Airport creation program

I've been using Gmax to create a scenery, but now I want to create an airport to go with this scenery. I tried using AFCAD, but it didn't seem to work very well for me. I got two runways to show up, but then when I tried to land on them, I went straight through. So I was wondering what I should do. Should I stick it out with AFCAD and see if I can get it to work, or should I get something else and try that.
Any other program MUST be freeware and compatible with FS2002.
Any other program MUST be freeware and compatible with FS2002.