Basically speaking, Dutch roll is a series of out-of-phase turns, when the aircraft rolls in one direction and yaws in the other. When the yaw is introduced, the strong “dihedral effect” will roll the aircraft due to the lift increase on the wing into wind. The increased induced drag on the rising wing will yaw the aircraft in the opposite direction, reversing the coupled oscillations.

The yaw damper's main purpose is to prevent Dutch roll. Since the possibility of a Dutch roll increases with increasing altitude, when the yaw damper is unserviceable, the flight will be restricted in altitude.