I have the same problem as the topic starter, but I use Windows 7. The only thing that works is setting a tutorial mission as the default flight. If I try to set something else as the default flight, I am in the middle of nowhere again, followed by the plane splashing. And if I start from a tutorial mission and change the scenario, I am always stuck on that mission. That means for example instant replay is not available (because I'm on a mission). Is there any solution, so I can start a "free flight"?