How many custom airplanes can I have in-game?

[Hasseo 1]

I currently have 2 custom airplanes installed. They both make random apperances in cities with airports and in region view, but how many more can I install before some of them just don't show up in-game?

[Xyloxadoria 1,098]

You can install as many as you want, but like the fist two they will appear randomly.   They should all still show up, just with each plane you add there is less of a cahnce of one in particular being displayled all the time. You shouldnt get to the point where it doesnt display at all unless you install a very large amount.