Which device is essential for maintaining an aircraft's speed indication?

The pitot tube is essential for maintaining an aircraft's speed indication because it measures dynamic pressure, which is critical in calculating indicated airspeed. The pitot tube captures the airflow as the aircraft moves forward, converting that kinetic energy into a pressure reading. This reading is then used in conjunction with the static pressure from the static port to provide an accurate airspeed indication on the aircraft's airspeed indicator.

Without the pitot tube, the aircraft would not be able to determine its speed relative to the surrounding air, as there would be no input of dynamic pressure to facilitate the calculation of airspeed. This is fundamental for pilots to safely operate the aircraft, as speed is critical for various phases of flight, including takeoff and landing.

In contrast, the static port provides atmospheric pressure information necessary for altimetry and vertical speed indicators, while devices like gyros are used for attitude and directional information, and the turn coordinator assists with monitoring turns and rate of turn rather than speed. Therefore, the pitot tube is the device specifically responsible for delivering accurate speed indications in flight.