Hi Daniel,
really ennoying these CTDs - I have them sometimes and hate them. Allways difficult to say what causes them.
The 9.1 Patch is definetly not the problem - you should install it by all means.
Which addons do you use (Sceneries, additional tools, Addon planes)?
Do you use a wether tool like Active Sky? I experienced some problems with it under certain circumstances.
A simple reason may be that the CPU or the GPU become to warm. Simply switch off the heating and try it afterwards once more.
If it works, buy yourself a warm hat and coat

no, then you have to improve your cooling system.
Good luck!