Which of the following instruments is affected by a blocked pitot tube?

The airspeed indicator is directly affected by a blocked pitot tube because it relies on the dynamic pressure from the pitot tube to measure airspeed. When the pitot tube becomes blocked, the instrument cannot accurately sense the pressure change that corresponds to the aircraft’s speed through the air. As a result, the airspeed indicator can display an incorrect airspeed or potentially indicate zero airspeed, which is critical information for pilots to safely operate the aircraft.

In contrast, the altimeter, vertical speed indicator, and heading indicator operate on different principles. The altimeter is based on static pressure and would not be affected by a blockage in the pitot tube unless there is a simultaneous issue with the static port. The vertical speed indicator also derives its information from static pressure changes, making it independent of the pitot tube’s function. The heading indicator relies on a magnetic compass and gyroscopic principles, thus not influenced by pitot tube blockage. Understanding these distinctions is vital for pilots to effectively manage and respond to instrument failures during flight.