United Airlines Flight 93 was a domestic scheduled passenger flight that was hijacked by four al-Qaeda terrorists on the morning of September 11, 2001, as part of the September 11 attacks. The hijackers planned to crash the plane into a federal government building in the national capital of Washington, D.C. The mission became a partial failure when the passengers fought back, forcing the terrorists to crash the plane in Somerset County, Pennsylvania, preventing them from reaching al-Qaeda's intended target, but killing everyone aboard the flight. The airliner involved, a Boeing 757-222 with 44 passengers and crew, was flying United Airlines' daily scheduled morning flight from Newark International Airport in New Jersey to San Francisco International Airport in California, making it the only plane hijacked that day not to be a Los Angeles–bound flight.

The Hamburg cell was, according to U.S. and German intelligence agencies, a group of radical Islamists based in Hamburg, Germany, that included students from different Arab countries who eventually came to be key operatives in the 9/11 attacks. Important members included Mohamed Atta, who led the four hijacking teams in 2001 and piloted American Airlines Flight 11; Ramzi bin al-Shibh, who conspired with the other three members but was unable to enter the United States; Marwan al-Shehhi, who piloted United Airlines Flight 175; and Ziad Jarrah, who piloted United Airlines Flight 93 and failed to hit a target in Washington, D.C.. Other members included Said Bahaji, Zakariya Essabar, Mounir el-Motassadeq, and Abdelghani Mzoudi.