What does a vertical speed indicator (VSI) measure?

The vertical speed indicator (VSI) specifically measures the rate of change of altitude, which is correlated with changes in static pressure. The VSI operates by sensing changes in static pressure due to altitude changes and displays this as a rate of climb or descent. This instrument provides vital information to pilots, allowing them to understand whether the aircraft is climbing, descending, or maintaining level flight.

Understanding the VSI's operation is crucial for maintaining safe and efficient flying practices, as it directly informs the pilot of altitude changes in feet per minute. This can be valuable, especially during takeoffs, approaches, and landings.

While aspects of engine performance and fuel consumption impact flight dynamics, the VSI itself does not directly measure these factors. Instead, it primarily focuses on the relationship between altitude changes and the varying static pressure resulting from those changes.