Indeed looks like they did disable MCAS using the stabilizer trim cutout switches, but the aircraft was trimmed nose down when they did so. Aerodynamic loading prevented manual trimming using the trim wheels. They eventually turned electric trim back on, as they didn't really have any other options, but didn't trim back enough, and left it turned on. At this point the right airspeed indicator (which should be more reliable) reads 365 knots. VMO is 340, so they're already in big trouble. 5 seconds later, MCAS kicked back in, and then it was all over. Very sad.
> At 05:40:35, the First-Officer called out “stab trim cut-out” two times. Captain agreed and First Officer confirmed stab trim cut-out.
[...]
> At 05:41:46, the Captain asked the First-Officer if the trim is functional. The First-Officer has replied that the trim was not working and asked if he could try it manually. The Captain told him to try.
> At 05:41:54, the First-Officer replied that it is not working.
[...]
> At 05:43:04, the Captain asked the First Officer to pitch up together and said that pitch is not enough.
> At 05:43:11, about 32 seconds before the end of the recording, at approximately 13,4002 ft, two momentary manual electric trim inputs are recorded in the ANU direction. The stabilizer moved in the ANU direction from 2.1 units to 2.3 units.
> At 05:43:20, approximately five seconds after the last manual electric trim input, an AND automatic trim command occurred and the stabilizer moved in the AND direction from 2.3 to 1.0 unit in approximately 5 seconds. The aircraft began pitching nose down. Additional simultaneous aft column force was applied, but the nose down pitch continues, eventually reaching 40° nose down. The stabilizer position varied between 1.1 and 0.8 units for the remainder of the recording.
Seems this debunks the initial implicit commentary how this was due to 'third world' pilots and couldn't happen in the US.
Interesting, that when they turned the electric trim back on, they only momentarily blipped the switches to trim up, and the stabilizer did move. Then five seconds later MCAS pitched down again and it was over.
Wonder why didn't they trim up more when they turned the electric trim back on. On the surface it appears that was their last chance to salvage the situation.
That's what I think is most interesting. Given the position they found themselves in, going against the directive from Boeing to leave the trim cutout for the duration of the flight, means they were desperate to get the trim back up. So why did they not immediately make use of the reenabled electric trim control to counteract MCAS for as long as it took? They had kept the plane flying up until reenabling the electric trim, but that one action pushed it over the edge and could not be reversed? Confusing.
They made two small trim up commands. But looking at the flight data graph, the stablizer on the bearly moves. The motor was probably stugling against the aerodynamic forces too.
Prehaps they didn't think it moved at all and decided they stablizer was jammed. 5 seconds later, MCAS commands down and because that's in the same direction as the aerodynamic forces it moved a lot easier.
They are also pulling with all their might on the yoke and have been for several minutes. At this point probably fighting fatigue or even getting close to muscle failure (how many pounds of force for how long?) and starting to question their sanity.
Yeah, from my computer screen I can wonder why they didn’t sit on that ANU switch hard and long. But in that cockpit Boeing had already sealed their fate.
Here, no pilot had any simulator training for the new MAX. Because Boeing was selling the planes as the "same as old ones, no training needed." It seems Boeing also claimed up to just a few days ago that the simulator training is still not going to be needed for the MAX, just the "one hour iPad" game.
But a whole lot of social and political engineering was put into ensuring that simulator drills of emergency scenarios related to this system would not be part of any pilot's training.
And if training for this scenario in a MAX-specific simulation was recommended/required then Boeing wouldn’t sell many planes because that would mean buying simulator time and retraining your existing 737 pilots.
For specific training to be reqired I assume it would need to be made a different certification entirely? Is that even a plausible scenario that this could change?
So MCAS put them in a hard to recover position which required electric trim to recover, and as soon as they turned on the electric trim MCAS turned on again and forced them into a crash?
Then this is much worse than initially suggested, it means a pilot can be aware of MCAS and still be put in a extremely dangerous position due to the extreme control authority of the module.
Per the article a combination of things put them in that situation. Not just MCAS. Why is everyone so wedded to the narrative that this is the fault of MCAS and nothing else? Complex systems that have millions of man hours spent making them safer don't usually have back to back failures because of one faulty subsystem. We've incrementally refined commercial air travel to the point where single source accidents are basically nonexistent.
I'm not saying that MCAS isn't mostly to blame but the fact that the maximum inputs from the pilot is still lesser than the control authority from the trim raises some serious questions MCAS or not. Had "extend flaps" been at the bottom of the checklist that would have disabled MCAS and likely prevented this crash.
It's true there were aggravating factors, like the inability to manually rectify trim, which (would seem to me) would be a aerodynamic or design issue.
The point still stands, the root cause was MCAS, without it this would never have happened. MCAS would not have pitched them into a dive, and even if they were pitched into a dive by some non MCAS system, they would have been able to turn on electric trim and recover. MCAS both caused the situation, and made fixing it impossible, so it was the root cause of the crash.
Agreed. One could argue that the AoA reading mismatch was the root cause, but the plane alerted the pilots to the discrepancy just as it was meant to (through stick shake and panel readouts).
They were aware of the issue, took measures to mitigate them, and MCAS still drove the plane into the ground.
> It's true there were aggravating factors, like the inability to manually rectify trim, which (would seem to me) would be a aerodynamic or design issue.
I don't see in the report that the pilots attempted to both operate the manual trim wheel at the same time. I'm not sure if its explicit in the training, but in the manual its made clear that pilots may need to work together to move the trim out of extreme positions when the electric system is not available, and that doing so will not break the manual trim system.
I don't think they were concerned about snapping the cable, but based on a simulation run last week by a Swedish pilot (who needed both arms locked around the column to keep it held back, towards the end), and the reports' notes of the pilot repeatedly instructing the co-pilot to help him trim up, the forces on the column were such that the pilot couldn't assist in cranking AND continue to pull back on the column at the same time.
Releasing the stick to assist with the wheel would have meant allowing the plane to nose-dive. This might have allowed them to crank in the stabilizer in time to recover, but they only had 7,000 feet above the ground to work with.
Likewise had Boeing designed a control surfaces system such that the pilot always has more control authority than the trim this also would not have happened.
I didn't say that MCAS wasn't the lions share root cause here. It's just not as simple as the "hurr durr, MCAS bad" that a lot of people keep trying to portray the more nuanced statements of various regulatory agencies as being equivalent to. MCAS might be bad but on an aircraft with a different trim system it wouldn't be "hurr durr" levels of bad.
Airbus just gives you a joystick with no force feedback at all. So yes ... but an entirely different philosophy. You tell the aircraft what you want it to do and it figures out how to do it. I suppose these recent events could be used as an argument against the idea of doing essentially fly by wire but then putting in a whole lot of extra stuff to make it seem that you are not doing fly by wire.
Even if things degrade all the way down to "direct law" the pilot does not feel any aerodynamic force caused by the trim position.
We are talking about two different interpretations of the word "authority". In the case of the incidents, the pilots were physically unable to overcome the simulated force for an extended time.
MCAS issues nose-down, speed increases and nose pitches down. Nose never pitches back up. Plane crashes.
Sure, maybe some complex combination of maneuvers could have helped them out of this but there's really everything pointing the blame at this one system. Pilots did what the boeing manual suggested (even included at the end of this report).
MCAS forced the trim to a point where (because of aerodynamics) it was impossible to manually change the trim even after disabling MCAS, and was designed in such a way that it was impossible to engage the electrical trim controls (which could have saved the plane in this case) without also reenabling MCAS.
Maybe, when they started thinking about a plan B, they were anyway already much too fast to use flaps?
I guess that there is a max speed for flaps (maybe the computer even actively refuses to extend them if the airspeed is higher than X to avoid that wings are destroyed).
Why exactly? if Boeing did not updated the manuals and checklists how would pilots know that? from internet forums? Should a pilots ignore the checklists and try steps he read on the internet ?
I could not find if Boeing updated their manuals/checklists after the first crash.
This bulletin notes that electric stabilizer can be used to neutralize the control column prior to STAB CUTOUT, which it appears the Ethiopian crew did not do.
The bulletin completely fails to note that if you don't time the STAB CUTOUT immediately after you use manual electronic control but instead the MCAS acts again before you cutout, you're left trying to manually trim the stabilizers in a situation where the elevators are putting so much force on the jackscrew that manual stabilizer trim may be impossible.
Appears? Where are you reading this to come to that conclusion?
Page 11 of the preliminary report, 05:40:35 "stab trim cut-out".
Page 26, five manual trim up inputs before that time. Manual trim is electric trim instigated with yoke toggle switch.
What is not certain (to me) is if continuous nose up toggle for sure would have inhibited the automatic nose down from MCAS shown at 05:40:45. It really looks like pitch trim still needed to come up more in order to relieve the control column force to bring it back to neutral.
Why didn't they continue to manually trim (electric) after 05:40:35 to relieve yoke back pressure and also to improve climb rate and also reduce speed? I suspect they actually got ahead of themselves, setting trim stab cutoff too soon, not realizing how much more insideous the MCAS upset case is compared to runaway stabilizer trim.
And that is the problem with no training. They had no way to iterate various scenarios of working and failed MCAS behaviors.
It seems the "yo-yo manoeuvre" required to manually trim when severely mistrimmed with deflected elevator stopped being taught or mentioned in Boeing manuals decades ago.
The Boeing/FAA directive re: MCAS does not instruct them to extend flaps.
Further, there's other things going on in the cockpit due to the malfunctioning AoA sensor that's the root of all this.
Specifically one of the effects is that they get an Unreliable Airspeed Indication, and run that checklist. That checklists memory items include maintaining the current flap configuration (in this case, flaps up).
The Boeing/FAA directive does not instruct them to deviate from this and extend flaps. They have a checklist memory item instructing them to in fact do the exact opposite, and not touch flaps.
You're correct that the AD and runaway trim procedure does not instruct them to extend flaps. What I was addressing was the statement upthread that "Flaps out supposedly would have kept MCAS off but the pilots weren't expected to know that."
If I'm a 737 MAX pilot, after the Lion Air crash I'm learning absolutely everything I can about MCAS. And from information Boeing provided I would learn that it operates with autopilot off, flaps up, at high indicated AoA.
You mention unreliable airspeed, that was actually their first problem. Flaps were extended at that point, as according to the narrative they were not retracted until after the AoA disagree, stick shaker, and airspeed disagree. In fact it almost reads like they were intending to continue the flight, engage autopilot, and climb to 32,000 ft with the stick shaker going the whole time. That seems very odd to me.
>If I'm a 737 MAX pilot, after the Lion Air crash I'm learning absolutely everything I can about MCAS. And from information Boeing provided I would learn that it operates with autopilot off, flaps up, at high indicated AoA.
And in a crisis situation you skip the checklists and think fast and apply your instincts because you read something on a forum? Sure if you have a lot of time you can try thinking but this is not debugging a bug where you have hours to observe the issue, try different inputs, observe again, Google some questions etc..
We don't want pilots to be creative. Air safety is so good because pilots learn memory items and checklists and actually follow them instead of making stuff up.
If the checklist doesn't mention flaps and the plane crashes if you keep the flaps up, that's on Boeing.
Sadly, it looks like those millions of man hours of incremental safety refinement also created a false sense of security. That (and management overriding engineering concerns) are the only explanations I have for how MCAS was implemented: because it had to be able to correct the pitch-up tendency of the 737 MAX and stay "invisible", so additional training could be avoided, Boeing apparently chose to use only one AOA sensor as "single source of truth" - because using both would have increased the chance of the system having to deactivate itself, which would probably have made the FAA mandate the additional training that Boeing wanted to avoid. This is just my personal theory however...
