A few hijackers drew suspicion from some airport security personnel and observant civilians, but all 19 managed to board their flights eventually.

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Sept. 11, 2001 -- The Ominous Beginning

On Sept. 11, 2001, Mohamed Atta and four other hijackers arrive at Portland (Maine) International Airport before 6 a.m. From there, they take a small plane to Boston's Logan International Airport. Then they board American Airlines Flight 11. Flight 11 takes off from Boston at 8 a.m., bound for Los Angeles. Meanwhile, the 17 other terrorists are busy boarding their own flights. Five hijackers board United Airlines Flight 175 in Boston, which takes off for Los Angeles at 8:14 a.m. Six minutes later, American Airlines Flight 77 leaves Washington Dulles International Airport, in Dulles, Va., with five terrorists aboard.

At 8:19 a.m., two attendants on Flight 11 tell ground personnel that the plane had been hijacked. They relay key information, such as the hijackers' seat numbers, that helps authorities begin their investigation immediately as the morning's events unfold. Within 20 minutes, the Federal Aviation Administration (FAA) has notified the North American Aerospace Defense Command (NORAD) about the suspected hijacking. At about the same time, the fourth and final plane, United Airlines Flight 93, departs Newark International Airport, in Newark, N.J., and heads toward San Francisco. Four hijackers prepare to make their moves.