March 9, 20179 yr Quote Cycle them off. Wait a few seconds, and then cycle them back to NAV. (i.e. For sim purposes only) Normally, in the real world, if you move the IRU selectors to OFF, it's best to wait 30 seconds (to allow the IRU to save vital data into its non-volatile memory). On the Boeing 767, you could tell the IRUs were doing this (via annunciator lights), but on the 747-400, there are no lights, so extra caution is advised. Note that the aircraft must be stationary during the cycling process, and, of course, in the real world, navigation mode would not be achieved for a full 10 minutes (The Navigation Displays show "+7", but the actual time required is around 10 minutes). Cheers JHW John H Watson (retired 744/767 Avionics engineer)
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