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737 Max: 1960s Design, 1990s Computing Power and Paper Manuals

nytimes.com

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Re: 737 Max: 1960s Design, 1990s Computing Power and Paper Manuals

#91

Post by myth2018 »

flyinglizard wrote: post #58
kacamak wrote: post #52

Earlier quoted context omitted.

>Like, why does such a critical system like MCAS take only a single AoA sensor as input The classic approach is to have three sensors, so in case one fails you can know which one. Having two only indicates something is wrong but is not useful on the fly.

Three with a disagree algorithm is definitely what I’d expect out of such a critical system, but two with signal averaging would still be much better than just one.

Averaging would be disastrous in this case. You don't want to use faulty data to average inputs to a flight control computer.

Re: 737 Max: 1960s Design, 1990s Computing Power and Paper Manuals

#92

Post by myth2018 »

cm2187 wrote: post #63
flyinglizard wrote: post #58

Earlier quoted context omitted.

Three with a disagree algorithm is definitely what I’d expect out of such a critical system, but two with signal averaging would still be much better than just one.

Or alternatively with two, and disabling MCAS if they disagree, seems a better solution than having one and having no way to tell if it is working (keeping in mind both can still fail simultaneously). Not an ideal solution but better.

This is one of the features of the MCAS software update.

Re: 737 Max: 1960s Design, 1990s Computing Power and Paper Manuals

#93

Post by myth2018 »

JauntyHatAngle wrote: post #56
myth2018 wrote: post #46

Mass media in general is stressing too much the fact that 737 MAX is allegedly based on dated designs. I think it's fair to say that MAX versions present some compromise solutions (like the now-infamous MCAS, which is there to compensate for the "unnatural" bigger engines). But I think that is not the main point. They would be good solutions it they worked as intended. There are some other more fundamental and more d…

>Like, why does such a critical system like MCAS take only a single AoA sensor as input, when there are two sensors available? Specially considering that the inputs from both are hardware-available to MCAS (the new software version is going to take data from both). Are you saying the answer in the article didn't give enough information? "Airbus addressed this potential problem on some of its planes by installing thre…

It doesn't answer the question because it's still a speculation.

Full investigation is hopefully going to tell us what has really happened.

Re: 737 Max: 1960s Design, 1990s Computing Power and Paper Manuals

#94

Post by DanielBMarkham »

huffmsa wrote: post #68
dmix wrote: post #35

Earlier quoted context omitted.

Wait until they finds out what software powers the nuclear weapons of 90%+ of the world, top-tier fighter jets, "critical" infrastructure like power (including nuclear), and countless financial/banking systems. To be fair the article doesn't critique using 1990s (or earlier) hardware/software. It's merely a clickbait headline. The only reference is dismissed by the very next sentence as insignificant [Boeing could be…

The NYT fired basically their entire editorial staff in 2017. The accelerated degradation has been noticable.

Everybody's talking about how we're going to pay for good content. How will newspapers operate in the future?

We don't need to pay for content. The world is full of people who will write for nothing more than getting their name out there. What we need are good editors. The news media are firing the very people who could get them out of this mess they ended up in.

Re: 737 Max: 1960s Design, 1990s Computing Power and Paper Manuals

#95

Post by VBprogrammer »

myth2018 wrote: post #88
VBprogrammer wrote: post #66

Earlier quoted context omitted.

Instrumentation on an aircraft is usually designed with a pilot and copilot set. Everything down to the pitot tubes which feed the information is unique to that side of the aircraft. This harks back to the day when it was the only sensible solution when your guages are actually just directly reading airpressure differences. Clearly these signals can be cross connected, because that's the solution Boeing are testing a…

Uhm.. I don't know.. I'm aware this is the case of airspeed indicators and many others, but, for instance, the autopilot is fed with readings of Pitot tubes from both sides and it disengages when the sensors disagree beyond sensible thresholds. Besides, such issue is brought clearly to the knowledge of pilots. In the MCAS case, however, we are speaking about a computer which not only interferes in the flight controls…

To be clear, I think MCAS was a massive engineering failure for Boeing, I'm just pointing out why I think they didn't automatically say "hey, we've got two sensors, lets compare the readings before we act on it".

However, for the autopilot example, I don't think you are quite right. Typically there are multiple autopilots (2 or 3 is quite common), and each is driven by a different set of flight data. In some scenarios multiple autopilots are engaged at same time, for example during CATIII auto-landings but as far as I'm aware that is the exception rather than the rule.

It's true that the autopilot may disconnect if there is a warning like 'IAS Disagree', I suspect this is driven by a separate monitoring process though, rather than being an integral part of the system.

