perhaps this should go to the 'bugs' section:
I flew under the Tower Bridge, and then my engine slowed down and stopped. and so did my plane. In mid-air. The water in the Thames was moving, so it wasn't a freeze. I was just sitting there. Didn't fancy jumping from that height, either...

Never seen anything like it...maybe reinstall.

Also maybe make sure your system is not overclocked nor overheating.

WM