The FAA’s Indianapolis Center finally learns that there are other hijacked aircraft, and now doubts that Flight 77 crashed. They discuss this possibility with the FAA Command Center in Herndon, Virginia.
Also, at about this time, United Airlines Flight 23, bound to Los Angeles from JFK International in New York cancels takeoff. It was scheduled to take off at 8:30, but left the gate late and has been sitting in line. Several Arab passengers become aggressive at this news and refuse to debark the plane. Security is called but before it arrives, the men will have vanished, leaving behind box-cutters, copies of the Koran, and al-Qaeda instruction sheets.
It is reasonable to conclude that Flight 23 was supposed to be the fifth plane to be hijacked. However, the target is unknown.