What manual port allows the pitot-static instruments to sense static pressure from an alternate location if the primary static port is blocked?

• A. Alternate static source
• B. Alternate air
• C. Altimeter
• D. Altitude (AGL)

Answer: (A)

Static pressure is what the pitot‑static system uses to feed the instruments that show altitude, rate of climb, and airspeed. When the primary static port is blocked, a manual alternate static source provides a separate path for static pressure so those instruments can continue to operate. This alternate source is a dedicated port that you can select to draw static pressure from a different location, often inside the cockpit or from a different exterior point. Because it isn’t exactly the same as the outside ambient pressure, using the alternate static source can cause some instrument readings to differ momentarily or settle to different values, but it keeps the system functioning.

Alternate air pertains to supplying cabin or environmental control system air and isn’t used to feed static pressure to the instruments. The altimeter and altitude (AGL) are instruments or concepts that rely on static pressure, but they are not sources of static pressure themselves.