What instrument indicates the aircraft’s altitude?

The altimeter is the instrument designed specifically to measure and display the aircraft's altitude. It works by measuring air pressure; as an aircraft ascends or descends, the ambient air pressure changes, which the altimeter uses to calculate altitude. The altimeter is calibrated to standard atmospheric pressure at sea level, allowing pilots to understand their elevation relative to the ground or sea level.

In aviation, accurate altitude information is crucial for safe flying, especially during takeoff, landing, and in air traffic control scenarios. When flying at altitude, it is essential for maintaining separation between aircraft, adhering to airspace regulations, and ensuring a safe flight path. The altimeter provides this essential information and is a fundamental instrument in any aircraft cockpit.

The attitude indicator shows the aircraft's orientation relative to the horizon, but it does not provide altitude data. The vertical speed indicator indicates the rate of climb or descent but does not specify an altitude measurement. A speedometer provides airspeed information and is unrelated to altitude. Therefore, the altimeter is definitive for indicating an aircraft's altitude.