What is the recommended action to take when encountering turbulence?

When encountering turbulence, slowing down to V_A, or maneuvering speed, is the appropriate action to take. V_A is designed to allow for better control of the aircraft in turbulent air while minimizing the structural loads imposed on the airframe. This speed is often lower than the aircraft's maximum speed and provides a safety buffer, allowing the pilot to maintain control without overstressing the aircraft.

Slowing down can help maintain stability and control in bumpy air conditions, as well as increase the responsiveness of the controls. It also helps to protect the aircraft from excessive forces that can occur during turbulence, thus ensuring a safer flight experience.

In contrast, other options like ascending to a higher altitude might not always yield a smoother ride since turbulence can occur at various altitudes. Banking left to avoid rough air could lead to misjudgment, as turbulence may not be easily avoidable by just changing the aircraft's direction, and activating the autopilot does not necessarily mitigate the effects of turbulence and can sometimes even complicate the pilot's response to the situation. Therefore, slowing to V_A is the most effective and recommended course of action when confronted with turbulence.