Pitot tube blockage affects which instrument?

• A. ASI
• B. Altimeter
• C. VSI
• D. Attitude indicator

Answer: (A)

The main idea is that the airspeed indicator relies on the Pitot tube to provide dynamic pressure. The Pitot tube takes the stagnation (dynamic) pressure from the airstream and, together with the static pressure from the static port, the airspeed indicator computes the difference to show airspeed. If the Pitot tube is blocked, that dynamic pressure signal can’t reach the airspeed instrument, so it can’t reflect true speed and may read zero or otherwise give misleading readings. The altimeter and vertical speed indicator depend only on static pressure, so they stay accurate as long as the static port is clear. The attitude indicator is powered by its own gyros and is not affected by the Pitot-static system.