Aterpster
Dual GNSS
Dual FMS
FMS must provide continuity, integrity, accuracy, and alerting.
Indeed, that's what ours says too. But as far as I am concerned a little message on the scratch-pad of the FMC or on the PFD, is not the same as a big red flag on the PFD or the GPWS shouting 'glideslope'.
And dual GPS receivers are of no benefit if there is ghosting or other signal interference, as both receivers will pick up the same error. GPS signals are not as strong as an ILS, and low-level GNS navigation is a whole new ball-game.