The horrific morning of September 11, 2001 as it unfolded - from the hijacking of American Airlines flight 11, to the collapse of both World Trade Center towers and the downing of United flight 93 in Pennsylvania. 'As It Happened' uses Air Traffic Control audio, NYPD and FDNY radio transmissions and images that captured the chaos, bravery and heartbreak of that day. Without narration, or dramatization, the raw, unfiltered voices of that day speak for themselves, on a day that changed the world.