I recently noticed that all 36.5 thousand airports on an AFS2 competitor's scenery gateway are GPL licensed. If you download one, there's a file named "copying" that includes the full GPL licence.
There's no legal ambiguity about this, it means you can use, modify and redistribute it as long as you include the GPL licence and stick to its terms.
It's also not revocable. That version of the file has been released under the GPL so can't now be restricted.
The airports usually have taxiways hand drawn and many other features hand positioned. It's pretty rich data. The file format is open and well documented.
There's nothing to stop someone downloading all 36k airports and writing something to convert them to AFS2 format.
Thoughts, opinions, concerns? or