Hello streamfire,
first of all, maybe try to use the Search Function next time. Often issues were already discussed and you will get a solution for your problem really fast.
https://forums.flightsimulator.com/t/ctds-during-flight-planning/297502/2
https://forums.flightsimulator.com/t/ctd-only-when-loading-a-saved-flight/144332/14
I made a little guide with my mate @AmbitiousPilots some time ago, maybe you will find some help there:
Also, I recommend providing some more information, like the type of crash (f.e instant crash to desktop, display freeze etc.).
Tell us your computer hardware etc. .