[thinkthenpost]

My opinion here:
The planes being relatively modern, most likely just punch in the destination's coordinates in the the autopilot/navigation system.

[bennowens]

Part of pilot training is navigation, by instruments and also by "dead" reckoning.

[edzo4]

all the planes that struck the WTC came from the northeast

you need no navigational aids you fly west till you see the hudson river and turn south or you head south till you see the coast and head west
on a clear day you could see the WTC from miles away
not to mention the WTC was one of the tallest buildings in the world and the pentagon is one of the largest building in the world
neither are too difficult to spot from the air