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, the new film by British director , is docu-drama at its brilliant best.

Since I was to record interviews with Ben Sliney, the former FAA director who plays himself in the film, and some of the relatives of passengers who lost their lives on United Airlines flight 93, the distributors kindly arranged for me to see the film on Tuesday morning, ahead of the the press launch. So I found myself in an empty cinema near Broadcasting House, for a private viewing.

As the film began, the rows of cinema seating ahead of me conspired to look like seatbacks on a commercial aircraft, and the rectangular-shaped cinema began to look like the inside of an airplane. That wasn't just because I was alone in a darkened cinema; it was because Greengrass's film draws the audience so compellingly into the experience of the passengers on that hijacked .

There are no politicians in the film; no mention of al Qaida or the war on terror. Instead, Greengrass invites us to live through the events of September 11, 2001, in real time, before terms like 'al Qaida' became household names, and, for the most part, with a director's eye view of three groups of people in three locations: the passengers on United 93, the FAA officials at the air traffic control centre at Herndon; and military ground commanders at NORAD's Northeast Air Defense Sector (NEADS).

We watch as the FAA operations director Ben Sliney, on his first day in a new job, takes the decision to shut down the skies over America -- a decision which, with hindsight, seems so obviously the right thing to do, but which was absolutely unprecedented in the history of American aviation and defence. Then, in quietly harrowing scenes, we watch passengers on the hijacked plane making calls to friends, family and loved ones, using their cell phones and airphones. As they learn about the attack that morning on the World Trade Centre, the passengers analyse the information they receive and formulate a plan of action: they realise this is no ordinary hijacking, but an attempt to turn the plane into a missile, and they resolve to fight back.

The decisiveness and level-headedness of the FFA managers and the passengers contrasts starkly with the muddle of misinformation and mismanagement that overtakes the military commanders at NEADS and elsewhere. A confusion about the rules of engagement; planes flying in the wrong direction; F16s dispatched without weapons; serious communication breaks in the chain of command -- it's little wonder that the military only realised the United 93 flight had actually been hijacked four minutes after it crashed in Pennsylvania.

In one scene, we see Ben Sliney being told that President Bush had taken off on Air Force One to destinations unknown. I read this as an attempt by Greengrass to implicate the president, as Commander-in-Chief, in the muddle and mess of the military response that day.

You can hear my interview with Ben Sliney on this week's Sunday Sequence. I also talk to Alice Hoglan and Kenny Nacke. Alice's son, , became an icon of heroism across America following the crash, and Kenny's brother , a toy company executive with a weightlifter's physique, is shown in the film holding aloft a bomb wrestled from one of the terrorists and yelling that it is a fake.

One of the questions I want to explore on Sunday is whether the scenario played out in United 93 constitutes a challenge to an ethic of non-violence. What would a pacifist on United 93 have done in those morally fraught circumstances? And how does our proposed response to that concrete scenario inform our approach to terrorism more generally?