> Why is everyone so wedded to the narrative that this is the fault of MCAS and nothing else?
Because the other factors don't single this flight out, and the plane wouldn't have crashed without MCAS misbehaving, or more fundamentally, without the flawed plane design that required such a system in the first place.
> Aerodynamic loading prevented manual trimming using the trim wheels.
Are the trim wheels mechanically connected to the trim mechanism in the back? Is there no way to trim the horizontal stabilizer electrically without also enabling MCAS? What would happen if the pilots continually pressed the trim up switch on the yoke? That should've prevented MCAS from activating, right?
I thought Boeing airplanes were built such that "the pilot is always in control". That doesn't seem to be the case anymore, if by cutting the power to certain subsystems you can't control the airplane anymore.
Yes they are manually connected but not mechanically assisted in any large (maybe any) part and the nose down trim and full back on the yoke made the manual wheel impossible to use. Thumbing the switch will work to disengage the mcas temporarily yes.
I think the only way to survive this is to use the electrical trim assist to get to level flight and then shut off the system. After it’s level you can go ahead and trim using the manual wheel. Well the other way to survive this is to not have Boeing design the mcas to read from one sensor only and also have mcas operate in a narrow authority.
Yes, pilots selecting "up" on the trim switch should stop and override MCAS. But it also "resets" MCAS so that it will pitch down again on its next cycle. So you'd have to be constantly correcting it, or switch the electric trim off entirely (i.e. treat it as runaway trim).
this video[0] from "mentour pilot" on youtube explains the stabilizer system quite well.
it seems the trim wheels are connected manually to the trim mechanism in the back, but when the trim stabilizers are in an extreme position the wind loading on them makes it very hard/impossible to rotate the trim wheels manually.
from what i understand, one way to relieve/lessen the wind loading so that the manual wheels can be used again is to (in the case of trim down) dive the plane. this would lessen the wind loading on the stabilizer and allow the manual wheels to move again. but you would need "room" to dive, something they did not have in this case.
Its possible and I think it was demonstrated in one of Mentour Pilot's videos that both pilots can work together to manually trim. Boeing put notes in the manual that this may be needed and it would not break the manual trim system to apply that much force to the trim wheels.
the fact that the combined strength of two humans would not be enough to _break_ the manual trim system does not tell us whether that combined strength would be enough to _turn_ the trim wheels at all.
https://news.ycombinator.com/item?id=19575318 "option 2)" (on this same page) refers to a situation where a "dive" could be executed in a situation where manual strength is not enough to trim the aircraft.
Recall that at the same time it's taking the strength of both pilots on the yoke to keep the plane approximately level. You're saying they should both let go at low altitude and see if they can crank a trim wheel together?
> Is there no way to trim the horizontal stabilizer electrically without also enabling MCAS?
Correct. One wonders if this is a consequence of trying to maintain the type rating and therefore not being able to introduce any pilot training about the MCAS feature, and therefore not being able to introduce any control features for it.
Good question. This is what makes these accidents so bad in my eyes: they weren't caused by a defect or flaw in the traditional sense, but rather by a system that seems to have been conceived solely to allow Boeing to skirt retraining/recertification requirements, to sell more planes.
Such a system should have been subject to extreme scrutiny, and honestly it beggars belief that the potential for these accidents wasn't seen. "This system can trim the nose down beyond the authority of the manual controls, based on readings from a single non-redundant sensor" should have been more than enough to get the gears turning, and it seems that the deeper one looks it only gets worse.
Being capable of performing a glide without electricity does not necessarily imply that a no-power glide can safely be entered from extreme conditions like diving too fast with trim set to insane.
But being able to actually utilize all your control surfaces without electrical power must be a basic requirement.
They could make the trim control wheel mechanically assisted, for example (since there are cases where electronic trim control is required because because of the amount of force needed to turn the wheel)
> They could make the trim control wheel mechanically assisted
I'd imagine it already IS mechanically assisted. There is a limit to how much you can amplify a pilot's input mechanically, and I'd imagine the load on the aircraft exceeded the amount of amplification needed.
I.e. your car has power steering, so the car manually adds power to the turn based on the user's input. That doesn't mean that something in the road can't override the input of both the driver and power steering and jerk the wheel.
If the AoA was truly way too high then insane trim would be required to correct that. MCAS and similar systems came about in response to AF 447 where the pilots entered a high AoA situation and stalled the plane into the Atlantic.
It's true in the case of the 737 MAX where the pitch-up moment caused by the engines exceeds the elevator authority in a low-speed, high-thrust situation if the pitch trim is also set too high.
MCAS will evidently work with less maximum nose-down trim than the current version has, as the proposed update places a limit on it.
Sure, but that's assuming the plane was trimmed somewhat correctly to start with. The only reason the pilots had problems manually moving the trim was because the electric motor moved it far out of the correct trim range.
Also, it's not zero power. A ram air turbine deploys and provides hydraulic pressure to move the controls. And there are batteries to keep a small number of essential flight instruments powered.
The planes when setup correctly have a pretty good glide slope actually. When there is no power the pilots can deploy the apu to restore basic power for flight controls.
Nope. (And arguably it shouldn't: a stall at low altitude is much worse than a stall at high altitude, because you lack recovery time. Most fatal stalls begin below 1000ft AGL, which is where this plane was. So your stall avoidance system shouldn't shutdown just because you're at low altitude: that's when you want to avoid stalls.)
Had they paid closer attention to their airspeed. The aircraft could have been saved. By reactivating the system at such high speed, adding further nose down trim, there was no way to keep the aircraft level. Tunnel vision.
> 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.
This is very damning to Boeing. It's precisely the procedure they prescribed and intended to mitigate possible MCAS caused trim runaway. In light of the fact that they put this in place as a justification for moving the engines forward without reclassifying the plane, I don't see how they can get around fault here.
What a tragedy.
I can't imagine the emotion those pilots must have felt after attempting to do exactly what they were told to do to keep the aircraft in the air, only to have the nose lurch back downwards. Godspeed, gentlemen. It wasn't your fault.
This means that Boeing is now 100% liable for the crash, as there was nothing the airline could've done in this scenario.
It also means that the aircraft will have to be re-designed and re-classified before it ever flies again (it's now a very clear design error, not a training or communication error)
Thechnically they could have used the thumb switch and regained level flight to override the mcas system temporarily and then shut off the electrical system to the stab and trim manually thereafter. However, they didn’t know about the mcas system and the troubleshooting steps that Boeing has for that mode of failure were insufficient for this precise scenario.
At 05:43:20, approximately five seconds after the last manual electric trim input, an AND automatic trim command occurred and the stabilizer moved in the AND direction from 2.3 to 1.0 unit in approximately 5 seconds. The aircraft began pitching nose down. Additional simultaneous aft column force was applied, but the nose down pitch continues, eventually reaching 40° nose down. The stabilizer position varied between 1.1 and 0.8 units for the remainder of the recording.
It seems they tried it but MCAS kicked 5 seconds after they turned on the electrical trim. They didn't have enough time to correct the stabilizer. I don't know how fast returning a stabilizer to neutral position can be done, but they probably thought they had more than 5 seconds. They were probably going to turn off electronic trim control afterwards.
I've read that it takes the trim motor 30 seconds to move the jackscrew completely along its path. It was found all the way at one end in the wreck. So naively, it takes up to 15 seconds of continuous motor operation to recover level flight.
this may be a naive question but with all of the advanced technology on these planes, why isn't there a check for altitude before any automated command runs which says "hey we just took off, are 400ft above ground, MCAS is saying nose down, we will crash if that command runs, CANCEL"
Because right after takeoff is the single most common point at which you might stall the aircraft. What's more, at that point it is likely to be a power-on stall, which is the specific situation that MCAS is intended to fix (because the 737 MAX has a tendency to pitch upwards in power-on scenarios).
Really there should just have been a separate cutout for MCAS itself, but that would have triggered retraining requirements, so Boeing wanted to avoid that. But very simply, there should just be an 'off' switch to disable this system if it starts to run away, distinct from the whole runaway trim procedure.
(as well as 2-of-3 redundancy on the sensors, the lack of redundancy is seriously exacerbating the rate of incorrect MCAS system activations)
And the AoA disagree needs to be actually used and not just an "option feature pilot warning". AoA disagree on ground = plane doesn't take off. In flight = MCAS cuts out.
And if it's reporting a difference, it could just be because there's no airflow and the vanes aren't at identical positions. You can't rely on the difference meaning anything.
MCAS system is supposed to stop the plane from stalling.
The faulty AoA sensor is causing the plane to think it’s about to stall and therefore MCAS works as designed to prevent the pilot from putting the plane into a stall.
Of course the design is wrong because the plane is actually pointing toward the ground and MCAS thinks it’s pointing to the sky...
What about a single button to turn MCAS off and return to trim to a neutral position? Or a setting where the pilot is telling the system to ignore the sensor input.
Maybe a bit like a self driving car planes will eventually have a system where they can use visual markers as a check on what sensors are reporting.
The 737 max was designed to not be any different to fly than previous 737s, so adding a button to disable this system was not allowed as I understand it.
As these two tragic accidents have made clear that specification was pretty wrongheaded...
Seriously, a MCAS indicator light (if MCAS is actively issuing commands), a big red button below it called "Disable MCAS" , and a MCAS disabled light (so pilots actually remember when it is disabled) should be more than enough to prevent this.
Besides adding the AoA disagree light AND having MCAS use a triple AoA sensor vote to determine the AoA angle.
I just took a look at the take-off procedure in the checklist, and it lists that one should extend flaps before and during take-off/ascent. The checklist says that one should start retracting the flaps at 1000'AGL, the altitude where they seem to have started having problems.
MCAS is disabled while flaps are extended. It would have activated the second they retracted the flaps.
It only overrides the MCAS inputs when they're actively adjusting the trim. So, they did try and correct the trim with the manual inputs, and five seconds after the last push of a trim adjust button the malfunctioning MCAS activated and adjusted the trim to something far worse than when they'd started. If I'm reading this right, the plane hit the ground killing everyone on board less than 30 seconds later.
Refer to the graph on Appendix 1, the automatic AND commands begin about 5 minutes before the crash. They counter them partially with the manual ANU electric trim for the first 1.5 minutes before issuing STAB CUTOUT.
Just out of curiosity, will there actually be any punishments handed out beyond just a slap on the wrist? Or is Boeing far too large of a corp to take on?
- Boeing will lose 10s of billions of dollars because of this in damages, lost contracts, and redesign costs.
- Their CEO will resign.
- The FAA will revamp many procedures to vastly increase certification costs and not allow these types of same-class-rating bullshit.
- The FAA or similar EU agencies may slap some fine against Boeing
- The families will sue and win a large settlement.
- One or more engineers may commit suicide. (which would be itself tragic)
- Middle management will pay zero or nearly zero price.
- No one will be internally fired by Boeing as the problem is systemic.
- No criminal charges.
Many of these things will only happen with a sustains public relations compaign against Boeing, congressional hearings, persistent news articles, documentaries highlighting the harrowing crash, etc.
EDIT: I’d say there’s a small chance even that a system called MCAS never flies again, even if that means the entire MAX concept has to be shelved.
