Sometimes planes are stuck in one place and are spinning endleslly with the attacking sound. I dont know if its a pathfinding bug or the plane was just shot down and something goes wrong.

I5-4670@4.4Ghz, MSI Z87-G45,Crucial Ballistics lp 8Gb Ram, Crucial MX100 256 SSD, GTX 980, 1980x1080, Win10 64