Which instrument is primarily used for tracking altitude during flight?

The altimeter is the primary instrument used for tracking altitude during flight. It measures the aircraft's altitude above a standard pressure reference, usually sea level. The altimeter works based on the principle of atmospheric pressure, where a decrease in pressure corresponds to an increase in altitude. By measuring the ambient air pressure, the altimeter can calculate and display the altitude of the aircraft, allowing pilots to maintain or adjust their flight level as necessary to ensure safe flying.

In contrast, the other instruments listed serve different purposes. The air speed indicator measures how fast the aircraft is moving through the air, which is critical for understanding performance and handling characteristics. The vertical speed indicator provides information about the rate of climb or descent, indicating how quickly the aircraft is gaining or losing altitude. Finally, the attitude indicator shows the orientation of the aircraft relative to the horizon, helping pilots maintain proper control in various flight conditions. While all these instruments are important for flight, the primary focus on altitude tracking is served specifically by the altimeter.