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"So Boeing produced a dynamically unstable airframe, the 737 Max. That is big strike No. 1. Boeing then tried to mask the 737’s dynamic instability with a software system. Big strike No. 2. Finally, the software relied on systems known for their propensity to fail (angle-of-attack indicators) and did not appear to include even rudimentary provisions to cross-check the outputs of the angle-of-attack sensor against other sensors, or even the other angle-of-attack sensor. Big strike No. 3.
None of the above should have passed muster. None of the above should have passed the “OK” pencil of the most junior engineering staff, much less a DER.
That’s not a big strike. That’s a political, social, economic, and technical sin."
This article is the best and most complete explanation of this problem.
Yes Boeing dropped the ball on this one, all in the name of corporate greed. Fancy basing the system off just one AoA sensor with no cross check, for a system that could plunge you into the ground in seconds.
That was a great article. And well worthy of its own thread.
Unfortunately
There will be a congressional investigation
A few people will get burned and maybe some fines that will disappear into general funds
Lawsuits will be filed and settled
It will all quietly go away
Last edited by homelessinseattle; 04-20-2019 at 11:09 AM..
Reason: Crosscheck
I take exception to this article, specifically this paragraph:
"It is astounding that no one who wrote the MCAS software for the 737 Max seems even to have raised the possibility of using multiple inputs, including the opposite angle-of-attack sensor, in the computer’s determination of an impending stall. As a lifetime member of the software development fraternity, I don’t know what toxic combination of inexperience, hubris, or lack of cultural understanding led to this mistake."
I've been a software engineer in the aerospace industry for 25 years and it's been my experience for every one of those years that software engineers don't make the decisions on which inputs to use. Software engineers are given requirements by systems and safety engineers, which they implement in code and verify through rigorous testing that the implementation is correct (of course, it's much more complicated - for reference read DO-178C). While I don't have specific information pertaining to the implementation of the MCAS, my assumption is that the software performed it's function flawlessly; it was a failure of the safety engineers and the system engineers to recognize that a single point of failure - the angle of attack sensor - combined with other failures, would lead to the catastrophic failure of the aircraft and the loss of lives. Otherwise, the software engineers would have been given requirements to read multiple sensors and implement appropriate logic to determine which input to use.
Whenever I've been given requirements to implement in software and I have a concern or doubt about the effectiveness or validity of those requirements, I've always raised my concerns to the systems and safety engineers. In some cases, those concerns resulted in a revision to the safety analyses and system requirements; other times, my concerns were addressed by clarifying the safety analysis to assure me that the original approach is correct and valid. The author's speculation that "no one who wrote the MCAS software" ... "raised the possibility of multiple inputs" is not the way the industry functions, in my experience.
At least the Boeing fanboys have begun to lay off the personal attacks on anyone who dares to criticize Boeing. It is clear now, as it has been for some time, that Boeing made a lot of questionable decisions in their efforts to get a new version of the plane on the market faster and cheaper (to hold off new competition from Airbus). It's not one thing, it's just layers and layers of bad decisions. The linked article focuses mainly on the design and engineering problems, but they also did an unprecedented level of self-review, self-analysis and self-certification of the safety of this aircraft. At minimum, that was done to inappropriately save time and money again, but at most, they may have also been trying to slide all this questionable stuff past the FAA and avoid any pushback. What they did submit for information about MCAS was wrong, and it just so happened to minimize the impressions of how big a role the system would play in flight characteristics and what the risks were. Boeing insists they weren't trying to deceive anyone, they just changed the design of MCAS multiple times and "forgot" to update the documentation submitted to the FAA. Maybe, but those were awfully convenient mistakes.
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As an engineer myself.... I don't fault or consider the staff or safety / systems team purposely proceeded in error. I do wonder how 2 yrs elapsed without adequate experiential warning to avoid these crashes. Where is the data for all the successful flights? Was there warning not heeded?. How many interventions as done as per the Lion Air flight before the crash? I was browsing my photos of previous flights and note several Max8s, as I also flew subsequent to first crash. No irregular climbs, just wondering how many reported lapses of software / system before crashes. There is a lot of available info from previous flights. I Would like to know the stats. Lion Air crash was very avoidable. That aircraft should not have been in service.
It is astounding that no one who wrote the MCAS software for the 737 Max seems even to have raised the possibility of using multiple inputs, including the opposite angle-of-attack sensor, in the computer’s determination of an impending stall.
As a lifetime member of the software development fraternity, I don’t know what toxic combination of inexperience, hubris, or lack of cultural understanding led to this mistake.
That's a pretty clear and pretty d@mming statement. I wonder sometimes if Boeing will be forced to go back to manufacturing the B738 just so they have something to sell if there is a third hull loss accident.
The explanation is pretty simple. The pilots did not take the necessary corrective action. I'm not a Boeing pilot, but I did have a Boeing pilot explain it to me...turn off power to the horizontal stabilizer trim and manually trim the airplane. That's all they had to do.
Here is a YouTube video that explains what happened. If you just want to see the simulator portion, skip to 16:50. Bear in mind they are running a checklist, so additional actions were taken, to include disengaging the autopilot and auto throttles. But the basic corrective action is to turn off power to the stab trim and manually trim.
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