The debian/copyright file does not very specifically document the
package. Please fix it in general. I have found this to be lacking
documentation for the files in Fonts directory, some of which I know to
be DFSG-free. Most prominently, monoMMM_5.ttf is probably not under a
free license. Other non-free candidates are 7-Segment.ttf, LED-8.ttf,
and LED-16.ttf.

I do not know about the debian package specific parts, but any issues
regarding the core FGData package should be raised upstream at
https://gitlab.com/flightgear/fgdata. Otherwise things get messy fast if
changes get made only here, and they will not benefit the whole community
which debian apt users are only a very small minority of.  There is a very
low chance that the people who can resolve this will be looking at debian
apt issues. I just stumbled across this by chance looking for something
unrelated.

Hi Rhys,

It is up to the package maintainers and one of their specific tasks to
decide whether to forward an issue to upstream.

I have just found that you have documented the monoMMM_5.ttf to be
licensed under GPL (version not specified) at
https://gitlab.com/flightgear/fgdata/-/commit/436f67105a9e2ae450a395ca01ccea0c9049fb5a
This part of the issue is a Debian-only one (document it properly in the
copyright file).

For the other mentioned files I have just created an upstream issue.

Thanks,
Bastian