What effect does static blockage have on the altimeter?

Static blockage occurs when the static port, which is responsible for providing ambient air pressure to the altimeter and other instruments, becomes obstructed. When this blockage happens, the altimeter becomes unable to receive accurate pressure information from the atmosphere. As a result, it can no longer adjust to changes in altitude accurately.

In this situation, the altimeter will freeze at the altitude it was reading at the moment of blockage. This means that if the aircraft climbs or descends, the altimeter will not reflect those changes. The reading will remain constant, which is an indication of the last altitude before the static port became blocked. Hence, the altimeter effectively shows a "frozen" value rather than an accurate representation of the aircraft's current altitude, making it crucial for a pilot to recognize the signs of static blockage and to take corrective action if necessary.