Which instrument becomes inoperative if the pitot tube becomes clogged?

The airspeed indicator relies on the dynamic pressure obtained from the pitot tube to provide accurate readings of the aircraft's speed through the air. When the pitot tube becomes clogged, it is unable to measure the impact air pressure necessary to indicate speed. Consequently, the airspeed indicator fails to function correctly, leading to a loss of airspeed data for the pilot.

In contrast, the altimeter is primarily reliant on static pressure from the static port to determine altitude. The vertical speed indicator also utilizes static pressure for its operation, measuring changes in altitude over time. The heading indicator, meanwhile, operates based on the Earth's magnetic field and does not depend on input from the pitot system at all. Therefore, the airspeed indicator is the only instrument that becomes inoperative due to a clogged pitot tube.