Please keep in mind that this is purely idea, I'll check if it is possible soon, but for now I'm just brainstorming ideas

The reason why metro doesn't work in this mod is because the game requires a SUBTYPE_METRO for the rail connection to be registered as a metro connection. But if I add SUBTYPE_METRO, then the game will ignore SUBTYPE_AIRPLANE (or the metro subtype depends on whether metro is above airplane or not), which will disallow you to build the airplane parking space INSIDE the building's bounding box.

So the solutions here, I'm guessing, are:

1. Push the area where you can build the airplane parking space to be outside of the current bounding box.

2. Remove the part sticking out of the airport's main building, effectively shrink the airport's bounding box, so that the current airplane parking space will be outside of the new bounding box.

3. Add the parking spots into the building itself, so the players don't have to build them. Ofc the downside is that you cannot customize it.

Number 1 and 2 relies on the fact that the airplane parking space does not extend the building's bounding box. Currently I don't think that's the case, but I'll need some testing for that.

Regardless, it would be great if you guys can tell me which one you want, as well as any other suggestions that you might have. I would be extremely grateful.