Unpredictability
I put unpredictable because most of the design effort was put to avoid the extremes.
After the "threshold" there are a lot of extra issues. And the interface is crucial.
One thing is clear: The System manager (PF) ideally should be capable to "avoid" (WX radar use, Comm. resources use, etc.) and to properly "administrate the crisis" after a System degradation.
But the optimization of the advanced designs "comes at a price" when unexpected (or unexpectable") situations arise.
The NYU risk Engineering professor introduced the "Black Swan" concept about "the highly improbable" events. I posted earlier a mention on him.
May be this case after BEA analysis may fit.