I have recently been having a problem with FlightGear: when I click "Fly" on the starting page, it closes and a Command Prompt window with some text opens for a short time, and then also closes. I don't know what it is trying to tell me, as it vanishes before I can even read a word .
This might be a coincidence, but: it started doing this after I turned off multiplayer and changed the time in the Settings.
I am using this on a Windows 10 desktop PC.