United Airlines 93 departed New York-Newark for San Francisco at 08:01. The aircraft was hijacked by four terrorists.
The hijackers took over control, reportedly switched off the transponder and changed course to, probably, Washington. At 09:35, near Cleveland, the aircraft changed course to the South and later (09:45) Southwest at FL350. At 10:10 the aircraft crashed out of control in a field near Somerset, PA. The hijackers possibly had the intention to crash the plane into Air Force One, Camp David or perhaps Washington.
The aircraft probably crashed following passenger attempts to take down the hijackers.