All i can say about this problem is if you have SP2 installed the get the it the hell out of your pc.
Ever since i uninstalled SP2 i have NEVER had this problem again.
But if it does still occur with you guys with only SP1 installed, i would suggest reinstalling FSX.
And also make sure there are no mistakes in any CFG files, that might be kinda hard to do but, if that could possibly be the case here, i would uninstall and reinstall FSX but before hand totally delete all CFG files for FSX and inside FSX. (including anything you edited)
Cause doing that and then doing a reinstall gives you a whole new copy of FSX on your pc, where just going and reinstalling without deleting anything leaves traces of x and certain files of x still lurking around your pc.
And also another problem that can cause this is if you don't have a very good PC for fsx, putting major work loads on it like having high settings that your pc really can't handle will crash the game, it might look good at first with the high setting but if your pc sucks then your pc is working it's ass off to run the game and will eventually just crash, thus the fatal error that crashes FSX.
Couple other things, make sure their are NO other big programs and such running other then FSX and what's needed.
Like before you play X, close certain programs like any virus protection, or any extra stuff you installed for your pc that you don;t need running well playing fsx.
Basically close ANY UN-NEEDED programs that are running before playing X, because some of them can start doing somthing that wil interfere with fsx and can make it crash.
Hope any of this advice works.