It was always going to be one of the most difficult films to make - and to watch - of all time. But in United 93, which opens in the UK this weekend, the critics are unanimous that Paul Greengrass has achieved a triumph in his depiction of what happened on board the plane hijacked on 11 September 2001, which crashed in a field near Pennsylvania killing everyone on board.
Before it was completed, there were strong objections to the movie being made at all. Particularly in the United States, it was felt that the images would be too raw for the victims' families and friends.
A trailer for the film in a Los Angeles cinema was greeted with cries of "too soon" and it was pulled by one New York theatre.
But despite these doubts, the film was eventually well received in the United States, where 400,000 Americans saw it in its opening weekend in April. At its premiere in New York, some members of the audience were moved to tears.
Elsa Strong, the sister of one of the victims, said, "the intent of the movie was ... completely honourable.'' Now, in the UK, film critics have also given United 93 their seal of approval. What Greengrass achieves, according to the reviewers, is to convey the unsuspecting nature of people going about their everyday business, unaware of the terrible fate that awaits them.
In the opening scene, a voice utters Islamic prayers in a darkened motel room. The action then cuts to Newark airport, where flight preparations are under way. Using a cast of actors and real pilots, air controllers and crew, the film switches between control centres in New York, Boston and Virginia. Even the operation head of the Federal Aviation Administration, Ben Sliney, who was on his first day in the job, plays himself.
Critics have also applauded the decision not to use famous faces, which could have detracted from the story. Handheld cameras are used to convey the final moments in the lives of those who died. Like 24, the hit fictional drama series based on terrorism, Greengrass sets the action in real time.
Passengers on the flight discovered from mobile phone calls that planes had crashed into the World Trade Centre, spurring them on to take counter-action against the hijackers.
The Independent's film critic Anthony Quinn saw the film's rendering of the heroism of the young men who tried to regain control of the cockpit as "low-key" - "Even the famous 'let's roll' line is un-emphasised. Not a war cry, just a quietly determined exhortation."
Greengrass is no stranger to difficult topics. In 2002, he dramatised the Irish civil-rights massacre in Bloody Sunday, and he made Omagh, about the 1998 bombing, for Channel 4.
What the reviews said
"Paul Greengrass pushes cinema as close to an ordeal as it can get. This movie forces us to contemplate the unbearable: the last minutes and seconds of passengers who knew they were about to die." - Anthony Quinn, The Independent
"This account of the only hijacked plane on 9/11 that failed to reach its target is a genuinely engrossing achievement. We should applaud the fact that Working Title, the British production company, and Paul Greengrass, a British director, [refused] to sink into the well of easy patriotism, or uneasy sentimentality." - Derek Malcolm, Evening Standard
"A remarkable cinematic achievement that navigates all the potential pitfalls of such an enterprise. It is gripping without being sensational, moving without pulling the heartstrings and a powerful rallying cry for common values without taking sides." - Henry Fitzherbert, Sunday Express
"Since every detail is freighted with the knowledge of what comes later, even the blandest of scenes becomes one of seat-gripping tension ... almost too unbearable to watch." - Jim White, The Daily TelegraphReuse content