[Klemm]

The aircraft installer contains the new Flight models for the new planes, so if you installed a new plane but have an old aircraft installer, the game will crash at 60% loading because that's the time it reads the buttons file. If that file doesn't contain the flight model for a plane that is now in game, loading will be aborted and the game will exit to desktop.
So in essence it is best if you install the newest AC-installer whenever you install a new plane. Unused entries in the buttons file don't seem to be a problem, so you don't have to install all new planes that come out.