Fortunately this does not happen often but when it does I always end up restarting the flight so it becomes one of those wastes of 40 minutes of time only to have to restart as I don't want to hand fly long flights. Normally I will hand fly to ~10K feet then engage the AP and all normally works as it should, but sometimes it just never wants to engage. Today, from LIPZ to EDDB went all the way to 18K feet hand flying and it never would engage. I always make sure the rudder is neutral and flight director is perfectly aligned before engaging and outside of that not sure what else might prevent the AP from engaging. The route is all verified and all seems normal. One other tipoff is I notice when this has happened typically the elevator becomes overly sensitive. I can pull up slightly on the yoke and it wants to bound up much more than normal. And typically a reboot/restart always resolves the issue.

Thanks in advance!

Edited August 18Aug 18 by Noel

Maybe this reddit thread may help.

Did you go LVR CLB ?

https://www.reddit.com?utm_source=share&utm_medium=android_app&utm_name=androidcss&utm_term=1&utm_content=1

Happened to me once or twice. Solved it by going direct to the next waypoint

1 hour ago, willy647 said:

Happened to me once or twice. Solved it by going direct to the next waypoint

Yeah .that's is also what I do.

Does not mean that is your solution but something to look into.

You mean the autopilot does not engage at all?

56 minutes ago, Ron Lefebvre said:

Yeah .that's is also what I do.

Does not mean that is your solution but something to look into.

You mean the autopilot does not engage at all?

Yep the autopilot does not engage at all so I would have to hand-fly the entire flight. I'll try the next waypoint maybe that will fix this.

Thanks!

3 hours ago, willy647 said:

Happened to me once or twice. Solved it by going direct to the next waypoint

That's what I do when AP will not engage. I go to the next way point in FMC, As I get very close to that point in heading mode, then switch to VNAV and engage AP. AP will take over the remaining of flight.

I used to have a similar problem that I tracked down to my key bindings for rudder trim and rudder. Basically I use my numpad for cockpit views always have done for over a decade, but since the sim allows multiple assignments to one button my numpad 7 for example would be rudder trim left. Now it doesn't just nudge it left and then it moves back to neutral like a set of pedals, it actually holds it there, this will then stop the autopilot from engaging since it thinks there is an input still being made.

Might be nothing to do with what's going on on your end but something to maybe consider.

It happened again at a different departure airport. This time I tried Direct To the next waypoint and was then able to engage the AP. Thanks! I will look into rudder as a factor in this as it probably is something I'm doing that gets this happening.

8 hours ago, Noel said:

It happened again at a different departure airport. This time I tried Direct To the next waypoint and was then able to engage the AP. Thanks! I will look into rudder as a factor in this as it probably is something I'm doing that gets this happening.

Have you checked to make sure the AP itself has not been setup with more then one binding. Just in case.

1 hour ago, Ron Lefebvre said:

Have you checked to make sure the AP itself has not been setup with more then one binding. Just in case.

Good thought. I just looked and there is a key combi, Ctrl-1, that is a binding I don't use and can't think of anytime I would use that key combi, as I use a button on my yoke. And, this never happens w/ any birds except Fenix, and even with it, only a handful of times. It shouldn't hurt to disable this key combi though, so I will. Cheers

This happened again this morning flying out of EFIV. No direct to next or subsequent waypoints fixed this. And here is the really bad part and to me this is clearly a defect, unless I simply don't understand what's happening which is very possible--in fact this tendency to bound upwards is probably related to why the plane AP does not engage: whenever this happens, when the autopilot will not engage when it appears it should be able to, the plane becomes bizarrely oversensitive to elevator inputs. Barely pull the yoke back and up she goes--very hard to control. Any other ideas?

Edited September 4Sep 4 by Noel

31 minutes ago, Noel said:

This happened again this morning flying out of EFIV. No direct to next or subsequent waypoints fixed this. And here is the really bad part and to me this is clearly a defect, unless I simply don't understand what's happening which is very possible--in fact this tendency to bound upwards is probably related to why the plane AP does not engage: whenever this happens, when the autopilot will not engage when it appears it should be able to, the plane becomes bizarrely oversensitive to elevator inputs. Barely pull the yoke back and up she goes--very hard to control. Any other ideas?

Are you in a stall?

1 hour ago, Fiorentoni said:

Are you in a stall?

That is the right question and out of EFIV the constraint is at 185kts or so, but I hand fly up to about FL010 and by the time we were at around FL066 constraint went to 220kts. I use the FD to stay on course and at altitude so doesn't seem like stall related.

21 hours ago, Fiorentoni said:

Are you in a stall?

I believe that would exclude the oversensitive response to pitch rate inputs...

Edited September 5Sep 5 by jcomm

18 hours ago, jcomm said:

I believe that would exclude the oversensitive response to pitch rate inputs...

One would think, but the only situation I remember where the pitch in the Fenix seemed „off“ and really sensitive was when I was playing around with it and creating stalls.