It looks to me like you're getting things from inheritance and containers mixed together. An Airport may contain an Arcade, but it would not implement collect_quarters() any more than a Directory class would implement the methods of a File class. If you want to do something with the arcade, you qould query the Airport with a get_arcade() or something, and then operate on the returned Arcade object.

Same deal with the Car interface: $car->get_wheel->throw_hubcap(). Inheritance doesn't enter it, and neither does sharing interfaces.