I've had a few occasions where the autopilot on the FBW A320 disconnects by itself.  When it happened, it was always in "selected" heading/speed mode (not being directed by MCDU, but what I have selected manually on the FCU).  Today it happened while practicing RNAV approaches (which aren't currently modeled in the FBW A320 completely) hence the "practice".  I'm tracking along the approach, I'm not happy and decide to turn around by switching from managed heading mode to "selected": Spin the heading knob roughly 120 degrees to the left and initiate a left turn to try again.  At some point during the turn, maybe 1/2 way through, autopilot disengages.  If I try to re-engage, it disconnects immediately with the audible alert.    Only way I can get it to allow me to re-engage is by leveling the wings, and hitting autopilot again.  This doesn't happen every time in auto pilot manual heading mode, with makes it difficult to track down what might be going wrong.

Also I should mention this never happens in "managed" autopilot, ie:  NAV mode and speed controlled by the MCDU.  I don't have issues with spurious controller inputs etc. as I've seen people discuss causing disconnects, and I'm not touching any of the controllers.  That and the fact that it only happens when I manually select a heading on the FCU.

Anyone else experience this?  I'm guessing it is something I am doing wrong, but I can't determine what that might be.

1 hour ago, billkirk888 said:

I've had a few occasions where the autopilot on the FBW A320 disconnects by itself.  When it happened, it was always in "selected" heading/speed mode (not being directed by MCDU, but what I have selected manually on the FCU).  Today it happened while practicing RNAV approaches (which aren't currently modeled in the FBW A320 completely) hence the "practice".  I'm tracking along the approach, I'm not happy and decide to turn around by switching from managed heading mode to "selected": Spin the heading knob roughly 120 degrees to the left and initiate a left turn to try again.  At some point during the turn, maybe 1/2 way through, autopilot disengages.  If I try to re-engage, it disconnects immediately with the audible alert.    Only way I can get it to allow me to re-engage is by leveling the wings, and hitting autopilot again.  This doesn't happen every time in auto pilot manual heading mode, with makes it difficult to track down what might be going wrong.

Also I should mention this never happens in "managed" autopilot, ie:  NAV mode and speed controlled by the MCDU.  I don't have issues with spurious controller inputs etc. as I've seen people discuss causing disconnects, and I'm not touching any of the controllers.  That and the fact that it only happens when I manually select a heading on the FCU.

Anyone else experience this?  I'm guessing it is something I am doing wrong, but I can't determine what that might be.

Well I do use heading when on vectors, and I've never experienced that. You were talking about RNAV approaches. Are you in approach mode or are you in landing configuration? It's possible that there is some protection at work when you try to violently turn the aircraft while in approach mode or in landing configuration, but I never heard of it. I guess it was not Alpha Floor, was it?

51 minutes ago, Fiorentoni said:

It's possible that there is some protection at work when you try to violently turn the aircraft while in approach mode or in landing configuration, but I never heard of it.

That would be my wild guess as I have this occasionally when turning during approach and getting too slow with wrong (ie too little) flaps 

Edited March 20, 20224 yr by DAD

Maybe hitting bank angle? or Alpha floor protection.

I believe I've figured it out.  My speed appears to have been the issue.  I had it set for 200kias with no flaps.  Once the speed dropped into the protection area during the turn, the autopilot disconnected.