Producers of the movie were concerned that actual terrorists could use the information in the film to disrupt airport/airplane communications in real life. Most of the "sensitive" information in the film is not only wrong, it is purposely misleading to prevent terrorists from attempting what we see in the movie.
The film is based on a book called "58 Minutes" by Walter Wager. In the book, it is the hero's young daughter, not his wife, that is on one of the planes.
When the older lady is showing off her tazer in the beginning of the film she is holding a magazine. On the back of the magazine is an advertisement for Lethal Weapon. Joel Silver, who produced Lethal Weapon, also produced this film.
In March 1993, the Boeing 747-100 cargo aeroplane featured in this film (registration N473EV) was involved in an incident at Anchorage International Airport, Alaska, USA. Shortly after take-off the plane experienced troubles due to severe weather and the number two engine separated from the plane. Strangely enough, the number two engine is what "ingested" Major Grant after the encounter with McClane on the wing. The plane managed to land safely after this incident with no injuries.
The majority of the airport shots in this film were not filmed at Dulles, it is Stapleton Airport in Denver hence the trees scenes.