What impact does a blocked static port have on the airspeed indicator during a descent?

When a static port becomes blocked, it effectively isolates the airspeed indicator from external pressure changes in the atmosphere. This condition leads to scenarios where the airspeed indicator’s readings become inaccurate.

During a descent, the airplane's altitude decreases, which would normally result in an increase in static pressure outside the aircraft. However, because the static port is blocked, the static pressure within the airspeed indicator does not change as it should with the descent.

As a result, the airspeed indicator continues to reflect conditions based on the last calibrated static pressure it received, which is higher than the actual ambient pressure experienced in the descent. This leads to a situation where the airspeed indicator overreports the actual airspeed, leading to an over-reading.

This phenomenon is critical for pilots to understand because it highlights the importance of proper static port function and the implications of static port blockages on flight operations.