For those of you who are experiencing a sudden drop and pegging FPS to about 10, the CoherentCTDraw bottleneck still seems to be lurking somewhere deep in the matrix …
Check out this thread for more details (Limited by coherentGTdraw); try turning off VFR map (and removing from the tool bar), if that doesn’t help, same with the ATC panel. Not a guaranteed fix, but both these have been demonstrated as causes of this problem.