Crashes is one of AFP's low points (along with ground handling in general). No it's not a bug . . . though if I was a developer I would probably call it that. Sometimes you will notice you touch the ground and you crash, other times you basically have to try to crash. One thing that maybe part of the issue is where you set the surface roughness under options, I have not tried this to see what it's effect might be. I am not particularly bothered by the crashing, because I know when it's a crash or not even if the plane doesn;t fly into bits.