Reasons for VNAV to not work?

[b0gey_dead_six 11]

I started the plane from cold and dark - went through the usual motions, IRS align, routes, dep/arr, then performance init.. but during climb out, VNAV will not engage but LNAV will.. what are the possible reasons for this?

[Mats_J 2]

I started the plane from cold and dark - went through the usual motions, IRS align, routes, dep/arr, then performance init.. but during climb out, VNAV will not engage but LNAV will.. what are the possible reasons for this?

User input error? ;) Check you have both FD switches ON. CPT and FO side. It's all in the FM (NGX Introduction)! :)

[b0gey_dead_six 11]

Yes, both FD were on..

[Mats_J 2]

Ah... Now I see your full question. I would suspect an incomplete FMS flight init.Valid route entered obviously as you got LNAV to kick in.Flight levels? Any fields related to vertical navigation in the CDU missed? Sorry I can't be of more help,

[b0gey_dead_six 11]

No i really looked through everything.. FL set, etc..

[Mats_J 2]

Care to take us through it step by step? Can you arm VNAV before T/O?

[Hdarkace 2]

Autothrottle is engaged?

[emvaos 13]

Have you EXEC'ed your PERF INIT page ? Should be ACT PERF INIT. NOTE : You either arm VNAV on the ground (two FD's ON) or above 400 agl.

[b0gey_dead_six 11]

Autothrottle is on, of course. and Vaos, I will try making sure the perf init page is active.

[Three.Green 0]

Have you EXEC'ed your PERF INIT page ? Should be ACT PERF INIT.

That helped me with my VNAV

[Heffron 29]

Search and Function come to mind

[Edmoore 1]

Try pressing LVL CHG, that seemed to wake up the VNAV in my case.

[rsrandazzo 6,353]

David- You aren't the first sim-pilot to run down this road- and you definitely won't be the last! VNAV is an GREAT mode for the airplane because the FMS plans out the entire climb and descent for you- but while easy to use- it is extremely sophisticated and requires that the airplane be properly set up in order for it to be available to you. The key activity related to getting VNAV operable is to properly initialize the FMS with the correct information before your flight. If you follow the tutorial it will take you step-by-step through this process- and after one or two flights you will be blowing through the setup in about 30 seconds.... Stick with it!