At 8:21, American 11 turned off its transponder, immediately degrading the information available about the aircraft. The controller told his supervisor that he thought something was seriously wrong with the plane, although neither suspected a hijacking. The supervisor instructed the controller to follow standard procedures for handling a "no radio" aircraft.¹⁰⁷

The controller checked to see if American Airlines could establish communication with American 11. He became even more concerned as its route changed, moving into another sector's airspace. Controllers immediately began to move aircraft out of its path, and asked other aircraft in the vicinity to look for American 11.¹⁰⁸

At 8:24:38, the following transmission came from American 11:

American 11: We have some planes. Just stay quiet, and you'll be okay. We are returning to the airport.

The controller only heard something unintelligible; he did not hear the specific words "we have some planes." The next transmission came seconds later:

American 11: Nobody move. Everything will be okay. If you try to make any moves, you'll endanger yourself and the airplane. Just stay quiet.¹⁰⁹

The controller told us that he then knew it was a hijacking. He alerted his supervisor, who assigned another controller to assist him. He redoubled his efforts to ascertain the flight's altitude. Because the controller didn't understand the initial transmission, the manager of Boston Center instructed his quality assurance specialist to "pull the tape" of the radio transmission, listen to it closely, and report back.¹¹⁰

Between 8:25 and 8:32, in accordance with the FAA protocol, Boston Center managers started notifying their chain of command that American 11 had been hijacked. At 8:28, Boston Center called the Command Center in Herndon to advise that it believed American 11 had been hijacked and was heading toward New York Center's airspace.

By this time, American 11 had taken a dramatic turn to the south. At 8:32, the Command Center passed word of a possible hijacking to the Operations Center at FAA headquarters. The duty officer replied that security personnel at headquarters had just begun discussing the apparent hijack on a conference call with the New England regional office. FAA headquarters began to follow the hijack protocol but did not contact the NMCC to request a fighter escort.¹¹¹

The Herndon Command Center immediately established a teleconference between Boston, New York, and Cleveland Centers so that Boston Center could help the others understand what was happening.¹¹²

At 8:34, the Boston Center controller received a third transmission from American 11:

American 11: Nobody move please. We are going back to the airport. Don't try to make any stupid moves.¹¹³

In the succeeding minutes, controllers were attempting to ascertain the altitude of the southbound flight.¹¹⁴

Military Notification and Response. Boston Center did not follow the protocol in seeking military assistance through the prescribed chain of command. In addition to notifications within the FAA, Boston Center took the initiative, at 8:34, to contact the military through the FAA's Cape Cod facility. The center also tried to contact a former alert site in Atlantic City, unaware it had been phased out. At 8:37:52, Boston Center reached NEADS. This was the first notification received by the military-at any level-that American 11 had been hijacked:¹¹⁵