What does it mean to bank an aircraft?

Banking an aircraft refers to the action of turning the aircraft in such a way that it rolls and inclines to one side. When a pilot banks an aircraft, they manipulate the ailerons and rudder to achieve a roll, which causes the wings to tilt and the aircraft to make a turn. This rolling motion is essential for achieving smooth and controlled turns, as it allows the aircraft to maintain lift and stability during the maneuver.

In contrast, the other options do not accurately describe the action of banking. Simply increasing speed in a direct line does not involve any lateral movement or rolling. A sudden descent toward the ground is an entirely different maneuver that does not require banking to perform. Lastly, maintaining level flight while adjusting altitude does not necessitate a turn or rolling motion but rather focuses on managing the aircraft's vertical position without changing its horizontal direction. Thus, the concept of banking is specifically about the lateral rotation of the aircraft during a turn.