If the MAX can fly without MCAS but just under a new type rating, that could be the way they go. Boeing simply has not been successful introducing computer-moderated flight controls and envelopes the way that Airbus has over the last decade (and those lessons were hard learned too).
Incidentally, Boeing has received billions of dollars in illegal tax subsidies from the US (as in, anti-competitive with non-US manufacturers like Airbus): https://www.bbc.com/news/business-38131611 So it's hard to imagine fines or market penalties actually conveying any productive sense of punishment.
>This marks a victory for Airbus in a war without end.
>Back in September the European aerospace giant, which employs 15,000 people in the UK, was on the receiving end when it was found that billions of euros in low interest loans amounted to illegal subsidies.
>Boeing celebrated that moment as a comprehensive victory which would deal a mortal blow to Airbus and result in more US jobs.
>The reality is that neither of these companies can exist without government subsidies.
Both of these companies are strategic assets to the countries that have them. So no surprise here. I'm not even upset at it- it's realpolitik.
I've read a couple of these things (strongly recommended — aviation postmortems are a model for us all) and my impression is that "too large" or "slap" are foreign terms in their debugging culture.
Their priority list is, AFAICT: 1. Find out what happened. 2. Find out why. 3. Find out how to make sure it doesn't happen again. 4. See point 3. 5. See point 3.
I don't think you would say that if you had read such a report.
The ones I have read do not feature three-word explanations, but rather say things like "the chain of events that led to the accident could have been stopped at any of these single points: <seven items> and would also have been stopped if both a&b had been done, or if both c&d, or both c&e" and then discuss how each of the many might be changed. They don't say "five of the links in the event chain were at a profit-hungry corporation, whose CEO should be thrown in gaol, then they'll know to do that differently in the future".
"Runaway corporate greed" is fine reason for a quick and angry post on a social network, but aviation postmortems are a different kind of beast, heavy on analysis and prevention, light on anger.
We are at the 'accident investigation' stage. Accident investigators do not hand out punishments. That comes later, during civil or criminal procedures in the various courts of jurisdiction, and by the regulators.
It is certainly within the realm of possibility that there will be severe consequences, up to and including criminal charges.
This is an absurd comment. The rule of law works in the USA as much as it does in other developed countries. There is no such thing as "too large to take on". I note though that there is not yet any evidence of a crime having been committed.
> There is no such thing as "too large to take on"
Let me get you up to date:
"The deal — four years after the 2008 collapse of Lehman Brothers nearly brought down the financial system — was criticized at the time, raising concerns about whether some banks had grown too big to face criminal indictment."
"Citing anonymous officials close to the case, the New York Times reports that federal prosecutors spent months debating whether to issue criminal indictments for money laundering. Authorities eventually ruled it out as such charges could ultimately cost HSBC its charter to operate in the US, seriously undermining the country’s fragile economic recovery."
[...Quebec Premier François Legault said that SNC-Lavalin was one of ten publicly-traded companies headquartered in Quebec that the province considers to be "strategic" and therefore in need of protection from a takeover that would force the company to leave the province....]
I'm not versed in the terminologies. What I understood was told previously is that
In similar condition (nose down) in other plane just pulling the stick would work but with MCAS you have shut it down using some switch and just the stick won't work.
And now the report is saying even that switch doesn't work? That one MCAS goes bonkers there's essentially no recourse?
The switch works to disable MCAS, but at the cost of also disabling the trim motor, which is what you need to use to recover from what MCAS was doing before you disabled it.
> 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.
Are they talking about manual electric trim, or physically moving the trim wheel with its handle?
I would expect manual electric trim to stop working after you STAB TRIM CUTOUT, since that kills the trim motor. Did the pilots try physically moving the trim wheel?
It does not appear to be "precisely" the procedure, in that sufficient nose up trim was not selected by the yoke manual trim switch prior to pulling the trim cutouts. And then they did not work the mechanical trim wheel hard enough to reset the residual nose down trim.
And, the crew left the power setting at climb throughout almost the entire sequence, so they oversped the airframe.
And, when they (against procedure) (apparently) turned the electric trim system back on, they did not use the yoke manual trim switch to fix the nose down trim problem -- which is a big mystery.
The MCAS design inhibits its FCC trim down output when manual trim is utilized. So, if they had just continuously pushed the nose up manual trim switch on the yoke until they got the trim to neutral, then pulled the cutout (either the first time or second time), the accident could have been avoided.
History shows this is not a good human factors design on the part of Boeing, but the crew does not look good, either, IMO.
> sufficient nose up trim was not selected by the yoke manual trim switch prior to pulling the trim cutouts
The EAD/service bulletin doesn't talk about sufficient nose up trim or caution against performing the cutout with even a slight mistrim.
> And then they did not work the mechanical trim wheel hard enough to reset the residual nose down trim.
It's possible that aerodynamic load (of the stabilizer opposing the elevator) made it physically impossible to manually trim given any mistrim at the time the cutout happened, given the airspeed they had. And, the captain is pulling back on the yoke as hard as he can, so he's unavailable to let go of it and grab a trim wheel instead without immediately losing altitude.
> And, when they (against procedure) (apparently) turned the electric trim system back on
It seems sensible to assume -- and the report states -- that they did this because they found that manual trim was impossible in these circumstances.
You're right that the service bulletin doesn't talk about selecting selecting a sufficient nose up trim because control of the aircraft using manual trim is a continuous action performed in combination with the pitch up command of the control yoke. Just pulling up on the control column and activating momentary manual trim isn't sufficient or intended. I understand why people think the checklist implies that performing a STAB TRIM cutout occurs instantly after the autopilot is disengaged because of the "if runaway continues" language.
The Boeing/Ethiopian ETH-2 bulletin quoted in the above linked AAIB preliminary report on page 33 says "Initially, higher control forces may be needed to overcome any stabilizer nose down trim already applied. Electric stabilizer trim can be used to neutralize control column pitch forces before moving the STAB TRIM CUTOUT switches to CUTOUT ..."
> Electric stabilizer trim can be used to neutralize control column pitch forces before moving the STAB TRIM CUTOUT switches to CUTOUT ..
Which really under explains the situation. In reality the STAB TRIM CUTOUT must be switched to CUTOUT within 5 seconds of using the electronic stabilizer trim, or the MCAS will re-establish the forces.
Wow. This sub-thread is making the images of the grounded MAXs look a whole lot less like an overabundance of caution. If accurate this failure dynamic sounds more like some nasty boss at the end of an escape room game than standard fault diagnostics.
Yeah, I think that's fairly put. The MCAS system was pretty straightforwardly trying to kill them, and the only way to disable it also disabled their method of recovering from what it was doing.
> It's possible that aerodynamic load (of the stabilizer opposing the elevator) made it physically impossible to manually trim given any mistrim at the time the cutout happened, given the airspeed they had.
Its been noted in previous discussions that while it would be difficult, the load can be overcome if both pilots were to operate the manual trim wheel at the same time.
> Its been noted in previous discussions that while it would be difficult, the load can be overcome if both pilots were to operate the manual trim wheel at the same time.
I haven't seen that noted anywhere, and have seen it theorized as impossible without motor assist, given their airspeed and with the elevator opposing. Got a link?
Excessive airloads on the stabilizer may require effort by both pilots to correct the
mis-trim. In extreme cases it may be necessary to aerodynamically relieve the
airloads to allow manual trimming. Accelerate or decelerate towards the in-trim
speed while attempting to trim manually.
To be clear, that's a link that agrees with me that it can be impossible, not a link that says they just needed to work harder.
It's also from a 20 year-old manual, and isn't present on newer manuals, and pilots haven't trained on it in decades. Not appropriate to expect pilots to know, and possibly not helpful here: the pilots were low altitude, so allowing the nose to drop even further (to relieve aerodynamic load) may have been deadly too.
Is it still possible at or near VMO? And when the trim is maxed out? I don't think I've seen an authoritative answer on that, and that's the situation they faced.
Another commenter pointed out that the captain is pulling back as hard as he possibly can on the yoke; releasing it to turn a trim wheel instead may have been just as deadly.
Vmo incorporates a factor of safety in its specification, so exceeding it is not a "parts fall off the aircraft" event.
Vne is where things start to get scary because it's usually based on flutter, which can catastrophically damage/destroy the aircraft in very short order.
Yes. But it doesn't include full control deflections and certainly not control deflections in opposition to one another. Even at Va rapid control movements and control movements in multiple axes can permently damage the aircraft.
> And, the crew left the power setting at climb throughout almost the entire sequence, so they oversped the airframe.
I believe that's correct given that they had an Unreliable Airspeed Indicator warning (due to the malfunctioning AoA sensor), per the memory items on the UAI checklist.
It makes the forces on the trim wheel much worse, which explains why they couldn't turn it, but it's the correct checklist response to the conditions observed, and the Boeing/FAA directive completely failed to take the impact of this response into account.
> I believe that's correct given that they had an Unreliable Airspeed Indicator warning (due to the malfunctioning AoA sensor), per the memory items on the UAI checklist.
The idea that a pilot would knowingly leave thrust at climb power while in modestly level flight at low altitude and expect not to overspeed is very strange to me, checklist or no checklist.
I think they were too busy fighting the controls to worry about that.
"In the event of an uncommanded horizontal stabilizer trim movement, combined with any of the following
potential effects or indications resulting from an erroneous Angle of Attack (AOA) input, the flight crew
must comply with the Runaway Stabilizer procedure in the Operating Procedures chapter of this manual:
- Continuous or intermittent stick shaker on the affected side only.
- Minimum speed bar (red and black) on the affected side only.
- Increasing nose down control forces.
- IAS DISAGREE alert.
- ALT DISAGREE alert.
- AOA DISAGREE alert (if the option is installed)"
"the high speeds observed" ... "were logical. It’s a consequence of following the Emergency checklist for “IAS disagree” (IAS is Indicated Airspeed, i.e. the dynamic air pressure experienced by the aircraft) after takeoff."
In short, seeing that Boeing indeed wrote about the IAS alert being activated when the sensor fails, and MCAS gets activated, I can only conclude that Boeing indeed knew that the pilots would make the plane uncontrollable if they followed Boeing's instructions. It seems they just gambled on the chance that the second crash won't happen so soon after the first.
Either that, or we'd have to believe that what a single pilot manage to do for his Youtube video a company which is to deliver the planes in worth of hundreds of billions (!) of USD wasn't able to do.
Part of the procedure is to keep thrust or augment it, after disengaging auto-throttle. Remember that they were in stall warning, too (stick shaker), which certainly shouldn't incite anyone to throttle down.
Why? Because your instruments disagree about your airspeed. You want to have a large margin to keep your speed high enough that you won’t accidentally stall while you try to establish what’s reliable.
Sure, and you then hold that until the aircraft stalls at 45000ft? Of course not.
You can't point at a memory item and treat it like the pilots can only apply what's in there in exclusion to everything else. The structural limits of the aircraft are there for a reason.
Aside from anything else the pilots were trying to maintain altitude by their communication with ATC.
Not that I'm blaming them. I think they had too much going on to even consider moving the throttles, and thats 100% on Beoing, but it probably didn't help their chances of recovery.
No, the wheel has an extendable crank handle and is meant for manual use precisely when the electronic stabilizer trim is cutout.
But aerodynamic forces can conspire to make it very hard or physically impossible for human force to rotate it if the elevator is being used to combat the stabilizer at high speeds. See here for more discussion of the physics behind it: https://www.satcom.guru/2019/04/stabilizer-trim-loads-and-ra...
