Aircraft System Failure

One of the most dangerous failures that can occur in an aircraft is the blockage of the pitot-static system. The pitot static system consists of the pitot tube and the static port. The pitot tube is responsible for measuring dynamic pressure which is present when the aircraft is moving, and static pressure, which is always present, whether the aircraft is at rest or moving. The pitot tube collects total pressure (dynamic and static pressure) but sends only the dynamic pressure to the airspeed indicator (ASI). The static port collects the undisturbed air on the side of the aircraft and as atmospheric pressure changes, the air is moved freely to correspond to the changes in pressure. The altimeter and vertical speed indicator (VSI) both utilize static pressure to correctly display altitude and rate of climb or descent. When the pitot tube becomes blocked, it will display incorrect airspeed information and will act as an altimeter. Blockage can be due to moisture, ice, insects, and debris. When the static port becomes blocked, but the pitot tube remains clear, the airspeed indicator continues to work but will work inaccurately. The altimeter will freeze on the altitude at where the blockage began, and the vertical speed indicator will continuously read zero. If both the pitot tube and static port become blocked, the ASI, VSI, and altimeter’s readings will remain constant at any given shift in altitude or speed. (PHAK, 2016)

 

Failure in the pitot-static system can prove to be deadly due to the inaccurate instrument readings they provide, especially when flying in Instrument Meteorological Conditions (IMC). If moisture freezes up and causes ice to block the pitot tube, the pilot can enable pitot heat to undue the blockage and resume normal operating conditions. Additionally, on some aircraft, there is a secondary static port to be used if the primary static port is blocked, usually located inside the aircraft.

 References: Pilot's Handbook of Aeronautical Knowledge