Ok, so lets just look away from the big airport/vast ocean/quite nice weather scenario for a moment and take a glance at the little airport in the mountains with a non-precision approach.
You're taking a 757 size aircraft in there. It's snowing and the wind at 3000ft is 45knots across the procedure axis with a bit of a tail component and with some shear at about a thousand feet, but on the ground it's within limits for the equivalent of medium braking action on the runway. The Airport is a bit third-world and the PAPIs are just a tad out of alignment but the regular guys/gals know this and make the necessary adjustment. There's a hill 1 mile left of the C/L at about 3 miles out and if the wind's about 30-50 deg off the C/L at more than about 15kts there's usually a hellova downdraft with some real cobblestone turbulence for about 200ft then you tend to balloon up again, but you know this and are ready for the increase and then decrease in thrust.
Once you've landed, if you use autobrake 4, you'll make the turnoff if the weight is around 80 tonnes but not higher, so you need to know that the turning circle at the end isn't snow-cleared at the edges so you have to go round it with extreme care using not too fast and not
too slow a speed, but with a quite low steering angle if you want the nosewheel to actually point you in the right direction and not take you off into the local suburb.
Parking is a b*gger, because the terminal area isn't cleared at all but the 'follow me' guy is usually pretty good, but there is a new guy there (the one with the beard) that you've got to watch because he's a hint enthusiastic with his bats sometimes and he'll have your wing in that fuel tanker if you don't watch out. Oh, and they need to know just when to start de-icing.
OK, OK - you get the picture ... a day in the life eh? So.. tell me, if the system is planned to only have general aviation/military aircraft with actual pilots, just how do you write a computer programme to encompass all the implications of the above? Now, I'm not saying it can't be done ... as Arthur C Clarke fans will attest "any sufficiently advanced technology is indistinguishable from magic" ....but I'll bet you it'll cost more than, what was it? 525 million? Yeah, right.
