What should have been done in response to the briefing that Bin Laden planned to attack the US?

[jeff47]

52. They were over the Atlantic.

The assumption had been that the Air Force only needed to worry about aircraft flying into US airspace, not aircraft already within US airspace. So the armed jets were flying out of Cape Cod. They flew out over the Atlantic to check on planes flying to the US.

Air Force jets within US airspace were generally not armed for safety - you can't accidentally fire missiles that aren't attached to your plane.

This "outside-only focus" even extended to our RADAR systems. We could detect aircraft that were flying to the US, but once within US airspace we relied on transponders to locate aircraft. When the hijackers turned off the transponders, the Air Force could not "see" the planes easily.

So, after the first two planes hit, the AF tried to scramble F-15s from that base on Cape Cod. The planes that were already in the air were pretty far away. The scrambled planes got in the air about when the Pentagon was hit, and were directed to search for flight 93. It crashed before the F-15s got there.