I'm absolutely sure I'm doing something wrong here but I'm sitting on 25R at KLAX with a route planned to KSFO. I've entered all the performance data and a cruising alt of FL330; there are calculated speeds and altitudes in all the legs pages. Both FDs are on, the A/T is armed. What are the conditions that need to be met for VNAV to be able to be switched in? Ed Moore

To engage VNAV I believe you must be 400ft or greater

To engage VNAV I believe you must be 400ft or greater

VNAV should ARM on ground. Do not know all the criteria though.

To engage VNAV I believe you must be 400ft or greater

In the tutorial flight though, you're able to arm VNAV on the ground and it seems to work quite happily. I've just tried taking off and still won't turn on even over 400ft AGL. I think it must be something to do with the flight plan but it's giving no message at all. Had the same thing earlier and it was saying "NO DES AFTER..." which I was able to fix.

What's your departure like? If there's more than a 5 deg turn at departure then it won't arm on the ground (iirc!!)

It's the CASTA2 sid from KLAX 25R - it heads straight out initially. Just tried reducing cruise altitude to FL270 from 330 to see if it liked that better but still no VNAV.

Weird.

I'm sure it's something really bloody obvious that I will kick myself for :) Have tried looking through the FCOM but a) there's 400 million results for VNAV and :( there's apparently no list of requirements that I can find.

Huh - appears to have suddenly come on now. I think all I did was (whilst still on ground), press LVL CHG and that seemed to wake up the VNAV mode which will now toggle on and off quite happily. Be grateful if any of the VNAV wizards from PMDG could let me know whether this is expected behaviour?

I'm absolutely sure I'm doing something wrong here but I'm sitting on 25R at KLAX with a route planned to KSFO. I've entered all the performance data and a cruising alt of FL330; there are calculated speeds and altitudes in all the legs pages. Both FDs are on, the A/T is armed. What are the conditions that need to be met for VNAV to be able to be switched in? Ed Moore

You don't engage vnav on the ground because toga commans heading select to keep the wings level.If you engage a pitch mode then you will exit takeoff mode !!

I think it depends on the MCP you choose.I think Collins allows arming VNAV/LNAV on ground. I even did it before starting the engines.

Ah so you're saying it's an operational thing?I did try engaging VNAV after takeoff the first time and it still didn't engage. Plus although I'm very new to this I was basing the "arm VNAV on the ground" procedure from this bit of Ryan's tutorial:

Arm the LNAV and VNAV modes by pressing the LNAV and VNAV buttons. You’ll see LNAV appear in small white letters at the bottom of the FMA roll mode column and VNAV in the pitch mode column. LNAV will engage and turn green at 50 feet after you lift off and VNAV will engage at 400 feet.

I am having the same issue. I was able to arm VNAV on the ground in the tutorial but I was trying to do a test hop from KATL to KBHM via the GEETK5 departure and despite having gone through the same steps I could not arm VNAV on the ground. I am using the Collins MCP.

I am having the same problem. Can't arm VNAV while on the ground or once I get airborne. FMC is complete, both flight directors turned on, and auto throttle armed. LNAV works perfect.

VNAV doesn't decend on its own for me, it only follows the altitude bug...