@WingCommander:
i only use blender for shadowmaps (and work on windoze) but as far as i know the .ac import/export script is only in Blender 2.48/2.49.
i tried blender 2.61 too, but apparently you need an external script. i tried the script from here:
https://github.com/majic79/Blender-AC3Di could not get it to work though but that might be due to some error on my part (or 2.61 is too new for it).
propably the flight gear forum might be a good point for information because they also use the ac format.