Originally Posted by
bsieker
This was supposed to be a system to prevent accidents, but it is quite clear that in this case it was a causal factor of an accident. It is hard, or maybe impossible to say how many accidents it has prevented (plausibly: none). Given the law of small numbers one cannot yet say that the MAX would be better off without the system altogether, and some system was also arguably required to fulfill certification criteria for longitudinal stability. Such systems have a long tradition, often in the form of stick pushers, to mitigate adverse aerodynamic effects. Using hardware already available is a "cheap" solution, compared to the complexities of an actual pusher, but in terms of certification, "just good enough" is good enough.
Bernd
I don't think that you can say that anymore than you can say that the ADIRUs that gave UAS indications due to the same AOA vane fault and caused the FMS to remain unengaged were a causal factor., Had the crew cut off the stab trim when it repeatedly re-trimmed ND for them - this crash would not have happened. The causal factor if any was the AOA disagree that was allowed to propagate errors through the system, all errors that could be and were handled by the crews on the previous flights. If there was a reasonableness check of AOA using other non-pressure instrument indications then a grossly misreading AOA vane could be identified and disabled. The organizational fault is that an aircraft with a fault that repeats over several fights should be grounded for a full maintenance check and then given a test flight without pax by a crew that have been fully briefed on the fault and symptoms and self briefed on the actions to be taken if those symptoms recur.