If any airliner is hijacked and the FAA’s Air Traffic Control knows it, ATC’s first call will be to the North American Aerospace Defense Command. NORAD would immediately dispatch jet fighters to intercept and the President’s National Security Advisor would be notified. From there, the fighters would monitor the airliners’ intentions and a shootdown order could be given by the President. There were four separate but coordinated attack plans. American 11, a Boeing 767 bound from Boston to Los Angeles, was hijacked first and was crashed into the north tower of the World Trade Center. United 175, also a Boeing 767, also departed Boston for LAX and was hijacked over New Jersey just as AA11 impacted its target and would hit the south tower just 14 minutes later. American 77, a Boeing 757, departed from Washington Dulles for Los Angeles and was hijacked 33 minutes after takeoff, reversed course, and impacted the Pentagon 40 minutes later without meeting any interference. United 93 from Newark to San Francisco encountered two intangibles that caused the only complete failure among the Raiders’ four plans. The flight was delayed for forty minutes taxiing out to the end of the runway, and then the cockpit takeover was 30 minutes late, leaving the aircraft over 270 miles from its target when it was finally commandeered.
For an airliner at cruise altitude commandeered for use as a guided missile, ideal attack position does not mean a location directly over the target. The best attack position for an aircraft at 35,000 feet is somewhere within 120 miles of the target. Because airliners require three horizontal miles to descend each 1,000 feet, pilots plan a descent from 35,000 feet at around 105 miles from the destination. The 3 to 1 ratio can be increased to 2 to 1 for a more aggressive descent using spoilers and higher airspeeds, but the pass/fail of the hijackers’ mission depended on the ability to commandeer all the aircraft within a critical 120-mile window.
Getting the four scheduled airliners into an ideal strike position, as close as possible to the same moment, was perhaps the most challenging aspect of the plan. Drawing 120-mile circles around New York and Washington shows the windows that the planes needed to be within for success. Based on the departure airports and the targets hit, it is clear that all four flights were planned to be within ideal position soon after takeoff. Any delay in the hostile takeovers would open a new can of worms. Most importantly, the U.S. military’s blanket of supersonic fighters would begin to defend American skies. AA11 was commandeered only 15 minutes after takeoff and was in perfect attack position at 8:14 a.m. UA175 was commandeered 33 minutes after liftoff and was in an ideal attack position at 8:46 a.m., just as AA11 struck the north tower.
The snapshot at 8:46 shows AA11 about to hit the north tower and, in perfect synchrony, the attackers storming the cockpit of UA175. AA77 — the Pentagon plane — was heading west at cruise altitude, moving away from its target at 500 mph, and still five minutes from takeover. The hijackers on UA93 had lifted off only four minutes earlier from Newark, after a 40-minute taxi out and delay due to normal traffic. They came extremely close to missing their first critical time window, but the window was met, if only by four minutes.
Long taxi outs from busy airports are hard to predict. The UA93 attack was in jeopardy before liftoff because of the long taxi time. Getting an early pushback away from the gate by the ground crew can make a huge difference in the placement for takeoff. There are many scheduled departures around 8:00 a.m. from all major airports. If you’re first in pushing back, your taxi time will be minimal. But if you don’t call for pushback until, perhaps, 8:02, there might be 15 airplanes getting into position ahead of you. Each takeoff takes an average of three minutes, so 15 airplanes equals around 45 minutes. So it appears that UA93 was somewhere around number 12 in line for takeoff — completely normal, but not good for the tactical plan.
This long taxi nearly busted one of the tactical plan’s critical windows. The goal was to have all four airplanes in the air and in attack position before ATC or NORAD knew what was happening. Preserving the element of surprise requires calculating the amount of time it will take for the system to switch from a normal operating day to a day in which there is one odd occurrence to a day with one emergency to the realization that the country is under attack. A further delay for UA93 of just four minutes would have blown their critical time window, because the controllers and even United 93’s pilots would have seen the World Trade Center on fire with their own eyes, from the ground at Newark Airport.