Help! Objects are disappearing in FS

I put several GMAX created objects into Microsoft Flight Sim 2002. The problem is that sometimes as I fly toward an object it disappears. Sometimes it reappears, sometimes not. I thought it would help to apply color. I did this by doing a drag-and-drop from the material navigator (is that as good as applying color from the material editor?). It didn't work; the objects still disappear. Would it help to apply texture too? Where do i get textures from?
Does anyone have any ideas on what else could be causing this and how to fix it?
Thank you very much.
Does anyone have any ideas on what else could be causing this and how to fix it?
Thank you very much.