What is the function of an alternate static source?

The function of an alternate static source is to serve as a backup for a clogged primary static source. In an aircraft, the static pressure system is essential for accurate readings on various instruments like the altimeter, airspeed indicator, and vertical speed indicator. If the primary static port becomes blocked—due to ice, dirt, or other obstructions—it can lead to erroneous instrument readings, which can pose a safety risk during flight.

The alternate static source is typically located inside the cockpit or elsewhere on the airframe and provides an alternative way for the static system to receive external atmospheric pressure. When the switch for the alternate static source is activated, the instruments can then function using this alternate source of static pressure, ensuring that the pilot has accurate information to make informed decisions during flight.

While other options touch on various aspects of aviation systems, they do not pertain directly to the static system's operation or the critical function of the alternate static source in maintaining accurate instrument readings, especially in conditions where the primary source is compromised.