What happens to the VSI readings in the event of a blocked static port?

When the static port becomes blocked, the Vertical Speed Indicator (VSI) is affected because it relies on the differential pressure between static air and the air pressure in the cabin to determine the rate of climb or descent. If the static port is blocked, the VSI cannot measure this pressure differential accurately. As a result, the instrument may get 'stuck' at a constant value, which often manifests as reading zero. This occurs because the VSI does not experience any change in the pressure differential, leading it to indicate no vertical movement, even if the aircraft is climbing or descending.

Understanding this concept is crucial for pilots as it directly affects their ability to gauge the aircraft's performance during flight. Knowing how each instrument operates and the consequences of instrument failure is essential for maintaining safety and situational awareness.