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Virginia, which oversees daily traffic flow within the entire airspace system.
FAA headquarters is ultimately responsible for the management of the
National Airspace System.The Operations Center located at FAA headquarters
receives notifications of incidents, including accidents and hijackings.
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FAA Control Centers often receive information and make operational deci-
sions independently of one another. On 9/11, the four hijacked aircraft were
monitored mainly by the centers in Boston, New York, Cleveland, and Indi-
anapolis. Each center thus had part of the knowledge of what was going on
across the system.What Boston knew was not necessarily known by centers in
New York, Cleveland, or Indianapolis, or for that matter by the Command
Center in Herndon or by FAA headquarters in Washington.
Controllers track airliners such as the four aircraft hijacked on 9/11 primar-
ily by watching the data from a signal emitted by each aircraft's transponder
equipment.Those four planes, like all aircraft traveling above 10,000 feet, were
required to emit a unique transponder signal while in flight.
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On 9/11, the terrorists turned off the transponders on three of the four
hijacked aircraft.With its transponder off, it is possible, though more difficult,
to track an aircraft by its primary radar returns. But unlike transponder data,
primary radar returns do not show the aircraft's identity and altitude. Con-
trollers at centers rely so heavily on transponder signals that they usually do not
display primary radar returns on their radar scopes. But they can change the
configuration of their scopes so they can see primary radar returns.They did this
on 9/11 when the transponder signals for three of the aircraft disappeared.
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Before 9/11, it was not unheard of for a commercial aircraft to deviate
slightly from its course, or for an FAA controller to lose radio contact with a
pilot for a short period of time. A controller could also briefly lose a commer-
cial aircraft's transponder signal, although this happened much less frequently.
However, the simultaneous loss of radio and transponder signal would be a rare
and alarming occurrence, and would normally indicate a catastrophic system
failure or an aircraft crash. In all of these instances, the job of the controller was
to reach out to the aircraft, the parent company of the aircraft, and other planes
in the vicinity in an attempt to reestablish communications and set the aircraft
back on course.Alarm bells would not start ringing until these efforts--which
could take five minutes or more--were tried and had failed.
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NORAD Mission and Structure.
NORAD is a binational command estab-
lished in 1958 between the United States and Canada. Its mission was, and is,
to defend the airspace of North America and protect the continent.That mis-
sion does not distinguish between internal and external threats; but because
NORAD was created to counter the Soviet threat, it came to define its job as
defending against external attacks.
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The threat of Soviet bombers diminished significantly as the Cold War
ended, and the number of NORAD alert sites was reduced from its Cold War
high of 26. Some within the Pentagon argued in the 1990s that the alert sites
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