[Redwulf__32]

What map are you trying to mod? If the map in question has a large actors.static file (approx. > 750k) then the mapbuilder FMB will give up. Only solution is to make a temporary, smaller actors.static (see actors.static tool) that includes your airfield, mod it, save it and merge the items back into the original actors.static. It's a bit hairy but a bit of research will help you.

Hope this helps .....