"I don't have access to an aircraft or the sim until tomorrow but will give it a whirl then (if I remember)"
Thanks for the offer, "CJ"
I realised that the IRS's were running on the batteries, but my main concern was the statement in the books which says that L CDU uses the onside IRU (only) during ALTN NAV, yet the Captain's display is telling us that all three IRU's are active.
Does the L CDU also carry out the triple mix function? (I thought only the FMC(computer) would do this
).
The Boeing Schematics are no help, as they only show a single databus going from the L IRU to the L CDU (No interaction with the other IRU's). I'm sure the EIU doesn't do any mixing. Perhaps the EIU is simply looking at which nav systems are available... and making an educated
guess at what the FMC/CDU is doing with the data and putting up the update display (sounds a bit dodgy, tho').
Thanks again.
Cheers.
Q.