What does the vertical speed indicator (VSI) measure?

The vertical speed indicator (VSI) measures the rate of climb or descent in feet per minute. This instrument provides crucial information to the pilot regarding how quickly the aircraft is ascending or descending, allowing for better management of altitude during flight. When the aircraft is climbing, the VSI will show a positive rate, indicating how many feet the aircraft is gaining in altitude per minute. Conversely, if the aircraft is descending, the VSI will display a negative rate, reflecting the descent speed.

Understanding the VSI is essential for maintaining a controlled ascent or descent, particularly during takeoffs and landings, as it contributes to situational awareness and helps pilots adhere to altitude requirements. This instrument is not used to measure altitude, airspeed, or ground speed directly, which distinguishes it from the other instruments and their functions.