COLORADO SPRINGS, Colo. -- Fighter jets were only eight minutes away from one of the hijacked airliners that crashed into the World Trade Center, the North American Aerospace Defense Command said.

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Two other military jets were 12 minutes away when an airliner hit the Pentagon. But President Bush had not authorized military pilots to shoot down any civilian planes until after the crash at the Pentagon.

NORAD has released its official timelines of the Sept. 11 hijackings, when two jetliners crashed into the World Trade Center in New York and one struck the Pentagon. A fourth hijacked jet crashed in Pennsylvania.

The Federal Aviation Administration alerted NORAD's Northeast Air Defense Sector in Rome, N.Y., at 8:40 a.m. EDT that American Airlines Flight 11 had been hijacked after taking off from Boston en route to Los Angeles, according to the timeline.

At 8:43 a.m., 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, Mass., at 8:46 a.m. That same minute, American Flight 11 crashed into the World Trade Center.

The F-15s were airborne at 8:52 a.m. At 9:02, as United Flight 175 struck World Trade Center, the F-15s were eight minutes away, or 71 miles, according to the timelines.

The FAA notified NORAD at 9:24 a.m. that a third jet had been hijacked, American Flight 77 bound from Dulles International Airport in Washington to Los Angeles. NORAD ordered two F-16 fighters from Langley Air Force Base in Hampton, Va., to intercept the airliner.

The fighters were airborne at 9:30 a.m., but were 12 minutes, or 105 miles, away when the airliner struck the Pentagon.

After the Pentagon strike, Bush authorized fighters to shoot down any other aircraft that threatened targets in Washington. United Flight 93 from Newark to San Francisco was by then over Pennsylvania, headed back to the East Coast.

NORAD did not provide times for Flight 93 but said it was communicating with the FAA continuously on the Washington and Newark hijackings.

F-16s from Langley flew protective patterns over Washington after the Pentagon strike, but as Flight 93 headed toward them, it crashed outside Shanksville, Pa., at approximately 10:03 a.m., NORAD said.

NORAD monitors the skies over the United States and Canada for threats. Its operational center is inside Cheyenne Mountain Air Force Station and its headquarters are at Peterson Air Force Base, both near Colorado Springs.