Filmed with the same documentary look that made his Bloody Sunday so effective, Greengrass tells the story in something close to real time. He shows how routine the flight probably was for the people who boarded that plane. They take their seats, order their food and exchange pleasantries with flight attendants and fellow passengers. They are strangers going about their routines, oblivious to four passengers looking a little anxious and uncomfortable as they take off.
Greengrass shows the hijackers as religiously devout men, definitely nervous about their mission, but determined to see it through. A flight delay due to traffic on the ground resulted in United 93 getting airborne late, which may have been the saving grace for the U.S. Capitol Building (a possible intended target for the hijackers). Those few minutes allowed United 93 passengers some time to discover, via phone calls, the atrocities going on at the World Trade Center that day.
The film does a powerful job of showing just how fast the passengers had to think and act to combat the hijackers. The actual confrontation lasts just a few minutes as passengers ram a drink cart into the cockpit door, determined to get a fellow passenger behind the controls (one of them had single-engine flight experience). The realism in the sequence makes it harrowing and suspenseful, even when the outcome is already known.
United 93 isn't a sensationalistic portrayal of events. Passengers don't talk about saving U.S. landmarks or striking a blow against terrorists. With the exception of some sketchy info from phone calls, they know very little about what they are up against. They are determined to survive at any cost, and Greengrass makes the final moments of the film very violent.
In his view, the passengers had no mercy against the hijackers, breaking their necks and tearing them apart. This, of course, is part speculation, but cockpit recordings make it fairly clear that passengers got past at least two hijackers before their assault on the cockpit.
As for the events on the ground, Greengrass shows the chaos brought on by an event for which nobody was prepared. Air-traffic controller Ben Sliney (playing himself) re-enacts his own horror and disbelief with the chain of events as the gravity of the situation becomes clear. Airport employees, with a full view of the Manhattan skyline, watch in horror as the second airliner slams into the World Trade Center. Military strategists are unable to get clearance to engage suspected hijacked airliners or even scramble fighters into the air.
The film points no fingers and puts no blame on political figures or government for the events of Sept. 11. It can't do that, because events are depicted strictly in the moment, when nobody knew why planes were disappearing, one after another, off radar screens. There's a brief mention of the president and his trip to Florida, but no revelation that he was sitting in a classroom with children while the military was seeking instructions on how to handle the situation. That knowledge comes from our personal memories, and Greengrass sees no need to include it in his film.
United 93 is a great movie ... a great movie I wish I never had to see. Its existence is yet another reminder that there are strange and terrible things in this world. This is not a movie to be enjoyed over a bag of popcorn and bucket of soda. It's one of the more painful movie experiences in the history of cinema, and it should be.