An aircraft rudder is a flight control surface used to control rotation around its vertical axis, known as yaw,[1] which is especially important during takeoff, landing, and emergency conditions. Rudders are typically found within the vertical stabilizer of the aircraft. Excessive use of rudder can exceed the ultimate load of the vertical stabilizer, causing structural failure.[2] For this reason, modern airliners and fly-by-wire aircraft often include a system to prevent excessive rudder deflection.