1. Wikipedia. Aircraft hijacking. Available at: http://en.wikipedia.org/wiki/Aircraft_hijacking.
2. Worldhistory.com. Aircraft hijacking. Available at: http://www.worldhistory.com/wiki/a/aircraft-hijacking.htm.
3. FAA historical chronology: civil aviation and the federal government, 1926-1996;Federal Aviation Administration,1998
4. Rumerman J. Aviation security. U.S. Centennial of Flight Commission. Available at: http://www.centennialofflight.gov/essay/Government_Role/security/POL18.htm.
5. National Commission of Terrorist Attacks upon the United States. Staff statement no. 4: the four flights. Initially presented January 26-27, 2004, in Washington, DC, at the Seventh Public Hearing of the Commission. Available at: http://news.findlaw.com/hdocs/doc/terrorism/911comm–SS4.pdf.