空速管原理图.docx

Figure 6: PFD in normal lawFigure 7: PFD in alternate 2 lawFigure 8: Pitot probe diagram1.6.9.6.3 Consequences of a drop in the measured total pressureThe first consequence of a drop in measured total pressure is a drop in the Mach and the CAS. The drop in Mach leads to a drop in standard altitude due to the correction of the measured static pressure. This drop is different according to the ADR under consideration: in the flight conditions of the event, it is of the order of 300 to 350 ft for the ADR 1 and 2 and of 80 ft for ADR 3.The drop in indicated standard altitude also causes a transient variation in Vzbi. Just as the drop in standard altitude is lower for ADR 3 than for ADR 1 and 2, the variation in Vzbi is lower for ADR 3 than for the two others, as illustrated by the graph below:Figure 10: Effect of a drop in total measured pressure on pressure altitude and vertical speedThe drop in Mach also impacts the SAT and thus the true air speed and the wind speed. In the following table, the case an A330-200 flying at FL 350 at Mach 0.8 instandard atmosphere with a 30 kt head wind is given as an example to illustrate the consequences of Pitot icing that would result in a drop in Mach from 0.8 to 0.3.Real valueIndicaded valueMach0.80.3Standard altitude (ft)35,000 34,700CAS (kt)27297SAT (C)-54-31TAS (kt)461182Wind speed (kt)-30249In a schematic manner, the threshold is stable below a Mach of the order of 0.3, then reduces in a quasi-linear manner to a Mach of the order 0.75, after which it falls more rapidly when the Mach increases up to Mach 0.82:Figure 11: Evolution of stall warning threshold in relation to MachA decrease in speed results in an increase in the angle of attack, if the load factor is constant and in a calm atmosphere. In this case, the decrease in speed corresponding to an increase in a given angle of attack depends on the flight conditions:Flight conditionCruiseTakeoff / ApproachLevel of decrease in indicated speed for an increase of 1 in the angle of attack25 kt5 ktThe wind and temperature charts show that the average effective wind along the route can be estimated at approximately ten knots tail-wind. On the chart for FL340, the highest air temperature is located around the equator. It is estima