If the pitot tube and outside static vents become clogged, which instruments would be affected?

• A. The attitude indicator
• B. The turn coordinator
• C. Altimeter only
• D. The altimeter, airspeed indicator, and vertical speed indicator

Answer: (D)

The main idea is that pitot and static pressures feed specific instruments, and when those pressure sources are blocked, those instruments lose their reference and stop giving reliable readings.

The airspeed indicator depends on dynamic pressure from the pitot tube, so a clogged pitot tube means it can’t measure airspeed accurately. The altimeter relies on static pressure from the outside air, and the vertical speed indicator also uses static pressure to show how quickly the air pressure is changing. If the outside static vents are blocked, both the altimeter and the VSI can stop changing with altitude or show incorrect readings. Taken together, these three instruments would be affected: airspeed, altitude, and vertical rate.

The attitude indicator and turn coordinator use gyros powered by the aircraft’s vacuum or electrical system, not directly by pitot-static pressures. So with only the pitot and static ports clogged, those gyroscopic instruments would generally remain functional if their power source is okay.