What effect does static blockage have during a descent?

Static blockage occurs when the static port of an aircraft becomes obstructed, preventing accurate readings from altimeters and other pressure-driven instruments. When a static blockage happens during a descent, the static pressure is higher (as the external air pressure decreases with altitude) than what the aircraft’s instruments are reading. This means that the altimeter, which measures altitude based on static pressure, will interpret this higher pressure incorrectly and indicate a higher altitude than the actual altitude.

As the aircraft descends, the air pressure outside decreases more rapidly than the blocked static source can accurately reflect. As a result, the altimeter will show an altitude that is higher than the true altitude of the aircraft, causing an over-read of altitude. This incorrect indication can lead to dangerous situations, particularly during key phases of flight such as approaches and landings where precise altitude readings are critical for safe operation. Understanding this effect is crucial for pilots to recognize and mitigate the risks associated with static port malfunctions during flight.