I don't think there's a limit, but don't quote me on that. I was qualified on the:
at the same time. I can't think of an airline that has more A/C types than this in the U.S. I used to have a roommate who flew for Lufthansa. He was only qualified on the 737 and 747. He said German law only allowed them to fly 2 different types of A/C.
"Reality has a well-known liberal bias." --Stephen Colbert