Boeing 737 MAX crash and the rejection of ridiculous data • Hacker News Board

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

#131

Post by MFLoon » Wed, Apr 10, 2019, 9:25 PM UTC

mtnGoat wrote: post #51

js2 wrote: post #19

Earlier quoted context omitted.

Philip Greenspun is a highly experienced pilot: https://philip.greenspun.com/flying/milestones

I too have hundreds of flights and am also a programmer, but I would not assume having both skills would make you anything more then an armchair quarterback. If you have not written code that runs planes, what knowledge are you basing your idea off of. IMO. i too also play games, but i wouldn't assume to tell a game developer how to write their code.

I agree - being a pilot and a programmer is neither a necessary nor sufficient condition for being able to diagnose and solve an issue in a system as complex as a modern airliner. In fact I don't think any individual is capable of doing so on their own; maybe the sole exception being someone like the engineering lead of avionics for the 737 Max, who is probably not a pilot, and probably only a programmer in so far as it was a component of their engineering education.

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

#132

Post by SilasX » Wed, Apr 10, 2019, 9:27 PM UTC

chx wrote: post #70

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https://news.ycombinator.com/item?id=14720192#14720921

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

#133

Post by devy » Wed, Apr 10, 2019, 9:27 PM UTC

According to Captain Chesley Sullenberger (the former air force pilot who saved US 1549, dubbed the Miracle on the Hudson) that the existing avionics are not designed to take our best advantages[1]

     Humans are much better suited for the doers role with
     technologies monitoring us, instead of what we are 
     currently assigning the human component as exactly the 
     opposite.

[1] https://www.fastcompany.com/video/the-future-of-aviation-acc...

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

#134

Post by [deleted] » Wed, Apr 10, 2019, 9:34 PM UTC

linuxftw wrote: post #118

VBprogrammer wrote: post #100

Earlier quoted context omitted.

That's not nearly the case. MCAS is a stupidly simple system intended to cut in during very unusual phases of flight were a normal commercial flight would not be operating.

> MCAS is a stupidly simple system So, you have reviewed the software? If it's so stupid simple, why did it kill a bunch of people?

[deleted]

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

#135

Post by tzs » Wed, Apr 10, 2019, 9:43 PM UTC

bilbo0s wrote: post #66

noxryan wrote: post #18

Earlier quoted context omitted.

I agree that we frequently see this on HN in regards to aviation. However, I don;t think it applies to Greenspun. He's a knowledgeable and active pilot himself.

Lots of people are, that doesn't mean they aren't armchair quarterbacking. I know how to fly airplanes and helicopters, does that make me an expert on the flight dynamics of 737 MAX?

Are there any airliners for which a sustained 60-70 degree angle of attack over a span of several minutes is not overwhelmingly likely due to sensor failure?

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

#136

Post by mannykannot » Wed, Apr 10, 2019, 9:45 PM UTC

ChuckMcM wrote: post #90

Ataraxic wrote: post #21

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…

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…

The problem with this approach is that it does not generalize. You might think that if pilots just had this one piece of information, it would be obvious what's wrong, so let's provide that information. But if you apply that consistently to every system, the crew will be buried in notifications all the time, most of which are perfectly normal, and most of the rest are normal responses to the abnormal conditions produced by the actual fault.

Even in a space shuttle, the flight crew did not see most of the data, and NASA had a room full of engineers following the telemetry.

When you have less than a minute to save everybody, the last thing you need is something like an SQL explain result.

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

#137

Post by prmph » Wed, Apr 10, 2019, 10:01 PM UTC

Xixi wrote: post #37

If you read about Air France Flight 447, at some point instruments data went so ridiculously far from expected values that the stall warning stopped, because the computer did exactly what is suggested here: rejecting ridiculous data. So trying to fight the stall would... trigger the stall warning, adding confusion and cognitive load to an already dire situation (IIRC it is very likely, though we will never know, that…

There is a difference between the AF 447 situation and what is recommended in the article.

What is suggested is that the aircraft refrain from performing risky manoeuvres based on such wildly out-or-range sensor outputs.

This does not mean that aircraft should suppress warnings of such sensor readings from the pilots.

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

#138

Post by mannykannot » Wed, Apr 10, 2019, 10:07 PM UTC

erentz wrote: post #117

Ataraxic wrote: post #21

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…

His proposal makes no sense. Under his new logic, it would be fine for the MCAS to continue forcing the trim to full deflection and crash the plane if the AoA was stuck anywhere between 15 and 24 degrees. He's simply not solved the root problem and added a bad kludge for a single error case (AoA stuck > 25 degrees). While at the same time removed a potential safety control for a real world case where the AoA was vali…

It is difficult to be sure from the flight data chart that was published in the Seattle Times, but it looks possible that the faulty AofA reading was below 25 degrees for most of the Lion Air flight.

Reading between the lines, Greenspun has presented these crashes as "the first mass killings by software". That claim looks clearer if you present it as wholly due to the absence of a few common-sense lines of code, and downplay the other systems design issues, such as the lack of triple redundancy, the failure to use the dual redundancy to detect sensor error, and the fact that the system was unnecessarily powerful, being able to drive the trim all the way forward.

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

#139

Post by VBprogrammer » Wed, Apr 10, 2019, 10:08 PM UTC

linuxftw wrote: post #127

VBprogrammer wrote: post #123

Earlier quoted context omitted.

Sigh. I've reviewed almost everything written about the accidents including the information supplied by Boeing to the airlines to explain the function of the MCAS system. There is no lower limit on the complexity of a system required to kill people.

> including the information supplied by Boeing to the airlines to explain the function of the MCAS system So, you're essentially parroting Boeing's narrative IMO. Yes, they want you to think that the system is 'stupid simple' and it's 'no big deal, just one little fix' because obviously that's good for their business. Maybe, the system required for safe operation is not so simple, and Boeing is no longer competent en…

Or maybe they forgot to add the flying unicorns to power it.

I'm not sure why you think boeing would lie about it. Or how they'd convince the regulators in two different countries to cover it up since you can see the behaviour by reading the graphs in the preliminary report.

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

#140

Post by sdinsn » Wed, Apr 10, 2019, 10:24 PM UTC

This 'article' is very low quality and is written by a layman. If his main source of information is one line of wikipedia, he shouldn't be telling experienced engineers how to write flight software.

Furthermore, it is incredibly unsafe to reject so-called "ridiculous" data completely.