Aircraft hijacking is also employed as a terrorist tactic . On September 11 , 2001 , 19 al-Qaeda terrorists hijacked American Airlines Flight 11 , United Airlines Flight 175 , American Airlines Flight 77 , and United Airlines Flight 93 and crashed them into the Twin Towers of the World Trade Center , the southwestern side of the Pentagon building , and Stonycreek Township near Shanksville , Pennsylvania in a terrorist attack , killing 2,977 victims , most of them American citizens
United Airlines Flight 93
United Airlines Flight 93
Tactics of terrorism