747-400 FMC Update Status Display on ND
Would some kind person/aka -400 guru be able to explain the following?:
The FMC Update Status display in the lower RH corner of the Navigation Display shows which nav systems are providing position info to the FMC (e.g. "IRS(3)"). When I pull the FMC CB's, the display disappears (as might be expected). However, when the aircraft is running on Standby Power, the display _remains_ in view even though the FMC's are unpowered.
I realise that the Captain's CDU, should still be operating under these circumstances, however, even though my manuals tell me that the CDU uses the onside IRU for navigation (when ALTN Navigation is available during Stby Pwr ops), the "IRS(3)" display remains. Is this a software anomaly?
Thanks.
Rgds.
Q.