In a static system dump, which instruments stop functioning?

• A. Altimeter, VSI, and Airspeed Indicator
• B. Altimeter only
• C. VSI only
• D. Airspeed Indicator only

Answer: (A)

The static pressure reference feeds three instruments: the altimeter, the vertical speed indicator, and the airspeed indicator. When the static system is dumped, that reference pressure is lost in the lines feeding all of these instruments. The altimeter relies on static pressure to show altitude, and the VSI relies on how quickly static pressure changes to indicate climb or descent; without a stable static reference, both will cease to provide meaningful indications. The airspeed indicator uses the difference between pitot (dynamic) pressure and static pressure, so without a usable static pressure source, it can’t display a correct speed either. Hence, all three instruments stop functioning.