Hi,Today, I have started to get seasonal CTD's, don't have any idea why, but the MaskClassMap fix in the terrain.cfg has fixed it a treat.Basically, what I wanted to know was, what is the visual effect of changing this parameter?.CheersDan.

Hi Dan.The airport background polys are different in FS9. In FS2002, they were actual textures displayed on the ground. In FS9 they are a runtime-blended poly, that tries to blend into the landclass texture under the airport. This masking, or blending of the landclass is what causes the crash.The fix turns off this blending. Joachim's solution then uses textures to display at the airports for the backgrounds, in place of the blending. These textures have no autogen associated with them, so they don't cause bushes and trees to pop up in the runways.It's a bug that only seems to come up during seasonal changes that involve snow... fall to winter and winter to spring.Dick

Actually the fix should not change the airport backgrounds. They are controlled by MaskClassMap values of 2, which you don't have to change. You need only change the 1's and 3's, which control masking around water, roads, and utility lines.

If you don't change the airport MaskClassMap to 0, I believe you will get seasonal crashes near some airports.I have changed all instances of MaskClassMap to 0 in my terrain.cfg file, and added Joachim's textures... no more crashes. It's my recommendation.Dick