UPDATE!
Apologies for closing this one apparently prematurely. I got a few more reports of this and started investigating deeper. There was indeed a memory leak that was consuming memory continuously, at a rate of roughly 400 MB/hr. So after 10 hours, it would have consumed 4000 MB. If you were doing a long multi-sector flight on a machine with 16GB or less of memory, or perhaps left the sim open overnight, this was most likely an issue of out-of-memory crashes.
Anyway, fixed in update 1.3. Apologies again for prematurely closing this issue.