Hazardous events typically demand more than one sensor — except when they are outside normal flight conditions and unlikely to be encountered, such as a wind-up turn.
"Hazardous", as most know is a specific category.
In this detailed summary there were perhaps four significant things I was unaware of. The above is one of them. It seems a small factor, but when you think what the term's qualifiers were, it becomes a major factor - inasmuch that if that qualifier wasn't there this thread might never have existed.
The article also gives several hints of how lives within the corporation must have been affected. Profoundly so.