under what circumstances is it acceptable for your instrumentation to go away? none is the answer.
If the event was caused by the instrumentation going away it's bad. If the instrumentation went away because of the event, that's also bad.
Instrument failures happen. That's why redundancy is built in.
> If the instrumentation went away because of the event, that's also bad.
That is bad. But not as bad a FBW system bug.
> That is bad. But not as bad a FBW system bug.
The event in question is better than the plane plummeting out of the sky and killing everyone. That doesn't make it ok for the event to have happened.