I found the solution here : Game freezes while loading a flight - Bug Reports / Install, Performance & Graphics - Microsoft Flight Simulator Forums
may, also if it is already known, because lots of search results points to it, I would ask whether you have/had the google-maps-addon installed ?
If so, remove the C:\Windows\System32\drivers\etc\hosts file 
This addon had changed host file in system32 so msfs couldnt load map and freezes.
BE CAREFUL WHEN USING GOOGLE MAP ENHANCEMENT MOD!