What is the primary purpose of the VSI?

The primary purpose of the Vertical Speed Indicator (VSI) is to provide pilots with information about the aircraft's rate of climb or descent, along with the direction of vertical movement. This instrument is essential for safe flight operations, as it allows pilots to be aware of how quickly they are ascending or descending, typically measured in feet per minute.

Understanding the VSI's readings helps pilots maintain optimal flight paths, especially during critical phases such as takeoff and landing when managing altitude changes is vital. Unlike other instruments that measure different parameters like heading or altitude, the VSI specifically focuses on vertical velocity, making it a key tool in ensuring proper aircraft management in the vertical plane. In contrast, the other options address different aspects of flight information that the VSI does not provide.