What can blockage of the static air vents cause?

Blockage of the static air vents can lead to errors across all pitot-static instruments because these instruments rely on accurate static pressure to function correctly. The static air vents provide critical information about the atmospheric pressure surrounding the aircraft. If these vents are blocked, the static pressure readings become erroneous, which in turn affects all instruments that depend on this input.

This includes the altimeter, which measures altitude, the vertical speed indicator, which shows the rate of climb or descent, and the airspeed indicator, which measures airspeed based on the difference between static pressure and pitot pressure. When the static pressure is inaccurately sensed due to a blockage, it can result in misleading readings on all of these instruments, making it crucial for pilots and air traffic controllers to monitor and ensure these vents are unobstructed for safe flight operations.