What is the effect on the airspeed indicator with a blocked static port during a descent?

When the static port becomes blocked, the airspeed indicator is affected by changes in atmospheric pressure that it can no longer sense. In a descent, as the aircraft descends, the ambient pressure outside the aircraft increases. Since the static port is blocked, the indicator will not register this increase in pressure effectively.

The airspeed indicator relies on both dynamic pressure, which is affected by the airspeed of the aircraft, and static pressure from the static port. If the static port is blocked, the static pressure reading remains fixed at the last value it sensed when it was unblocked. During a descent, while the dynamic pressure continues to increase due to the aircraft's descent path, the static pressure does not update, leading the instrument to show a lower indicated airspeed than the actual airspeed. This creates a situation where the airspeed indicator under-reads the true airspeed of the aircraft, confirming that the selected answer is accurate.