Actually, there is. Check out the Air Force's missions.
Link please. It's just too hard to believe that the National Security Act of 1947 was prescient enough to include a clause covering a terrorist hijacking of a commercial airliner.
The Air Force is allowed to enforce border control?
Actually, I did just that. Here is a link to the entire text of the National Security Act of 1947 pertaining to the Air Force:
http://www.wpafb.af.mil/museum/history/postwwii/nsa47.htm
And now I know what the problem has been around here, Poohbah. You are full of shit, Poohbah.
Where in the text does the Act task the Air Force with intercepting commercial airliners that have been hijacked by terrorists?