Thanks, that makes sense. When the report says that the pilots found manual trim impossible after STAB TRIM CUTOUT, do you think it's referring to an attempt at manual electric trim (expected to fail) or both pilots manually moving the trim wheels with the handle?
My (non-expert) reading is that the co-pilot couldn't move the wheel, while the pilot was engaged in fighting to to keep the stick pulled back (a Swedish pilot tried this scenario in a simulator last week and literally had to keep both arms locked around the stick towards the end).
Counter-intuitively, letting go of the stick in brief increments might have been the correct move. Letting the nose pitch down would take force off the jackscrew and let both pilots crank hard on the stabilizer. Boeing manuals once covered this, but apparently they haven't since the 1980s, and their directive after the Lion Air accident made no mention of the necessity of such a procedure. Also they were only 7,000 feet above the ground so whether or not they'd have recovered in time is hard to say. Quite possibly the MCAS had already doomed the flight.
No, it's worse: the origin airport is at 7000ft elevation. They only had around 1000ft height AGL for all of the flight. So I agree that releasing the elevator at all seems surely suicidal.
Oh! I think this is new information in the report -- the FlightRadar24 ADS-B data never shows them above 8500ft altitude, ~1000ft AGL. FlightRadar24 must have missed the final few minutes?
But high enough to re-enable a system you know is malfunctioning?
I guess we will have to wait for the final report but the pilot's actions are perplexing here. Even if we accept that they can't trim with the wheel, why enable electric trim and then not use it? Why not enable it, trim to where you want, and then use the cut out switch again?
> But high enough to re-enable a system you know is malfunctioning?
They couldn't land with the stabilizers mis-trimmed. If the wheel wouldn't budge, re-enabling it and trimming electronically was the only option likely to occur to them, since the only other possible option (release the column, let the plane nose down so that the forces on the screw ease and they can trim manually) is completely counter-intuitive and was removed from Boeing's documentation and simulator training 30-40 years ago and was not covered in the FAA/Boeing MCAS directive.
> Even if we accept that they can't trim with the wheel, why enable electric trim and then not use it?
They did use it after re-enabling it. They just didn't re-disable it within 5 seconds of their last input manual electronic trim command, so the MCAS ran again a final time.
Whether that's because they just didn't get to the switches in time, weren't aware they had such a short window to do so (the FAA/Boeing bulletin does a piss poor job of communicating this), or were just so thoroughly overwhelemed by everything that was going on is hard to say at this point.
>They couldn't land with the stabilizers mis-trimmed. If the wheel wouldn't budge, re-enabling it and trimming electronically was the only option likely to occur to them, since the only other possible option (release the column, let the plane nose down so that the forces on the screw ease and they can trim manually) is completely counter-intuitive and was removed from Boeing's documentation and simulator training 30-40 years ago and was not covered in the FAA/Boeing MCAS directive.
They could have just kept flying. They weren't in any immediate danger and had time to reach out for help. Worst case scenario, you fly straight for the next 30 minutes while ascending to 20-30k until you figure out what's going on.
>They did use it after re-enabling it.
Not really. The barely blipped it. Not what I would expect if they had a clear intention to re-enable electric trim in order to get the trim to where they wanted it.
> They could have just kept flying. They weren't in any immediate danger and had time to reach out for help. Worst case scenario, you fly straight for the next 30 minutes while ascending to 20-30k until you figure out what's going on.
The stabilizer's trimmed down. The pilot is repeatedly requesting the co-pilot's assistance in maintaining elevator trim up, and says to the co-pilot at 05:43:04 that the pitch is not enough to keep the plane level. They're well above Vmo at this point.
> In the test, the two European pilots in the 737 simulator set up a situation reflecting what happens when the pre-software fix MCAS is activated: They moved the stabilizer to push the nose down. They set the indicators to show disagreement over the air speed and followed normal procedures to address that, which increases airspeed.
> They then followed the instructions Boeing recommended and, as airspeed increases, the forces on the control column and on the stabilizer wheel become increasingly strong.
> After just a few minutes, with the plane still nose down, the Swedish 737 training pilot is exerting all his might to hold the control column, locking his upper arms around it. Meanwhile, on his right, the first officer tries vainly to turn the stabilizer wheel, barely able to budge it by the end.
They're absolutely not climbing 14,000 feet in that condition. The control forces on the column in this situation are absurd. Their arms couldn't have held them level for more than a few minutes max.
>They're absolutely not climbing 14,000 feet in that condition. The control forces on the column in this situation are absurd. Their arms couldn't have held them level for more than a few minutes max.
If I'm reading the charts right it took them about a minute to go from 5,000 to 7,000 feet. So even if they hold on for just a few minutes more they're almost to 14,000 feet.
And you're taking speculation based on assumed facts too seriously. If they were struggling to keep the plane level then their simulation was different. In reality the plane was climbing all the way up until they enabled the electric trim and MCAS kicked in.
It cuts out any electronic input, namely autopilot influence and the electric trim control present on the yoke. The trim wheel is not electric, and is the intended control when electric stabilizer control is either unavailable or intentionally disabled.
The thing is, it looks like they did try and use the manual trim switch to get the trim correct prior to pulling the breaker - they just didn't do it for quite long enough to fully correct for the misbehaving MCAS system's actions. If they hadn't I suspect the plane would've crashed several minutes earlier than it did. And remember, if they take more than a few seconds to consider whether the trim is correct before pulling the breaker, the MCAS system activates again, undoes their manual trimming, and tries to kill everyone on board.
You can still point back to Boeing for not recommending flight simulator training of this failure scenario.
One thing that I've wondered though as I've read more about MCAS. MCAS can't kick in till the flaps are fully retracted. Usually when something goes wrong in response to an action, the response is to undo the action. Why isn't the procedure or even the pilot instinct to re-extend the flaps when the nose down occurs just after having retracting the flaps?
> One thing that I've wondered though as I've read more about MCAS. MCAS can't kick in till the flaps are fully retracted. Usually when something goes wrong in response to an action, the response is to undo the action. Why isn't the procedure or even the pilot instinct to re-extend the flaps when the nose down occurs just after having retracting the flaps?
When the two AoA sensors began to disagree during takeoff, the left and right side airspeeds started disagreeing as a result. That leads the pilots to execute the Unreliable airspeed indicator checklist memory items, which include levelling off for troubleshooting and leaving the flaps in their current configuration (retracted), and to keep thrust high to avoid stalling due to the unreliable airspeed indicators.
It's precisely at this point that MCAS now kicks in and starts nosing them down. Extending flaps will cut it back out but: 1) they're now instinctually fighting the stabilizer with elevators to stay out a nose dive, 2) the checklist they were running when this started says not to extend flaps, 3) the Boeing/FAA directive tells them to hit the STAB CUTOUT, so they do that, but 4) the elevator/stabilizer fight + the high speed from the thrust being set to climb due to the checklist they were running when this started results in so much force on the manual stabilizer crank that the co-pilot can't turn it by hand and now they're so engaged in this stabilizer fight and trying to get the plane trimmed for landing that the flaps are the last thing on their mind, and the Boeing/FAA directive never instructed them to try re-extending them, airspeed disagree be damned. They're completely out of the manual and FAA/Boeing directive at this point. Nothing covers this (anymore, 30 year manuals would have had a procedure to ease the forces on the wheel here).
So lacking any other means of trimming for landing, they turn the electronic stabilizers back on, and trim electronically, which works...but they don't cut it again within 5 seconds (the FAA/Boeing directive didn't really spell out how crucial this timing is, or even consider that manual trim would have been made impossible by everything else going on), and the MCAS runs again, and the dive becomes fatal.
There's also a lot going on at that point in flight. It's within ten seconds of autopilot, for example. Would be hard to pinpoint. Besides, they have checklists to follow: airline piloting is not supposed to be creative and experimental.
I would guess that the node down attitude quickly put them over VFE, so even it they could extend the flaps (I don't know if the flight system would prevent that or not) they would at least second guess doing so and continue other avenues of troubleshooting.
Just to put their "mistakes" in context - Sully, America's favorite hero pilot, accidentally put his airplane into an almost stall as he was performing the Miracle on the Hudson (due to the A320's design philosophy, the airplane prevented the stall...). It goes to show- even great pilots doing good work in a stressful time can make critical oversights.
That's the opposite to the actual conclusion of this story! He intentionally tried to flare, but the Airbus flight envelope protections disallowed it, so they hit the water harder than they ought to have.
Because the story that I heard is that he purposefully commanded max pitch knowing that alpha protection would prevent the airplane from stalling, as his landing speed would be lowest at max AoA.
And I heard a third story, which is that the aircraft nearly botched his deliberate attempt at flaring for the water landing due to envelope protections he hadn't known about:
> I was commanding for more, pulling back full aft on the stick and the flight control computers prevented me from getting more lift therefore we hit harder than we would have (...) It turns out there's a little-known software feature known only then to a few Airbus software engineers, and to no pilots to no airlines that was the case. It's called a phugoid mode. And it was not the way we were trained the airplane should work, apparently it is the way the airplane does work. But that was not apparent to us.
Even if this wasn't successfully done they would still be at fault. A plane is suppose to operate without have to have to do this, the procedures are a safety protocol. For the MCAS and safety protocol to fail is a double whammy.
Because this report does not indicate a new problem, but rather the same one as before, which has already been accounted for in the stock price.
It's a truism of stocks that they move opposite of what you would expect when the final result comes in, and that's because they have already moved when news of whatever it is is released.
Eg: Company announces we will get 1 billion cash for free, stock goes up. when they actually get the cash, stock will go down.
Replace that scenario with whatever is making news about the company (mergers, new sales, personal changes, etc, etc).
Except they didn't "follow procedure." MCAS trimmed down repeatedly on one instance for 9(!) seconds and yet the pilots waited 3 seconds longer to counteract that with an electric trim up command on the yoke. The procedure is not 1. Let MCAS do its thing 2. Pull back on the stick 3. Hit the stab trim cut off when you have had enough. Attempting to counteract the the trim down command with manual trimming commands should occur continuously "as needed." If you don't attempt to override the trim runaway with manual trim up commands on your control yoke you aren't following the checklist. On the 737 you can see the trim wheels move and if unintended follow the checklist.
The pilots didn't do that at all. Sustained manual trim only occurred after MCAS kicked in again at 5:40:27 and the pilots still waited before invoking the trim up command. The pilots never invoked sufficient trim up to counteract the automatic trim down command. Again, there is a reason the trim controls are on the control yoke in the first place. Of the three major MCAS trim down commands the pilots only stopped the second one with manual commands after it had already pushed the nose dangerously low. If the pilots had simply invoked manual trim promptly and counteracted the erroneous trim manual trim would have been successful after invoking a STAB CUT out.
If you think the pilots are following procedure why at 05:41:46 did: "the Captain ask[ed] the First-Officer if the trim is functional." ? That doesn't make sense, of course the trim doesn't work, the STAB TRIM cut out switches were engaged! But the response by the first officer was that "The First-Officer [has] replied that the trim was not working and asked if he could try it manually." which again doesn't make sense. But it gets worse because this happened a FULL MINUTE after the stab cut out switch was engaged, which means that neither pilot tried to manually trim the aircraft during that time at all!
But it gets better: "At 05:40:27, the Captain advised the First-Officer to trim up with him. " Which again doesn't make sense because it wouldn't make any difference if the both pilots were trimming up or not, the stabilizer doesn't move any faster.
