During checkouts of rated pilots, I usually ask them to explain why the rudder is on the airplane. More than half of rated pilots will tell me the rudder helps turn the aircraft, which is not only wrong but is a very dangerous belief. Less than half of pilots will correctly identify the main purpose of the rudder, to correct for adverse yaw. By failing to correctly understanding the rudders purpose, these pilots exhibit a failure in our training system. Moreover, by misusing the airplanes primary controls, they arent flying it properly or efficiently. This realization has many implications-an indictment of our training systems among them-but the dangers of misusing the rudder also must be acknowledged. Lets discuss the rudders proper role, plus the effects and dangers of misusing primary controls.