well there are some black areas on that texture map so im guessing it has alpha? but it doesnt seem to have any fading alpha so no banding should occur from DXT3
You are such amateurs, always use DXT1 if possible, if you cannot because alpha channel, delete alpha channel, since those textures are not supposed to have alpha, but even DXT1 can have alpha, just no gradients in it. DXT1 gives best performance, since it is half the size of DXT3 or 5.
And someone should go to the Flightgear developers and punish them for their development style crimes, but hey wait a minute, I just realized why they may do it that way, the reason is if you have an atlas texture with no textures right or left to it, you can tile the texture horizontally using the atlas texture without creating new polygons. So this may be the reason for that weird format, but I see they also have textures next to each other, which breaks this system again, so no idea, if they are genius or just stupid. The textures are also too small, should be at least 512 pixels or even 1024, think about upwards compatibility, which open source developers usually never care about, but a professional developers usually always keeps the high res versions.