A static port is a flush-mounted hole located on the aircraft's fuselage where it can access the air flow in a relatively undisturbed area. Positioned at a point where movement creates minimum air pressure, the port is designed to measure the static air pressure outside the airplane. By allowing air into the instrument, it feeds the same pressure simultaneously to the altimeter, the vertical speed indicator, and the airspeed indicator, giving each the reference it needs to turn raw pressure into reliable flight data.
Expert behind this article
Jim Goodrich
Jim Goodrich is a pilot, aviation expert and founder of Tsunami Air.
What is the static port on an aircraft?
The static port is a part of the pitot static system, which is used in aviation to determine an aircraft's airspeed, Mach number, altitude, and altitude trend. It takes in air at ambient pressure, which remains relatively constant, unlike the pitot tube that measures dynamic pressure affected by the aircraft's speed.
The static port is located on an aircraft's fuselage. It appears as small flush mounted openings situated on either side of the fuselage. These ports are placed in aerodynamically neutral points to allow neutral air pressure measurements. A hole that is flush to the surface and perpendicular to the airflow is the only place where you can measure true ambient static atmospheric pressure on a body moving through the air at high speed. Static ports measure the atmospheric pressure around the aircraft. Static pressure is always present whether an aircraft is moving or at rest. The air pressure data provided by the static port is vital pressure data to flight instruments. These instruments include the airspeed indicator, the altimeter, and the vertical speed indicator. Static ports are connected to the airspeed indicator and the vertical speed indicator.
Commercial aircraft have at least two completely independent static systems to provide redundancy in case of system failure. Alternate static source is provided in some aircraft to provide static pressure when the primary static source becomes blocked. Static vents are often plugged when the aircraft is parked for more than a short period of time to reduce chance of blockage or contamination. Vents are electrically heated to prevent blockage by ice.
What does a static port do on a plane?
A static port is a flush-mounted hole on the fuselage that admits undisturbed outside air into the pitot-static system. The admitted air is called static pressure and it provides a constant reading of the current atmospheric pressure surrounding the airplane.
The pitot-static system uses this pressure to operate three primary instruments. Static pressure is delivered to the altimeter, which utilizes static pressure to determine altitude. The same pressure goes to the airspeed indicator: the ASI introduces static pressure into the airspeed case so that the instrument can compare both types of air pressure - dynamic and static - to generate an airspeed value. Finally, the vertical speed indicator uses static pressure to translate changes in that pressure into vertical speed in feet per minute. Beyond the three classic instruments, the pitot-static system provides data to the autopilot and cabin altimeter so that automatic flight-control and pressurization systems receive reliable altitude and rate-of-climb information.
Because the static port is only a small opening and not an active sensor, it cannot detect blockage by itself. A blocked static port will cause the altimeter to freeze at the altitude at which the blockage occurred, the airspeed indicator to display lower than actual airspeed when the airplane is above that altitude, and the vertical speed indicator to show a constant zero indication. To guard against such failures, commercial aircraft mount several static vents that feed into a common tube, and an alternate static source located inside the flight deck will be selected if the primary ports become blocked.
How does an aircraft static port work?
The aircraft static port works by giving the static system an undisturbed sample of the surrounding atmospheric pressure. This pressure is fed through a static line to the three pitot-static instruments: the airspeed indicator, the altimeter, and the vertical-speed indicator.
Inside the airspeed indicator the static pressure is paired with ram air pressure delivered by the pitot tube. The instrument is a differential-pressure gauge; it measures airspeed from the difference between ram air pressure and static pressure. As airspeed increases, ram air pressure rises while static pressure stays unchanged, so the expanding diaphragm connected to the pitot tube moves farther and the indicator displays a higher value.
The altimeter, a barometric altimeter, uses static pressure alone to determine altitude. Because static pressure decreases as the airplane climbs, the altimeter translates the falling pressure into a climb indication. Likewise, the vertical-speed indicator senses the rate of change in static pressure; a quick drop in static pressure produces a high rate-of-climb reading, while a sudden rise signals a descent.
When ice, dirt, or bugs block the normal static port, the pilot opens an alternate static source located inside the flight deck. The alternate source still provides static pressure, so the pitot-static instruments continue to operate and the flight can proceed safely.
