FAA - 2002 Fact Sheets: "0940. (approx.). American Flight 77 crashes into the Pentagon.

0945. In the first unplanned shutdown of U. S. airspace, the FAA orders all aircraft to land at the nearest airport as soon as practical. At this time, there were more than 4,500 aircraft in the air on Instrument Flight Rules (IFR) flight plans.

1007. (approx.) United Flight 93 crashes in Stony Creek Township, PA.

1039. Reaffirming the earlier order, the FAA issues a Notice to Airmen (NOTAM) that halts takeoffs and landings at all airports.

1215. (approx). The airspace over the 48 contiguous states is clear of all commercial and private flights.