What is the function of a vertical speed indicator (VSI)?

The vertical speed indicator (VSI) plays a crucial role in monitoring the aircraft's performance in the vertical plane. It provides pilots with immediate feedback on whether the aircraft is climbing or descending, and at what rate. This information is vital during various phases of flight, especially during takeoff and landing, as it helps the pilot maintain the desired altitude and ensure safe flight operations.

In practical terms, the VSI shows the rate of climb or descent in feet per minute, which allows pilots to make informed decisions about their altitude changes. By understanding the vertical performance of the aircraft, pilots can manage their approach to land more safely and efficiently, as well as maintain altitude during different stages of flight. Thus, the functionality provided by the VSI directly supports safe operation in instrument flight conditions where visual references may be limited or unavailable.