Thirty-one minutes after takeoff, the attackers stormed the cockpit and forced the passengers and crew to the rear of the cabin, threatening the hostages but initially sparing all of them.

Lead hijacker Hani Hanjour assumed control of the aircraft after having undergone extensive flight training as part of his preparation for the attack.

In the meantime, two people aboard discreetly made phone calls to family members and relayed information on the situation without the knowledge of their assailants.

By 10:10, the damage inflicted by the aircraft and ignited jet fuel led to a localized collapse of the Pentagon's western flank, followed forty minutes later by another five stories of the structure.

[1] Led by Khalid Sheikh Mohammed, who was described as being the "principal architect" of the attacks in the 9/11 Commission Report,[2] al-Qaeda was motivated by several factors, not least of which was anti-Americanism and anti-Western sentiment.

[3] Though bin Laden himself expressed a preference for the destruction of the White House over the Capitol, his subordinates disagreed, citing its difficulty in striking from the air.

"[10] Hanjour returned to Saudi Arabia after being certified as a pilot, but left again in late 1999, telling his family he was going to the United Arab Emirates to work for an airline.

He had associated with three Qatari citizens who flew from Los Angeles to London (via Washington) and Qatar on the eve of the attacks, after allegedly surveying the World Trade Center and the White House.

Eleanor Hill, the former staff director for the congressional joint inquiry on the September 11 attacks, said the cable reinforces questions about the thoroughness of the FBI's investigation.

[22] The three Qatari men were booked to fly from Los Angeles to Washington on September 10, 2001, on the same plane that was hijacked and piloted into the Pentagon on the following day.

At 07:15 AM ET, Khalid al-Mihdhar and Majed Moqed checked in at the American Airlines ticket counter for Flight 77,[30] arriving at the passenger security checkpoint a few minutes later at 07:18.

Hanjour, al-Mihdhar, and Moqed were chosen by the Computer Assisted Passenger Prescreening System (CAPPS) criteria, while the brothers Nawaf and Salem al-Hazmi were selected because they did not provide adequate identification and were deemed suspicious by the airline check-in agent.

[30] The flight's autopilot was promptly engaged and set on a course heading eastbound towards Washington, D.C.[45] The FAA was aware at this point there was an emergency on board the airplane.

[47] Sometime between 09:17 and 09:22, Hanjour broadcast a deceptive announcement via the cabin's public address system, advising those aboard that the plane was being hijacked and that their best chance of survival was by not resisting.

[35] During the phone call, she made the erroneous claim that "six persons" had forced "us" to the rear of the airplane, but did not explain whether the people crowded together were crew members, passengers, or both.

At 09:16, Barbara Olson made a call to her husband Ted, quietly explaining that the plane had been hijacked and that those responsible were armed with knives and box cutters.

[57] He then made his wife aware of the suicide attacks on the World Trade Center, causing her to go quiet; Ted wondered if this meant she had been shocked into silence.

After expressing their feelings and reassuring one another, the call cut off for the last time, at 9:26 a.m.[58] "The speed, the maneuverability, the way that he turned, we all thought in the radar room, all of us experienced air traffic controllers, that that was a military plane.

[45] Turning and descending rapidly as it made its final approach toward Washington, the airplane was detected again on radar screens by controllers at Dulles, who mistook it for a military fighter at first glance due to its high speed and maneuvering.

[63][64] Flying at a speed of 530 miles per hour (850 km/h; 240 m/s; 460 kn) over the Navy Annex Building adjacent to Arlington National Cemetery,[65] Flight 77 crashed into the Pentagon's western flank at 09:37:46.

In the minutes leading up to the crash, Reagan Airport controllers had asked a passing Air National Guard Lockheed C-130 Hercules to identify and follow the aircraft.

The pilot, Lieutenant Colonel Steven O'Brien, told them he believed it was either a Boeing 757 or 767, observing that its silver fuselage meant it was most likely an American Airlines jet.

We went a little farther, turned a corner and came into this bombed out office space that was a roaring inferno of destruction and smoke and flames and intense heat you could feel searing your face."

ACFD Assistant Chief James Schwartz implemented an incident command system (ICS) to coordinate response efforts among multiple agencies.

While on fire and escaping from the Navy Command Center, Lt. Kevin Shaeffer observed a chunk of the aircraft's nose cone and the nose landing gear in the service road between rings B and C.[96] Early in the morning on Friday, September 14, Fairfax County Urban Search and Rescue Team members Carlton Burkhammer and Brian Moravitz came across an "intact seat from the plane's cockpit",[97] while paramedics and firefighters located the two black boxes near the punch out hole in the A–E drive,[98] nearly 300 feet (91 m) into the building.

The Washington Field Office, National Capital Response Squad (NCRS), and the Joint Terrorism Task Force (JTTF) led the crime scene investigation at the Pentagon.

[116] Rumsfeld returned to his office, and went to a conference room in the Executive Support Center where he joined a secure videoteleconference with Vice President Dick Cheney and other officials.

[123] The Department of Defense released filmed footage on May 16, 2006, that was recorded by a security camera of American Airlines Flight 77 crashing into the Pentagon, with a plane visible in one frame, as a "thin white blur" and an explosion following.

The footage is "grainy and the focus is soft, but a rapidly growing tower of smoke is visible in the distance on the upper edge of the frame as the plane crashes into the building.

"[129] On September 12, 2002, Defense Secretary Donald Rumsfeld and General Richard Myers, Chairman of the Joint Chiefs of Staff, dedicated the Victims of Terrorist Attack on the Pentagon Memorial at Arlington National Cemetery.