-a message ENTER PPOS is displayed on the CDU (DATA DISPLAY
 selector switch in STS position). The miscompare is removed and the position data verified by the IR when:
 -
the last two Set Latitudes received by the IR are identical and the last two Set Longitudes received by the IR are identical, or

 -
the last Set Latitude and Set Longitude received by the IR compare within one degree (or one degree divided by cos(latitude)) of the latitude and longitude from the previous flight.

 (b)
 Latitude comparison The IR compares Set Latitude with a self-computed gyro-compass latitude after 10 minutes into alignment or any subsequent time when a valid Set Latitude is available. In case of discrepancy, on the ADIRS CDU the ALIGN light flashes. The message ENTER PPOS is displayed on the CDU (DATA DISPLAY selector switch in STS position). The discrepancy exists when:

 -the entered latitude differs from the computed latitude by more than 0.5..
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 MCDU - INIT Page
 Figure 009
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 The miscompare is removed if a subsequent entry of Set Latitude
 passes the test.
 If latitude test fails two times with identical set latitude
 inputs then:

 -
the IR FAULT legend flashes on the CDU

 -
the message IR FAULT appears on the CDU liquid crystal display (DATA DISPLAY selector switch in STS position)

 -a warning message appears on the upper ECAM DU:
 NAV IR 1(2)(3) FAULT.

 (c)
 Excessive motion The IR performs an excessive motion test during the Align submode. If taxiing or towing causes a step input which exceeds 0.2 ft/s in the X or Y velocity, then:

 -
the EXCESS MOTION message is displayed on the CDU (DATA DISPLAY selector switch in STS position)

 -
the following message is displayed on the upper ECAM DU: NAV IR 1(2)(3) NOT ALIGN EXCESS MOTION IR 1(2)(3) IN ALIGN

 -
the attitude information is flagged on the PFD.
 Thirty seconds after motion detection, the system reverts to a
 full alignment (time to the end of alignment will revert to 9 min
 30 s).
 It is not necessary to re-enter the position.

 (d)
 Thirty-second rapid realignment A thirty-second rapid realignment is provided by moving the OFF/NAV/ATT selector switch on the CDU from NAV to OFF and back to NAV within five seconds. A subsequent switching on the selector switch from NAV to OFF and back to NAV within 5 seconds during the 30-second realignment causes the system to start the 30-second realignment again. The realignment is initialized with existing attitude and heading angles. Velocities are zeroed. Valid position data must be received and verified by the IR during the 30-second realignment.

 (4) ATT (Attitude) mode The IR has a reversionary mode which can be activated only by manual selection of ATT mode on the CDU. The mode can be activated on the ground or in flight and is intended to provide a rapid attitude/heading restart capability in the event that the IR has
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 experienced a total power shutdown or a failure has occurred resulting in the following:
 -
IR FAULT legend flashing on the CDU

 -
IR 1(2)(3) FAULT message displayed on the upper ECAM DU: IR x MODE SEL...ATT

 -SELECT ATT message displayed on the CDU (DATA DISPLAY selector
 switch in STS position). The IR is designed so that the ATT mode can be used after BITE has detected failures which will cause excessive NAV mode data errors but does not disable the ATT mode mechanization. However, it is recommended to stay in NAV mode even with excessive navigation errors because of higher accuracy of attitude signals and a more complete signal processing. The ATT mode must always be used after loss of power or a similar situation in flight where a new alignment/leveling is required. The ENTER HEADING message is displayed on the CDU (DATA DISPLAY selector switch in STS position) when the ATT mode is selected until valid heading initialization is received from the MCDU or the CDU. The ATT mode is normally engaged with the aircraft in level flight. A 30-second period is needed with the aircraft in level flight to perform an attitude erection to initialize a "level" attitude. During this period, the data normally computed in ATT mode have SSMs set to NCD.
 B. Indicating Attitude and heading information is computed by the ADIRU (IR portion) and processed by the associated DMC. The attitude data are displayed on the PFD and the heading data are displayed on the PFD, the ND and the VOR/DME RMI. In addition, vertical speed (V/S) is displayed on the PFD and Ground Speed and wind indications are displayed on the ND. In normal configuration, with the ATT/HDG selector switch in NORM position, the IR1 data are displayed on the CAPT PFD, ND and the VOR/DME RMI (Ref. ATA 34-57-00). The IR2 data are displayed on the F/O PFD and ND. The following parameters can be displayed on the CDU liquid crystal display according to the position of the DATA DISPLAY selector switch on the CDU:
　
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