7:59 a.m.: American Airlines Flight 11 takes off from Boston. Eleven crew members, 76 passengers, and five hijackers are on board.

8:15 a.m.: United Airlines Flight 175 takes off from Boston for Los Angeles. Nine crew members, 51 passengers, and five hijackers are on board.

8:19 a.m.: Flight attendant Betty Ann Ong alerts American Airlines ground personnel to a hijacking underway on Flight 11, reporting that the cockpit is unreachable.

8:20 a.m.: American Airlines Flight 77, en route to Los Angeles, takes off from Washington Dulles International Airport. Six crew members, 53 passengers, and five hijackers are on board.

8:42 a.m.: Flight 93 takes off. Seven crew members, 33 passengers, and four hijackers are on board.

8:46 a.m.: Five hijackers crash Flight 11 into floors 93 through 99 of 1 World Trade Center (north tower). The crash severs all three emergency stairwells and traps hundreds of people above the 91st floor.

9:03 a.m.: Five hijackers crash United Airlines Flight 175 into floors 77 through 85 of 2 World Trade Center (south tower), killing the 51 passengers and nine crew members on board the aircraft and an unknown number of people inside the building. The impact renders two of the three emergency stairwells impassable and severs a majority of the elevator cables in this area, trapping many above the impact zone and inside elevator cars. Shortly after hijacked Flight 175 strikes the south tower, some workers in the building jump or fall to their deaths, a phenomenon already witnessed after the attack on the north tower. Estimates of the number of people who die as a result of falling from the twin towers range from 50 to more than 200.

9:37 a.m.: Five hijackers crash American Airlines Flight 77 into the Pentagon. The crash and ensuing fire kill 125 military and civilian personnel on the ground.

9:42 a.m.: FAA orders all civilian planes in U.S. airspace to land and prohibits departures.

9:59: a.m.: After burning for 56 minutes, the south tower collapses in 10 seconds. More than 800 civilians and first responders inside the building and surrounding area are killed.

10:03 a.m.: Four hijackers crash Flight 93 in a field near the town of Shanksville in Somerset County, Pennsylvania, after passengers and crew storm the cockpit. The 33 passengers and seven crew members on board perish.

10:15 a.m.: A damaged section of the Pentagon’s west-facing outer ring collapses.

10:28 a.m.: The north tower collapses after burning for 102 minutes. More than 1,600 people are killed.

11:02 a.m.: New York City mayor orders evacuation of Lower Manhattan.

12:16 p.m.: The last flight still in the air above the continental United States lands. In two and a half hours, U.S. airspace has been cleared of an estimated 4,500 commercial and general aviation planes.

5:20 p.m.: After burning for hours, 7 World Trade Center collapses

- Source, 9/11 Memorial & Museum