A hijacked passenger jet, American Airlines Flight 11 out of Boston, Massachusetts with Mohammed Atta and the other hijackers aboard crash the plane into floors 93-99 of the North Tower of the World Trade Center, killing everyone on board and hundreds inside the building tearing a gaping hole in the building and setting it afire.
The two F-15s that were at battle stations were ordered to scramble (an order that begins with engine start-up, a process that takes about five minutes), and radar confirmed they were airborne by 08:53.