Which instrument is primarily used to indicate the aircraft's orientation?

The attitude indicator is the primary instrument used to show the aircraft’s orientation in relation to the horizon. It displays the aircraft's pitch and roll attitudes, allowing pilots to determine whether the wings are level, and whether the airplane is climbing, descending, or in straight and level flight. This is crucial for maintaining control during flight, especially in conditions where visual references are limited, such as in clouds or at night.

The other instruments serve different purposes; for example, the altimeter measures altitude based on atmospheric pressure, the airspeed indicator displays the speed of the aircraft through the air, and the vertical speed indicator indicates the rate of climb or descent. While these instruments are important for overall situational awareness and flight safety, they do not provide direct information about the aircraft's orientation relative to the horizon. Thus, the attitude indicator is essential for ensuring proper aircraft control and for executing maneuvers safely.