Which instrument reading group would be affected by a blocked pitot-static system?

• A. Attitude indicator, heading indicator, and airspeed indicator
• B. Altimeter only
• C. Airspeed indicator and vertical speed indicator only
• D. The altimeter, airspeed indicator, and vertical speed indicator

Answer: (D)

The pitot-static system provides the pressures that three instruments rely on: dynamic pressure for the airspeed indicator, and ambient static pressure for the altimeter and the vertical speed indicator. If this system is blocked, those three instruments lose the pressure signals they need and will misread. The airspeed indicator would no longer reflect true airspeed, because the trapped pressure prevents it from responding to changes in ram pressure. The altimeter would stop changing correctly with altitude, since static pressure is no longer being sensed. The vertical speed indicator would also misread, since it relies on the rate of change of static pressure. Attitude and heading indicators are gyro-based and draw power from their own systems, so they aren’t directly affected by a pitot-static blockage. Hence, the instruments that would be affected are the altimeter, airspeed indicator, and vertical speed indicator.