Paul Greengrass’ “United 93” is a viscerally lacerating, emotionally wrenching experience, a recreation of the horrific events of 9/11 that melds the starkness of documentary with the power of drama in an extraordinarily vivid way. The writer-director achieved a similar result with the brilliant “Bloody Sunday” back in 2002, but the impact here is even greater because of the enormity and immediacy of the event. It’s impossible not to be shaken by viewing this retelling of how the passengers on the fourth plane highjacked by terrorists that September day got word of the destruction of the World Trade Towers and mounted a counter-offensive, forcing the plane to crash in rural Pennsylvania before reaching its Washington target but losing their lives in the process.

Considered simply as a film, then, this is a masterful work. Greengrass has fashioned a taut, clear narrative from the historical record and plausible supposition, moving smoothly (with the expert assistance of editors Clare Douglas, Christopher Rouse and Richard Pearson) between the doomed aircraft, the air traffic control centers in Boston and New York and the Northeast Air Defense military command, and he’s coaxed compelling performances from a mix of actual participants (including Ben Sliney, the FAA’s national operations manager, recreating his first day on the job, and Maj. James Fox of the NEAD) and little-known actors, capturing the action in a flawlessly naturalistic style through the largely hand-held camerawork of Barry Ackroyd. The film walks a tightrope one might have though impossible: on the one hand, it’s not simple-mindedly panegyrical, but on the other it avoids being in the least sensationalistic or exploitative.

What the picture portrays most powerfully is the incredible confusion that swelled up everywhere as the events transpired: the sense of absolute disbelief that filled the FAA headquarters and air traffic centers as the realization of what was actually happening slowly dawned, capped by the stunned reaction among the New York controllers as a plane hurtled into the yet-untouched second tower, a sight presented here in a way that will elicit the same appalled shock in the audience; the sense of desperation at NEAD, as military men at their consoles tried ineffectually to scramble warplanes and secure authorization to engage from unreachable politicians; the terror aboard Flight 93 itself as the four highjackers threatened the passengers, slaughtered much of the crew and tried to reach their Washington target despite the fact that they had initiated their assault somewhat later than their compatriots aboard the other planes and the passengers were thus able, using in-flight phones, to learn what had already happened and decide to try to retake the airliner.

It’s in this third area, so to speak, that Greengrass is forced to use his imagination most liberally, but his construction of what might have happened is both riveting–the camera moves here are amazing in their almost surreal combination of precision and murkiness–and brutally honest. The passengers aren’t presented as plastic heroes, but as ordinary people acting from desperation more than a feeling of destiny (the famous “Let’s roll!” is here repeated not as some decisive call to arms but a simple statement, almost an afterthought), and amazingly enough, the highjackers are delineated with sensitivity, too–not just as crazed madmen, but as individuals dedicated to a cause, however misguided and atrocious. And though the treatment doesn’t mitigate the violence of what happened on the plane, it doesn’t wallow in it, either; this is a respectful as well as a astonishingly realistic account.

Of course, since the in-flight portion of “United 93” is necessarily the one most dependent on elaboration of the record rather than fidelity to known fact, it will be here that one can challenge Greengrass’ decisions. One may wonder, for instance, why he chose to have a passenger with a foreign accent (Dutch?) be the one counseling compliance with the terrorists’ demands against suggestions of mounting an attack against them. But such points are the merest quibbles when considered in light of the integrity with which the writer-director has dealt with this horrendous event and the staggering immediacy of his accomplishment.

There is, of course, an extra-cinematic issue that’s been raised about “United 93.” Is it, as some have argued, “too soon” for this event to be treated on screen? And will reliving the national nightmare in this fashion act less as catharsis than as incentive to hatred? These are serious issues, and commentators will no doubt pontificate on them endlessly on 24-hour cable “news” networks. (My answers, for what they’re worth–which isn’t much–is that no, it isn’t too soon, or at least that each person can make that decision for him or herself; and that if it causes some viewers to react in vituperation rather than feel the “pity and fear” that Aristotle spoke of as the purpose of drama, the fault lies not in the film but the viewer. It’s also important to note that the film raises, in a way mere words will never do, the question of whether our institutions of government and transport were negligent in their preparations prior to 9/11, and whether things have been significantly improved since then.)

But a film critic will never be able to address these matters authoritatively. What he can do is to praise “United 93” for its incredible dramatic power, happily coupled with a real sense of fidelity to the historical record and, in particular, to the passengers who died on that flight. Like “Bloody Sunday” before it, this is a great film, and an important one as well.