5:45 AM – Mohamed Atta and Abdul Aziz al-Omari, two of the intended hijackers, pass through security at the Portland International Jetport in Maine. They board a commuter flight to Boston Logan International Airport, they then board American Airlines Flight 11.

7:59 AM – Flight 11 takes off from Boston, headed for Los Angeles, California. There are 76 passengers, 11 crew members, and 5 hijackers on board.

8:15 AM – United Airlines Flight 175 takes off from Boston, also headed for Los Angeles. There are 51 passengers, 9 crew members, and 5 hijackers on board.

8:19 AM – A flight attendant on Flight 11, Betty Ann Ong, alerts ground personnel that a hijacking is underway and that the cockpit is unreachable.

8:20 AM – American Airlines Flight 77 takes off from Dulles, outside of Washington, DC, headed for Los Angeles. There are 53 passengers, 6 crew members, and 5 hijackers on board.

8:24 AM – Mohamed Atta, a hijacker on Flight 11, unintentionally alerts air controllers in Boston to the attack. He meant to press the button that allowed him to talk to the passengers on his flight.

8:37 AM – After hearing the broadcast from Atta on Flight 11, Boston air traffic control alerts the US Air Force’s Northeast Defense Sector, who then mobilize the Air National Guard to follow the plane.

8:42 AM – United Flight 93 takes off from Newark, New Jersey, after a delay due to routine traffic. It was headed for San Francisco, California. There are 33 passengers, 7 crew members, and 4 hijackers are on board.

8:46 AM – Flight 11 crashes into the World Trade Center’s North Tower. All passengers aboard are instantly killed, and employees of the WTC are trapped above the 91st floor.

9:03 AM – Flight 175 crashes into the WTC’s South Tower. All passengers aboard are killed instantly and so are an unknown number of people in the tower.

9:05 AM – President George W. Bush, in an elementary school classroom in Florida, is informed about the hit on the second tower. His chief of staff, Andrew Card, whispers the chilling news into the president’s ear. Bush later wrote about his response: “I made the decision not to jump up immediately and leave the classroom. I didn’t want to rattle the kids. I wanted to project a sense of calm… I had been in enough crises to know that the first thing the leader has to do is to project calm.”

9:28 AM – Hijackers attack on Flight 93.

9:37 AM – Flight 77 crashes into the Pentagon. All passengers aboard are instantly killed and so are 125 civilian and military personnel in the building.

9:45 AM – US airspace is shut down under Operation Yellow Ribbon. All civilian aircraft are ordered to land at the nearest airport.

9:55 AM – Air Force One with President George W. Bush aboard takes off from Florida.

9:57 AM – Passengers aboard Flight 93 begin to run up toward the cockpit. Jarrah, the pilot, begins to roll the plane back and forth in an attempt to destabilize the revolt.

9:59 AM – The South Tower of the World Trade Center collapses.

10:02 AM – Flight 93 plows into an empty field in Shanksville, Pennsylvania. Although its ultimate target is unknown, it was likely heading for either the White House or the US Capitol.

10:18 AM – President Bush authorizes any non-grounded planes to be shot down. At that time, all four hijacked planes had already crashed but the president’s team was operating under the impression that Flight 93 was still in the air.

10:28 AM – The North Tower of the World Trade Center collapses.

10:53 AM – Secretary of Defense Donald Rumsfeld orders the US military to move to a higher state of alert, going to DEFCON 3.

11:45 AM – Air Force 1 lands at Barksdale Air Force Base near Shreveport, Louisiana.

12:15 PM – Airspace in the United States is completely free of all commercial and private flights.

1:30 PM – Air Force 1 leaves Barksdale.

2:30 PM – Rudy Giuliani, the mayor of New York City, visits the fallen Twin Towers of the World Trade Center at what becomes known as Ground Zero.

3:00 PM – Air Force 1 lands at Offutt Air Force Base in Nebraska, and President Bush is immediately taken to a secure bunker that is capable of withstanding a nuclear attack.

4:30 PM – Air Force 1 leaves Offutt and heads back toward Andrews Air Force base near Washington, DC.

5:30 PM – Building 7 of the World Trade Center collapses.

8:30 PM – President Bush addresses the nation.