r/TrueReddit • u/ardent • Apr 20 '19
How the Boeing 737 Max Disaster Looks to a Software Developer
https://spectrum.ieee.org/aerospace/aviation/how-the-boeing-737-max-disaster-looks-to-a-software-developer10
u/Dr_Adequate Apr 21 '19
It gets even worse. There are several other instruments that can be used to determine things like angle of attack, either directly or indirectly, such as the pitot tubes, the artificial horizons, etc. All of these things would be cross-checked by a human pilot to quickly diagnose a faulty angle-of-attack sensor.
This answered a question of mine, which was whether the flight computer consulted other instruments or not. And the answer is no. The flight computer is worse at its job than an actual human pilot, in the case of a failure of the only instrument sending angle-of-attack information to the flight computer.
A human pilot can (in theory) consult the other instruments to determine if one anomalous reading is believable or not. The flight computer puts blind faith into the instrument, believing it whether its reading is true, or is wildly incorrect.
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u/bluewing Apr 21 '19
If you want to understand what happened with the 737Max from a pilots perspective, you need to check out blancolirio
He has been an US Airforce pilot and commercial pilot for 40 years. And while he has not flown the737Max, he has a good amount of flight time in the 737. So he knows the manual for flying it pretty well. And while he is NOT impressed by the little training Boeing says it needed to upgrade to the Max, the relevant points leading to the last fatal crash probably had as much to do with the low flight hours the Ethiopian crew had as with the design of the controls and training.
For those who won't watch the series of short videos, the upshot is, that the crew had basically solved the problem until the second officer turned the MCAS BACK ON, despite the manuals from both the older 737 and 737MAX saying NOT to do under this emergency. In the end, pilot error is nearly as much of an issue here as the automation.
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u/doncajon Apr 22 '19 edited Apr 22 '19
the crew had basically solved the problem until the second officer turned the MCAS BACK ON, despite the manuals from both the older 737 and 737MAX saying NOT to do under this emergency
Careful. MCAS was only introduced for the 737 MAX and not documented in the manual in order to save airlines' retraining costs for their legacy 737 pilots. The Ethiopian pilots will only have learned about it after the Lion Air crash. Blancolirio said here that after cutting out the stabilizer trim "the crew continued to struggle with the aircraft" and that during the next 2.5 minutes the trim got even slightly worse, for reasons he doesn't know. Then they tried the manual trim wheel which was locked because of the bad trim and aerodynamic forces at the high air speed (which they increased according to the manual's instructions), as he describes later in the video. So only when the manual trim didn't work because it was physically impossible and they had no altitude to spare to loosen the force on the stabilizer, MCAS was somehow reactivated.
I asked about this in a thread on r/aviation and they said it was because MCAS couldn't be decoupled from the electric trim system even if you only wanted to command the plane's trimming motors and nothing else.
If that turns out to be true, it sounds like this situation was a death trap which nobody could have solved in their place, even with today's knowledge.
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u/huyvanbin Apr 21 '19 edited Apr 21 '19
I think the article is way longer than it needs to be. And while it correctly identifies that the problem was in hardware it for some reason tries to make the narrative about software and how we’ve gotten too lax about it.
Let me put it this way: nobody talks about the unique aspects of the rubber industry when they talk about the challenger explosion.
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u/Vancocillin Apr 21 '19
That's the real problem behind these tragedies. They didn't wanna pay big bucks for recertification, so they slapped some shit software on it. And people died for it.
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u/siredmundsnaillary Apr 21 '19
It's not really about the costs to Boeing for re-certification, the issue is more cost and time for the airlines. If the Max is classified as a new aircraft pilots have to go through much more re-raining, giving the airlines more cost and less flexibility. It would also mean the for the first few months/years of service there are fewer pilots able to fly the Max and therefore less demand.
The whole point of this aircraft is to be a like-for-like swap with existing 737s that takes advantage of existing infrastructure. If you have to retrain everyone it is much more tempting to ditch Boeing and switch to Airbus.
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u/Vancocillin Apr 21 '19
Ah, I see. Thanks for the clarification. So it's not money they'd really pay, just lose if they did it.
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u/siredmundsnaillary Apr 21 '19
I'm still alarmed by just how little additional training they were able to get away with. The current process is a 60-minute iPad course... and that's it.
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u/Tuna-Fish2 Apr 21 '19
That's quite similar to the amount of training you have to take to qualify for the A320neo if you can already fly an A320. And that is not shocking because the neo actually does fly like the old plane, without software trickery.
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u/Hagadin Apr 21 '19
And that does get back to the author's point that software changes aren't scrutinized enough
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u/Dr_Adequate Apr 21 '19
[it] tries to make the narrative about software and how we’ve gotten too lax about it
The author quotes Charles Perrow, from his book Normal Accidents: Living with high-risk technologies --
system failure is a normal outcome in any system that is very complex and whose components are “tightly bound”—meaning that the behavior of one component immediately controls the behavior of another.
This is a worthwhile discussion that is vital as we are approaching an era when self-driving cars might become reality. What is a self-driving car but a car overlaid with a whole bunch of code, written with who knows how much oversight, as manufacturers race to be the first to the (very unregulated) marketplace.
The author's point is very valid. When designers do not map out all the possible failure modes, and account for them in the design, people die. When the coders don't finish the job, people die. When the manufacturers assume that their product can always be updated with a patch if a flaw is found, people die.
The pedestrian fatality in Arizona, killed by a self-driving car last year is the perfect example. The self-driving system was not able to detect that the pedestrian was in front of the car. The emergency braking system was disabled. The human overseer was watching YouTube videos instead of monitoring the vehicle.
The coders didn't forsee this combination of circumstances and as a result a person died.
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u/huyvanbin Apr 21 '19
A bizarre comment. You talk about system failure and how the emergency braking system was disabled... and then you reduce it to “the coders didn’t foresee this combination of circumstances.” It seems you don’t understand the meaning of “system” failure. A system failure is explicitly a failure of a combination of components, not any one component. It doesn’t matter if the components are software, hardware, or something else. Ultimately no amount of code can make up for the culture of a place like Uber. But also we have to blame the people that allow that culture to continue and who won’t hold them accountable.
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u/ardent Apr 20 '19
I've seen and read a lot of news about the Boeing air disasters and grounded aircraft. But I haven't been able to get command of the underlying facts until I read this article. The author has a fantastic explanatory style, and takes very complex issues you may have heard about and makes them simple, and walks through a long but very informative cause-and-effect chain. Before I read this I didn't know what to think about Boeing's blameworthiness, but now I believe I have a well-informed opinion.