HelloI have a small issue with the NGX post SP1C update. Before I take off I arm LNAV and VNAV per procedure and when i apply take off thrust through the autothrottles VNAV disengages just after take off. When i apply the autopilot it automatically reverts to LVL CHG mode during the climb. However I can then reapply VNAV and it works fine. Prior to the service pack i could keep VNAV active throughout the take off with no problems. The plane still handles beautifully and all other systems are working as advertised. I'm just wondering if there is something i'm not doing properly that is causing the VNAV to turn off after take off? Its not a huge issue but it would be nice to figure it out.thank youMatt T

VNAV disengages just after take off

What does your FMA say?Screen captures will save you a lot of time in diagnosing the problem.

Check to make sure you're flying the same aircraft on the same procedure. If it's a different airport in a different livery, different settings may be lurking in the background, and the procedure may be different enough that it might be out of the AP limits.Agree with Matt, though - screenshots are really necessary here.

Hi,have you tried waiting until >400 ft AGL with arming the autopilot again?It is normal, that LNAV and VNAV lights go out on TO/GA and come back after passing 400 ft AGL.

^ The MCP lights are *not* indicative of what the modes are - if you still see VNAV in white in the FMA pitch column, you are fine. The MCP lights blank after pressing TOGA to let you know the AP is now committed to the TOGA modes. They'll come back after you're through the takeoff procedure in the air.

Thanks you all for the help. The FMA shows LNAV but not VNAV. I think it is probably a procedural error on my behalf. I'll run through the procedure again tonight and report back just to make sure i'm not missing something. Thank you all for your timely advice. It is appreciatedthanksMatt Thierens