Originally Posted by Non Believer
AA77 was a Boeing 757, not a Boeing 767. Your account also isn't entirely true. AA77's transponder was turned off at 0856EDT, and it crashed into the Pentagon at 0937EDT. That's 41 minutes. Looks good so far for you right?
Not quite. AA77's transponder was turned off in a part of the USA with no primary radar coverage. Yes, that right, there's gaps in the primary radar coverage. With simultaneous loss of communications and transponder, the ARTCC controller rightly assumed the aircraft had crashed.
Indianapolis Centre then followed correct procedure and notified surrounding ARTCCs so airspace along AA77's flightpath could be sterilised. Meanwhile, of course, AA77 had turned around and was heading east, not west. When it entered an area with primary coverage at 0905EDT, no one noticed because they were looking west.
At 0908EDT Indianapolis Centre activated the USAF's Search and Rescue units at Langley AFB, to commence a search for AA77's wreckage.
By 0920EDT, Indianapolis Centre staff had learned that there were multiple suspected hijackings in progress. At this moment they began to suspect AA77 may have not crashed, but been hijacked.
At 0921EDT the FAA began searching for AA77 on radar, and Dulles TRACON were notified of suspected hijackings. They were directed to check all unknown radar contacts.
At 0932EDT Dulles TRACON located AA77 (although they didn't know it was AA77).
At 0934EDT NORAD hear about the unknown contact being tracked by Dulles TRACON, and direct fighters to intercept it.
At 0936EDT an ANG C-130 departs Reagan, and Tower controllers direct the aircraft to follow the radar track located by Dulles TRACON.
At 0937EDT the ANG C-130 reports that the aircraft has hit the Pentagon.
Thus by my calculation AA77 was hijacked for 41 minutes, which comprised of:
24 minutes during which the aircraft was believed to have crashed
12 minutes during which the aircraft was missing and suspected of being hijacked
5 minutes during which the aircraft was a suspect hijack but being tracked on radar