I doubled the page file size of my manual SSD from 8 to 16GB and tried again. (but left the system SSD to automatic)
But this time I monitored the actual usage live while playing using the system resource monitor on a separate screen.
I also lowered the texture size in the game from ultra to high to see if that helps (and restart the game as recommended to take effect)
Take off from London city, fly around Buckingham palace
The game uses on average 10GB physical ram and 30GB page file.
Fly away from the city towards the south, I notice I have firefox open, so I close it.
The game’s physical memory usage goes down to 8GB, page file 28GB
Turn around, and fly to Heathrow.
When directly overhead Heathrow, Ram stays the same (8GB) even though there is some ram available, the game does not appear to try to use it. Page file usage goes up 30~31GB
The frame rate goes down significantly, but the game holds on.
I goof around Heathrow for at least 15 minutes, and the game appears stable.
I leave Heathrow, back to London city through London city center.
Mid-way through the transit, all of a sudden the page file shoots up to 34GB, the game slows down to a crawl, freezes for a second and CTD.
Windows event manager reports running out of page file and 3 seconds later the application crash for unknown reason.
I wonder if Windows automatic page file assignment could be freaking out when an application uses more than 2x physical RAM and would perhaps send some kind of signal to force MSFS to reduce page file usage (for which MSFS would fail and crash) ?