<P> In June 1974, while President Nixon was on his way to a scheduled stop in Syria, Syrian fighter jets intercepted Air Force One to act as escorts . However, the Air Force One crew was not informed in advance and, as a result, took evasive action including a dive . </P> <P> The Air Force usually does not have fighter aircraft escort the presidential aircraft over the United States but it has occurred, for example during the attack on the World Trade Center . </P> <P> On 11 September 2001, President George W. Bush was interrupted as he attended an event at Emma E. Booker Elementary School in Sarasota, Florida, after the attack on the World Trade Center South Tower in New York City . He took off on a VC - 25 from Sarasota - Bradenton International Airport with Colonel Mark Tillman, the senior pilot of Air Force One that day, in charge . Air traffic controllers gave Air Force One an ominous warning that a passenger jet was close to Air Force One and was unresponsive to calls . Tillman recalls: "As we got over Gainesville, Florida, we got the word from Jacksonville Center . They said,' Air Force One you have traffic behind you and basically above you that is descending into you, we are not in contact with them--they have shut their responder (sic) off .' And at that time it kind of led us to believe maybe someone was coming into us in Sarasota, they saw us take off, they just stayed high and are following us at this point . We had no idea what the capabilities of the terrorists were at that point ." </P> <P> In response to this reported threat, Col. Tillman said he flew Air Force One over the Gulf of Mexico to test whether the other aircraft would follow . The other jet continued on its route, and Tillman said that it was later explained to him that an airliner had lost its transponder and that the pilots on - board neglected to switch to another radio frequency . An aircraft transponder broadcasts an electronic identification signal . A threat came again when Tillman received a message warning of an imminent attack on Air Force One . "We got word from the vice president and the staff that' Angel was next .' Angel being the classified call sign for Air Force One . Once we got into the Gulf (of Mexico) and they passed to us that' Angel was next,' at that point I asked for fighter support . If an airliner was part of the attack, it would be good to have fighters on the wing to go ahead and take care of us ." At this point, Tillman said that the plan to fly the president back to Washington, DC was aborted and instead Tillman landed at Barksdale Air Force Base, Louisiana and Offutt Air Force Base, Nebraska, where the president made a speech . Tillman explained that this was due to his concern that because of the reported threat, Air Force One would be attacked when he returned to Andrews Air Force Base . </P>

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