What causes instrument error?

• A. Misalignment of the Pitot tube with the relative wind
• B. Frictioning and binding of the instrument
• C. Static vent blockage
• D. Magnetic interference with the compass

Answer: (B)

Instrument readings become inaccurate when the moving parts inside the instrument itself don’t operate smoothly. Friction and binding in the mechanism of Pitot-Static instruments—such as the airspeed indicator, altimeter, or vertical speed indicator—can cause the needle to stick or respond sluggishly, leading to readings that don’t reflect the actual pressure differences. This kind of error originates in the instrument’s own mechanical wear, lubrication issues, or binding, so the indication is off even if the pressure signals coming from the Pitot tube and static ports are correct. By contrast, problems like a blocked static vent or a misaligned Pitot tube affect the pressure inputs themselves (system or sensor errors) rather than the instrument’s internal mechanism, and magnetic interference affects the compass instead of the Pitot-Static instruments.