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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

#161

Post by auslander »

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...

> my reaction wouldn't be to speed the vehicle back up to avoid the warning...

In car you can see and feel what's going on. In a jet at night, with complex behaviour in 3D, you'll have much less sensory input, close to zero. Hence Instrument flying.

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

#162

Post by olliej »

salawat wrote: post #154
olliej wrote: post #57

I mean of course Arizona does get hot enough to melt street signs: https://www.accuweather.com/en/weather-news/its-so-hot-in-ar... Maybe those were metal ones a 400+ degrees does happen? I mean survivor bias means we won't have met anyone from Arizona who went out in that heat :D

Completely off topic, but I hate Accuweather. The guy that runs it has lobbied left and right to keep the NWS and NOAA from being able to just deliver weather products because they'd cut into his revenue stream he's developed by charging people for access to public data. Anyway... End rant.

I agree entirely, but we all use adblockers right? :D

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

#163

Post by dramm »

toast0 wrote: post #130
dramm wrote: post #104

Earlier quoted context omitted.

You seem to be arguing multiple sides here. Philip Greenspun's speculation is a plausible concern, that is all it needs to be a valuable point, that type of data limit handling ought to be considered as the system is looked at. I read his post that he was talking a specific simple example, all the other types of things you mention could also be looked at. How the AoA sensors failed, any potential issues with signal h…

> not even having a standard AoA disagree alert Sorry to nitpick on one thing here; but I don't know that having an AoA disagree alert would be that useful. There was already an airspeed disagree alert, and AoA disagree strongly implies airspeed disagree, because AoA is involved in the airspeed calculation. Furthermore, knowing an AoA sensor is broken wouldn't be super useful without a workable procedure to do someth…

AoA disagree does not imply airspeed disagree. Indicated airspeed is purely a pitot and static pressure driven measurement. AoA is there largely as part of the anti-stall warning system, e.g. driving the stick shaker/pusher. An important point of having AoA sensors is to provide a stall warning systems that is independent of IAS, you don't want these systems crossed with each other.

B737 airspeed disagree I believe just requires 5 knots disagreement for more than 5 seconds between left/right IAS. No AoA involved.

There may be some confusion happening due to the events in the Lion Air B737 Max. The maintenance crew tried to address what they believed were ADIRU/ADR issues in previous flights... including as a possible source of erratic airspeed indications and airspeed disagree warnings. So there are some discussions of airspeed disagree in relation to that aircraft. There may be a lot going on there we don't know about yet, with say faulty ADIRU/ADR causing multiple problems. The ADIRU has inputs from the AoA vane but does not use that in calculating airspeed, it is using that to drive stick shakers/pushers and optional display AoA, and unfortunately in these cases to also drive MCAS.

Having a AoA disagree indication (and/or full AoA display option) might have allowed more prompt diagnosis of problems, but only if pilots were aware of and trained on MCAS. And even then, yes it's a minor point. I was not intending to claim that itself is a deep solution here, just not having a disagree warning as standard was a bad decision. The entire system, and overall approach taken by Boeing seems tragically deeply flawed.

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

#164

Post by cmurf »

smadurange wrote: post #147
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…

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.

and

de-structuring of crew cooperation fed on each other until the total loss of cognitive control of the situation

OK so you need two better pilots, right? And what specifically would make them better in your view?

The final report is pretty clear, the most relevant cause bullets are on page 203, there's no need to speculate and provide your own version. It very clearly cites training deficiencies, cockpit ergonomics in that there was no clear display of airspeed inconsistencies and flight director indications that could have led the crew to believe their actions were correct even though they weren't, and significant simulator deficiencies.

The training and ergonomics basically set them up to be shocked at the situation they were in upon autopilot disconnect.

BEA even blame regulatory oversight of Air France for an inspection regime that failed to identify any of the rather numerous problems BEA found across the board.

Pinning this accident on a pilot is inappropriate.

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

#165

Post by aidenn0 »

ronilan wrote: post #35
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.

Down by 4 at the Super Bowl, 2nd & Goal, 27 seconds on the play clock, Lynch in the back field. Run the ball About 10 characters of code. Sometimes armchair quarterbacking has a point.

