What visual check can help ensure that the airplane is laterally level?

Visually checking the relationship of the wings to the horizon is essential for ensuring that the airplane is laterally level. This method involves simply looking outside at the horizon and observing whether the wings are parallel to it. When the wings are level, the airplane is in straight and level flight, which is important for maintaining control and achieving coordinated flight. This visual confirmation allows pilots to detect any bank or roll that may not be captured by instruments, particularly during maneuvers or when in turbulent conditions.

Other options provide useful information about the airplane's performance and climbing or descending states; however, they do not specifically indicate whether the aircraft is level laterally. For example, the altimeter shows altitude, the vertical speed indicator reflects the rate of climb or descent, and the turn coordinator indicates the rate of turn, but none of these instruments directly inform the pilot whether the aircraft is laterally level based solely on visual observation of the horizon. Therefore, using the horizon as a reference is the most effective way to maintain lateral control of the aircraft.