Originally Posted by
bigduke6
Yes, exactly. The aircraft is navigating using the FMC position.
So if that position is in error, then the navigation is that much in error.
However, as you point out, with multiple sources, that error is likely small or essentially none with GPS. And there is an alerting/monitoring feature if the FMC predicts that its possible navigation error will exceed the tolerance for the airspace or the approach being flown.
Thanks for the quick answer!