IRS mode selector unit MSU.


    System is switched off. The IRU transfers the last calculated position to its memory.
    When set to ALN, the IRU initiates the alignment sequence. To complete the alignment, present position has to be entered via the FSM CDU.
    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.
    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.