A yaw damper prevents

• A. Directional instability
• B. Roll instability
• C. Pitch instability
• D. Lateral acceleration

Answer: (A)

The key idea is directional stability. A yaw damper automatically applies rudder input to oppose yaw rate, damping side-to-side oscillations around the vertical axis. This helps suppress yawing motions like Dutch roll and keeps the aircraft from developing directional instability, maintaining coordinated flight. It doesn’t primarily address roll or pitch stability (those are handled by the ailerons/roll damper and elevator/stability systems, respectively), and it isn’t a direct control for lateral acceleration, which involves other forces and dynamics.