- OFF.
- System is switched off. The IRU transfers the last calculated
position to its memory.
- ALN.
- When set to ALN, the IRU initiates the alignment sequence. To complete
the alignment, present position has to be entered via the FSM CDU.
- NAV
- Permits system to enter navigational mode when alignment sequence is
completed. If NAV is selected from OFF position, a normal alignment is
initiated followed by automatic transition to NAV mode. Provided the
present position is entered.
- ATT
- Selects attitude and directional gyro only mode of operation.
- ALIGN light.
- Illuminates steady when the IRS is operating normally in the align mode.
- ON BATT light.
- Illuminates when the IRS is powered from its back-up battery. Will
also illuminate for a short period when system is turned on.
- BAT FAIL light.
- Illuminates to indicate that the voltage of the 24V DC source has fallen
below 19 volts.
- FAULT light.
- Illuminates to indicate a system failure requiring maintenance action.
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