Even there though, the fact that the Pats scout team ran that exact play twice in practice with the backup nickelback in was something that the coach perhaps could not have anticipated?

Any result other than an INT means Lynch still has a chance to run.

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

#166

Post by aidenn0 »

If the leaked information so far is at all reliable, it seems that the MCAS system was obviously inappropriate for FAA certification; a single AOA sensor cannot be used as a critical component of a DIL B system, full stop.

The suggested change makes the system not actively crash the airplane under ordinary situations, but does not account for the increased load on a pilot due to the need to manually trim down under the conditions that a properly operating MCAS would be needed. If the MCAS is necessary to prevent crashes due to pilot overload, then this 10 character change is insufficient.

Sure the suggested change makes the cure no longer be worse than the disease, but doesn't address the fact that the cure was needed in the first place.

Another way of putting it is that the crash could have also been avoided by using this pseudo code instead of what is suggested:

    IF FALSE THEN RUNAWAY_TRIM();
but the MCAS system wasn't added by Boeing because they wanted to spend more money on the aircraft, so it (like the fix suggested in the article) seems likely to be insufficient from the point of view of passenger safety.

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

#167

Post by cjbprime »

dramm wrote: post #163
toast0 wrote: post #130

Earlier quoted context omitted.

> not even having a standard AoA disagree alert Sorry to nitpick on one thing here; but I don't know that having an AoA disagree alert would be that useful. There was already an airspeed disagree alert, and AoA disagree strongly implies airspeed disagree, because AoA is involved in the airspeed calculation. Furthermore, knowing an AoA sensor is broken wouldn't be super useful without a workable procedure to do someth…

AoA disagree does not imply airspeed disagree. Indicated airspeed is purely a pitot and static pressure driven measurement. AoA is there largely as part of the anti-stall warning system, e.g. driving the stick shaker/pusher. An important point of having AoA sensors is to provide a stall warning systems that is independent of IAS, you don't want these systems crossed with each other. B737 airspeed disagree I believe j…

I think the Ethiopian preliminary report says they were in IAS disagree for the whole flight too. I don't know what caused the IAS disagree. It played a role in the crash, since its checklist disallowed lowering flaps (which would have disabled MCAS) or throttling back (which would have avoided surpassing Vmo, which likely made manual retrim impossible).

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

#168

Post by cjbprime »

treis wrote: post #107
tbabb wrote: post #30

There are several inexcusably egregious errors in the design of the MCAS system, and this "solution" addresses none of them. - Single point of failure: The system makes command decisions based on the readings from a single sensor. The fact that nobody asked (or was bothered by the answer to) the question "what happens when that sensor fails?" is negligence. - No re-training of pilots: Pilots were not aware of new way…

>No re-training of pilots: Pilots were not aware of new ways in which the plane might take command away from them, and were left in the dark with only seconds to react to a deadly situation Both the Lion Air and Ethiopian Air flights recovered from the initial MCAS. The mistake was assuming that pilots could reliably recover from a runaway trim situation. That might have been true when that was a more common failure…

Agree with you, though as a small correction it now appears (according to Ethiopian preliminary report) they made it to 7k altitude AGL, not 1k AGL. Still not so much to work with when you're above the plane's max airspeed and trimmed all the way down.

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

#169

Post by cjbprime »

chupa-chups wrote: post #61
zippergz wrote: post #16

Earlier quoted context omitted.

Vimeo is based in NYC USA, how is it "European version of YouTube"?

You're right. I was always of the opinion vimeo was european (it incorporated quite some european platforms like viva)

You might have been thinking of DailyMotion, which actually fits that description.

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

#170

Post by cjbprime »

Diederich wrote: post #26
chupa-chups wrote: post #2

This video from "Mentour pilot" has been deleted (supposedly upon request from boeing): https://www.youtube.com/watch?v=EzgBft-79U8 You can see it here (european version of youtube): https://vimeo.com/329558134 Or more info here: https://news.ycombinator.com/item?id=19627525

Strongly suggest everyone check out the video. It's...kind of shocking.

I wonder how the simulator decides to change the required torque on the trim wheels. I suppose it must be a full aerodynamic load model?
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