It's not exactly difficult, I mean I have one ARFF battalion Chief and I know the area that it's stationed in. If I see that a call is in the area I just deselect the ARFF and send the next chief over. This is a strategy game, not an "everything has to be perfect and easy" game.
I never said I wanted it easy. I no what area my airport chiefs are stationed at. But when your clicking on alarm calls via the app (when it's running slow) it makes the game harder to select and deselect the next OIC.
I saw this post and thought that sounds good, I hoped It was put in place so that the airport units were unique to the airport only and not have to worry about other alarms taking your dedicated airport units.
Upon reading more this thread was wrote before the ARFF extention was added to the game. So it now makes this thread a future idea of a dedicated airport fire service if it was ever brought up again to be added.