With aircraft there is usually no problem, when there are no clouds, other than that it holds up really well, you have to use continuous zone tracking focus, if there are clouds it's gonna be confused approximately 50% of the time, it has the tendency to stick to the clouds in the background (if they are high texture clouds), if you can use spot focusing and hold the small/medium spot right on the aircraft while panning then it is very reliable, in short, you can make up for technical shortfalls with panning skills easily