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

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

#81

Post by foldr » Wed, Apr 10, 2019, 7:37 PM UTC

chupa-chups wrote: post #77

foldr wrote: post #72

Earlier quoted context omitted.

It's not well sourced. It's a speculation in an old Popular Mechanics article published before the official accident report. The official accident report does not identify the sidesticks as a factor in the crash (because they weren't).

https://www.pprune.org/tech-log/539756-af-447-thread-no-12-a... https://www.ainonline.com/aviation-news/2012-07-08/final-af4... https://www.flightglobal.com/news/articles/stall-warning-con... https://www.quora.com/Why-did-the-pilots-of-AF447-pull-up-in... And an explanation why bonin did react as he did: https://www.flightsafetyaustralia.com/2015/08/without-warnin... Downvotes are so cool, right? Just post your bette…

The general consensus on pilot forums is that the side sticks were not a factor. See e.g. here:

http://www.airliners.net/forum/viewtopic.php?t=772033&start=...

https://aviation.stackexchange.com/questions/14027/sidestick...

The thread you link to explains why the sidesticks are a red herring:

>Again, the stick inputs from the PF are very easy to see if you just look at them. You would see that immediately if you sat in an airbus pilot seat.

The PNF is going to spend most of his time looking at the instruments. He's hardly any more likely to be looking off to the side at his own control stick than he is to be looking at the other control stick, so linking them would be unlikely to make any difference.

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

#82

Post by FartyMcFarter » Wed, Apr 10, 2019, 7:37 PM UTC

Maybe someone can illuminate this.

This comment seems to say that Boeing has recently implemented a bunch of fixes to prevent MCAS from activating in various scenarios, which allegedly make MCAS safety a non-issue:

https://philip.greenspun.com/blog/2019/04/08/boeing-737-max-...

I'm not knowledgeable on planes, but some parts of this make me wonder if these fixes will cause the opposite problem.

For example if the two sensors disagree then MCAS now won't activate. How long until a crash happens because of that new behaviour? Either MCAS is necessary safety equipment, in which case this sounds dangerous, or it isn't, in which case why bother?

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

#83

Post by [deleted] » Wed, Apr 10, 2019, 7:37 PM UTC

astrodust wrote: post #24

gowld wrote: post #15

Earlier quoted context omitted.

Do you think the analysis is invalid? Do you think that an autopilot response to "AOA > 15 degrees" should be the same regardless of whether AOA is 20, 40, 60, or 80 degrees?

Is there an industrial coding standard that makes recommendations here? What does NASA do?

[deleted]

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

#84

Post by linuxftw » Wed, Apr 10, 2019, 7:39 PM UTC

laydn wrote: post #55

Despite all we've read about this subject, are we really still implying that this is a software problem?! Very basic rules of commercial aircraft design were violated during the development of 737MAX. No point in listing all the issues here again. Let's just point out one: There should have been more than 2 AoA sensors feeding MCAS. No excuses.

> Despite all we've read about this subject, are we really still implying that this is a software problem?!

We don't know it's not a software problem (in addition to lack of hardware inputs). We don't know that anything in the system is fit for purpose whatsoever. That's what an obvious exclusion of basic failure testing tells us. That the system had NO critical oversight.

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

#85

Post by sk5t » Wed, Apr 10, 2019, 7:39 PM UTC

js2 wrote: post #19

yongjik wrote: post #8

With all due respect, this sounds too much like the kind of armchair quarterbacking that routinely appears on HN when avionics/politics/astronomy is mentioned, where a lone programmer feels competent enough to criticize an industry for missing "something obvious". I mean, this particular change might have saved the particular 737, but I'd rather hear it from someone who actually knows how 737s fly.

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

Honest question, is his experience in small aircraft applicable at all to jetliners? How much carryover, beyond core theory of flight dynamics, is there from piloting a single prop to an Airbus or even a regional jet?

