World Trade Center Health Program
On September 11, 2001, 19 terrorists associated with the Islamist militant group al-Qaeda hijacked four passenger jets in a series of suicide attacks on the United States, killing 2,996 people and injuring more than 6,000 others. Hijackers flew planes into two main towers of the World Trade Center, resulting in the collapse of three buildings of the World Trade Center complex, and the Pentagon, resulting in the partial destruction of the western side in the building. The resulting dust cloud due to the collapse of the World Trade Center covered Manhattan for days and contained thousands of tons of toxic debris, including asbestos and other known carcinogens. Another hijacked plane crashed into a field in Shanksville, Pennsylvania following an attempt by the passengers to retake control of the plane. No one in the airliners survived.
As of 2011, approximately 18,000 people have received medical treatment for illnesses related to toxic dust from the World Trade Center site. A study of rescue workers released in April 2010 found that all those studied had impaired lung functions, and that 30–40% were reporting little or no improvement in persistent symptoms that started within the first year of the attack. In 2011 a major research study showed significant long term medical and psychological effects among first responders to the World Trade Center site. These effects include elevated levels of asthma, sinusitis, Gastroesophageal reflux disease and posttraumatic stress disorder.
American Airlines Flight 77
On the morning of September 11, 2001, the five hijackers arrived at Washington Dulles International Airport. At 07:15, Khalid al-Mihdhar and Majed Moqed checked in at the American Airlines ticket counter for Flight 77, arriving at the passenger security checkpoint a few minutes later at 07:18. Both men set off the metal detector and were put through secondary screening. Moqed continued to set off the alarm, so he was searched with a hand wand. The Hazmi brothers checked in together at the ticket counter at 07:29.[Hani Hanjour checked in separately and arrived at the passenger security checkpoint at 07:35. Hanjour was followed minutes later at the checkpoint by Salem and Nawaf al-Hazmi, who also set off the metal detector's alarm. The screener at the checkpoint never resolved what set off the alarm. As seen in security footage later released, Nawaf Hazmi appeared to have an unidentified item in his back pocket. Utility knives up to four inches were permitted at the time by the Federal Aviation Administration (FAA) as carry-on items. The passenger security checkpoint at Dulles International Airport was operated by Argenbright Security, under contract with United Airlines.