AP ALT HOLD and VNAV not engaging

[rhelle1]

Guys,

Thanks for any help you can give me.  For whatever reason my autopilot altitude hold button and VNAV will not engage (heading hold, autothrotttle, etc all work).  I have searched the forums and have disabled plugins (Groundhandling, XUIPC), moved the null zone to the far right, etc...and nothing seems to work.  Can anyone point me in the right direction.  I have looked everywhere here for a solution before i posted this so my apologies if it is something very small i am not doing.  

[JetNoise]

Check your CDU/FMC legs page.

Everything okay there, Altitudes calculated?

Check for errors in SID for example. Had that problem on a EIDW SID showing zeros for the first 2-3 waypoints. LNAV would not engage. Passing these, everything was okay again.

Cheers

[mmerelles]

attach a screen capture of your cockpit to see what the display screen says.

 

as per your description, sounds to me if use a joystick/yoke and the potentiometers are sending noise, go to the igex menu and set the cws slider all the way to the right.

[Litjan]

Are other pitch modes working? Like V/S and FL CHG? Try increasing the "CWS deadband" in the PREFERENCES menu - it governs how quickly the autopilot will disconnect when it detects joystick input.

 

If other modes are working, it could also be due to some prerequisite for VNAV missing. Most likely the PERF INIT page was not filled out (weights, crz alt, etc.).

Cheers, Jan

 

Edited December 14, 2016 by Litjan

[Lairyliam]

This may have answered my question... Thanks.