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

#86

Post by chupa-chups » Wed, Apr 10, 2019, 7:40 PM UTC

foldr wrote: post #81

chupa-chups wrote: post #77

Earlier quoted context omitted.

https://www.pprune.org/tech-log/539756-af-447-thread-no-12-a... https://www.ainonline.com/aviation-news/2012-07-08/final-af4... https://www.flightglobal.com/news/articles/stall-warning-con... https://www.quora.com/Why-did-the-pilots-of-AF447-pull-up-in... And an explanation why bonin did react as he did: https://www.flightsafetyaustralia.com/2015/08/without-warnin... Downvotes are so cool, right? Just post your bette…

The general consensus on pilot forums is that the side sticks were not a factor. See e.g. here: http://www.airliners.net/forum/viewtopic.php?t=772033&start=... https://aviation.stackexchange.com/questions/14027/sidestick... The thread you link to explains why the sidesticks are a red herring: >Again, the stick inputs from the PF are very easy to see if you just look at them. You would see that immediately if you sat…

I didn't say anything about sidesticks (in a comment below i did). I don't believe myself that the sidesticks were a real factor in themselves - but if the PM had sensed that PF (bonin) was pulling up he would have reacted earlier.

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

#87

Post by fixermark » Wed, Apr 10, 2019, 7:41 PM UTC

geggam wrote: post #78

fixermark wrote: post #63

Earlier quoted context omitted.

I'll be honest, I still prefer it to the world where lack of software kills people. ... I avoided running over that child I couldn't see in my rear-view because the infrared sensors picked him up as a mobile object intersecting my path and the backup warning screamed at me. I like not killing people, so I call that a win.

Have you had to fight your lane assist yet ? I am all for the sensors to give me information but when the systems take over control I am not a fan. Cyclists in the EU have learned that the car sensors will slam on the brakes. Quite irritating when the car slams on the brakes and they are laughing at you.

Ah, see, I'm American. ;)

The lane assist can be disabled and a cyclist who hard-brakes in front of me is taking their life in their hands because my Ford only stops if I touch the brake (it just stops as hard as it needs to to minimize risk of impact, regardless of how soft I push the pedal).

(Sidebar: I almost feel like that cyclist game is something that should be solved with more sensors. If it's a common issue, you really want a dash cam to capture their image and report them to police, as inentionally hard-braking to trigger a car safety system is clearly endangering their lives and the lives of the car occupants, since the auto-brake is designed with a bias towards injuring occupants over killing anyone).

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

#88

Post by the_mitsuhiko » Wed, Apr 10, 2019, 7:41 PM UTC

geggam wrote: post #40

How does it feel to enter a world where software is killing people ? Driven a new car lately ?

> How does it feel to enter a world where software is killing people ?

How is this new? Software has been killing people for a long time.

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

#89

Post by foldr » Wed, Apr 10, 2019, 7:41 PM UTC

cco wrote: post #75

ninkendo wrote: post #36

Earlier quoted context omitted.

Fascinating. But it seems like the kind of scenario that would be odd for the pilot, no? You nose down, a stall warning goes off, so you nose back up again? That's exactly the opposite of what a pilot would be trained to do, right? I'd imagine in a car, if my vehicle warned me that I was going too fast when I slowed down, my reaction wouldn't be to speed the vehicle back up to avoid the warning...

Yes, if memory serves in AirFrance 447 that upon finding out the co-pilot had been pulling up the whole time the other pilot is shocked to hear this and realizes the problem. I remember being really affected by this so I went out and found the transcript: 02:13:40 (Robert) Climb... climb... climb... climb... 02:13:40 (Bonin) But I've had the stick back the whole time! [At last, Bonin tells the others the crucial fact…

What you're pasting there is an editorialized quotation of the transcript from an old Popular Mechanics article. The transcript and its English translation are here:

https://www.bea.aero/uploads/tx_elyextendttnews/annexe.01_04...

https://www.bea.aero/uploads/tx_elyextendttnews/annexe.01.en...

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

#90

Post by ChuckMcM » Wed, Apr 10, 2019, 7:43 PM UTC

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 is the SQL explain command. That command will generate the complete decision tree for how records are included or excluded from a SQL query. The air equivalent might be display that shows the flight status, and the state of the instruments that are being used to determine that status. And then it is up to the pilots (or DBA :-) to figure out if what is happening is what they think should be happening.

To use this particular example, it is, in my opinion, negligent on Boeing's part not to include an indicator for every change in the flight control laws. If MCAS activates to avoid a stall it should always indicate that it is, and why it is activated. It has been reported that this was an "extra price" option for the jet, and it is that choice that makes it feel negligent to me.

Generally, there seems to be enough indications with backups in the cockpit so that the pilot can ascertain what is going on with the aircraft reliably (backups and such), but what was missing here was, again in my opinion, was the rationale the plane was using for the flight laws it was implementing being available as well.