Which instrument is directly affected by a blocked pitot tube?

The airspeed indicator is the instrument that is directly affected by a blocked pitot tube. The pitot tube measures the dynamic pressure of the air as the aircraft moves through it, which is essential for calculating airspeed. If the pitot tube becomes blocked, it can lead to an erroneous airspeed reading or could cause the airspeed indicator to indicate a lower speed or zero airspeed altogether, especially during flight when the dynamic pressure is necessary for proper function.

The altimeter operates based on static pressure, which comes from a separate source, so its operation is not directly impacted by a blocked pitot tube. The vertical speed indicator also relies on changes in static pressure and would not be affected by a blockage in the pitot system. The heading indicator, often a magnetic instrument, is unrelated to the air pressure measurements and would remain unaffected by a blockage in the pitot tube as well. Therefore, understanding the relationship between the pitot tube and the instruments it influences is crucial for recognizing potential errors in flight.