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ABNORMAL OPERATIONS
NAVIGATION
ADR/IRS FAULT
Applicable to: ALL
Each ADIRS has two parts (ADR and IRS), that may fail independently of each other. Additionally the IRS part may fail totally or may be available in ATT mode.
Single NAV ADR FAULT or NAV IRS FAULT are simple procedures, and only require action on the switching panel as indicated by the ECAM.
Dual NAV ADR or NAV IRS failures will cause the loss of AP, A/THR and flight controls revert to ALTN LAW.
Due to the low probability of a triple ADR failure, the associated procedure will not be displayed on the ECAM. In this case, the crew will refer to QRH procedure for ADR 1 + 2 + 3 failure.
There is no procedure for IRS 1 + 2 + 3 failure but the ECAM status page will give approach procedure and inoperative systems. In this unlikely event, the standby instruments are the only attitude, altitude, speed and heading references.
Note: To switch OFF an ADR, the flight crew must use the ADR pushbutton. Do not use the rotary selector, because this would also cut off the electrical supply to the IR part.
UNRELIABLE AIRSPEED INDICATIONS
Applicable to: ALL
PREFACE
Most failures modes of the airspeed/altitude system are detected by the ADIRS. These failures modes lead to the loss of corresponding cockpit indications and the triggering of associated ECAM drills.
However, there may be some cases where the airspeed or altitude output is erroneous without being recognized as such by the ADIRS. In these cases, the cockpit indications appear normal but are actually false and pilots must rely on their basic flying skills to identify the faulty source and take the required corrective actions. When only one source provides erroneous data, a straightforward
crosscheck of the parameters provided by the three ADRs allows the faulty ADR to be identified. This identification becomes more difficult in the extreme situation when two, or even all of three, sources provide erroneous information.
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
CONSEQUENCES OF OBSTRUCTED PITOT TUBES OR STATIC PORTS
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