Which instruments would be affected if the static vents are clogged but the pitot system remains functional?

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

Answer: (A)

Static pressure is the reference for several flight instruments. The altimeter and the vertical speed indicator rely on sensing changes in static pressure to display altitude and rate of climb or descent. The airspeed indicator uses the difference between dynamic pressure from the pitot tube and the static pressure to show speed. If the static vents are clogged, the instruments lose the correct static pressure input. The altimeter would no longer reflect true altitude and could freeze or malfunction, the vertical speed indicator would fail to show actual vertical speed, and the airspeed indicator would produce unreliable readings because its reference pressure is no longer the ambient static pressure. The attitude indicator, on the other hand, is driven by a gyroscope (and its own power source) and is not affected by static pressure, so it would remain unaffected. Therefore, the instruments affected are airspeed, altimeter, and vertical speed.