The scene: Tehran’s Mehrabad airport, January 1980. Six U.S. diplomats, disguised as a sci-fi film crew, are about to fly to freedom with their CIA escorts. But suddenly there’s a moment of panic in what had been a smooth trip through the airport.

The plane has mechanical difficulties and will be delayed. Will the Americans be discovered, arrested, even killed? CIA officer Tony Mendez, also in disguise, tries to calm them. Luckily, the flight leaves about an hour later.

If you saw the film "Argo," no, you didn’t miss this development, which is recounted in Mendez’s book about the real-life operation. It wasn’t there because director Ben Affleck and screenwriter Chris Terrio replaced it with an even more dramatic scenario, involving canceled flight reservations, suspicious Iranian officials who call the Hollywood office of the fake film crew (a call answered just in time), and finally a heart-pounding chase on the tarmac just as the plane’s wheels lift off, seconds from catastrophe.

Crackling filmmaking — except that it never happened. Affleck and Terrio, whose film is an Oscar front-runner, never claimed their film was a documentary, of course. But still, they’ve caught some flak for the liberties they took in the name of entertainment.

And they aren’t alone: Two other high-profile best-picture nominees this year, Kathryn Bigelow’s "Zero Dark Thirty" and Steven Spielberg’s "Lincoln," have also been criticized for different sorts of factual problems.

Filmmakers have been making movies based on real events forever, and similar charges have been made. But because these three major films are in contention, the issue has come to the forefront of this year’s Oscar race, and with it a thorny cultural question: Does the audience deserve the truth, the whole truth and nothing but? Surely not, but just how much fiction is OK?

The latest episode involved "Lincoln," and the revelation that Spielberg and his screenwriter, the Pulitzer-winning playwright Tony Kushner, took liberties depicting the 1865 vote on the 13th Amendment, which outlawed slavery. In response to a complaint by a Connecticut congressman, Kushner acknowledged he’d changed the details for dramatic effect, having two Connecticut congressmen vote against the amendment when, in fact, all four voted for it. (The names of those congressmen were changed, to avoid changing the vote of specific individuals.)

In a statement, Kushner said he had "adhered to time-honored and completely legitimate standards for the creation of historical drama, which is what ‘Lincoln’ is. I hope nobody is shocked to learn that I also made up dialogue and imagined encounters and invented characters."

His answer wasn’t satisfying to everyone. columnist Maureen Dowd called on Spielberg this weekend to adjust the DVD version before it’s released — lest the film leave "students everywhere thinking the Nutmeg State is nutty."

One prominent screenwriting professor finds the "Lincoln" episode "a little troubling" — but only a little.

"Maybe changing the vote went too far," says Richard Walter, chairman of screenwriting at the University of California, Los Angeles. "Maybe there was another way to do it. But really, it’s not terribly important. People accept that liberties will be taken. A movie is a movie. People going for a history lesson are going to the wrong place."

Walter says he always tells his students: "Go for the feelings. Because the only thing that’s truly real in the movies are the feelings that people feel when they watch."

Carson Reeves, who runs a screenwriting website called Scriptshadow, says writers basing scripts on real events face a constant problem: No subject or individual’s life is compelling and dramatic enough by itself, he says, that it neatly fits into a script with three acts, subplots, plot twists and a powerful villain.

"You just have to get rid of things that maybe would have made the story more truthful," says Reeves, who actually gave the "Lincoln" script a negative review because he thought it was too heavy on conversation and lacked action. He adds, though, that when the subject is as famous as Lincoln, one has a responsibility to be more faithful to the facts.

Screenwriter and actor Dan Futterman, nominated for an Oscar in 2006 for the "Capote" screenplay, has empathy for any writer trying to pen an effective script based on real events, as he did.

"This is fraught territory," he says. "You’re always going to have to change something, and you’re always going to get in some sort of trouble, with somebody."

Futterman recalls seeing "Lincoln" and wondering briefly why Connecticut would have voted the way the movie depicted it. On the other hand, he says, he has so much admiration for Kushner’s achievement in writing an exciting movie about 19th-century legislative history that he’s inclined to overlook the alteration.

Futterman also doesn’t begrudge the "Argo" filmmakers, because he feels they use a directorial style that implies some fun is being had with the story. "All the inside joking about Hollywood — tonally, you get a sense that something is being played with," he says.

He recalls his own object lesson in the difficulty of writing about real people and events: In "Capote," he combined three of Truman Capote’s editors into one, for the sake of the narrative. He ended up hearing from the son of New Yorker editor William Shawn, actor Wallace Shawn, who wasn’t totally pleased with the portrayal of his father. Futterman says he was sympathetic to those concerns and would certainly have addressed them in the script, had he anticipated them.

Of the three Oscar-nominated films in question, "Zero Dark Thirty" has inspired the most fervent debate. The most intense criticism, despite acclaim for the filmmaking craft involved, has been about its depictions of interrogations, with some, including a group of senators, saying the film misleads viewers for suggesting that torture provided information that helped the CIA find Osama bin Laden.

There also have been questions about the accuracy of the depiction of the main character, a CIA officer played by Jessica Chastain; the real person — or even combination of people, according to some theories — that she plays remains anonymous.

Mark Boal, the movie’s screenwriter, said in a recent interview that screenwriters have a double responsibility: to the material and to the audience.

"There’s a responsibility, I believe, to the audience, because they’re paying money, and to tell a good story," he said. "And there’s a responsibility to be respectful of the material."

In a later interview with the Wall Street Journal, he added: "I think it’s my right, by the way, if I firmly believe that bin Laden was killed by aliens, to depict that. … In this country, isn’t that legit?"

The debate over "Argo" has been much less intense, though there has been some grumbling from former officials in Britain and New Zealand that their countries were portrayed incorrectly in the film as offering no help at all to the six Americans, whereas actually, as CIA veteran Mendez writes, they did provide some help.

And as for the Canadians, the Toronto Star detailed late last year how Affleck (who also stars as Mendez) agreed to adjust the postscript to his film to more generously credit Canada and its ambassador at the time, Ken Taylor, who protected the Americans at great personal risk.

To Walter, the screenwriting professor, keeping track of all the historical details is a losing battle.

"When I am hungry and crave a tuna fish sandwich, I don’t go to a hardware store," he says. "When I seek a history lesson, I do not go to a movie theater. I loved ‘Argo’ even though I know there was no last-minute turn-around via a phone call from President Carter, nor were there Iranian police cars chasing the plane down the tarmac as it took off. So what? These conceits simply make the movie more exciting."

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Associated Press writers Jake Coyle in New York and Josh Hoffner in Phoenix, and investigative researcher Randy Herschaft in New York, contributed to this report.