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> turning MCAS back on

This was not a mistake, and it's wrong to characterize it as correct procedure not followed.

a. Strictly speaking, MCAS cannot be turned off. Autotrim can be turned off.

b. It's more clear than not, from at least the preliminary report on ET302, that the forces from MCAS induced mistrim at Vno were too high to manually retrim at the altitude they were at. The mistrim recovery maneuver requires releasing back pressure on the yoke to reduce the mistrim force in order for manual retrim to be possible. The transcript fairly clearly (not conclusively) suggests manual trim wheel would not budge. They were already at Vno at a low altitude, and it is reasonable they chose to reenable autotrim in order to gain leverage from the electric motor to overpower the wedged jackscrew.

At 05:43:11 (page 26 of the ET302 preliminary report) you can see two small trim events which are pilot yoke trim toggle switch electric motor assisted trim events; followed ~4 seconds later by an MCAS induced nose down trim that was a complete obscenity.

It was so extreme that the vertical acceleration sensor reports negative values. Only by being strapped in did they not hit the ceiling. That's how aggressive this last nose down MCAS initiation was, and within seconds later they were at 40 degrees nose down. For any automated system to have moved the stabilizer trim this much at Vno is a deeply flawed system. If a human pilot did the same thing in the same situation it would be considered attempted homicide, there is no possible alternative outcome but death for everyone.

You can correctly say: too bad they did not have our extreme mistrust of this MCAS system, too bad they did not realize at the time the extent of the betrayal they were facing. It is more clear than not that they still didn't know the details of how this system worked, that's why they didn't immediately return trim stab to shutoff after their two nose up trims.

It's flat out wrong to say the pilots did not follow proper procedure. They did follow it in the ET302 case. It didn't work. They almost certainly had to reenable stab trim, because the manual trim was stuck due to mistrim forces.

The question I have is: Would the plane have crashed if the plane was a non MAX 737?

I don't think so, but I'm open to being proved wrong. In that case the root cause of the two crashes is Boeing trying to save money.

I think it's not just that question and this is what I dislike about the whole discussion. It's all about Boeing and no one is also asking "if proper procedure was performed for runaway stab trim (again, a generalized memory item) would the plane have crashed? And it does seem the sentiment is to hell with anyone suggesting pilots and airlines involved share part of the blame despite evidence.

I could also ask, would the plane have crashed if it WASNT a max and another stab trim system failed?

It's both. We need to look at everything otherwise we will end up solving only 1 part of the issue.

Edit: To address something you mentioned about root cause (in aviation it's almost never a single root cause and I will give an example that shows such cases here). Let's look at another situation: Assume P&W designs an engine model a plane uses. The plane they are used in has in-air engine fire procedures that must be performed in order to mitigate disaster regardless of the engine model used. Now imagine the new engine design causes more engine fires. If pilots don't manage the problem appropriately when it occurs, what is the root cause? The poor engine design? Improper training from the pilot? In my opinion it's, again, both. Poor training coupled with higher chance of system issues.

The pilots and the airlines didn't design, build, and release a semi-autonomous system which isn't resilient to erroneous data, despite the failure case for that problem being catastrophic.

If an Automotive OEM released a vehicle with an adaptive cruise control system that refused to disable itself except by the human driver intervening through power cycling the vehicle, while driving, it's difficult to put much warranted blame on the driver. The OEM sold a potentially catastrophically faulty system, irrespective of that the fault can sometimes be managed into a fail-safe condition by the driver.

The reason people put the blame on Boeing is because the system implementation didn't fail, the design did.

It doesn't refuse to disable. People are mixing this up with overriding control inputs. It is still possible to take MCAS out if the control loop using stab trim cutout. However when left active it does override pilot inputs. Think of it as the alpha authority that exists on airbuses. However if you follow proper stab trim runaway procedures you cutout stab trim taking MCAS out which restores pilot authority. Again this procedure should be second nature to 737 pilots of any submodel.

In your example, if there were adaptive cruise control, I would turn off cruise control by hitting the button. Same options are present here. However it does mean that braking or acceleration would be overriden until that happens. But the real analogy is if all drivers had to be trained that you turn off cruise control in runaway. If you don't do that, well then you will crash and it's from system failure AND improper general procedure

The example analog I chose is actually a thing, and hitting the button does nothing.

