What do the static ports on an aircraft sense?

The static ports on an aircraft are specifically designed to sense static pressure. Static pressure is the ambient air pressure surrounding the aircraft, which is essential for determining various flight parameters. This pressure measurement is used by the altimeter to determine altitude, by the airspeed indicator to calculate indicated airspeed when combined with dynamic pressure from the pitot tube, and serves various other functions in flight instrumentation.

Static pressure is critical for the accurate functioning of these instruments because it provides a baseline measurement unaffected by the aircraft's speed or direction. Unlike dynamic pressure, which varies as the aircraft moves through the air, static pressure gives a stable reference point necessary for effective altitude and airspeed readings.