Originally Posted by
Pinkman
I've stayed silent, and like many, simply followed this shambles aghast over the past year. I understand what happened and the holes in the cheese both technical, managerial and political that got us to this point. I accept that it may- may - just be statistics (rather than competency or training) that the two 737 max fatalities occurred outside the US. What i dont understand though is why, given the 737 max user base in the US, there wasnt a significant stream of precursor/near miss reports prior to the incidents or commentary after the incidents "oh, yeah that happened to us but we managed the situation". I may have missed that but it just seems.. odd. If the situation was so common that it lead to two very similar crashes within months, would you not have expected that the common mode causative factors, presumably present in the entire fleet, would have generated substantial numbers of near misses... and pre / post comment..?
This issue was discussed some time ago. The main points are that:
1. AOA sensor failure are relatively rare, but do occasionally occur.
2. A number of AOA failures have been recorded on other aircraft, but mostly with benign outcomes.
3. On the new B737 MAX an AOA failure triggers MCAS, with every case producing a very serious outcome.
IMO this explains the lack of prior feedback as to the magnitude of the risk.
There are probably many other ways of explaining the story:
1. In Russian Roulette firing an empty chamber produces no result, so the incident is not reported.
2. In the Sherlock Holmes story of the dog who didn't bark in the night, you have to infer evidence from a negative result.
3. Draw up a fault tree, and analyse the prior probabilities with Bayesian Statistics.
4. The Swiss Cheese model requires all the factors to line up, for an accident to occur.
Edit:
PEI_3721 In the absence of an accident investigation, there is no download from the FDR, so we have limited historical AOA data for reference.