my only suggestion is to open a system monitor in order to see what is going on. Then adjust. Or fly anywhere else. I need to do that, too, XP10 eats a lot of memory and as you have read on the link I provided we are a bit unlucky with our Macs: The limit is not even 4GB, but 3.5GB. I'm mostly flying islands with version 10. When there is a lot of water around, the memory usage is much lower.