The New York Stock Exchange closes. It will not reopen until September 17th.
Dulles air traffic control notices a plane moving very fast (500 mph+) heading eastbound on their radar. This is American Airlines Flight 77. The plane is headed towards the prohibited airspace surrounding the White House. Over the next several minutes, this plane’s path will be tracked and various nearby facilities will be notified and will engage disaster plans. Some people are evacuated from the Pentagon.