My view on this topic is that Creative Commons Attribution can use in for sounds, artwork and models.
there is a but.
CC0 and CC-BY 4.0 or later we can use with our gpl version and only a notify the text of the aircraft for the source and the file license (CC-BY only).
Where CC-BY 4.0 can be use
For CC-BY-SA, CC-BY-NC, CC-BY-NC-SA can use in a dual license setup where CC license are use as a standalone licenes for the case that is out of the scope of the GPL e.g. use in a TV series, movie, 3d printing, etc.
Where the CC-BY-ND and CC-BY-NC-ND is forbidden for use in the as a part of main stream flightgear release(fgaddons/fgdata).
But this my 0.02 euro on the CC vs GPL discution.
source:
https://www.gnu.org/licenses/license-li ... leLicensesIn a other case i see not a problem that we use 3th party data for navaids database e.g. navigraph this is allow in the gpl so long if the user install or allow by the provider in this case navigraph.
This mean is that linux distribution need to have a flightgear-navdata-nonfree pagacket or flightgear ask user with navigaton database the user wand to use include the advantage/disadvantage each option.
When a user select navigrave demo file than flightgear download the demo file form ower server or from navigraph else use the current building data.
Beside this there is also option for loading a newer navdatabase from navigraph for the users that have a navigraph account.
The only problem with this is that on each change of navigation database there is a rebuild of the scenery but this is easy to do as a overlay.
This is also a good idea to depricade the navigation database (nav.dat) from the scenery builds.
I see there are more problems if re going on this route.
But this is need to discus in his own toppic.