Of the four aircraft hijacked on September 11 – the others were American Airlines Flight 11 , United Airlines Flight 175 and American Airlines Flight 77 – United Airlines Flight 93 was the only aircraft that did not reach its hijackers ' intended target . Vice President Dick Cheney , in the Presidential Emergency Operations Center deep under the White House , authorized Flight 93 to be shot down ; upon learning of the crash , he is reported to have said , " I think an act of heroism just took place on that plane . " A temporary memorial was built near the crash site soon after the attacks . Construction of a permanent Flight 93 National Memorial was dedicated on September 10 , 2011 , and the concrete and glass visitor center situated on a hill overlooking the site was opened exactly four years later
United Airlines Flight 175
United Airlines Flight 175
United Airlines Flight 93