Hmm, the POD in your module has more of the same.. I see what you're getting at, kind of. Usually if I have to implement such a thing as in your examples, I wouldnt dream of saying that Airport inherits from Arcade just to make the methods of Arcade available in Airport.. I can't see why anyone would.
I'd create an Arcade object in Airport, and provide something like a 'getArcade()' method in Airport, for anything that needed to communicate with Arcade through Airport.

Regardless.. Interfaces are good for other reasons, as some people here have already indicated..

C.