Once the hijackers have taken control of the plane and the passengers have been sent into desperate panic, a handful of American passengers begin planning how they'll rush the cockpit, take control and install the only half-qualified pilot on board to take control. On that score, no problem: transcripts of conversations conducted via the in-flight phones leave no doubt that that's pretty much what happened.
Eventually, however, a European-accented passenger pointedly makes the case for negotiation - and then, come the storming of the flight deck, attempts to place himself in the way.
Given the patriotic legend of flight 93 ("Let's roll," said one passenger, unwittingly launching a tub-thumping Neil Young record, several thousand T-shirts and a catchphrase that crystallised a very American derring-do), this little subplot packs a very hard punch: when the film plays in the US, there will surely be all kinds of cries about old European surrender monkeys, the US's contrasting backbone etc.
So, from where did this episode come? As it turns out, nowhere. We know there was a German passenger - one Christian Adams, aged 37 - on board, but that's it. His role in the movie is the product of something several light years away from artistic license, as is proved by the exchange between Greengrass and Kirsty Wark on Thursday's Newsnight:
KW: There was one passenger [in the film] that actively tried to stop the others going forward. That was the German passenger.
PG: Erich, the actor who played him, who was German ... One of the interesting things he talked about was Mogadishu [eventual destination of a hijacked Lufthansa flight in 1977], saying that a German passenger of his age would well remember that [and] it would have given him a very clear view that the correct thing to do - and bear in mind that was operating in a pre 9/11 context - was to get the plane down.
KW: It might be difficult for the German passenger's family, in a sense, to think that he was the one saying: "Hold back, do nothing." You don't know that.
PG: We don't know, no, but you have to set the parameters of the film as they actually are and explore it, and in the end, audiences have to make their own minds up about whether that's a credible, believable portrait.
By definition, it's not credible; it's not believable either: given passenger Adams's actual age, he would have been eight years old at the time of the Mogadishu hijack. But who cares about that? Thousands of Americans will make their judgments at a stroke. That's how the continental divide works right now. So thanks, Mr Greengrass.
And a parting thought: if such a potent moment is actually founded on thin air, can we be forgiven for wondering about the whole film?
