Why close it? The planes that hit WTC came from BOS, 182 miles away. The plane that hit the Pentagon came from IAD, and the one that went down in Pennsylvania came out of EWR, also apparently targeted at Washington.

With modern commercial aircraft capable of moving at over 500 mph, how big a no-fly zone do you need to insure safety around DC? A hundred mile radius? That means worst case that controllers would have a maximum of a quarter hour to ascertain the intentions and intercept any wayward aircraft. Not realistic, IMO. Anything less than a hundred miles and it gets worse. And a hundred miles means you have to close IAD, BWI, and PHL too.

Keep DCA open. Closing it is an illogical, hysterical response.