Cannot Disengage APP Mode for new leg

[swiftyc123 0]

Hello,

I just did a leg in which I landed using a GPS approach with FAC and G/P captured (APP button lit).  I did not restart a new flight but continued in the same session.  Even after disengaging autopilot multiple times I cannot select LNAV/VNAV - the APP stays engaged with FAC and G/P still in green on my PFD.  Any help on to get autopilot to function normally after a leg?  thanks!

 

-Casey

[Tony747-400 44]

Try switching both Flight Directors off then back on again. 

[scandinavian13 5,192]

22 hours ago, swiftyc123 said:

Any help on to get autopilot to function normally after a leg?

The Flight Directors need to be cycled at the end of each leg to cancel any previous modes. The IRS should also be turned off and spun up again during the turn. All part of flying the plane.

Clear out old data by turning things off.

[berts 97]

12 hours ago, scandinavian13 said:

The Flight Directors need to be cycled at the end of each leg to cancel any previous modes.

Kyle, although this is mentioned in the FCOM as part of the SHUTDOWN procedure, it is not uncommon for the FD's to be selected OFF as part of the After Landing procedure and might in fact be more appropriate to include this selection there.  Disconnecting the A/P's and turning the FD's off and back on again is also necessary when coupled on an ILS and changing to another parallel ILS approach.   

[scandinavian13 5,192]

1 hour ago, berts said:

Kyle, although this is mentioned in the FCOM as part of the SHUTDOWN procedure, it is not uncommon for the FD's to be selected OFF as part of the After Landing procedure and might in fact be more appropriate to include this selection there.  Disconnecting the A/P's and turning the FD's off and back on again is also necessary when coupled on an ILS and changing to another parallel ILS approach.   

That's when I do it, honestly, but I didn't want to dive into all of the minutia. At the very least switch them off between legs. When between legs (or any airborne corner cases) are for a more in-depth discussion. My mention here was simply to help the OP solve his issue.