I am aware that GSX will supposedly only read complete afcads of airports but according to my tests, this isn't true.
I can only confirm that GSX will read any correct and complete AFCAD and, of course, it does it in priority order, so the highest layered ones for the same ICAO will be read by preference.
If your AFCAD is not read, it can only due to one the following:
- The AFCAD is not complete, so it doesn't contain at least one parking and a taxiway connected to it.
- The AFCAD has a lower priority compared to another one for the same ICAO
- The AFCAD is bigger than the default threshold size, which is used to speed up the search for airports, as discussed here:
http://www.fsdreamteam.com/forum/index.php/topic,13489.msg100092.html#msg100092There might be other minor mistakes triggering an AFCAD rejection, but if you enable Logging in the Troubleshooting sections of the GSX - Settings, the log created will tell you why an AFCAD has been rejected by GSX.