If you select an ILS approach at the map, the approach centerline is highlighted yellow and there is a pop-up menue where You can select NAV frequency and ILS approach. The plane is well positioned just before the initial point of this approach.
Now You have to adjust the parameters of Your AP, then switch on SPD, APP and CMD button (e. g. B737-800).
After this procedure I observe that the speed of the plane is increasing more and more and will not follow the adjusted speed of the AP. In this situation the AP is engaged and the speed button is indicated green.
What is going wrong or is this just a bug?
As work around I find out, that firstly disengage theAP, secondly make a manual 360 and thirdly switch on the AP funtionalities step by step.
1. Switch on F/D
2. Switch on A/T
3. Press the speed button
4. Press the CMD button
5. If You are back on the centerline of the selected ILS Approach, press the VOR-LOC button and observe the small diamond of the glidepath indicator
6. If You are established on the glidepath, press the APP button.
After this operation the plane will follow the adjusted speed,the glidepath and centerline and the touch down will be done properly.
I am using X-Plane 11 with the latest released Version.