The four flights, minute by minute

The hijackers chose transcontinental flights, which carry heavy fuel loads, and passed through checkpoints in Portland, Boston, Dulles and Newark. A computer prescreening system called CAPPS flagged several of them, including Atta, but under the rules then in force the only consequence was that their checked bags were held until they boarded. [1]

In each case the hijackers waited until the plane was at cruising altitude, then forced their way into the cockpit, killed or removed the pilots, and turned off or changed the transponder. Flight attendants and passengers phoned airline offices and relatives with descriptions of knives, Mace or pepper spray and claims of a bomb. [1]

United 93, which left Newark late and carried only 37 passengers including the four hijackers, was the only plane where the people aboard learned what had happened in New York before their own hijackers struck. Their revolt began at 9:57; at 10:03:11 the plane hit the ground at about 563 mph, upside down. [1][2] Both towers collapsed within an hour and three quarters of being hit. [3] The individual pieces are in the towers file, the Pentagon file, the Flight 93 file and the air-defense file.

The National September 11 Memorial lists 2,977 people killed in the attacks, from 90 nations: 2,753 in New York, 184 at the Pentagon and 40 aboard United 93. The 19 hijackers are not counted. [1]

The 9/11 Commission, writing in 2004, gave 2,973, calling it the largest loss of life on American soil from a hostile attack in the nation’s history. The FDNY lost 343 members and the Port Authority police 37. [2] The memorial’s higher figure reflects later work identifying who was killed.

At the Pentagon, 125 people died inside the building and 59 passengers and crew died aboard Flight 77, besides the five hijackers. [3] The deaths since then from illnesses linked to the Ground Zero dust are covered in the health file.