In the very early morning of September 11, Mohamed Atta and Abdulaziz Alomari boarded a small commuter plane in Portland, Maine, for a flight to Boston. Authorities are still unsure why Atta and Alomari drove from Boston to Portland the day before, only to fly back to Boston the morning of September 11, since it exposed them to more airline scrutiny and the possibility of arrest. Once the two men arrived in Boston, they boarded American Airlines Flight 11 for Los Angeles, which took off on time at 7:59 A.M.Within the next fifteen minutes, United Airlines Flight 175, United Airlines Flight 93, and American Airlines Flight 77—all making transcontinental flights with relatively few passengers on board—took off from Boston; Newark, New Jersey; and Washington, D.C., respectively.

The first clue that American Airlines Flight 11 was not going smoothly was at 8:28 A...