Which instrument indicates rate of climb or descent by measuring pressure change?

• A. Velocity
• B. Vectoring
• C. Venturi tube
• D. Vertical speed indicator

Answer: (D)

Understanding how fast your altitude is changing requires sensing how quickly the outside air pressure is changing. The instrument that does this is the vertical speed indicator. It uses a sealed pressure capsule connected to the static pressure port through a restricted passage. Because the passage slows the pressure change slightly, the capsule’s pressure changes at a different rate than the outside air. When you climb and static pressure falls, the outside pressure drops faster than the capsule, causing the diaphragm to move and the needle to indicate an upward rate (feet per minute). When you descend, the outside pressure rises and the needle shows a downward rate. This device, therefore, measures the rate of change of altitude, not the current altitude itself.

By contrast, an airspeed indicator derives from dynamic pressure and shows velocity, not vertical movement; a Venturi tube is a principle used in some airspeed systems to create a measurable differential pressure; and vectoring is not an instrument for measuring climb or descent.