The production was shot in 22 days and Mel Gibson himself expressed he was surprised when the final running time clocked in at merely 91 minutes, making this his shortest-directed film.
121.5 is a real frequency for emergencies. This is accurately portrayed in the movie.
According to Mel Gibson, Mark Wahlberg improvised much of his character's dialogue, explaining, "Mark's got a good dark side he takes stuff from. Every now and again he'd let it out and I can't even repeat some of the stuff he'd say, in fact we had to cut most of it out, it was like REALLY sick- but we hint at it."
It was Mark Wahlberg's idea to have the pilot be bald. The filmmakers acknowledged his appearance strongly mirrored that of the BTK killer Dennis Rader.