There was not enough warning time for North American Aerospace Defense Command (NORAD) to take effective action. Langley Air Force Base in Virginia launches three F-16s that are still approximately 150 miles from Washington, DC when Flight 77 crashes into the Pentagon seven minutes later. The fighters had flown over the ocean in accordance with standing instructions and did not turn toward Washington until ordered to do so at almost the same time that the Pentagon was struck.1

1 Goldberg, A. Papadopoulous, S., et al “Pentagon 9/11” Historical Office, Office of the Secretary of Defense n.d PDF. March 16, 2011 page 12-13 http://osdhistory.defense.gov/docs/Pentagon%209-11.pdf