Are some ILS weird?

[Dan Morera]

Hey guys, I can regularly land any plane using an ILS landing but, sometimes in particular runways my AP approach acts a little weird. I know some ILS are only horizontal guides and not vertical. But my AP acts weird, it starts zig zagging not bening able to stay lined up with the runway. Does anything like this happen to you guys?

One example is rwy 22R at KORD. This particular time I was using a 737-800 from POSKY

Thanks
Dan

[Iwannabeapilot]

I expect that this is because of that particular aircraft's flight dynamics. POSKY deliberately make their aircraft heavy on the controls and it's because of this that the autopilot has a hard time keeping the aircraft on the localizer. You could try and intercept the ILS from a smaller angle, reducing the work the autopilot has to do to get lined up. But apart from that I don't know.

[Dan Morera]

Yeah I thought that might have to do with it, I intercepted at a high angle and at a short distance about 10nm. And yes the plane was heavy.

I just remembered something. After doing a couple of practice runs, I tried to line up manually and the plane was still a little hard to turn, so it may be weight related, going to play with the cfg, and see if it improves.

[JBaymore]

That is usually an indication that the aircraft is not configured correctly for approach and/or the approach speed is wrong for the current aircraft weight.

best,

...................john