Flysimware Learjet 35A autopilot disconnect problem

Flying an ILS the jet is on glide slope and localizer and configured for landing. At 500' AGL I disarm the GS, then the NAV mode and finally disengage the AP (on the panel and not the main AP switch). The aircraft performs a serious bank and I do well to land anywhere on the runway.
I never turned fuel crossfeed on and both standby pumps were off. So I don't believe there should have been a fuel imbalance. I have wind set to zero. Aileron and rudder trim were set to neutral at takeoff and not touched by me.
So why did the AP give me an airplane out of trim?
By the way, other than this, the autopilot worked flawlessly during this 45 minute flight. That includes LVL, HDG, NAV, SPD on climb, VS on descent as well as localizer and GS capture.
I am surely doing something wrong. Any help would be much appreciated.

Steve
 

 

Addendum

Reviewing my flight recording I see that the ailerons were deflected during AP ILS. I will try again with autorudder off to see if that is my problem.

Steve

Turning the AP master off is all it takes to disconnect it for landing.

It looks like I got caught in an old FSX trap. My default aircraft had its fuel selector on the left tank. It has no setting for both tanks which the Learjet requires to draw fuel evenly from both wing tanks. So I was landing with a severe imbalance. Changing my default flight to a Beech Baron with fuel on both tanks seems to have fixed my approach problem.

Hello Bjoern,

I have the habit of disengaging the AP this way because, on some airplanes, doing so by just turning the master off has left me without elevator control. I thought I might have seen this once with the Lear but maybe not. If I find it repeatedly I will post again. Thanks for your input.

Steve