Aircraft Instruments

Pitot-Static System

The aircraft pitot-static system includes instruments that operate on the principle of the barometer. The system consists of a pitot tube, static air vents, and three indicators, which connect with pipelines that carry air. The three indicators are Airspeed, Altimeter, and the Vertical Speed.

The airspeed indicator shows the speed of the aircraft through the air, and the altimeter shows the altitude. The Vertical Speed Indicator (VSI) indicates how fast the aircraft is climbing or descending. All of these indicators operate on air that comes in from outside the aircraft during flight.

The pitot tube mounts on the outside of the aircraft at a point where the air is least likely to be turbulent. The tube points in a forward direction parallel to the aircraft’s line of flight. One general type of airspeed tube mounts on a streamlined mast extending below the nose of the fuselage. Another type mounts on a boom extending forward from the leading edge of the wing. Although there is a slight difference in their construction, the tubes operate identically.

The Pitot System measures impact pressure, which is the pressure of the outside air against the aircraft flying through it. The tube that goes from the pitot tube to the airspeed indicator applies the outside air pressure to the airspeed indicator. The airspeed indicator calibration allows various air pressures to cause different readings on the dial. The purpose of the airspeed indicator is to interpret pitot air pressure in terms of airspeed in knots.

Generally, static air vents  are small, calibrated holes in an assembly mounted flush with the aircraft fuselage. Their position is in a place with the least amount of local airflow moving across the vents when the aircraft is flying.

Static means stationary or not changing. The static part of the pitot-static system also introduces outside air. However, the outside air is at its normal outside atmospheric pressure as though the aircraft were standing still in the air. The static line applies this outside air to the airspeed indicators, the altimeter, and the vertical speed indicator.