Definition
A static pressure intake mounted level with the aircraft's outer skin, with no protrusion into the airstream, used to sense the undisturbed ambient (static) air pressure surrounding the aircraft in flight. The sensed pressure is supplied to the altimeter, vertical speed indicator, and airspeed indicator.
Plain English
A small opening in the side of the aircraft, sitting perfectly flat with the surface, that lets the flight instruments measure the still air pressure outside the aircraft.
Context Anchor
Seen in instrument system diagrams and blocked static system discussions, especially when explaining how the altimeter, airspeed indicator, and vertical speed indicator get outside air pressure.
Derivation
Flush' comes from Middle English meaning 'level with' or 'even with a surface.' 'Static' is from Latin 'staticus,' meaning 'at rest' or 'standing still' — referring here to still, undisturbed air pressure rather than the moving (ram) air sensed by the pitot tube.
Why Pilots Care
Blockage prevents correct static pressure from reaching the altimeter, vertical speed indicator, and airspeed indicator, producing dangerous false readings in instrument conditions.
Intuition Check
Flush does not mean cleaning or washing here. It means the port is even with the aircraft surface, rather than sticking out.
Example Sentence 1
During preflight, the pilot checked that the flush static port on the side of the fuselage was clear and free of obstructions.
Example Sentence 2
Ice forming over the flush static port caused the altimeter to stop climbing even though the airplane continued to gain altitude.