@GtE:
They seem to be in Germany, too, at least I hear of D-Mxxx flying into the less big airports like Leipzig, Kassel, Hannover, ...
Mind you, there seems to be an exception even in tiny crowded Belgium: there are directions in the AIP for flying a microlight into EBOS Oostende, though I never heard of anybody actually doing so.
surely Captain Haddock is Scottish?
I don't think so. In the original (Francophone) texts he is, like Tintin, a Brussels French-speaker, and a famous forefather of his was a captain in the French Royal Navy, by the name of "Haddoque".