I’ve submitted a support ticket for this but I’m wondering if anyone else is seeing the. Basically the autopilot doesn’t seem to have sufficient control influence to capture a localiser or glide slope.
Basically the Autopilot isn't responding fast enough to capture the VOR/Localiser/GS and then tries to overcompensate. Eventually it seems to capture the localiser - but it takes a long time (which just isn't workable if you're flying a precision approach on the ILS. I'm trying to remember my control logic from Uni and I think this means the autopilot is over-damped (but I'm not certain of that).
For example when capturing the glide slope the autopilot doesn’t pitch down enough to maintain the correct descent rate/angle. Then when it does get on the glide path, it takes overshoots and ends up below, then when it decreases the rate of descent it then overshoots the GS (goes above).
In general the autopilot seems unable to respond quickly enough to control the aircraft. Eg, when the flaps are deployed that obviously increases lift, so the autopilot has to compensate for that, but the autopilot can’t respond quickly enough (or with enough control input), so that can lead in a rapid increase in vertical speed, eg when I was in a 1500 fpm descent putting out the first stage of flaps lead to a temporary 1000 fpm climb.
I had a similar issue with this for a while, but I think it was mostly down to technique (I'm very new to all this). This is what seems to work for me now.
The autopilot doesn't seem to like to change more than one thing at once, so ideally arrive with your aircraft flying level at the entry point to the ILS slope, alligned as close as you can manage to the runway angle and as close to your landing speed as possible (based on your current weight) and with flaps and wheels down. That way it can make the small incremental adjustments to get you pretty much down to the runway correctly. Generally, the slower the better, so long as you are above the stall speed for your weight.
Also, check the compass is alligned (default: "D" key in FSX). I never knew about this last bit so kept arriving and wondering why I was perfectly missaligned each time.
Now I can usually get on the ground in one piece.
Hope this helps.