US President George W. Bush listens as White House Chief of Staff Andrew Card informs him of a second plane hitting the World Trade Center while Bush was conducting a reading seminar at the Emma E. Booker Elementary School in Sarasota, Florida in this September 11, 2001 file photo. [Photo/Agencies]

Hijacked United Airlines Flight 175 (L) flies toward the World Trade Center twin towers shortly before slamming into the south tower (L) as the north tower burns following an earlier attack by a hijacked airliner in New York City, Sept 11, 2001. [Photo/Agencies]