A318/A319/A320/A321 机组训练手册 FCTM Flight Crew Training Manual(150)

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MAIN REASONS FOR ERRONEOUS AIRSPEED/ALTITUDE DATA
The most probable reason for erroneous airspeed and altitude information is obstructed pitot tubes or static sources. Depending on the level of obstruction, the symptoms visible to the flight crew will be different. However, in all cases, the data provided by the obstructed probe will be false. Since it is highly unlikely that the aircraft probes will be obstructed at the same time, to the same degree and in the same way, the first indication of erroneous airspeed/altitude data available to flight crews, will most probably be a discrepancy between the various sources.
 

  ABNORMAL OPERATIONS
NAVIGATION
A318/A319/A320/A321
FLIGHT CREW TRAINING MANUAL 

CONSEQUENCES OF OBSTRUCTED PITOT TUBES OR STATIC PORTS
All aircraft systems, using anemometric data, have been built-in fault accommodation logics. The fault accommodation logics are not the same for various systems but, all rely on voting principle whereby when one source diverges from the average value, it is automatically rejected and the system continues to operate normally with the remaining two sources. This principle applies to flight controls and flight guidance systems.
NORMAL SITUATION
Each ELAC receives speed information from all ADIRUs and compares the 3 values. Pressure altitude information is not used by the ELAC.
Each FAC (Flight Augmentation Computer) receives speed information from all ADIRUs and compares the 3 values.
ONE ADR OUTPUT IS ERRONEOUS AND THE TWO REMAINING ARE CORRECT
The ELAC and the FAC and/or FMGC eliminate it without any cockpit effect (no caution, normal operation is continued), except that one display is wrong and CAT III DUAL is displayed as INOP SYS on STATUS page.
TWO ADR OUTPUTS ARE ERRONEOUS, BUT DIFFERENT, AND THE REMAINING ADR IS  CORRECT, OR IF ALL THREE ARE ERRONEOUS, BUT DIFFERENT :
The autopilot and the auto thrust are disconnected (whichever autopilot is engaged). The ELAC triggers the F/CTL ADR DISAGREE ECAM caution. Flight controls revert to Alternate law (without high and low speed protection). On both PFDs, the "SPD LIM" flag is shown; no VLS, no VSW and no VMAX is displayed.
This situation is latched, until an ELAC reset is performed on ground, without any hydraulic pressure.
However, if the anomaly was only transient, the autopilot and the autothrust can be re-engaged when the disagree has disappeared.
ONE ADR IS CORRECT, BUT THE OTHER TWO ADRS PROVIDE THE SAME ERRONEOUS  OUTPUT, OR IF ALL THREE ADRS PROVIDE CONSISTENT AND ERRONEOUS DATA :
The systems will reject the "good" ADR and will continue to operate normally using the two "bad" ADRs. This condition can be met when, for example, two or all three pitot tubes are obstructed at the same time, to the same degree, and in the same way. (Flight through a cloud of volcanic ash, takeoff with two pitots obstructed by foreign matter (mud, insects)).
　
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