On the 24th anniversary of September 11, 2001, National Geographic presents a special mega episode that uncovers the global and personal stories of a day that changed the world forever. 9/11: Control the Skies 4,500 planes are in the air over North America when the second jet strikes the Twin Towers of the World Trade Center on September 11, 2001. The FAA declares ATC Zero, no planes in US airspace. 9/11: Where Were You? Never Forget Survivors of the 9/11 attacks recount their harrowing stories