Re: 737 Max: 1960s Design, 1990s Computing Power and Paper Manuals

#96

Post by ssully »

theclaw wrote: post #69
crimsonalucard wrote: post #62

Earlier quoted context omitted.

I think the author was referring to processors handling UI displays rather than a computer system that has only the processing power to only handle a blinking LED. For example if a UI display showed: "Warning: MCAS overriding pitch up. Disable?" Is better than a LED #234 and LED 412 are on. Consult manual for instructions. I would imagine that a lot of the fly by wire or control systems nowadays are either analog sys…

It's a moot point anyway - the could not change the UI beyond converting physical dials to virtual ones, because that would have required retraining which they wanted to avoid. Even if they could have changed the UI they still needed to hide the existence of the MCAS system, again to avoid retraining, so it's doubtful such a clear an helpful error message would be allowable.

It isn't a moot point, it is literally the point of the article. The whole article is explaining the history of the 737 and explaining why they designed the max to avoid retraining. It mentions digital UIs, fly-by-wire, and other designs found in modern jets to paint the picture that the Max was successful in avoiding retraining, but that requirement restricted the engineers and led to a potentially compromised design.

Re: 737 Max: 1960s Design, 1990s Computing Power and Paper Manuals

#97

Post by Arnt »

huffmsa wrote: post #68
dmix wrote: post #35

Earlier quoted context omitted.

Wait until they finds out what software powers the nuclear weapons of 90%+ of the world, top-tier fighter jets, "critical" infrastructure like power (including nuclear), and countless financial/banking systems. To be fair the article doesn't critique using 1990s (or earlier) hardware/software. It's merely a clickbait headline. The only reference is dismissed by the very next sentence as insignificant [Boeing could be…

The NYT fired basically their entire editorial staff in 2017. The accelerated degradation has been noticable.

What? I googled, and found this: "The Times newsroom staff peaked in early 2008 at about 1,332 employees, [...] still employs about 1,300 in its newsroom."

What are the correct numbers?

Re: 737 Max: 1960s Design, 1990s Computing Power and Paper Manuals

#99

Post by mannykannot »

cm2187 wrote: post #80
JauntyHatAngle wrote: post #72

Earlier quoted context omitted.

The article also states that 2 sensors is not enough as then you have two sensors that can disagree with no way to figure out the correct one.

Yes but at least you know the reading is faulty and avoid applying dangerous commands. Now I don't know if the stall it is meant to avoid is a greater risk than MCAS pushing the plane in the wrong direction.

The analysis is not as simple as asking whether a stall is more or less dangerous than an MCAS failure. Firstly, MCAS does not prevent a stall; it is intended to make it harder to accidentally stall (and no sane pilot would deliberately stall an airliner in normal operations), in order to compensate for the design change that made it easier to do so. When considering alternatives such as whether to disable MCAS on a sensor discrepancy, one should ask both how likely each possible scenario in each alternative is, and how much risk it adds.

Where the risk analysis seems to have gone most wrong is that Boeing apparently grossly underestimated the difficulty of both figuring out what actions were needed to respond to the symptoms of MCAS failure, and to perform them. I don't know whether it was a significant factor in the former, but when the AofA sensor failed, it caused the stick shaker, as well as MCAS, to kick in.

The other mistake in analysis seems to be that when the power of MCAS was increased after initial flight testing, the additional risk it created was not properly taken into account. In particular, the ability of MCAS to drive the trim all the way forward appears to have been an unintended and overlooked side-effect of one design change.

Re: 737 Max: 1960s Design, 1990s Computing Power and Paper Manuals

#100

Post by iSnow »

CivBase wrote: post #31

Why exactly does this author think an airplane needs a lot of computing power? Airplane software does not deal with especially large amounts of data or intense computations. Faster hardware does not provide an inherent safety benefit. There is a large degree of coupling between avionics hardware and software amd updating that software is prohibitively expensive. There's just no point in doing it unless you get a tang…

>Why exactly does this author think an airplane needs a lot of computing power?

I think the way you criticize the article is about as faulty as the article itself.

This piece is about detailing how the 737 is an outdated design that got patched and patched till it more or less broke. The processing power is just /one/ aspect and is given as a point of reference, like the 1968 photo.

I am no expert in aviation, but I guess it's quite a safe guess that fly-by-wire systems need more processing power than mechanical/analog designs. And that a glass cockpit with a trouble database needs more than a blinking LED and a paper handbook.

Nowhere in the article does the author claim the 737 MAX crashed because it had too weak CPUs. It is, however, one indication of an obsolete design - newer jets like the A320 or the 787 have more beefy processors for a reason.

I know I worked in 1-dimensional transportation and their 486-based onboard-processors felt cramped, the software engineers had to hack around their limitations and they wished they could switch to something newer. I doubt 3-dimensional transportation is easier to implement.

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