I am posting this just because I could find no posts on this subject, and it caused me so much frustration until I found the solution. Using the Carenado Seneca V and the PMDG DC-6 (both of which were purchased through the Marketplace), every time I set up a flight and then clicked on “Ready to Fly”, as soon as the cockpit view came up, the sim crashed to desktop. It turned out to be because I was using Direct X 12. Apparently, the cockpit view in these (and potentially some other) aircraft are not compatible with DX12. I went back to using DX11 and it solved the problem. I hope this saves someone else from having the same frustrations.