the pressure difference , where is the height difference of the columns; is the density of the liquid in the manometer; g is the standard acceleration due to gravity. Therefore, Aircraft and accidents A pitot-static system is a system of pressure-sensitive instruments that is most often used in aviation to determine an aircraft's airspeed, Mach number, altitude, and altitude trend. A pitot-static system generally consists of a pitot tube, a static port, and the pitot-static instruments. Errors in pitot-static system readings can be extremely dangerous as the information obtained from the pitot static system, such as airspeed, is potentially safety-critical. Several commercial airline incidents and accidents have been traced to a failure of the pitot-static system. Examples include Austral Líneas Aéreas Flight 2553, Northwest Airlines Flight 6231, Birgenair Flight 301 and one of the two X-31s. The French air safety authority BEA said that pitot tube icing was a contributing factor in the crash of Air France Flight 447 into the Atlantic Ocean. In 2008 Air Caraïbes reported two incidents of pitot tube icing malfunctions on its A330s. Birgenair Flight 301 had a fatal pitot tube failure which investigators suspected was due to insects creating a nest inside the pitot tube; the prime suspect is the black and yellow mud dauber wasp. Aeroperú Flight 603 had a fatal pitot-static system failure due to the cleaning crew leaving the static port blocked with tape. Industry applications In industry, the flow velocities being measured are often those flowing in ducts and tubing where measurements by an anemometer would be difficult to obtain. In these kinds of measurements, the most practical instrument to use is the pitot tube. The pitot tube can be inserted through a small hole in the duct with the pitot connected to a U-tube water gauge or some other differential pressure gauge for determining the flow velocity inside the ducted wind tunnel. One use of this technique is to determine the volume of air that is being delivered to a conditioned space. The fluid flow rate in a duct can then be estimated from: Volume flow rate (cubic feet per minute) = duct area (square feet) × flow velocity (feet per minute) Volume flow rate (cubic meters per second) = duct area (square meters) × flow velocity (meters per second) In aviation, airspeed is typically measured in knots. In weather stations with high wind speeds, the pitot tube is