United Airlines Flight 93

United Airlines Flight 93 was a passenger flight which was hijacked by four al-Qaeda terrorists on September 11, 2001, as part of the September 11 attacks. It crashed into a field near Shanksville, Pennsylvania, during an attempt by some of the passengers to regain control, killing all 44 people aboard including the 4 hijackers. No one on the ground was injured. The aircraft involved, a Boeing 757–222, was flying United Airlines' daily scheduled morning domestic flight from Newark International Airport in Newark, New Jersey, to San Francisco International Airport in San Mateo County, California.

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 in the direction of Washington, D.C. The hijackers' specific target is believed to have been the United States Capitol.

After the hijackers took control of the plane, several passengers and flight attendants were able to make telephone calls and learn that attacks had already been made by other hijacked airlines on the World Trade Center in New York City and the Pentagon outside Washington, D.C. Some of the passengers then attempted to regain control of the aircraft. During the attempt, however, the plane crashed into a reclaimed strip mine in Stonycreek Township, near Shanksville in Somerset County, Pennsylvania, about 65 miles (105 km) southeast of Pittsburgh and 130 miles (210 km) northwest of Washington, D.C. A few witnessed the impact from the ground and news agencies began reporting the event within an hour.

Subsequent analysis of the flight recorders recovered from the crash site revealed how the actions taken by the passengers prevented the aircraft from reaching the hijackers' intended target. Of the four aircraft hijacked on September 11 – the others were American Airlines Flight 11, American Airlines Flight 77 and United Airlines Flight 175 – United Airlines Flight 93 was the only one that failed to reach its hijackers' intended target.

A temporary memorial has stood on the site since the attacks; the first phase of construction of the permanent Flight 93 National Memorial at the crash site was dedicated on September 10, 2011.