Rainboe,
1- how does the system 'know' RA1 is at fault? Who is to say what the correct reading should be? It's in failure mode- to the RA, -8 was a perfectly valid reading.
Yes, perhaps. But its occurence - sudden drop from 2000 feet or whatever to 'on ground' value without transitioning through values consistent with flare - IS NOT and is a clear evidence of malfunction (seemingly a failure mode not taken into account by designers, not quite uncommon as it turns out).
Putting aside obvious airmanship issues, situation of a malfunctioning instrument feeding erroneus data into (whichever) system is not a desired one. Malfunction should have been detected by RA's logic and the RA just flagged INOP, I think you agree.
There's nothing wrong with enhancing onboard safety systems. Eventual modification to the RAs (simple trend monitoring) would not inflict any weight penalty, being made purely in software. One hole in a swiss cheese less.
Regards,
MikeEPBC