9/11

On September 11, 2001, Islamist terrorists hijacked American Airlines Flight 11 and crashed it into the northern façade of the North Tower at 8:46:40 a.m.; the aircraft struck between the 93rd and 99th floors. Seventeen minutes later, at 9:03:11 a.m., a second group crashed the similarly hijacked United Airlines Flight 175 into the southern façade of the South Tower, striking it between the 77th and 85th floors.The terrorist organisation Al-Qaeda, led by Osama bin Laden, carried out the attacks in retaliation for certain aspects of American foreign policy, particularly U.S. support of Israel and the presence of U.S. troops in Saudi Arabia. The damage caused to the North Tower by Flight 11 destroyed any means of escape from above the impact zone, trapping 1,344 people. Flight 175 had a much more off-centered impact compared to Flight 11, and a single stairwell was left intact; however, only a few people managed to descend successfully before the tower collapsed. Although the South Tower was struck lower than the North Tower, thus affecting more floors, a smaller number, fewer than 700, were killed instantly or trapped.

At 9:59 a.m., the South Tower collapsed after burning for approximately 56 minutes. The fire caused steel structural elements, already weakened from the plane's impact, to fail. The North Tower collapsed at 10:28 a.m., after burning for approximately 102 minutes. At 5:20 p.m. on September 11, 2001, 7 World Trade Center began to collapse with the crumbling of the east penthouse; it collapsed completely at 5:21 p.m. owing to uncontrolled fires causing structural failure.