MD-11 Aux IRU

[New on NG]

:confused: Hello Everyone!!
Does anybody could answer me why we can not switch the batteries between auxiliary and #2 or #1 IRU for dispatch?
The MEL item says that the IRU aux is minimal for dispatch if the airplane is equipped with SFD Secondary Flight Display.
Thanks in advance!

[Flightmech]

Should be in tech/questions forum. However, If your MD-11 fleet has the Secondary Flight Display System (the EFIS one) installed then the AUX IRU and all of it's related components (ie. battery) are required as the SFDS needs it for attitude etc like the PFD's get from IRU 1/2. If the aircraft has the original analogue standby instruments (standby horizon and combined altitude/airspeed indicator) then you can despatch with the AUX IRU inoperative, or swap any of its components to make the number 1 or 2 system serviceable.

[Huck]

the SFDS needs it for attitude

Needs it for attitude, or just needs the aux battery power? We're getting these installed - I don't know the answer....