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 Tuesday at 02:43 PM2 days 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.