What is the primary purpose of the vertical speed indicator?

The primary purpose of the vertical speed indicator (VSI) is to indicate the rate of climb or descent of an aircraft. This instrument provides pilots with crucial information about how quickly they are gaining or losing altitude, typically measured in feet per minute. By continuously displaying this rate, the VSI allows pilots to make informed decisions regarding their ascent or descent, which is vital for maintaining safe flight profiles and complying with air traffic control instructions.

The VSI can show whether the aircraft is climbing, descending, or in level flight, making it an essential tool during takeoff, landing, and while operating at various altitudes. Changes in vertical speed help pilots adjust their control inputs to achieve desired flight paths and maintain situational awareness during flight.