 5-15 seconds before anything happens. While this is true of any high bypass ratio jet, it is especially true on the larger T7 engines like the GE90-115B. Come back to me on the original question and then we'll see where things stand.ThanksDave

[Guest Segwin]

Hello Dave:>This may sound like a dumb question, but where did you set it>up? Did you reset the step size in the FMC or did your reset>the altitude to 2000 on the MCP. On the MCP Also, I don't recall if you>were climbing or descending.In CRZ Mode. Setting up restrictions for a SATR If descending, my recommendation>is not to be on VNAV; since unless you have programmed it>exactly correct in the FMC and have the correct altitude>dialed into the MCP, it won't work...and you won't even know>it.>>If you are climbing, my recommendation is NOT to use VNAV>below clean speed and/or 5000ft. Below these altitudes, you>need the precision of V/S + SPD (and tightly controlling both)>or FLCH if you are making a small altitude change and want to>stay at the same speed. Remember too, that on the 777, the>engines have to spool up or down, and that can take between>5-15 seconds before anything happens. While this is true of>any high bypass ratio jet, it is especially true on the larger>T7 engines like the GE90-115B. >>Come back to me on the original question and then we'll see>where things stand.>>Thanks>DaveOk, let me know and Thanks!

[Guest D17S]

You may have set up a vertical fix that Vnav wouldn't have been able to reach. So it "just said no." If Vnav is available, a single press of the Vnav button will get it.