Which performance flight instrument assists in determining climb or descent rates?

The vertical speed indicator (VSI) is the performance flight instrument that directly measures and displays the rate of climb or descent. It provides a readout typically in feet per minute, indicating how quickly the aircraft is ascending or descending. This information is crucial for pilots during ascent and descent phases, allowing them to manage and maintain desired altitudes effectively.

The VSI works by detecting changes in air pressure and converting these differences into a visual rate on its gauge. As the aircraft climbs, the pressure decreases and the VSI reflects this by showing a positive rate of climb. Conversely, during descent, the pressure changes in the opposite direction, indicating a negative rate. This is essential for ensuring a smooth and controlled flight when transitioning between altitudes.

In contrast, the other instruments serve different functions: the altimeter measures altitude based on ambient air pressure, the course indicator helps track navigation and heading relative to a designated course, and the attitude indicator displays the aircraft's orientation relative to the horizon. While all these instruments are vital for flying, the VSI is uniquely focused on providing real-time data about vertical speed.