Flight 93 Memorial ceremony marks 20 years after September 11 attacks. On September 11, 2001, 33 passengers, five flight attendants and two pilots aboard United Airlines Flight 93 were killed after four members of the Islamic extremist group al Qaeda crashed the plane in a field in Shanksville, Pennsylvania. While the plane’s target is still not definitively known, it is believed that the terrorists were potentially targeting the White House or the U.S. Capitol. The passengers and crew had already begun their counterattack, bravely working their way toward the cockpit and worrying the hijackers who then plowed the aircraft into the ground at 563 miles per hour.