Hi,
Difficult question! (Presented by an "instrumentation professional")
We could pinpoint the moment the AS started to change in respect to "ground speed" (supposing AS sensors LYING and presenting the "identical" info.) BEA is doing all necessary correlations.
But i understand your question is no about BEA task. Is for the System: Until the point (time) the sensors present different info.
how to detect they are "failing"?
The "band-aid" we learned is being considered using (for short periods) other references could reduce the criticality of the issue: Reliable "speed info." required by the System.
But the only way to "kill" adequately the issue is with really redundant AS sensors. The ideal is to have at least three (methods) allowing a "voting scheme".
Again AoA comes to my mind...
How the System could work properly if ALL AS SENSORS "lie" to it? How it can detect? Detectors, (sensors) if the System requires (the truth) the real AS, can not LIE together. Itīs simply dangerous (to the a/c). And can (i guess) today generate undetectable "strange behavior".
Introducing "extra components", not just "robbing precious time".