This is classic. Apparently the mayor of Chicago wants a “no-fly-zone” over his city for non-commecial aircraft, apparently in order to stop things like that accident in New York from happening “on purpose” as it were.
But ignoring the fact that this is just a crazy rant, let’s think how you’re going to enforce a “no-fly-zone” like this. Let’s imagine the conversation between air traffic control, and the terrorists:
Air Traffic Control: You are not authorized to fly in this airspace, please turn back.
Terrorists: Sorry? What? We can’t hear you.
Air Traffic Control: Repeat, you are not authorized to fly in this airspace, please turn back.
Terrorists: Oh, sure. Hang on a minute, I just spilled my coffee...
Air Traffic Control: Please turn back immediately!
Terrorists: You want us to keep going?
Air Traffic Control: No, turn back!!
Too late! A plane can travel over a city in a straight line in maybe 30 seconds. That means that air traffic control would have 30 seconds to scramble the fighter jets or the surface-to-air missiles or whatever counter-measure they decide to put in place. And once you shoot the plane down, what do you get? A screaming fireball over your city.
Sure a no-fly-zone over a city will stop law-abiding people flying over it, but terrorists are not law-abiding.