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Boeing 737 MAX crash and the rejection of ridiculous data

philip.greenspun.com

191–194 of 194 posts

Re: Boeing 737 MAX crash and the rejection of ridiculous data

#191
post #164

Earlier quoted context omitted.

This is incorrect. If you read the original script of pilot conversation in the cockpit, you'd know that he simply forgot he was pulling back on the stick. He disregarded clear pilot training and did what he was exactly not supposed to do, I reckon out of nervousness. That flight, needed a better pilot. Period.

Forgot? Better? Neither of those things is supported by the final report, the cockpit voice or flight data recorders. The occurrence of the failure in the context of flight in cruise completely surprised the pilots of flight AF 447. Which pilot needed to be better? The crew, progressively becoming de-structured, likely never understood that it was faced with a “simple” loss of three sources of airspeed information. a…

You can say what you like, but that was incompetence and no technology can make up for downright incompetence.

The report statements are diplomatic. No report will point fi ger at anyone. In that particular case, the entire conversation in the cockpit was publicised. So, instead of letting others tell you what is and what is not, learn to read and draw opinions for yourself. Just because the investigators didn't explicitly say it, doesn't mean I'm wrong.

The pilot who have been pulling on the stick for a very long time was the incompetent pilot there. The guy who did the exact opposite of what should have been done during a stall warning out of nerves. That's incompetence. Many factors might have caused that unfavourable scenario, but he brought that plane down.

Re: Boeing 737 MAX crash and the rejection of ridiculous data

#192

It should be noted in the doomed Air France 447 flight, the plane activated the stall warning because of a high angle of attack that was leading to stall. (thanks pdx for the corrected info) At some point the system rejected the data and stopped the stall warning because the angle of attack was so severe that it considered the data erroneous. This is speculated to have caused the co-pilot to keep pulling back on the…

1. The pitot tubes froze (this was already a known possibility) and this particular plane was scheduled to replace those tubes; 2. When the speed metrics became unreliable, system didn't do anything uncommanded, disengaged autopilot gracefully, notified the pilots and handed control over to them; 3. Stall warnings went off and one of the pilots continued to pull on the stick (this baffled other pilots I heard speak about this too because this is the exact opposite thing to do during a stall) 4. It's clear from their exchanges in the cockpit that this particular pilot was very nervous during the whole thing.

What's complicated about that? I can't see how a computerised system could have helped here. Computer had no reliable grounds to make a decision and it did exactly what it should and what should have neen expected by the pilots at the time.

Re: Boeing 737 MAX crash and the rejection of ridiculous data

#193

Earlier quoted context omitted.

Your basic point is spot on, it isn't simple. The challenge I think is to keep two things separated, one is the flight control laws that the system is implementing to keep the plane in the air (to the best of its ability), and the other is the situational awareness indicators for the pilots so that they can tell what what the plane is "thinking" about how it is flying (or not). The closest analogy I can come up with…

This is not the problem. MCAS in itself sadly is the problem. They had to solve the issue that the pitch-up moment shouldn't be accelerating on its own just depending on AoA, which was (aerodynamically) inevitable without automated adjustments due to the placement of the engines. They had to resort to the worst possible cludge, since they weren't even allowed to add new electrical systems (which would have caused a r…

The video is gone (censored?), does someone have a backup copy?

Re: Boeing 737 MAX crash and the rejection of ridiculous data

#194
post #189

Earlier quoted context omitted.

How rude. Here I was thinking we were having a civil discourse over the Internet. More than born yesterday, less than since the Moon landing. Regardless, my assessment is based on most juniors I've worked with. By their third year most seem to have already grasped the need to test for boundary conditions, and to ensure proper error handling for GIGO failure. Any 1 year+ with at least FizzBuzz levels of understanding…

You think I was rude asking you about your experience. Now think how rude this unsubstantiated allegation of obvious simplicity of the code in question is to the person who wrote it -- with the weight of hundreds of lost lives on their shoulders. These control systems can get arbitrary complex. We don't know anything about the hardware this runs on and what it has to interface with. We don't know the constraints and…

>You think I was rude asking you about your experience.

You asked for a number. Who I am, doesn't factor in. The experiences and insights I can bring to the conversation do. Of which I provided more than enough to get you in the right ballpark experiencewise.

>We don't know anything about the hardware this runs on and what it has to interface with.

These are essentially networked embedded microcomputers, likely utilizing various potential protocol stacks such as

CAN, CAN FD AFDX® / ARINC 664 ARINC 429 ARINC 825 Ethernet CANopen for networking.

They are likely highly constrained, and must be compliant with DO-178B/C, which includes a need to verify the software down to the op codes spit out by the compiler.

The most popular languages for this purpose are known to be C, C++, FORTRAN, and Ada.

There's this wonderful place called the Internet where Engineers and other really dedicated people share information about what they use to do things.

>Arbitrary complexity Is a possibility, but tends to be bounded by the fact humans still need to be able to implement and verify the systems they make in a reasonable amount of time. Which coincidentally, seems to have missed a few layers or so given we're here talking about this.

The world has very little that can't be found with a little digging, and in the interests of saving time, we tend to reuse technologies when appropriate from things like, cars, in other things, like airplanes.

If you can gain a mastery of how to network and program computers in general, you gain insights into how other physical systems, even though they aren't Turing machines, interconnect and propagate information and forces.

If you can then understand engineering principles well enough to decompose complex things into a network of simpler basic parts, and understand how to employ mathematics to analyze and predict the behavior of those systems, you can quickly formulate broad guesses about contributory factors to a failure state given the even small amounts of information.

And if you say all that's impossible to appear in one person, I don't know what to tell you. I'm not asking you to have faith, I'm asking you to think, question, imagine, and connect the dots between what information is available out there.

But hey, what do I know? I'm just a guy who objects to having credibility pidgeonholed based on some number instead of the content of what is being communicated.

I apologize if I sound aggravated or hostile, but I do not appreciate it when something as tightly regulated as aircraft out of the blue starts killing people, and the reason looks to be a lack of scrutiny/verification, rushed implementation, intentionally sparse communication, and unethical sales practices for whatever reason.

There are ways to do things, and there are ways not to do things. I expect a leader of an industry to at least show a level of effort such that I can entertain the benefit of a doubt that gross incompetence Or greed was not a factor. I have no such illusions left to me based upon what I've been able to work out. The cause is somewhere in their culture or business practices, and I want it ripped out into the light as an example to everyone, everywhere.

I don't care half as much about what happens to the people involved as long as it is enough to dissuade anyone thinking of doing the same thing from going down that path.

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