Yeah, that's the gist of it. It would have put us into the ground about 50 yards short of the runway because it was "chasing" the glide slope.

The glide slope is a radio beam shot from the appraoch end of the runway into the air at about 3 degrees. It, combined with the "localizer" (the same thing but aligned horizontally) gives you the ILS path (ILS=Instrument Landing System). It's basically the road you follow through the muck to the runway.

As you get closer to the runway the sensitivity of the ILS becomes greater, so smaller control inputs are needed as correction. For some reason, the autopilot overcontrolled to get back onto the glideslope. We had the plane put into maintenance because of the problem and the shop reported that they could find nothing wrong with the system.

I don't think I ever let the autopilot in that particular plane fly an ILS again (at least not in IFR).