[yardie]

...and under fair weather conditions. Under more adverse conditions will be done manually.

It's fairly easy to tell a computer, "See that line (runway slope), follow it".

[willyt]

I think the autopilot follows a ILS beacon in. Isn't that why less flights are diverted in poor weather now? http://en.m.wikipedia.org/wiki/Instrument_landing_system http://en.m.wikipedia.org/wiki?search=Autopilot