Dual fmc failure

[JammedStab]

Originally Posted by FE Hoppy

How can you navigate with reference to IRS if you don't have an FMS?
You need not only position accuracy but also flight technical error accuracy. Unless your avionics can bypass the FMC and display deviation from IRS(INS) DTRK you cannot fly RNP-10 without an FMS.

Thanks,

The CDU replaces the FMC for reference and uses Alternate navigation. It is more cumbersome but we still have navigation capability. Sort of like in the old INS days without a database where any waypoints are entered by lat/long. Other restrictions apply as well but we can continue to navigate.