My conclusion is that the pilots didn't know the checklist but its hard to tell because the CDR isn't presented completely.
The design of this system, from what I've heard so far sounds insane.
For some background, systems intended to automatically override pilot input upon detecting an impending stall have been used on large, complex aircraft for a long time. The most common mechanism is a stick pusher, which mechanically pushes forward on the stick to mimic what a pilot should do about an impending stall. The force of a typical stick pusher is low enough that a pilot can overcome it with arm strength.
A stick pusher, or a pilot pushing forward on the stick is not enough for the aerodynamics of the 737 MAX in certain circumstances. The position of the engines means the thrust tends to push the nose up, and at low speed, the elevator controlled by the stick alone is not enough to push the nose down when nearing a stall. Instead, the trim must be used, which moves the whole horizontal stabilizer rather than just the elevator. That's not part of the procedure on most aircraft, including other 737s, so regulators would not allow pilots rated for 737s to easily transfer their rating to the new aircraft, if they were willing to certify such an aircraft at all.
MCAS is the solution to this problem. It automatically uses the trim to force the nose down with greater authority than the elevator alone could provide. While the concept is sound, the implementation strikes me as reckless.
First, the system uses only one of the two angle of attack sensors to determine that the aircraft is nearing a stall. Such sensors have a fairly high rate of failure relative to the safe operation of a commercial aircraft. As far as I can tell, causing the system to use both sensors is a software change and all models of the aircraft had the required hardware. I can't imagine a good reason the system was designed this way, especially since Boeing has included MCAS on a previous aircraft, the tanker version of the 767, and it did use two sensors in that application.
Second, activating the system automatically, and allowing it to contradict the pilot's attempt to pitch up using the elevator seems like a mistake. While stalls are almost always the result of pilot error, I'm inclined to think automated systems should let humans have the last word. A better design might have been to automatically trim nose-down in response to full forward pressure on the stick at low speed. That could be in combination with a stick pusher providing full forward pressure on the stick when an impending stall is detected in the absence of pilot input to the contrary.
A compounding problem is, if the MCAS system is disable, now the flight characteristics are completely changed. Without additional training, there's no way for the pilots to know they have to trim down.
During otherwise normal flight conditions, the nose might unexpectedly pitch up. MCAS is designed to prevent that when AoA > somevalue to prevent stalling.
During normal flight conditions, the nose does not pitch up beyond the pilot's ability to control with the elevator, and the pilot doesn't fly especially close to the critical angle of attack.
MCAS is for an unusual combination of conditions where both elevator and trim might be needed to reduce the angle of attack. An example would be if the pilot set a fairly high nose-up trim to maintain the slow speed of final approach, then decided to go around (abort the landing), applied full thrust, and fully raised the flaps too early.
A pilot would definitely know that using trim is an option if the elevator was not producing enough nose-down pitch, but a pilot who has put the aircraft into the situation where a stall is imminent during a passenger flight has already made a series of errors.
> An example would be if the pilot set a fairly high nose-up trim to maintain the slow speed of final approach, then decided to go around (abort the landing), applied full thrust, and fully raised the flaps too early.
This scenario seems it would apply to previous generation 737s as well. But for some reason, MCAS was required for the MAX 800.
Everything I have read so far indicates the MAX 800 has some 'pitch up on it's own' type problem that can lead to a stall. So while I'm sure it's possible to crash the plane in a variety of ways, none of that has to do with MCAS.
All 737s have a nose-up pitch moment from the thrust of the engines because they're hanging under the wings. The engines of the MAX are more powerful, and positioned differently resulting in a stronger nose-up moment.
The elevator is not enough to overcome the nose-up pitching moment of the MAX under certain conditions, but the trim is.
I don't understand, either you need the MCAS to fly the plane or you don't.
If a 737 pilot can operate a 737 MAX only with MCAS, then the pilot shouldn't be able to disable it, right? What if he disables it and then the plane is stalling? There is no MCAS to help.
You don't need MCAS to fly the plane. You don't need ABS to drive a car. Both are designed to counteract erroneous user input based on the readings of fairly simple sensor systems that cannot understand the whole situation and are themselves capable of false readings.
when I drive a car without ABS I don't need a new driving license. Pilots switching to 737 MAX need new flight simulation training, except if the plane has MCAS. See the difference?
> "A stick pusher, or a pilot pushing forward on the stick is not enough for the aerodynamics of the 737 MAX in certain circumstances. The position of the engines means the thrust tends to push the nose up, and at low speed, the elevator controlled by the stick alone is not enough to push the nose down when nearing a stall. Instead, the trim must be used, which moves the whole horizontal stabilizer rather than just the elevator. That's not part of the procedure on most aircraft, including other 737s, so regulators would not allow pilots rated for 737s to easily transfer their rating to the new aircraft, if they were willing to certify such an aircraft at all."
I believe this is incorrect. From what I understand, the 737 NGs and 737 MAXes both pitch up when thrust is increased and both may need to be trimmed back to counteract this. The reason MCAS is there is because the characteristics of the MAX are different from NG (that is, the airspeeds and angles of attack at which particular trims are required have changed), making the MCAS system regulatorily necessary, not mechanically necessary. Because either the MAX needs a system that emulates the handling of the NG, or pilots need to be trained specifically for the MAX, and the former is cheaper.
In other words the MAX is not objectively mechanically worse, but rather objectively mechanically different.
All jets with low wings and underslung engines (most modern airliners) experience a pitch-up moment from engine thrust, and trim is used to compensate. When the plane is being flown in some steady state, pilots adjust the trim until no force on the controls is required to maintain that state - they're not getting a specific setting from a table or memory.
What's different is that at low speed, high thrust, and high angle of attack, the elevator of the MAX does not always have enough pitch moment to reduce the angle of attack.
I'm inclined to say having an elevator that's not effective enough to recover from all the stall conditions regulators test for without help from the trim is probably a flaw. Whether there's a good technical reason the elevator couldn't be more effective (probably just bigger), a regulatory reason (some rule says it's not a 737 anymore if they change it), or a non-technical reason (e.g. more shared parts to make it cheaper), I can't guess.
> "What's different is that at low speed, high thrust, and high angle of attack, the elevator of the MAX does not always have enough pitch moment to reduce the angle of attack."
It's my understanding that for the 737 NG as well, there are stall scenarios at particular speeds, levels of thrust and angles of attack where trimming the stabilizer is necessary to recover. That the difference between the NG and MAX is what those particular values are, not whether or not that scenario exists ever.
This puts the nail in the coffin of a quick software fix getting the max back in the air anytime soon. To have any credibility the FAA is going to have to recertify the entire flight control system with all failure modes considered. And no scout's honor with Boeing this time.
This isn't only MCAS issue anymore... If there are issues with manually rectifying trim after it went haywire because of any reason, that might be a problem. Interesting to find out was that an issue with older 737 models, just without severe runaway trim events.
> If there are issues with manually rectifying trim after it went haywire because of any reason, that might be a problem.
It's not so much a "problem" as it is "physics". If the stabilizers are forcing the nose down, and the pilot pulls back on the stick (engaging the elevators) to pull the nose up, the forces exerted on the stabilizer are such that, in extreme cases, human force is insufficient to move the manual wheel.
This is extremely (EDIT: No longer) well documented by Boeing going back decades, and it presents solutions of either: 1) reengaging the electronic stabilizer trim and trimming electronically back to a point where the forces are manageable, then cutting electronic trim again, or 2) relaxing the stick, letting the nose go the way the stabilizers want it to, which slackens the force, and makes cranking the wheel manually doable. Great if you're stabilizers are trimmed severely nose down at a height of 40,000 feet; less great at a height of 1,000 feet. (EDITED TO ADD: Apparently this information & procedure was removed from Boeing's manuals after the 1980s, and pilots no longer train on it, as the issues that led to its necessity were thought solved. The MCAS apparently has reintroduced the need for them.).
This is compounded by a new change in the 737-MAX: in prior 737 series aircraft, there are two stab trim cutout switches: one to cut the autopilot's ability to command the stabilizer trim, the other to cut electronic power to the stabilizer trim adjustment entirely, so you could stop the autopilot from changing the trim but still retain electronic control and not need to worry about the manual crank forces. The two switches are MAIN ELEC and AUTO PILOT.
In the MAX, this changed, and it's now an all or nothing setup: you have to kill electronic power to kill autopilot commands to the stabilizer. The two switches are now PRI and B/U. Both must be cut out to stop any stabilizer runaway, including MCAS runaway.
This all seems to add up to Boeing's narrative of "The MCAS is safe, pilots just need to know to hit the stab trim cutout" being grossly insufficient. They must cut it at a moment where the stabilizer isn't grossly mistrimmed with respect to level flight, OR they may well need to re-engage it and race the MCAS to get into a close-to-proper trim setup prior to cutting out the stabtrim and assuming manual trim control.
> They must cut it at a moment where the stabilizer isn't grossly mistrimmed with respect to level flight, OR they may well need to re-engage it and race the MCAS to get into a close-to-proper trim setup prior to cutting out the stabtrim and assuming manual trim control.
All while keeping the plane in the air, reading the manual, and attempting not to lose composure knowing that the same thing has happened to another flight that lost all hands.
I'm trying very hard to look at this objectively, but this is an extremely bad look for Boeing.
> > They must cut it at a moment where the stabilizer isn't grossly mistrimmed with respect to level flight, OR they may well need to re-engage it and race the MCAS to get into a close-to-proper trim setup prior to cutting out the stabtrim and assuming manual trim control.
> All while keeping the plane in the air, reading the manual, and attempting not to lose composure knowing that the same thing has happened to another flight that lost all hands.
Additionally an angle of attack (AOA) sensor failure also triggers an unreliable airspeed warning so the pilots no longer trust their airspeed sensors or their AOA sensors while trying to judge pitch and speed. If they go too fast the control forces overpower them, if they go too slow they are more likely to stall.
I don't think Boeing gamed out or tested in a simulator the human factors involved in an AOA failure at takeoff, particularly for pilots who - like the Lion Air pilots - are entirely ignorant of MCASes existence.
Thank you for that. Putting hundreds of aircraft into service before the simulators were available to airline pilots looks rather bad in hindsight.
I would hope that Boeing internally had simulators for the MAX while they were testing it - along with a borrowed supply of pilots who were competent but had no inside information. Even if they didn't, a pencil and paper exercise might have been useful:
1. AOA sensor fails at takeoff (A), the pilots receive an unreliable airspeed warning and the stick shaker activates. The pilots now mistrust their sensors and want to keep their speed up and the nose down.
2. At about 1000 feet above ground the pilots level the aircraft, raise the flaps and start the unreliable airspeed checklist. MCAS starts trimming intermittently.
3. The pilot flying is having to pull further back on the stick and trim correctively while the crew work through their checklist. At this point the crew need to avoid any over-focus, task saturation or over-stimulus from the many warnings and indicators and ask themselves why the aircraft is trimming the way it is. They have a fairly narrow window of time in which to do this and then disable the trimming with the plane in a well trimmed state.
(A) That this happened twice in relatively quick succession might be due to a common problem. Even if such a problem is found and fixed the AOA vanes and pitot tubes are delicate sensors sticking out of the nose of the aircraft; the system should be robust to failures in these sensors.
Runaway stabilizer is a memory item, there should be no reading of the manual involved.
