Originally Posted by
FlightDetent
Not so crystal.
I do not think mothergoose1 understands fully the technology behind MCDU BACK-UP NAV.
So, AP yes, RNAV yes-some. The whole feature as far as I understand it was developed to increase redundancy for ocean crossings, keeping the RNP capability as a sole objective.
Specifically about RNP5, I do not know. RVSM no problem.
Yes, you are right. Could happen that the AP is available because the FG part of the FMGC is working. In that case no problem with RVSM.