Which instrument indicates whether an aircraft is climbing or descending?

The Vertical Speed Indicator (VSI) is the instrument that specifically indicates whether an aircraft is climbing or descending. It measures the rate of change of altitude over time, providing pilots with crucial information about their vertical movement. When the aircraft is climbing, the VSI displays a positive rate of climb, and when descending, it shows a negative rate of descent. The readings are typically expressed in feet per minute, which allows pilots to understand how quickly they are gaining or losing altitude.

In contrast, the Airspeed Indicator measures how fast the aircraft is moving through the air, providing no indication about altitude changes. The Attitude Indicator displays the aircraft's orientation relative to the horizon but does not provide vertical rate information. The Turn Coordinator helps pilots understand the rate of turn and coordination, but it too does not reflect whether the aircraft is climbing or descending. This functionality of the VSI is essential for maintaining safe and effective navigation and altitude management during flight.