What does the vertical speed indicator (VSI) measure?

The vertical speed indicator (VSI) measures the rate of climb or descent in feet per minute. It provides important feedback to the pilot regarding how quickly the aircraft is ascending or descending. This information is critical for maintaining specific altitudes during flight, especially when following air traffic control instructions or during approach and landing phases.

The VSI operates based on a differential pressure mechanism that measures the difference between the static pressure inside the aircraft and the pressure outside. As the aircraft climbs, the internal pressure drops more slowly than the external pressure, resulting in a positive indication of climb rate. Conversely, during descent, the internal pressure decreases more rapidly, indicating a negative rate of climb.

Understanding the VSI is essential for pilots, as it allows them to make informed decisions about their flight path, ensuring safety and compliance with altitude regulations.