The flight instruments that rely on the pitot-static system and faults that can produce erroneous indications are:

• A. Airspeed indicator only
• B. Altimeter only
• C. Airspeed indicator and altimeter/VSI; blockages or leaks can cause erroneous indications
• D. Attitude indicator

Answer: (C)

The pitot-static system feeds instruments that rely on accurate air pressure readings to show speed, altitude, and rate of climb or descent. The airspeed indicator gets dynamic pressure from the pitot tube and compares it to the static pressure; the altimeter and the vertical speed indicator use the static pressure to determine altitude and the rate of altitude change, respectively. If there’s a blockage or leak in this system, those readings can become erroneous. For example, a blocked pitot tube can cause the airspeed indication to fail or read falsely, while a blocked static port can cause the altimeter to freeze or read incorrectly and the VSI to show the wrong climb or descent rate. The attitude indicator, on the other hand, is driven by gyros (vacuum or electric) and is not a pitot-static instrument, so it isn’t affected in the same way by pitot-static faults. That’s why the combination that includes the airspeed indicator and the altimeter with VSI best matches the instruments affected by pitot-static faults.