Which instrument indicates the rate of climb or descent?

The vertical speed indicator (VSI) is the instrument that specifically indicates the rate of climb or descent of an aircraft. It measures the vertical speed in feet per minute (fpm) and provides pilots with critical information regarding how quickly the aircraft is ascending or descending. This information is essential for maintaining safe altitude management during flight, especially during takeoff and landing phases.

The other instruments listed serve different purposes. The altimeter measures the aircraft's altitude above mean sea level, providing critical height information but not the rate of change of that height. The attitude indicator displays the aircraft's orientation relative to a reference plane, helping the pilot understand the aircraft's position in the sky. The airspeed indicator shows the speed of the aircraft relative to the surrounding air, which is crucial for performance calculations but does not provide vertical speed information. Therefore, the VSI is the only instrument dedicated to indicating how fast an aircraft is climbing or descending.