From Rise: The Vieneo Province
A yaw damper is a device used on many aircraft to damp (reduce) the rolling and yawing oscillations known as the Dutch roll mode. It consists of yaw-rate sensors and a processor that provides a signal to an actuator connected to the rudder. The use of a yaw damper helps provide a better ride for passengers by preventing the uncomfortable yawing and rolling oscillation. On some aircraft it is mandatory for the yaw damper to be operational at all times during flight above a specified altitude.