Unfortunately the design of MCAS defeated the checklist of this particular memory item when in lower flight altitudes - which goes back to the argument that the 737 MAX never should have been given the same type rating as the older models.
At the very least it seems that some specific "differences training" on MCAS should have been included. I don't know at what point the differences are enough to require a new type designation.
> This is extremely well documented by Boeing going back decades, and it presents solutions of either: 1) reengaging the electronic stabilizer trim and trimming electronically back to a point where the forces are manageable, then cutting electronic trim again, or 2) relaxing the stick, letting the nose go the way the stabilizers want it to, which slackens the force, and makes cranking the wheel manually doable. Great if you're stabilizers are trimmed severely nose down at a height of 40,000 feet; less great at a height of 1,000 feet.
They went for option 1 in this case, with the MCAS kicking in 5 seconds later.
> This all seems to add up to Boeing's narrative of "The MCAS is safe, pilots just need to know to hit the stab trim cutout" being grossly insufficient.
Yeah, and even that is understating it in my opinion.
> They went for option 1 in this case, with the MCAS kicking in 5 seconds later.
Yeah, they basically had to go with option 1. They were only 1,000 feet above the ground, the maneuvering room to let the nose dip, crank, dip, crank, etc until properly trimmed just wasn't there.
From the way you describe it, if the stabilizer reaches the point where human force is insufficient to bring it back then they're toast since MCAS is tied into the electronic stabilizer.
How did this scenario get missed during testing? You'd think they would do extra testing around the new changes.
> How did this scenario get missed during testing? You'd think they would do extra testing around the new changes.
Seems like systemic issues. Reportedly Boeing's submitted risk assessment of the MCAS was based on a single adjustment applied from it, not repeated cycles of application based on a failure of the AoA to recover to what it saw as "level".
The FSB noted the change to the cutout configuration as a difference, but didn't analyze how that could change anything during Autopilot or Speed Trim runaway situations. They didn't even make any note of the MCAS as a difference at all (possibly they were not informed of it?).
I suspect this all comes down to the fact that Boeing started with a conclusion -- The MAX series must not require new simulator time -- and that conclusion was the lens through which they analyzed (or didn't) everything else.
Am I reading the chart on page 27 wrong? Because it looks like they reached a maximum height of 7,000 feet. Also looks like they were continuing to slowly climb until they re-enabled electric trim.
EDIT TO ADD:
Page 12 also says:
>about 32 seconds before the end of the recording, at approximately 13,400 ft
Which is a bit under 6,000 feet higher than the airport.
But apparently the option 2 maneuver (relax pressure on stick, then crank) hasn't been covered in a Boeing 737 manual since the 200 series in the 1980s.
So even given the extra room, there was no documentation covering that possible recovery scenario.
Are there real scenarios where you want to have both control surfaces opposing each other so heavily? Are there real cases for having the trim trying to pitch the plane down while the pilot is trying to pitch up with the stabilizer?
Or should we limit the trim so it never actually opposes the pilots intentions? (Maybe set it to a neutral position and disengage auto function if this condition is detected?)
I'm not really an expert but my understanding is that the stabilizer will always out-muscle the elevator due to the physics of their respective positions on the aircraft.
In yet another change in the MAX series, there used to be what was called an aft column cutout switch which did more or less what it sounds like: engage when the stick was pulled back, cutting out autopilot commands to the stabilizer, so that it never attempted to outmuscle the pilot's input commands to the elevator.
This was removed in the MAX. Possibly this was to meet certification requirements: if the MCAS was needed to push down on the nose to meet the requirement that "During the approach to the stall, the longitudinal control pull force should increase continuously as speed is reduced from the trimmed speed to the onset of stall warning." If the MAX tends to pitch nose up at a certain point, the MCAS is intended to create a counter force against the pilots commands as it approaches that, rather than have the pilot pulling back at some point suddenly buck the nose upwards, then the MCAS needs to be active when the pilot is pulling back on the stick.
But it does argue that a LOT more thought needed to go into MCAS failure modes if it was necessary for it not to be cut out when the pilot is operating elevators.
I think the issue is the difference between the force needed to trim the aircraft and the acceptable control gain between the yoke and the elevator. I think with light aircraft trim is what you think of it. Slightly centers the yoke so the aircraft will fly level without control input.
I think what's going on with the 737-MAX is the needed trim is way beyond what's needed to fly the plane.
I'm now wondering is the MACS is needed because the tendency to pitch up also exceeds the pilots control inputs which is why it had to be on the elevator and have that much authority. Meaning once the aircraft pitches up the pilot doesn't have enough authority to push the nose back down.
> Meaning once the aircraft pitches up the pilot doesn't have enough authority to push the nose back down.
Or, alternatively, the pitch up happens so quickly and severely the risk of stall is too great above a certain AoA and the pilot won't have adequate time to respond.
If either is the case, it implies the aircraft is not safe to fly without MCAS operational, and possibly not at all.
MCAS is not an emergency system, it is a trim control system designed to make the plane behave predictably in an otherwise unstable flight regime. If you wanted it to move fast, you would use a stick pusher; moving the trim takes many seconds.
737 is a common plane. If there were a systemic problem it would have been discovered long ago. (In fact I think several such problems were discovered and fixed long ago.) Look how quickly this new problem was discovered by the public, with both the manufacturer and primary regulator working to hide it.
Doubtful. Older models don't have the oversized, forward-mounted engines, and thus don't have as much of an AoA problem as the MAX does in typical flight conditions.
That's the reason the MAX should have been a separate classification with specific hands-on training.
The MAX is stable in normal flight. It's only when you are pitched up does the engine placement make it want to pitch up even more (and it is only a problem at a speed that is low enough that the normal stabilizer control doesn't have enough control authority to push it back) hence MCAS forcing the nose down every so often via the trim. A normal flight does include pitching up but it does not include pitching up at such a low speed that a little more pitch would quickly cause a stall. MCAS (or at least the nose down function) is specifically designed for an edge case (in that it should be sitting there watching, not actually doing anything during a normal flight).
> MCAS (or at least the nose down function) is specifically designed for an edge case
Yes, and it will only activate during that edge case if the AoA inputs are accurate. But they weren't. And so MCAS activated when it shouldn't have, and did things that the pilots could not recover from because they were things MCAS should never have done in the first place. That's the problem.
Hence why I said "typical flight conditions", which includes pitching up. Point being, its utterly commonplace for a plane to pitch up at some point during the flight. They weren't doing anything out of the ordinary.
If the pilot, who hopefully has thicker skin than people on the internet, moves the buttons and levers properly MCAS should never have to do anything. It's only supposed to actually do anything when you let the nose pitch up a little too much (which the system will detect using the AoA sensors)[0]. It's like automatic braking in a new car, if you drive the way you're "expected to" you shouldn't be activating it often.
Again, please post a source backing this claim up. And it would be appreciated if the folks that died commanding this flight were not referred to as "meat bags".
> That's the first I've heard that it's only for edge cases.
It's only supposed to activate in a specific edge case (high angle of attack, manual flight, no flaps, low airspeed). That's been discussed plenty online (including previous threads here at HN).
But that assumes that the angle of attack sensors are accurate. If the AoA sensors are inaccurate, as they were on this flight (more specifically the left one), MCAS can activate when it's not supposed to. That's what happened here.
> You can exceed critical AoA (and therefore stall) at any airspeed.
I wasn't talking about at what airspeeds a stall is possible. I was talking about at what airspeeds MCAS is designed to activate (assuming correct AoA sensor input).
I think people are reading too much into an ambiguous statement. It says:
>At 05:41:46, the Captain asked the First-Officer if the trim is functional. The First-Officer has replied
that the trim was not working and asked if he could try it manually. The Captain told him to try. At
05:41:54, the First-Officer replied that it is not working.
"Manually" here could mean manual electric control. 8 seconds seems an awfully short time for the Captain to ask if trim is functional, FO to say no and ask to try manual, Captain to say Yes, and for the FO to try the wheel and conclude it's not working.
It appears that Boeing's directive was simply wrong, and doomed them. The right response to faulty MCAS is not to do a stab trim cutout and then manually retrim, but to first use the manual electric trim switches to fix the trim and then immediately do a stab trim cutout. This is mentioned at the end of the directive, but reads more like an afterthought when it should be the standard procedure.
In my opinion the pilots here have attempted to follow that checklist as well as could be expected (bearing in mind that their lives depended on it). Having to trim to neutral before disengaging the trim would have contradicted the normal trim runaway checklist.
We're now talking about pilots having to have abnormal levels of skill and possibly even strength to fly this aircraft.
That's an untenable state of affairs. Boeing have really screwed this one up.
I'm starting to think that disabling MCAS isn't even a sane option because then the pilots are exposed to unexpected aerodynamic characteristics due to the plane's weird design. Does this make sense?
Many people have this opinion. You can't both require MCAS and be okay with disabling it at the most critical portion of a flight where the system is needed most.
> You can't both require MCAS and be okay with disabling it at the most critical portion of a flight where the system is needed most.
If MCAS activates when it isn't supposed to, which is what happened here, disabling it is what you want to do--to stop it from doing an incorrect thing. The plane was not in a situation where MCAS was needed; it was perfectly flyable without MCAS in the flight regime it was in.
The problem is that, if you disable MCAS (which requires disabling the entire electric stability trim system) without first using the electric trim system to get back to something close to neutral trim, you will be stuck with a lot of nose down trim that you can't remove fast enough with the manual trim wheel. It looks like that's the situation this flight got into.
But if you first use the electrim trim system to get back to something close to neutral trim, and then, before MCAS has a change to mess it up again, disable the entire electric stability trim system, you're ok. How do we know? Because that's what the first Lion Air flight (the one the day before the one the crashed) did, because an off duty pilot that was riding in the jump seat figured out what was happening and how to deal with it and told the pilots what to do.
> The plane was not in a situation where MCAS was needed;
As far as I can tell, there is no takeoff (pitch up) situation where MCAS is not needed on the MAX 800. It's required for safe operation of the plane, otherwise the nose might pitch up unexpectedly into a stall.
As I said, the system can't both "be required for safe operation of the plane" and "it's safe to disable MCAS while it's malfunctioning during takeoff." You have to pick one.
> As far as I can tell, there is no takeoff (pitch up) situation where MCAS is not needed on the MAX 800.
Reference, please? I have not seen anything that says MCAS is required for safe operation at a normal angle of attack for takeoff and climb to altitude. Note that the key parameter is angle of attack, not pitch angle; if the plane is climbing the angle of attack is lower than the pitch angle, because the plane is climbing so the relative wind is coming from somewhat above the horizontal direction.
I usually enjoy HN discussions, but this is a pitiful and sad thread. I couldn't be bothered trawling past the responses to the top comment with back seat drivers, and "ooh but I read the 737's flight manual, they fucked up".
Likely 99% of the commentariate here are neither 737 Max pilots, let alone even licensed to fly commercial passenger jets, or even have a pilots license. And no, as much as I love the guy, watching Mentour Pilot does not make you an expert. They have fuck all knowledge about, or even experience, about the sudden cockpit workload that was imposed on these pilots until the point of hull loss. Have some respect. Oh, and you know what, this was Ethiopia's national carrier, I expect these flyers were at the top of their profession and as good a pilot as any other national carrier,
Can’t upvote enough. As someone who actually does fly airplanes for a living it’s disturbing to me the amount of ‘expert’ arm chair quarterbacks that have come out on HN in the wake of these two incidents. Immediately after the Ethiopian crash there were 200+ comment threads every few hours full of experts speculating about all the things that went wrong. People who were flat out wrong could not be told otherwise. I had to stop even engaging.
