Laptop

Hey Guys, for the past year now I've been running fs9 at 30 fps. Lately when I fly, i fly for 20 minutes and then my fps goes down to like 4. Does anyone know why I am having trouble with this?

Much Appreciated

Why is the topic title Laptop?

The standard things to check are:
-Make sure you don't have any extra stuff running in the background
-Defrag
-Check that your drivers are up to date

If none of those are the issue, then have you installed any new addons lately? That sounds like either you're running out of memory or you're overheating and the computer's throttling itself back. (Some CPUs will drasticlly reduce their clock speed if their core temp gets too high.)