What is the effect of a partially blocked static port on instrument readings?

• A. The airspeed indicator would be affected only.
• B. The pitot tube would fail completely.
• C. The altimeter and VSI may show erroneous readings, possibly inconsistent with actual altitude and rate of climb/descent.
• D. The fuel quantity readings would be affected.

Answer: (C)

A partially blocked static port disrupts the reference pressure that the altitude and VSI instruments rely on. The altimeter measures altitude by sensing ambient static pressure, and the VSI indicates rate of climb or descent from how that pressure changes. If the static port is partially blocked, the pressure fed to these instruments isn’t the true ambient pressure, so they can show readings that are incorrect or inconsistent with the actual altitude and rate of climb/descent. The airspeed indicator does use static pressure, but the key point here is that the altitude and VSI readings become unreliable with a compromised static source. The other options misstate the effects: the pitot tube wouldn’t fail completely from a partially blocked static port, and fuel quantity readings are not influenced by the pitot-static system.