I believe that the 9-11 terrorists used GPS on the planes to find their targets. I bring my GPS on the plane whenever I travel & you can see actual streets. All they would have to do is mark waypoints on the ground and then fly toward them.
I agree, I've read that Atta Visted the towers the Sept 10.
Walk up, set waypoint, Hijack airplane, follow the arrow. My Garmin does this and it cost about $200 bucks.
One thing of note, the front windscreen in a cockpit has a laminent on it, so a side window has to be used.