The disaster film parody trilogy!
I would say that "The Big Bus" is the first film of a trilogy that ends with "Airplane!" and "Airplane 2"! Even if this one wasn't directed by the Zucker-brothers, it's very similar in the style and I wouldn't depart it from the Airplanes. If you watch these 3 movies in a row, you will see what I mean!
It's a pity, that Scary Movie didn't stay a trilogy! But "The Naked Gun" trilogy is the best example of how far a parody franchise is possible to go - they stopped at the right time! The creators of "Date Movie" and "Epic Movie" shouldn't have even started!