Definition
A failure or blockage in the aircraft's static pressure system — the network of ports, lines, and instruments that sense the undisturbed outside air pressure surrounding the aircraft. A static system problem causes the altimeter, vertical speed indicator, and airspeed indicator to give incorrect readings, because all three depend on accurate static pressure to function.
Plain English
Something has gone wrong with the part of the aircraft's instrument system that measures outside air pressure. When that happens, the instruments showing altitude, climb or descent rate, and airspeed can all read wrong at the same time.
Context Anchor
Seen during instrument flying and pitot/static system failure checks, especially when instrument readings do not agree with what the aircraft is actually doing.
Derivation
Static' comes from Latin staticus, meaning 'standing still.' The static system measures the still, undisturbed air pressure around the aircraft — as opposed to the ram (moving) air pressure measured by the pitot tube.
Why Pilots Care
Unrecognized static system problems produce false altitude and airspeed data that can lead to altitude busts, terrain clearance errors, or loss of control in IMC.
Intuition Check
Static does not mean the airplane is not moving. Here, static means outside air pressure sensed without the added pressure from the airplane’s forward motion.
Example Sentence 1
When the altimeter, VSI, and airspeed indicator all began reading incorrectly, the pilot suspected a static system problem and selected the alternate static source.
Example Sentence 2
After landing in heavy rain, the maintenance crew cleared debris from the static ports to prevent a static system problem on the next flight.