World Trade Center site
On the morning of September 11, 2001, Islamic terrorists affiliated with Al-Qaeda hijacked American Airlines Flight 11 and United Airlines Flight 175, both which were en route to Los Angeles, and intentionally crashed them into the two main towers of the World Trade Center. The towers collapsed within two hours of the collisions. 2,606 people, including 2,192 civilians, 71 law enforcement officers, and 343 firefighters, who were in the towers and in the surrounding area died in the attacks, as well as 147 civilians and the 10 hijackers aboard the two airliners. After the collapse of the World Trade Center, hospital workers and law enforcement officers began referring to the World Trade Center site as "Ground Zero".
American Airlines Flight 11
The 9/11 Commission estimated that the hijacking began at 08:14, when the pilots stopped responding to requests from the Boston Air Route Traffic Control Center (Boston ARTCC). It is believed that Waleed al-Shehri made the first move. At 08:13:29, as the aircraft was passing over central Massachusetts at , the pilots responded to a request from Boston ARTCC to make a 20-degree turn to the right. At 08:13:47, Boston ARTCC told the pilots to ascend to a cruising altitude of but received no response. It is believed that Captain Ogonowski was stabbed to death in order for the hijacker pilot Mohamed Atta to take control of the plane and crash it into the North Tower of the World Trade Center. Before dying, Ogonowski keyed the cockpit microphone; "pushing its button intermittently to signal that something was wrong and at one point allowing them to hear the voice of the hijacker." At 08:16, the aircraft leveled off at and shortly thereafter deviated from its scheduled path. Boston ARTCC made multiple attempts to talk to Flight 11 without reply, and at 08:21, the flight stopped transmitting its Mode-C transponder signal.