Originally Posted by PJ2
The puzzle is, with so much information available prior to the accident, why did the accident occur at all?
Because it is
conflicting information - Nothing is clear.
Following the Air Caraibes events and the subsequent Memo, it was a known and accepted fact by Airbus that unreliable airspeed indication in cruise do happen and could be tricky. Airbus had to publish a clear and unambiguous note to all crews how to properly deal with such scenario that triggers a load of ECAMs but can be easily mastered if you do this this and that.
They knew that something was coming, hopefully not as bad as AF447, but something has to be done to inform crews before they face the situation.