Over and over in the weeks leading up to the release of Paul Greengrass' film I heard morning-show hosts, pundits, interviewers, columnists and critics ask the same question: "Is America ready to see a movie that recreates the harrowing tragedy faced by the passengers and crew of the fourth plane hijacked by terrorists on the morning of September 11th?"

That's the wrong question. A more pertinent one, I think, would be: "Is there any reason to buy a ticket to Greengrass' film if you've seen Flight 93, a made-for-cable movie depicting the same events and already watched by millions of Americans on A&E since January?" Or, for that matter, The Flight That Fought Back, a Discovery Channel production that aired in September 2005? The answer: There most definitely is. As TV movies go, Flight 93 and The Flight That Fought Back are strong stuff. They are fairly traditional in their approaches, however. A select number of individual passengers are brought into sharp focus. We get to know them as the full horror of their situation becomes clear to them. We listen in on calls they make on cellphones to loved ones. We spend time on the ground with some of the people on the other end of those lines experiencing their disbelief, shock and agonizing sense of helplessness.

United 93 takes an altogether different approach, one informed by the years Greengrass spent as one of England's top documentary filmmakers (he directed Bloody Sunday, about a day in 1972 when British troops opened fire on unarmed civil-rights demonstrators in Northern Ireland). Before making the movie, the director and his team conducted more than 100 interviews with families and friends of the flight's 40 passengers and crew, in addition to civilian and military personnel who played a role on that fateful day. He studied The 9/11 Commission Report, transcripts of calls made from the plane and the cockpit recordings. The result is an exercise in cinema verité unlike anything you've seen on screen before.

The film's documentary feel only intensifies the knot of dread that builds in your stomach from its opening scenes, in which the four hijackers prepare themselves in nondescript hotel rooms. The day begins unremarkably. Pilots make small talk as they run through their preflight checks. Flight attendants catch up with one another and share stories about their families. Passengers gather in the waiting area reading papers, making calls, and sitting next to the men who would kill them. Once they board the plane, takeoff is delayed and they all wait some more. "Just a normal day at Newark International Airport," one flight attendant jokes.

Of course, we know what the people on board United Flight 93 didn't know yet: that this will be unlike any other day. That knowledge gives special meaning to the smallest acts we observe, as well as the most significant. Without a hint of Hollywood sentimentality, the filmmaker allows us to take in the poignancy of people talking about plans for vacations, business trips and journeys home that will never be. Once in the air, their story unfolds in real time; we marvel at what some of them were able to do with the last 81 minutes of their lives.

One of Greengrass' masterstrokes is casting unknown performers along with nonactors, many of whom recreate the roles they played in real life on September 11. Among the latter is FAA head Ben Sliney, who started his morning with a routine air-traffic briefing and then watched his screen in disbelief as one plane after another veered off course and ultimately slammed into buildings. His awe in the face of the catastrophe's scope was equaled only by his shock at the system's inability to respond to it. On the ground, things were a mess. Chaos, miscommunication and indecision prevented any meaningful coordination between flight controllers, the FAA and the military.

Remarkably, clearer heads prevailed in the air. Under the most paralyzing circumstances imaginable, a handful of men and women pieced together a picture of what had already happened in New York City and Washington, D.C., deduced that their hijackers were on a suicide mission, too, and somehow found the courage to formulate a plan to retake control of the aircraft. No one will ever know exactly what happened after that cockpit door was smashed open. I doubt, though, that anyone will ever provide as likely a scenario as the one Greengrass has pieced together here. This film will leave you drained. It will leave you with an entirely new level of admiration for the passengers who fought back on that flight.

Is America ready for a movie about September 11? The question should be: Is America any more ready for an attack than it was on that day? That's a question United 93 will leave you pondering long after its credits have rolled.