Which of the following describes a symptom of a blocked pitot tube in flight?

• A. Erratic airspeed readings
• B. Zero airspeed readings
• C. Erratic or zero airspeed readings
• D. Altimeter malfunction

Answer: (C)

A blocked pitot tube disrupts how the airspeed indication receives dynamic pressure. The airspeed indicator depends on the difference between dynamic pressure from the pitot tube and ambient pressure from the static port. If the pitot tube is blocked, no dynamic pressure reaches the instrument, so the reading can drop to zero. Depending on how complete the blockage is or how airflow interacts with the tube, the signal can also become unstable, leading to erratic readings. Altimeter issues aren’t the primary symptom here because the altimeter uses the static port, not the pitot tube, so a pitot blockage alone won’t typically cause an altimeter malfunction. That combination of possibilities—erratic or zero airspeed readings—best describes what you’d expect with a blocked pitot tube.