which version of fms are you using and are you in chase view with the plane??
if you are in chase view yes you can run out of graphics..but in the newest version of FMS which is 8.1 you can't get to far from the plane and radio or it will crash just like radio out of range...new version is alot more realistic..but has le planes available at the moment..
I made a few models for the older FMS version and now on a quest to figure out the par file to the new version so I can start getting more of my trainner type planes working in it.