What does a vertical speed indicator measure?

A vertical speed indicator (VSI) is an essential instrument in the cockpit that measures the aircraft's rate of climb or descent in feet per minute. This instrument provides pilots with real-time information on how quickly an aircraft is ascending or descending.

Understanding this rate is crucial for maintaining safe operational practices during ascent and descent phases of flight, allowing pilots to make informed decisions regarding altitude management. For example, during a climb, knowing the rate of ascent helps ensure the aircraft is not climbing too quickly in relation to airspace constraints or performance limits.

Other options such as measuring horizontal distance, lateral positioning, or altitude above ground level relate to different instruments and functions within the aircraft's instruments. The airspeed indicator, for example, tracks horizontal distance, while altimeters measure altitude. Therefore, the primary function of the vertical speed indicator is to show how quickly the aircraft is moving vertically.