A-320/FMGS runway updating
 

How do you check FMGS runway updating if you have lost GPS primary and with GPS primary ?

Thanks

Think you'll find it's inhibited with GPS primary active - what would be the point of having it?

Without GPS primary, you would see the FM position 're-align' to the runway threshold.

FCOM 1.22.20

It updates when you go to takeoff thrust. If you load the wrong runway in the FMGC then it looks at the difference between the runway position (where you told it it was) and where the GPS thinks it is and will give you an ecam NAV FMGC POS disagree