The problem is in the design. Despite the fact that it's possible to defeat the failure in some instances (assuming it hopefully doesn't manifest itself too close to the disaster envelope to start with), the failure case 1) never should have happened and 2) shouldn't require unintuitive remediation.

It's bad design and bad functional-safety analysis. Neither of which fall to the fleet operator or system operator.

Yes I agree. And I'm pleading that everyone also recognise the other aspects of these.incidents such as improper basic procedure. It's all of the above.

Edit: And remember at the end of the day, these airlines and pilots agreed to fly the plane. Even in the wake of the LionAir incident. At the end of the day, the pilots choose to fly and can say no if they aren't comfortable. And if the answer to this is that there is pressure from airlines to keep flying? We just found another major issue and danger in aviation

Edit2: should clarify actually that I agree it's a bad design. Not about the procedures being "unintuitive". If the pilots think the corrective procedures are unintuitive they shouldn't fly any 737 since stab trim systems exist on all 737s and require the same corrective procedure in runaway stab trim.

Are you a pilot? If so what are your qualifications?

Have you read the ET302 preliminary report? In particular have you read page 25, section 2 "Initial findings" last bullet which I quote:

The crew performed runaway stabilizer checklist and put the stab trim cutout switch to cutout position and confirmed that the manual trim operation was not working.

How can you read that, and say multiple times in this thread "improper procedure"? On what basis?

You have no idea how much mental discipline it's taking me, as a pilot, to refrain from ad hominem attack. Your arguments are that bad, they are that willfully contrary to the available facts.

I get it. I understand everyone's frustration. In similar fashion I understand how unlikely it is a crew would have the mental capacity to deal with stick shakers, GPWS callouts, and still fix the problem and that is the tragedy here. However the report said they followed proper procedure but look at the data. 95% N1, turning auto trim on and off a few times, the last time causing the huge -2G bump. There also is not enough data to us yet to determine they did regain control of the plane before enabling electric trim again. I don't think in the case of runaway trim you are supposed to keep switching the cutoff and leave your plane above Vmo. Something doesn't add up according to the data imo.

This is such a bullshit response. You don't answer any of my questions. You proceed to armchair pilot. You use terms you cannot completely understand from a big picture yet claim to come at this from a big picture perspective. That's so out of order.

Do you know a power reduction causes a nose down moment and actually makes the problem worse?

What does "turning auto trim on and off" mean? Are you referring to the you're toggle it the stab trim switches flipped between normal and cutoff? If the latter you are wrong, zero evidence that happened a few times.

There was no -2 G vertical acceleration.

What you are doing is in my view a mental disturbance. You are using terms as if you know what you're talking about. You don't. You are a bullshitter.

Please stop.

Okay. Calm down for 1. Also the prelim data is there to review. The graph shows clearly there's a large plunge and there absolutely was a negative g report in the prelim showing that at the final few moments the trim settings from the FCC gave another correction. As for the cutoff, the report annotations tell you when they toggled the cutout switch. I went back and yeah actually you're right it was only once to cutoff and back to normal sorry for that mistake. However the overspeed is still supported from the data and yes the data shows vertical g forces and at the end there was a lurch of -2 Gs before total loss. It's on page 27.

As for less speed causing more nose down moment, yeah but at the same time they weren't in a descent for that portion either, nor were they nose down (this from page 26). The data shows they were oscillating though climbing slightly while they were overspeeding. In this case it could have helped to reduce the forces at play. I think it was more that they were just busy and left thrust settings where they were from takeoff.

Everyone hears you, most have taken your words into comsideration but I think the part you're missing is the fact that it was impossible for pilot and airline themselves to remediate problems because knowledge of the system wasn't there until it was too late, and even when information began trickling out from Boeing, it's been so slow, and so insubstantive, as to be worthless, likely because of concerns with legal exposure on Boeing's part.

The pilot's absolutely agreed to fly the plane. As far as they knew, it flew like a 737, and they knew everything they needed to know.

