Graphic. Flight path to WTC, Sept 11, 2001.
FEMA - Therese McAllister. Therese McAllister. Jonathan Barnett. John Gross. Ronald Hamburger,  Jon Magnuson
World Trade Center Building Performance Study: Data Collection, Preliminary Observations, and Recommendations. FEMA 403, May 2002 - Chapter 1, Introduction, <a rel="nofollow" class="external free" href="http://www.fema.gov/pdf/library/fema403_ch1.pdf">http://www.fema.gov/pdf/library/fema403_ch1.pdf</a> (pag 5)