John Judge has argued that Flight 77 should not have reached the Pentagon as it was under an area of restricted airspace called P-56-A:
The same claim has then been repeated by David Ray Griffin and others. It sounds like a solid argument, but there is one small problem: it isn't true.
Here's the map of P56, as we write (May 2009), sourced from the FAA's site:
Note the arrows pointing to the two P56 areas. Nothing extends for "17 miles in all directions". The Pentagon, across the river, is not included.
Has it changed? No. Here's an actual FAA description of the airspace from 2005:
These prohibited areas have been in effect for about 50 years. And they do not cover the Pentagon.
And even if you do fly into a prohibited area, what's likely to happen? Here's an iPilot article from 2002:
You're not going to be shot down. If you're sure to be intercepted then they don't mention it here. The most likely consequence before 9/11, according to this pilot and aviation writer, was "a warning letter". It seems these airspace rules weren't as relevant to 9/11 as Judge and David Ray Griffin would have us believe.