Am I mistaken or is there a missing item in the chronology where the pilots reactivated the electric stabilizer trim?
The timeline mentions stab trim being switched to cutout, and if you look at the FDR graphs there's a (relatively) long period of more-or-less stable trim after that. But then there's an automatic trim down, which is only possible if the electric stab trim is switched back on, and there's no mention of that.
I also can't help but wonder if exceeding Vmo was a factor.
(I don't mean to sound as though I'm trying to assign any blame here. Obviously this was a confluence of problems, the most significant of which is the control system reacting to an erroneous 75° (!) AOA indication.)
I find it amazing that there is no mention in the report of this fact. The investigators obviously know that they turned the cutout switches back to normal mode. Assuming there really was no mention of it on the CVR strongly suggests that it was the very inexperienced first officer who did this (the switches are on his side) without getting concurrence from the captain.
If you carefully study the graphs in the report, the plane was really not in bad shape up until this point. They were 7000 feet above ground and climbing. They were going too fast, but again, this is the fault of the crew. If they would have not flipped the cutout switch and taken stock in the situation and backed the throttles down, it is quite possible this flight would have ended very differently.
There are a lot of well-taken comments in this thread. However, in reading the Lion crash report and this one, it strikes me that there is a fundamental difference in the crashes. In this case, it appears that the pilots had very little knowledge about the reasons why the anti-stall system was implemented. And their combined flight time on the MAX is absolutely pitiful. In short, normally one thinks of a stall as a low speed event. In this case, by switching to manual with an improperly trimmed plane, it began a process which could be magnified by an accelerated turn (one of the reasons the MACS exists in the first place.) They began executing a rapid 180 degree turn at >300 knots, which is shown on the attitude graph, headed back to the airport. With a heavily loaded plane, is there any reason to doubt this wouldn't induce a high speed stall? The plane became so unstable, as it was outside of its operating envelope, they could not manually trim it. When they used electric trim it turned the anti-stall system back on, and it nose-dived the plane. The Boeing manual and/or directive says once you turn it off, it stays off. If they were unable to manually trim, is it really much of a surprise given their airspeed and rapid turn? So you ultimately see an electric trim which did little to help them, and assured anti-stall would kick in again. The report shows that neither of the pilots had signifcant experience in the MAX. The CVR is replete with ignored overspeed warnings, and stall warnings. An experienced pilot would know the danger is not a low speed stall, but a high speed stall accelerated by a mismanaged turn. By the time they tried to electrically trim it, it was over. Many planes are not aerodynamically stable without computer assistance. This crash is far different from the Lion crash. And I have not seen a single news outlet state the conclusions (or lack thereof) in the report accurately.
The graphs record the AND trim movement even if the electric trim is disabled. You can see that by comparing the pitch trim absolute position to the manual and automatic electronic trim graphs.
>The left Indicated Airspeed increased, eventually reaching approximately 458 kts and the right
Indicated Airspeed reached 500 kts at the end of the recording. The last recorded pressure altitude
was 5,419 ft on the left and 8,399 ft on the right.
How can the sensors record such different readings?
The reading from the pitot tubes (pressure sensors) for a particular airspeed varies with the sensors angle to the airstream so the airspeed value is adjusted based on the angle of attack (AoA). If the AoA sensor is on the fritz on one side the airspeed reading for that side changes.
For redundancy, each pilot receives separate instrument readings from independent sensors. When the airspeed readings disagree a warning is activated and the pilots are expected to follow a prescribed and memorized procedure. The warning that the AoA sensors disagree was a paid option before this crash and the Lion Air crash.
While the changes in the right pressure altitude indicator track those of the radar altimeter reading, the left falls below it -- except, in the last 15 seconds, there are blips where the left pressure altitude jumps to match the right one. These correspond to the the times when the errant left AofA indication briefly matches that from the (apparently working) right AofA vane.
The airspeed discrepancy has the same pattern: the left is reading low and also showing blips, where it equals the right reading, that also correspond to when the AofA indicators match.
All this would be consistent with the left AofA reading being used to correct the left static pressure reading by raising it at high angles of attack, and vice-versa for the right AofA vane and static port (this assumes there is a right static port used by the right pressure-driven instruments, an a left port for the left ones.)
This language is not clear, at least to me. MCAS is absolutely an anti-stall system. There's some correlation with yoke handling, but it's still with the goal of affecting yoke handling in order to prevent stalls.
> Also, the airspeed, altitude and flight director pitch bar values from the left side noted deviating from the corresponding right side values. The left side values were lower than the right side values until near the end of the recording
Hmm. Seems not just faulty AoA sensors? Perhaps some major malfunction in the flight computer? I've felt this entire time there's been a rush to claim 'faulty AoA sensors' because 'sensors' are known to fail, and it's an easy scapegoat.
My question is, does the flight recorder have raw inputs from the sensor, or just what the flight computer is reporting from the sensor? Seems like the latter.
Blaming the sensors seems pretty plausible, because the expected failure rate of that sensor is roughly 1:100000 and there have been about a quarter million 737-MAX flights since the plane was introduced.
The problem is all those other things are CALCULATED values off the AoA sensor.
Literally everything depends on a single tube which is known to get clogged with ice, bugs etc.
So for the 737 Max, a single clogged AoA sensor causes all these things immediately and simultaneously:
-- all your airspeed and altitude readouts go haywire, at least on one side of the cockpit
-- a bunch of alarms start going off and a bunch of lights start flashing, each indicating a different problem
-- your control stick starts shaking
-- a little-documented system immediately commands the nose straight down into the ground, and keeps commanding it until turned off (but turning it off effectively prevents you from counteracting the nose down command)
> From 05:40:42 to 05:43:11 (about two and a half minutes), the stabilizer position gradually moved
in the AND direction from 2.3 units to 2.1 units. During this time, aft force was applied to the
control columns which remained aft of neutral position. The left indicated airspeed increased from
approximately 305 kt to approximately 340 kt (VMO). The right indicated airspeed was
approximately 20-25 kt higher than the left.
This part is very interesting. This aircraft nose down (AND) trim occurred while the electric trim system was disabled. This means that either the pilots were moving the manual trim wheel in the wrong direction, or that aerodynamic forces were causing significant AND trim.
To avoid FAA scrutiny, Boeing developed and deployed MCAS covertly. This was done because they feared scrutiny would have led to huge losses in the face of competition from Airbus. Had Boeing management just laid all their cards on the table, potentially the FAA could have still approved the design, with small but crucial improvements. These changes might have included: using both AOA sensors, using a 3rd AOA sensor, not switching between left and right sensors each flight. Instead, the covert nature of the development and deployment of this feature allowed flaws in its design to go unchecked.
Imagine MCAS was never created. Instead pilots had to deal with the nose up stalls themselves. Would that have ended up being the outcome? Instinctively I feel like pilots could deal with the situation where MCAS was supposed to help, especially a lot better than when MCAS is dooming these two planes. What do you think?
Imagine being the one who was forced to develop this. Regardless of whether one did see something like this coming and raised objections or missed it, I would be unable to continue to function. Do we know how teams cope with this?
Aircraft crashes attract a lot of attention, and probably for a good reason. But just to keep folks' internal perception of risk - aircraft safety has improved a lot:
This shouldn't be marked as a dupe since it's the actual report.
It sounds like they did everything right. There are two fateful moments:
>At 05:41:46, the Captain asked the First-Officer if the trim is functional. The First-Officer has replied
that the trim was not working and asked if he could try it manually. The Captain told him to try. At
05:41:54, the First-Officer replied that it is not working
At this point they were in stable flight and the trim wasn't that extreme. An inability to manually adjust trim is a huge design flaw unless it was pilot error.
>At 05:43:11, about 32 seconds before the end of the recording, at approximately 13,4002 ft, two
momentary manual electric trim inputs are recorded in the ANU direction. The stabilizer moved in
the ANU direction from 2.1 units to 2.3 units.
>At 05:43:20, approximately five seconds after the last manual electric trim input, an AND automatic
trim command occurred and the stabilizer moved in the AND direction from 2.3 to 1.0 unit in
approximately 5 seconds. The aircraft began pitching nose down. Additional simultaneous aft
column force was applied, but the nose down pitch continues, eventually reaching 40° nose down.
The stabilizer position varied between 1.1 and 0.8 units for the remainder of the recording.
They re-activated electric trim control but only slightly adjusted it. MCAS kicks in to send them nose down. There's no further pilot correction recorded. Again, unclear here if there is an airplane issue preventing them from adjusting trim or a pilot error.
The report was the basis for this article and discussion yesterday: https://news.ycombinator.com/item?id=19570378. From Hacker News' perspective, since the report itself was prominently linked in the article and its contents were discussed directly in the thread many times, it qualifies as a duplicate.
You're absolutely right, it's not the same (in this sense “duplicate” is a misnomer—or at least should be applied to the thread or topic and not the submitted link).
If that's the case, it would be appreciated if this was moved back, or at least re-posted. It appears worthy of being visible based on the amount of discussion it generated in a short time. Moving it to this thread effectively threw a bucket on the fire.
The report wasn't prominently linked in that BBC article when it was posted here yesterday, because it hadn't been released yet.[1] It was edited into the article at around the same time the direct link was posted to HN. Also, all of the discussion of its contents on that thread seems to have happened after the comment complaining about this thread being marked as a dupe of it.
Agreed, an article based on the report is not the same as the actual report. Not to mention it pulled this off the front page, where it absolutely should be considering the traffic this issue has been garnering.
Reading through the chronology in section 1.1, it feels like a movie where the aircraft is a malevolent entity that's trying to kill them. So if I were in the cockpit I'm sure it would've been some mix of fear and anger. My life's not in danger though, so I'm only left with the anger, on their behalf, knowing some greedy bunch of assholes were effectively that malevolent entity, whose will was expressed via the aircraft.
EDIT: You guys can fucking blow me. Moderators ban my account please.
I swear I've encountered propaganda bots/shills on HN lately. Maybe it's just my imagination or maybe there are just people out there who wanna argue in favor of megacorps, but I've been getting downvoted and argued with lately for saying pretty obvious things lately.
Anyway, I'm on your side. Two planes falling from the sky killing hundreds I mean that's a non negligible percentage of 9/11 casualties. Maybe we don't know exactly the cause (tho it seems we do) but at any rate I'd wager a large sum of money that this is boeings fault.
Lol top comment. Seriously who sees this and is like NO I must downvote. Its a great comment, imagine a plane all of the sudden just fighting to crash you into the ground, what a horror show.
This subthread is clearly about gratifying rage, not intellectual curiosity. That makes it off topic for Hacker News. Yes, the rage is understandable and there are reasons for it. Nevertheless what's going on in this vortex of the discussion is not in keeping with the values of the site. To a weird extent actually.
I really like this comment because I agree and was trying to write a comment that said this but not in a toxic way. People act like Hacker News is some bastion of discourse that is raised above the rest of the internet but it's not. Most of the comments I read are people stroking their ego's and enjoying the echo chamber.
Your expectations may be too high. Collective behavior on the internet converges to toxicity. All we can do is mitigate it at the margins and try to slow down the decay. Your help would be appreciated.
Mother of god, that’s equal parts funny and just plain accurate.