Boeing revealed as little as they did about MCAS to spare pilot's the "gory details" because the plane was allegedly "just another 737".

Information does not perfectly diffuse, and doesn't diffuse at all without effort. Half the outcry over this probably isn't from pilot's or aerodynamicist's at Boeing at all, but from people passionate and informed enough to get the word of the colossal fuck up out in as many ways as possible to the people who need to know it most.

I've been in these threads on Hacker News since the Lion Air incident, and held my tongue at many times. Cautioning more and more that new information will drive the development, but in all likelihood, given the facts we have access to, the problems will have occurred in X, Y, Z spots, all of which have origins within Boeing and the FAA as organizations.

The FAA delegated responsibility for vetting to Boeing. Boeing CHOSE to accept that mantle of trust, then discarded the integrity part as soon as the bottom line was threatened by a competitor.

Airlines fly planes. They don't make them. That was Boeing's job, and they cashed in on the better part of a century of goodwill, and torched the entire pile by delivering a complete failure in terms of their own responsibility to the public.

We get it. You think the pilots and airlines should shoulder the blame too. Understood. Many though, myself included, understand that the world runs on incomplete information transfer between designers and operators, and given that, an enormous responsibility is put on designers of industrial scale systems to take extra care to make sure that "unintuitive designs" are very clearly documented and made known to their operators who will have lives and property on the line.

Buying the planes from Boeing came with an implicit trust on the part of airlines that anything different to look out for would be clearly communicated. That didn't happen. They relied on Boeing doing that part. Boeing failed. The fact that armchair aeronautics engineers got to the root cause in such a short time, with so little information beyond the FDR means that it is not unreasonable for the professional engineers at Boeing whose raison d'être is to design safe planes to have caught it.

I don't think anyone here has such a severe grudge against Boeing's existence to just go after them for merely existing. Many, or at least I, am just awestruck at the magnitude of collective failure that occurred.

The data all points to them. Of everyone involved, they alone had both the means and onus to prevent what happened.

But it didn't. So here we are. Something needs to be done, we have very specific rules about how to do it, but nevertheless, something has to changed.

We owe at least that to the lost that their unwitting and tragic sacrifice shall not have been in vain.

The families that have been broken; the sons, daughters, mothers, fathers, and grandparents who will never arrive at their destination demand it. Our integrity, "Our" being those of the will, hubris, and capability to take the lives and fates of others in the embrace of our works, demands it.

Somewhere, at some point, complacency, and cultural degradation happened for whatever reason.

It must be exposed. The historical annals decorated once more in blood, that we never lose sight of the cost of any shirking of our responsibility again.

How else than this, and the penance/contrition of any directly involved, can justice truly be served?

In the case of ET302, you are ignoring mistrim at high airspeed being essentially impossible to retrim manually (by handcrank). If they followed the runaway trim procedure exactly, and did not re-enable autotrim, they would have died, they were mistrimmed, decending, and with increasing airspeed. How do you propose they get out of that without enabling autotrim, in order to have the electric trim motor help them retrim?

In the case of LNI610, you are assuming MCAS upset and approach to mistrim looks anything like runaway trim. There's quite a lot of evidence that it doesn't look like that, but is rather insidious.

As an aside, I think it's an indictment of the changing culture here on HN that this well-written and detailed comment is being downvoted to gray.

Why downvote this? Because it's interrupting a hate-fest on "21st-century capitalism"?

IMO the Salon article itself is pretty worthless; most of the substance comes from the IEEE article that has been already been well-discussed here:

https://news.ycombinator.com/item?id=19694207

It's probably being downvoted because it's a long and rambling way of yet again blaming the pilots for not following procedures when the official investigations have proven that this was absolutely not the case.

Being "well-written and detailed" doesn't make it correct.

(I didn't vote either way, FWIW).

Yeah I clarified in the reply that I don't think it's one or the other but all of the above. I'm trying to supplement the author's write-up, not override it. I hat that it's become a case of a single fault. It's not. It usually never is. And people are arguing only one side or the other. In every incident we need to look at the whole picture.

Neither investigation has concluded or issued more than preliminary findings, so it's a bit early to close the books on this subject.