Casting
"One of the most important things we were looking for in casting was the actors' ability to play the subtleties – the little things that a character doesn't say or do that create the edge, the things that get under your skin and spook you", Morgan said about the auditions. Reddick originally envisioned Tobey Maguire and Kirsten Dunst for the lead roles of Alex Browning and Clear Rivers. Craig Perry envisioned Jessica Biel for the role of Clear.
Alex Browning, the last role cast, went to Canadian actor Devon Sawa, who previously starred in the 1999 film Idle Hands. Sawa said that when he read the script on a plane, he found himself peeking out the window at the engine every couple of minutes. Then he went down and met Morgan and Wong, and he thought "they were amazing and already had some great ideas". However, Morgan and Wong were undecided about casting him for the part, so they requested him to perform again as they reviewed his previous works. Morgan was astounded by Sawa's performance in Idle Hands, and Sawa was hired. Of the script, Sawa said, "There's not a lot of good stuff [...] for my age. You get a lot of scripts and all but they're teen ensembles and they're just crap. And then I got Flight 180 [...] it's just awesome."
Sawa described his role as "in the beginning, [Alex] was kinda loopy and cotter, and you know, probably not the most popular guy in school. I think he might have been a dork, you know, doing their stuff and they had their own thing going and they're after the two beautiful girls in school, but there's no chance of that happening. I guess after the plane goes down, his world completely changes". "Devon has an everyman quality that makes him accessible", Wong said. "He doesn't appear as if he's supremely self-assured. He's more of a regular kid who can take on the complexities of the role and become a hero". Perry was amazed by Sawa's vulnerability in acting, describing him as "a very distinctive actor. He's very loose and he's kind of a cut-up when he's not on camera, but the moment the camera's on, I'd never seen anybody to completely slide right through the moment."
Ali Larter, who starred in the 1999 film Varsity Blues, was cast as female lead Clear Rivers. "The film shows how easy it is to turn on someone, to blame someone when you're scared", Larter said. "It's also about trusting your intuitions and yourself". She defined her part as "that girl who has a lot of loss in her life and has fallen for herself and had made a life within that. She's an artist, she lives by herself, and she's kinda holding to her grip for what the world has given her".
Seann William Scott, famous for portraying Steve Stifler in the 1999 film American Pie, was hired as class clown Billy Hitchcock. Scott admired the film and felt that "it's [as] dark and eerie as any Twilight Zone". He laughed at his role, saying that "[he] is lacking some social skills, he doesn't have quite a few friends, and he's like the tag-along." Scott was surprised when in the script his character was written as fat. The writers eventually changed it for Scott.
Dawson's Creek star Kerr Smith was cast as jock Carter Horton. Smith identified Carter as "your typical high school bully whose life depends on anger" and mentioned the fact that Carter feared Alex not having control of his own life.
Kristen Cloke, Morgan's wife, was cast as teacher Valerie Lewton. "I have incredible respect for them", said Cloke. "Jim's the kind of director who knows exactly what he wants. As an actor, I can find a way to get there if I know specifically what I'm going for, and Jim gives me that. The fact that he won't move on until he's got exactly what he wants creates a safe environment, which allows me to experiment and try different things". Cloke described her part as "strong and sassy – in control. After the crash, she comes unglued, probably more than any of the kids, and it's a quick, drastic change. I had to understand the psychology of a person who can turn on a dime like that".
Newcomers Amanda Detmer and Chad Donella were cast as students Terry Chaney and Tod Waggner, respectively. "When I first read the script, the thing that struck me most was that the characters were well-written and the relationships between them were strong and believable", Detmer said. "That's important because you have to care about these people in order to be worried about what might happen to them". Detmer defined Terry as "very put-together [and] seems content to defer to [Carter] – to not make waves. But the stress of what happens affects their relationship and interestingly enough brings out a certain strength in her". On the other hand, Donella observed how similar his role was to himself. "I believe in fate. I think you come into this life with some things to accomplish and you're taken out earlier or later depending on the game plan".
Tony Todd, who played Candyman in the 1992 film Candyman, was cast as mortician William Bludworth. Morgan initially wanted Todd for the role because he felt his deep voice would give the film an eerie tone.
Additional cast members included Daniel Roebuck and Roger Guenveur Smith as FBI agents Weine and Schreck; Brendan Fehr, Christine Chatelain, and Lisa Marie Caruk as students George Waggner, Blake Dreyer, and Christa Marsh; Barbara Tyson and Robert Wisden as Barbara and Ken Browning, Alex's parents; and Forbes Angus as teacher Larry Murnau.
