Back in the 70's, when studios need an a/c for an air disaster films, a lot time they would charter jets from World Airways. A WO 707 was use in Skyjack and Magnum Force and a WO 727 was used in Mayday at 40000 feet.
Now, when Universal Studios decided to film Airport 75 and 77, they charter the 747s for the films from American Airlines. Now why would they charter 747s from AA, which could have cost more, instead of chartering 747s from WO?
PS: Do not get me wrong, I love AA 747s, but I thought it would a interesting question.