Same crews globally, Same training, Same AoA vane.
Boeing have done a unfortunate "natural experiment" between the NG and the MAX.
Almost everything remained constant, the only really significant change was the inclusion of additional software and larger engines. The engines have not been directly implicated in either accident.
Same crew training on the NG and the MAX, yet the fatality rate is
3.08 per million departures compared to
0.06 per million on the NG. Not only that, the NG has more than 100+ x the flights. This is a massive sample size of NG departures, I will also concede the sample size is relatively small for the MAX.
Everything is as constant as we could reasonably expect to perform a valid scientific comparison between two models.
Why did the MAX crash at more than 100 times the rate of the NG when they were almost indistinguishable from a crew perspective?
I posted on another thread
#2891
This comes back to the natural experiment that Boeing have performed between the MAX and the NG. Same AoA vane (IIRC same part number), and almost everything identical. So if you want to assume constant component failure rate, why are there no NG accidents related to flight controls or instrument failures that I can recall?
Boeing has been undone by this high degree of commonality. The difference in the accident rates with almost identical systems was too stunning to ignore. When investigation reveal there was a new MCAS system (previous rebuke for calling it software accepted in post #2459 ) there was nowhere for Boeing to hide. A single system change related to flight controls could be pin pointed as the single cause of the accidents. Sure there were plenty of other factors (training, experience, organisational, SOPs), but they were all held constant between the NG and the MAX.
Pilots have been dealing with AoA vane failures and faults since 1997 at the same rate as the MAX with the introduction of the NG without a fatality. MCAS is the only significant variable that has been implicated in these accidents. It simply could not be ignored.
I posted earlier, Boeing's October 2018 own data, that attested to the safety of the NG. Some 100+ million flights without flight control issues, and then 0.65 million MAX departures with two flight control fatal accidents. It was not the AoA vane failure that was the cause, it was the MCAS system, and only the MCAS system that the airworthiness authorities could not sweep under the rug and dismissed as pilot error and ignore because everything was so common with the NG.
Put yourself in the shoes of a senior CAA official looking at these figures comparing the max to the NG. Could you honestly let it fly in your airspace? Because I would be certain, this is the data that each CAA would have had compiled very quickly
As an aside, I keep thinking that this whole failure is looking more similar to the first computer accident, the Therac-25 accident X-Ray machine as documented by Nancy Leveson.
In that accident, a sequence of models of new software dose control were held constant, and a physical interlock preventing a lethal does of radiation to the patient was eventually removed. This interlock was from the previous non-computerised model where the operator could accidentally overdose a patient. What the company failed to understand, was the software was actually faulty right from the start, the interlock was saving patients for years without the company understanding the fault.
To me, the MAX accidents have a similar theme, engineering assumptions made on the basis of almost identical systems, with small iterative flawed changes that lay dormant until the accident sequences.
Here is Boeing's own data
Source: Boeing Statistical Summary of Commercial Jet Airplane Accidents Worldwide Operations | 1959 – 2017