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Boeing 737 MAX crash and the rejection of ridiculous data

philip.greenspun.com

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

#71

Post by foldr »

pdx_flyer wrote: post #42
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…

AF447 was an Airbus 330 which does not have a physical stick shaker. It has a "Stall Stall Stall" warning that sounds and was likely drowned out by the other alarms that were filling the cockpit. A330s also have disconnected sticks, so when a pilot has input on one side of the plane, that input is not replicated on the other side of the plane.

>AF447 was an Airbus 330 which does not have a physical stick shaker. It has a "Stall Stall Stall" warning that sounds and was likely drowned out by the other alarms that were filling the cockpit.

Just to be clear, an Airbus 330 won't let the pilot maintain an attitude that could lead to a stall, so it has a much higher degree of protection than a simple stick shaker. The situations in which these protections are turned off are situations in which a stick shaker would also fail to function reliably.

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

#72

Post by foldr »

chupa-chups wrote: post #56
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...

Exactly, and this is what caused the crash. The other pilots simply did not think of one of them trying to pitch up. This is well sourced, sadly not on wikipedia. But there are countless threads of real pilots. I guess Air France had some influence.

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).

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

#73

Post by [deleted] »

fixermark wrote: post #31
js2 wrote: post #19

Earlier quoted context omitted.

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

He doesn't seem to be an experienced owner of a home outdoor thermometer though. Or if he is, I need to know where he found one that goes to 452 degrees and why he even needs that much range. ;)

[deleted]

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

#74

Post by btrettel »

When working on my PhD in mechanical engineering, I created fairly large data compilations and I would include some assertions like this. I'd make them assertions because I considered data that had these faults to be not worth adding, so if the data wasn't a typo then I'd just cut it.

It can be hard to think of good tests for data like this. Sometimes my assertions were wrong, e.g., I thought R^2 couldn't go below 0. That's actually false.

One I've found useful to spot typos was to check whether a column which is incrementing is in fact incrementing. E.g., if a table is ordered by the pressure tested at, then obviously there's a typo is the pressure is not increasing.

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

#75

Post by cco »

ninkendo wrote: post #36
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…

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 whose import he has so grievously failed to understand himself.]

02:13:42 (Captain) No, no, no… Don’t climb… no, no.

02:13:43 (Robert) Descend, then… Give me the controls… Give me the controls!

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

#76

Post by pdx_flyer »

foldr wrote: post #71
pdx_flyer wrote: post #42

Earlier quoted context omitted.

AF447 was an Airbus 330 which does not have a physical stick shaker. It has a "Stall Stall Stall" warning that sounds and was likely drowned out by the other alarms that were filling the cockpit. A330s also have disconnected sticks, so when a pilot has input on one side of the plane, that input is not replicated on the other side of the plane.

>AF447 was an Airbus 330 which does not have a physical stick shaker. It has a "Stall Stall Stall" warning that sounds and was likely drowned out by the other alarms that were filling the cockpit. Just to be clear, an Airbus 330 won't let the pilot maintain an attitude that could lead to a stall, so it has a much higher degree of protection than a simple stick shaker. The situations in which these protections are tur…

Which is pretty much what happened. The pilot fought the plane into the ocean.

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

#77

Post by chupa-chups »

foldr wrote: post #72
chupa-chups wrote: post #56

Earlier quoted context omitted.

Exactly, and this is what caused the crash. The other pilots simply did not think of one of them trying to pitch up. This is well sourced, sadly not on wikipedia. But there are countless threads of real pilots. I guess Air France had some influence.

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 better informed opinion and enjoy the upvotes. This has the side-effect of not just informing me but others about your more correct opinion.

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

#78

Post by geggam »

fixermark wrote: post #63
geggam wrote: post #40

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

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.

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

#79

Post by darkpuma »

fixermark wrote: post #31
js2 wrote: post #19

Earlier quoted context omitted.

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

He doesn't seem to be an experienced owner of a home outdoor thermometer though. Or if he is, I need to know where he found one that goes to 452 degrees and why he even needs that much range. ;)

How else would you know there is a wildfire outside?

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

#80

Post by itronitron »

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?

a common practice is to limit the number of bits in the data value which will limit the range of values it can have
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