Which instrument is used to measure an aircraft's speed?

The airspeed indicator is the instrument designed specifically for measuring an aircraft’s speed through the air. It displays the current airspeed, which is critical for various phases of flight, including takeoff, cruising, and landing. By providing this information, the airspeed indicator helps the pilot maintain the appropriate speed for safe operations, ensuring the aircraft remains within its performance limits and enhancing situational awareness during flight.

The other instruments serve different purposes. The altimeter measures altitude by determining the atmospheric pressure relative to sea level. The vertical speed indicator provides information about the rate of ascent or descent. Lastly, the heading indicator shows the aircraft’s direction relative to magnetic north, which is not related to speed. Understanding the specific function of each instrument is essential for effective flight operations.