What is the recommended action when encountering severe turbulence?

Choosing to change altitude to find smoother air is recommended when encountering severe turbulence because it provides an opportunity to escape the turbulent air mass that is causing the discomfort and potential danger. Severe turbulence can significantly affect the aircraft's performance and passenger safety, so finding a more stable layer of air is crucial.

Pilots will often monitor their altitude and be aware of changes in atmospheric conditions to find a more favorable altitude, either higher or lower than the turbulent air. This action is grounded in the understanding that turbulence can vary significantly at different altitudes, and often, a minor altitude adjustment can make a substantial difference in the flying experience.

The other options might seem plausible in certain contexts but do not address the immediate concern effectively. For example, stabilizing the aircraft while maintaining the current altitude might be necessary during turbulence, but it does not resolve the issue of being in turbulent air. Similarly, a rapid descent can lead to further complications and is not typically recommended unless it's an emergency situation. Engaging the autopilot may help manage the aircraft’s handling, but it’s still essential to find smoother air, as autopilot systems can struggle in severe turbulence.