Try this:
- Open the CouatlAddons.INI file in the %APPDATA%\Virtuali folder using Notepad or another pure text editor.
- Find the section named [GSX], there will be several lines with all GSX preferences
- add a new line with the following:
airport_visibility_KMRZ = 0
Setting the visibility to 0 will ignore the dummy airport.
If you want to have it working, for example in cases when you have two very close airports and you want to use them both, or if there's an airport "inside" another one, like a military base (with its own separate AFCAD and its own ICAO code) inside a civilian airport, you can set a range lower than default (which is 3 NM), like 0.5 NM or so, which will allow GSX to "switch" between the two airports.
Of course, this is valid for any airport, just use several lines with this format:
airport_visibility_XXXX = Y
Where XXXX is the ICAO of the airport you want to set visibility for, and Y is the visibility range in NM, or 0 to exclude it. Note that, "visibility" here only means "visibility by GSX", it doesn't have any effect to the actual visual scenery in the sim.
