United Airlines Flight 93 was United Airlines' scheduled
morning transcontinental flight across the United States
from Newark International Airport in Newark, New Jersey, to
San Francisco International Airport in California. On
Tuesday, September 11, 2001, the Boeing 757–222 aircraft
operating the route was hijacked by four al-Qaeda terrorists
as part of the September 11 attacks. It subsequently crashed
into a field in Stonycreek Township, Pennsylvania near
Shanksville during an attempt by some of the passengers to
regain control.
The hijackers breached the aircraft's cockpit and
overpowered the flight crew approximately 46 minutes after
takeoff. Ziad Jarrah, a trained pilot, then took control of
the aircraft and diverted it back toward the east coast of
the United States. Although the evidence remains
inconclusive, it is widely presumed the intended target was
the United States Capitol in Washington, D.C. An alternative
suggestion has been the White House, possibly in hopes of
killing then-president George W. Bush. That morning,
however, the president was visiting an elementary school in
Florida.
source:
http://en.wikipedia.org/wiki/United_Airlines_Flight_93