On the morning of September 11, 2001, passengers board United Airlines Flight 93 bound for San Francisco at Newark Liberty International Airport. Among them are Tom Burnett, Mark Bingham, Todd Beamer, Jeremy Glick, Richard Guadagno, Louis J. Nacke II, William Joseph Cashman, and Patrick Joseph Driscoll. Four al-Qaeda terrorists (Ziad Jarrah, Saeed al-Ghamdi, Ahmed al-Nami, and Ahmed al-Haznawi) also board the flight.
Meanwhile, newly-appointed FAA National Operations Manager Ben Sliney is in a meeting when it is reported that American Airlines Flight 11 from Boston to Los Angeles has been hijacked after Mohamed Atta is overheard on the radio saying “We have some planes”. Soon thereafter it crashes into the World Trade Center’s North Tower. To Sliney and his staff’s horror, they learn that a second flight, United Airlines Flight 175 also from Boston to Los Angeles, has been hijacked, and after New York’s air traffic controllers attempt to contact the aircraft, it is seen on live TV plowing into the World Trade Center’s South Tower. Sliney and his staff realize they are dealing with several hijackings and order the military to be on the lookout for American Airlines Flight 77, which is reported missing and presumed to have also been hijacked.
On United 93, a hesitant Jarrah appears to have second thoughts of commencing the hijacking. Impatient, the other three hijackers prepare to attack. Al-Haznawi assembles a fake bomb out of clay and plastic during breakfast, then al-Ghamdi makes the first move and grabs flight purser Debbie Welsh and holds her at knifepoint. Passenger Mark Rothenberg is mortally wounded and the “bomb” is revealed, panicking the passengers; al-Nami and al-Haznawi force the first-class passengers to the back of the plane. Meanwhile, Jarrah and al-Ghamdi threaten Welsh and wrestle their way into the cockpit. The pilots send out a mayday call but are killed and dragged from the cockpit. Welsh is also killed. Jarrah takes the plane’s controls and changes its course, intending to crash the plane into the US Capitol.
Sliney, still debating on what to do about the unfolding situation, is shocked when American 77 crashes into the Pentagon, and he orders the closure of US airspace and the grounding of all commercial flights until further notice.
Aboard United 93, the passengers become aware of the dead bodies of the crew-members, and learn from family members via airphone of the attacks on the World Trade Center and the Pentagon; they decide to take action, organizing a revolt against the hijackers. They are encouraged by knowing that passenger Don Greene is a pilot himself and passenger Andrew Garcia is a former air traffic controller.
After passengers arm themselves, pray, and make final phone calls to loved ones, Todd Beamer says “Let’s roll!” The group begin their counterattack, rushing down the aisle and overpowering Ahmed al-Haznawi; Mark Bingham beats al-Haznawi to death with a fire extinguisher. With al-Haznawi’s “bomb” being revealed by Louis Nacke as fake, the rebellion is emboldened, and the group heads for the cockpit. Seeing this, al-Nami alerts Jarrah and al-Ghamdi in the cockpit of the ongoing assault. Jarrah shakes the plane violently to throw the passengers off balance, while al-Nami attempts to foil them with a food cart and a fire extinguisher from the galley, but al-Nami is also overpowered and killed by Jeremy Glick. Seeing the passengers succeeding, al-Ghamdi and Jarrah debate whether to crash the plane, realizing that their plan to reach their intended target will not succeed. The passengers then breach the cockpit door with the food cart, and al-Ghamdi orders Jarrah to crash the plane. The passengers enter the cockpit and attack the two hijackers over the controls. As the passengers and hijackers struggle for control of the yoke, the plane violently turns upside down and nosedives toward the ground, crashing into an empty field near Shanksville, Pennsylvania, killing everyone on board but preventing the terrorists from reaching their intended target.