I've been trying saving the flights and restarting from the save file for a while. It doesn't seem to cause any problems.
But I did see something that reminded me of this thread. I was flying from Madrid to a small airfield north of Munich. When I got to Switzerland, the frame rates went totally to crap. I didn't have that problem in Italy or Spain, and I don't remember it in Austria when I was there earlier. I was flying a helicopter out of Innsbruck. No problems in Greece or Egypt either. I don't remember any problems in France.
Now, Europe in general is rough on frame rates. I suspect it has to do with the density of airports and navaids, at least that's what I attributed it to when I first flew into Germany from UK. Switzerland has the above problem, plus all the mountains. The game has to render that haze layer, and winding it through the mountains must take a lot of machine cycles. It's the sort of thing that would cause a drop in frame rate every few seconds as it rendered ahead. At least that's how I think they're doing it. The terrain seems to be rendered in large blocks, but stuff like clouds seems to be rendered in small pieces.
In addition, the whole way across Switzerland I was getting shuffled back and forth between ATC frequencies. I'd get either 10 or 20 seconds from the time the ATC gave the barometric pressure to the time I was handed off to someone else. The longest I spent on one frequency was about 1.5 minutes. There were a few AI planes in the area, and the ATC was probably exercising them as well.
Add to that the changing winds and the icing conditions, and it didn't leave time for sightseeing. It barely left time to check the frame rate counter. It was a thoroughly unpleasant experience.
This must be why Switzerland was never invaded. Lousy framerates, strong winds blowing from all over the compass, icing conditions, and the invaders would be exhausted from switching radio frequencies constantly.
That, and all those mountains.
I flew north across Germany. Still lower than normal frame rates, but better, and no constant harassment from the ATC. After leaving Amsterdam flying towards Copenhagen, the frame rates got back to the normal 20 range.
Anyone else have problems with Switzerland or Europe?