You should have posted the code that you are using, this way it's only a guessing game: Some of your planes do not get close enough to their current path target, then they try to turn around but as the angular speed is limited, they never get the right angle and thus always fly around the current node.
"Falls das Resultat nicht einfach nur dermassen gut aussieht, sollten Sie nochmal von vorn anfangen..." - Manual
