Last week, members of the Senate Armed Services Committee questioned Air Force General Richard Myers about why the fighters had not been able to get airborne sooner, and military officials have questioned what fighters would have been able to do even if they had been in time.
According to the timeline:
* The Federal Aviation Administration alerted Norad's Northeast Air Defence Sector in Rome, New York, at 8.40 am (0040 NZT) that American Airlines Flight 11 had been hijacked after taking off from Boston en route to Los Angeles. At 8.43 am, the FAA notified Norad that United Airlines Flight 175 from Boston to Los Angeles had also been hijacked.
* Norad ordered two F-15 jet fighters into the air from Otis Air National Guard Base in Falmouth, Massachusetts, at 8.46 am. About that time, American Flight 11 crashed into the World Trade Center.
* The F-15s were airborne at 8.52 am Just after 9 am, as United Flight 175 struck the World Trade Center, the F-15s were eight minutes away, or 114km.
* The FAA notified Norad at 9.24 am that a third jet, American Flight 77 bound from Washington to Los Angeles, had been hijacked. Norad ordered two F-16 fighters from Langley Air Force Base in Virginia to intercept the airliner.
* The fighters were airborne at 9.30 am but were 12 minutes, or 169km, away when the airliner struck the Pentagon.
After the Pentagon strike, Mr Bush authorised fighters to shoot down any other aircraft that threatened targets in Washington.
* The fourth hijacked plane, United Flight 93 from Newark to San Francisco, was by then over Pennsylvania, headed back to the East Coast.
F-16s from Langley flew protective patterns over Washington after the Pentagon strike, but as Flight 93 headed towards them, it crashed outside Shanksville, Pennsylvania, at approximately 10.03 am following a fight between the hijackers and passengers.
The failure of defence agencies to protect the World Trade Center and the Pentagon has caused consternation.
Senior military officials have explained that their defence systems are geared primarily for threats from outside the United States' borders, not attacks from inside the country.
- STAFF REPORTER, AGENCIES
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