I guess I've been through different root cause training. From all of the RCA's I've been involved in, which all follows cause mapping, it'd be more like: yes it'll pinpoint MCAS as the main contributing factor but you don't just stop there and move on. You delve into why MCAS is the way it is, into the certification, management, design, etc. You go into the AoA sensor failure as another contributing factor and why it failed. And finally you also go into the pilots' reactions as another, lessor contributing factor then delve into that. Was it poor training, lack of training, sensory overload, incorrect personal choice, etc. To go along with the swiss cheese lining up metaphor, you don't just plug the biggest hole and move on, you plug all of the holes possible.
Thank you for having an insight into the process. What I believe you are missing is that a root cause investigation for a crash asks why did the crash occur. Not just why did the MCAS fail, and how the pilots reaction occured to that failure (although that can lead back to why the crash occurred). There are a lot of interconnected rabbit holes and tunnels....
Here is the outline of my thinking on this - and why I have my conclusions:
1) The MCAS/Flight Computer failure/issues was not the primary reason for the Lion Air crash. Yes that system failure created a problem and exposed a situation that led to the crash. The evidence to support this is that both the flight the day before adequately managed to fly the aircraft while resolving the issue (by turning MCAS off) and the Pilot of the flight that crashed was able to adequately fly the Lion Air aircraft with the problem.
2) While there are many aspects of workload, training, reactions, etc that then go into what the pilots are capable of or did do, and multiple possible factors that contributed to the event in some way (and if I were running the investigation - and I have run multiple many month root cause investigations with teams of people - I would likely have a contributing factor investigation of the confusion over what "continuous" meant in regards to the memory item for trim system cutout).
After thinking through everything that has been released about the Lion Air crash; and all the likely possibilities of the issues not yet released; my conclusion was what caused the Lion Air crash was "lack of key information" of the pilots that day. I actually don't see anything potentially out there that would invalidate that (although it may be stated a different way).
The pilots were faced with a system malfunction. No individual system malfunction should crash an aircraft, and in fact is that the pilots the day before and the pilot of the day did not crash the aircraft while the MCAS malfunction was occurring. The fact that Boeing missed this failure mode in their FMEA, and the FAA missed it as well, and other MCAS factors, is just part of the failure of that system (unfortunately, stuff like this happens - and the 738Max MCAS system is not the first case of it: Fortunately things of this magnitude are rare).
But the pilots of the day were faced with a problem caused by the failure of the system, which significantly increased their workload, etc. They apparently did not connect the response of the aircraft to the runaway trim failure memory item: perhaps because of a different meaning of "continuous" vs what Boeing apparently believed it meant, perhaps for other reasons.
I also do not believe that Boeing knew that this kind of failure event could happen in this way. My analysis also suggest that a similar failure could be caused with an intermittent wiring short (which does happen in other systems from time to time).
Boeing had adequately told the regulators and the Airlines about MCAS (although they had not told them that the amount of change had increased, which I consider fairly minor to the crash sequence). The Indonesia Regulators (as did all regulators except Brazil) agreed with Boeing's recommendation that no specific additional training be provided to the pilots about MCAS (and had the MCAS system been properly designed because the FMEA properly identified the failure mode and significance - with what will be Rev 2 software it's likely that would have been adequate as there are a lot of things pilots are not specifically trained on). The Airlines and Airline Maintenance departments fully knew about MCAS. NOTE: My understanding is that it was not and is not Boeings direct responsibility to notify and train the pilots about MCAS. It is the Regulators and Airlines responsibility (there seems to be a lot of misplaced blame on this point).
The key piece of information that would have prevented the crash, and notified the Airline and Boeing is that this system failed and in this way was from this very same aircraft the day before. The MCAS failed and created a problem that the pilots (with assistance from a 3rd pilot) were able to control while they troubleshot; and implemented their solution of turning off MCAS. Yet, it appears they told no one (and certainly not the pilots of the next flight), and apparently there is no kind of logs withing Lion Air for Pilots to report how their flights went and any issues dealt with (other than specific maintenance items).
It is my belief that had the Pilot retained control of the the aircraft and returned to the airport that there would not have been a crash. He was adequately controlling the situation by constant manual trim up commands. Once on approach and with flap extension the MCAS problem would have gone away. While I have a lot of questions, I have no conclusions as to why the Co-Pilot did not also continue the continuous manual trim ups that the Pilot had been doing (I hope that the CVR transcript will clarify that, when released). But, he didn't - and the trim then went low the aircraft crashed.
Imagine the difference if both the Pilot and Co-Pilot knew before they took off of the previous day's MCAS issue and resolution.
A root cause asks what caused the crash, and what key item or perhaps items would have prevented that specific crash. The MCAS/Flight computer failure was bad (and a clear contributing factor). But did not actually cause the crash, as demonstrated by the pilot adequately flying the aircraft during the failure (and the pilots the day before adequately flying the aircraft during the failure before they turned off MCAS). The lack of knowledge by the Pilots and Co-Pilot about that failure possibility on the day of the flight, and how to recognize and respond to it - in my opinion did cause the crash. The key information that this kind of event (with intermittent automatic trim downs), and its resolution, was held by the pilots of the flight on the day before. Why this information was not passed should (in my opinion) be a focus of the root cause investigation. Based on experience its far more likely to be inadequate Lion Air procedures and culture than other factors. No Crew Member goes to work intending to create a problem or not pass on key information (most people claiming Pilot or Operator Error - are actually citing examples where the Pilots and Operators were set up to fail by bad procedures, training, etc.)
Of course, with any root cause there are likely at least 20 other things that would be investigated as potential causes and a number of them listed as Contributing Factors.
I hope that helps people understand why I conclude that Lion Air hold the key responsibility for this crash, and the MCAS mis-design is just a contributing factor.
Have a great day,