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IR - Alignment Procedure from the MCDU
Figure 010
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IR - Mode State Diagram
Figure 011
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-a message on the UPPER ECAM DU indicates that the IRs are in ALIGN submode with the maximum time until NAV
-in the NAV mode, rapid realignment of the IR is initiated by switching the OFF/NAV/ATT selector switch from NAV to OFF and back to NAV within 5 seconds. The IR starts a 30-second realignment submode with existing attitude and heading angles and rezeroed velocities
-the system does not enter the rapid realignment sequence if the
ground speed is greater than 20 knots. The CDU permits to observe some particular parameters (Ref. 34-12-00).
(a)
Initialization data (Ref. Fig. 012) IR alignment is carried out on the ground before takeoff and after the entry of the current aircraft coordinates on the INIT page of the MCDU 1(2) (Ref. 22-72-00) or on the CDU (DATA DISPLAY selector switch in PPOS position). Valid initial position data must be received and verified by the IR during the 10-minute alignment or automatic sequencing to the NAV mode will be delayed after position data is received. Initial position data are verified by the IR if Set Latitude and Set Longitude compare within one degree of the last latitude and longitude from the previous flight. If a miscompare exists then: - on the ADIRS CDU, the ALIGN light flashes.
-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 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 cosine of entered latitude differs from the computed cosine of latitude by more than 0.01234, or
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MCDU - INIT Page
Figure 012
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-
the sine of entered latitude differs from the computed sine of
latitude by more than 0.01234. The miscompare is removed if a subsequent entry of Set Latitude passes the test. If sin/cos test fails two times with identical set latitude inputs then:
-
the IR FAULT legend flashes on the CDU
-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 0.5 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 the flight and is intended to provide a rapid attitude/heading restart capability in the event that the IR has
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