Dell wonders if maybe their hiring process can be improved. Hackernews debates whether this is a cynical attempt to mine talent from previously-overlooked seams or a genuine attempt to treat human resources as human beings. Some Hackernews consider labeling such personnel so their specific status is on display at all times, an idea that nobody got from Nazi concentration camps.
Hole in one. Sometimes the best thing to do is just log off and remember that some people would argue about the correct oil used to boil them alive.
The "greedy bunch of assholes" are the Boeing execs who optimized for profit over the lives of those pilots and their passengers. (I thought that was pretty clear from the comment, fwiw.) I think it's been pretty thoroughly established at this point that an underlying design constraint in the MCAS was that it was easier for Boeing to get a 737-with-modifications approved than a new airplane, despite the engines being configured rather differently from existing 737s, and the MCAS was a computerized hack to avoid instability caused by the design of the newer engines (specifically, the newer engines would risk pitching up and stalling if you flew a 737 MAX like a normal 737, so they added the MCAS to counteract that, and the problem in both crashes was the MCAS unnecessarily activated and pitched the plane down when the plane was actually flying fine). Certainly lots of other things went wrong too, but had they instead just built a new plane design, the problem wouldn't have arisen in the first place. (I can find links about this if you're curious but it seems to be the consensus interpretation of what happened.)
There's a piece of additional flavor, which is that as I understand it Boeing proposed building a new type of plane as an a320neo competitor, and the airlines announced that they'd only buy it if it's a 737 subtype to avoid having to retrain their pilots. It's not just "Boeing doesn't want to pay for certifications", but also -- and perhaps primarily -- "Airlines don't want to pay for training".
So while Boeing's ultimately responsible for building unsafe aircraft, I could imagine people being angrier at the airlines than Boeing.
Just to add an extra element to what you've already said. It's quite likely that the pilots themselves would have been reluctant to accept another entry level narrow body jet. In the current climate it's often the pilots themselves who are paying for the type rating, at least the first one they acquire.
That's fair, but also, salaries for pilots are not great, and Boeing's former CEO got a salary of $865K/year + $1.3M/year bonus + stock and now that he's retired gets a pension of $730K/year. I'm sort of curious what exactly it would have cost Boeing to say, "This is not a 737, but we will pay to retrain any 737-trained pilot who's interested." (Which still would have given them a negotiating advantage over Airbus!)
"The average Southwest pilot made $230,626 in 2015, according to the most recent data from the Massachusetts Institute of Technology Airline Data Project"
It's very cyclical. For reasons unknown to me, pilot unions have always negotiated a seniority-based pay scale. Where seniority is only how many years you been at the airline. How much total experience you have doesn't matter just how many years you've been with the airline.
So if you stay with the airline for a long time you move up from first officer to Captain and then as years of seniority add up you start making a lot more.
The trouble is the pilots can't threaten to change jobs because if you move from one airline to another your seniority goes back to zero.
Also if an airline declares bankruptcy, all the union contracts are null and void. The airline then has a ton of leverage because the pilots are all out of work. The pay scale that comes out of bankruptcy is typically very low.
Similar if one airline acquires another airline. The pilots at the acquired airline typically get screwed in the pay scale and seniority calculation.
Also jobs like flying cargo planes or piloting for a commuter airline pay very low wages. It's mostly just the big airlines that pay well.
That's still greedy assholes at work. rdiddly didn't specify that the greedy assholes involved are all Boeing executives; that airline executives have clean hands. And to VBprogrammer's point, airliners making pilots pay for their own training again comes back to airline executives being greedy assholes.
That doesn't really excuse Boeing though. The airline might what whatever but it's Boeing's responsibility to tell them something's not possible. Airbus didn't do this hack (as far as we know) so if Boeing didn't they would have just gotten into a tougher competition. The challenge that Boeing faced is the same as Airbus or any other manufacturer. The airlines at the end would have to buy planes to continue their service with whatever plane available. Boeing from all evidence made for them available an unsafe plane. It's unlikely to happen but a fair amount of people should be put in jail for this for a long long time but I doubt that will happen though.
And FAA is another sad excuse these days it seems. One doesn't let trivial things self certify and they let an airlines company self certify critical parts of a plane. What a joke.
It's not just Boeing, though (not that this exculpate them in any way), but cheap airlines insist in flying 737, but also have demand for more efficiency. This plane was trying to satisfy that impossible "I want the exact same plane but better" demand, so that the other greedy bunch of assholes that are airline execs wouldn't have to spend in training mechanics and pilots because the plane they're flying has another name now.
No. The redirection of demand would just give some more clients to Airbus and reduce the speed of the growth of the total number of planes flying.
Nobody should accept this attempt to excuse Boeing of its responsibility and even less the possible variant of it "we are all guilty we will buy the cheapest flight."
It seems a bit unlikely to me that an airline like South West, that only flies 737s, would sooner buy Airbus planes than non-737 Boeing planes. I mean, stranger things have certainly happened, but it doesn't seem like the kind of existential threat that would force the hand of Boeing executives in such a way that takes blame away from them.
Even if there was an existential threat to Boeing the people making the decisions should have decided "we can't do this safely". They were never forced. Maybe they wouldn't get their million $ bonus - well tough titties. Plenty of people didn't get a 7 digit bonus this year.
1) decided to move the engines forward making the aircraft dynamically unstable, but improve performance and potential sales
2) decided to counter the instability with a software system (MCAS) based on a single sensor, with zero redundancy or fail-safe mode, AND make a second sensor an optional extra cost for the airlines, AND bury the whole thing in a poor UI, in short: cheaping out on a band-aid fix to a critical problem of their own creation, to maximize profits
3) decided to evade normal requirements to make the airframe a new classification, so that airlines wouldn't need to spend money on retaining and separately qualifying pilots for the different airframe, again to reduce apparent costs of the new airplane and increase sales
4) minimized the training on the MCAS system and require no new training when they made changes to the system. AND make the MCAS system automatically re-engage, based on the single sensor to reduce customer costs
5) ensured that this cascade of bad decisions got implemented through the FAA and rolled out globally.
The effect of all of this was to overlook and minimize critical flaws in a complex human flight system, and do so in order to maximize sales and profits over safety.
They killed 346 people already, and nevermind the economic knock-on effects.
No, I'm not going to hunt back and provide a link to every bit of analysis I read gathering the above facts. It is all recent, non-obscure, and very google-able.
Yes, bad engineering and management decision that kill people will tend to get folks a bit riled up. This is a good thing. While this forum should indeed emphasize facts and intellectual argument, this is not a peer-reviewed journal, it is a forum for humans to discuss issues, and we should also keep here the human perspective on engineering.
> AND make a second sensor an optional extra cost for the airlines
This would be extremely egregious, but it's not what happened. Every MAX has two AoA vanes. Every MAX only hooks up the MCAS to one vane. The optional feature was just an "AOA disagree" light and display, which wasn't even hooked up to an error alarm. It's a red herring for these crashes, in my opinion. The pilots aren't going to hunt around the cockpit during an emergency and notice a disagree light and be able to conclude anything meaningful about what's happening to the plane and how to stop it.
They could have had "check for AoA disagree" as part of the pre-flight checklist though - I read somewhere that in at least 1 of the MAX crashes, the AoA vanes disagreed on the ground before departure.
You're right, they're literally vanes on the side of the aircraft, they don't do anything without airflow. Takeoff roll is when you could possibly first notice it.
> "decided to move the engines forward making the aircraft dynamically unstable,"
I don't believe that's true. Per Mentour Pilot, the 737 MAX and the 737 NG are both very stable aircraft that are not prone to stalling[0]. That there is a difference in performance characteristics that creates a difference in how an escape from stall maneuver is to be performed, and the MCAS is meant to paper over that difference.
[0] https://www.youtube.com/watch?v=TlinocVHpzk @16:25 "[...] The 737 MAX and NG are equally less indicative of getting stalled, okay? They are very good, very nicely flying aircraft. But once they're in a thrust stall, they have slightly different characteristics. [...]"
I'll have to track it down but from what I'd read, the change in handling characteristics was that once the airplane started to pitch up, the pitch-up forces would increase, making a stall much more likely if you didn't keep on top of it.
So, yes, if you;re actively flying the plane and staying on top of your trim & pitch, keeping it in the middle of the range is just a bit different. But, if it gets out of hand, it gets progressively worse at an increasing rate, which is what MCAS was apparently designed to prevent.
Of course, if they'd designed the MCAS with multiple redundant sensors, as well as integrating other data (thrust, accel, GPS trajectory, pilot inputs, etc.) into a complete image, or at least a solid series of sanity checks on then applied it, it could have been a great advance.
Instead, they cheaped out, with the result that they added to the design a single point of failure.
The result, within a year of its rollout, is 346 people dead.
Add to that the handling of the complaints about the system, handling of the first crash... The plane should have been grounded after the first crash and possibly some mitigating action should have been taken before that as well. There's going to be a final report and presumably this is far from the end of this story.
I've been on HN for years, and lately some of the downvotes have really been blowing my mind. See this post I made a couple of months ago: https://news.ycombinator.com/item?id=18937864.
Someone actually downvoted and argued against me that their dog's life is more valuable than "a stranger's". I have no doubt it's the same people downvoting your comment. I can't tell if these people are just really good trolls, or they truly don't value human life (including loss of life in an airplane crash).
I think you probaby struck a raw nerve with that dog issue in particular. Some people have family and dogs, but other people have no family (or not the one they want) and use dogs as surrogates. Pointing out the difference between family and dogs can provoke an intense emotional reaction, not rooted in their feelings towards dogs but rather rooted in the phantom pain they feel where their family should be. So what seems to be an irrational emotional outburst in defense of dogs is in fact their sense of familiar longing or loss. Viewed this way, maybe you can see some common ground.
(I'm sure somebody might want to tell me about how they have a family and a dog, and love both. That's great, but I'm quite sure losing a child would be a greater blow to you than losing a dog. The point here is that somebody who already feels pain from missing family might try to ameliorate that pain with dog ownership.)
I generally support your first paragraph and the first sentence of your second. But your final sentence is illogical and immature. If you want @dang and mods to ban you; just erase your account.
If what you mean to say is "if what I am saying is wrong, then ban me for saying it," you should say that.
Regardless you've created a little drama for your biologically degrading snowflake, and it's unlikely they'll want to make you a martyr, but does your second sentence really add much value except to air your protestations?
Why would it? Y Combinator is out of Mountain View, not in the EU. I doubt HN would offer special deletion privileges for any other polity in the world either unless they felt like it, everyone gets the same terms of US law and HN ToS.
I really feel as we're entering an era where full automation is the only solution. This current paradigm of the plane telling the pilots "I don't know what to do here - handing it back to you" doesn't make much sense. Do we just need better multi-modal and redundant sensors so the plane isn't flying blind?
This problem was one of too much automation, which decided that the best course of action was to fly the plane into the ground. In a less automated system, the pilots would have been able to enable electrical trim systems without also having their trim control overridden by MCAS and would have been able to recover flight control that way.
Arguably a fundamental problem with these planes is that they have a bit too much automation, which runs directly contrary to the historical attitude of Boeing that 'pilots are always in control'. So this is a surprising change for a long-time Boeing pilot.
If you want to see what it's like with far more automation, look at Airbus. They have a fundamentally different philosophy on computer controlled aviation. They also don't have a perfect record, there have been Airbus crashes due to malfunctioning automation.
