If the pitot tube becomes blocked, which instrument will be affected?

When the pitot tube becomes blocked, the primary instrument affected is the airspeed indicator. The airspeed indicator operates by measuring dynamic air pressure, which is collected through the pitot tube as the aircraft moves through the air. If the pitot tube is blocked, it will not be able to detect the incoming airflow needed to calculate airspeed accurately. Thus, the indicated airspeed will either read zero or will become unreliable, posing a significant risk to flying operations.

The altimeter and vertical speed indicator (VSI) are primarily functioning using static pressure, which is obtained from the static ports on the aircraft. Therefore, these instruments would not be directly affected by a blockage of the pitot tube. The altimeter measures altitude based on ambient air pressure and the VSI indicates the rate of climb or descent, both of which rely on static pressure rather than dynamic pressure from the pitot tube. Consequently, while all pitot/static instruments generally rely on both pressure sources, in this specific scenario, the airspeed indicator stands out as the one that will be immediately affected due to the blockage of the pitot tube.