Incident: American B38M near Nassau on Mar 29th 2021, pitch trim issue/failure
avherald.com"- A component of the main electric trim system became inoperative. Our pilots ran the appropriate checklist, which included manually trimming the aircraft. They returned to MIA and landed uneventfully. The issue was not related to MCAS."
Indeed. This was a part failing on an aircraft in flight. It landed without incident, and was likely never in any sort of danger. Losing electric trim is an annoyance but also trims safety margins by, as I understand it, making autopilot impossible. So, it's good that they returned.
If this had happened on a 767 or A320 we'd never have heard about it.
Not just the autopilot, but if pitch trim has failed then the Speed Trim System is disabled too.
What is Speed Trim? Well imagine MCAS, but instead of moving the stabiliser near the edge of the flight envelope, it moves the stabiliser all the time (when the speed is below mach 0.68). And instead of being introduced with the 737 Max, it was introduced 35 years ago with the 737 classic.
At least it's mentioned in the manual.
I agree but it’s like the galaxy phone that had the battery issue. It just killed confidence with the consumer.
The investigation (and what we learned form it) into Boeing also didn’t help with confidence levels.
After a few new iterations nobody talks about the battery anymore. I’m not so sure how Boeing can turn this around relatively quickly.
Southwest just placed a large order for 737MAX-7 two days ago - [0]. 100 firm orders plus 155 options. They may get a great deal from Boeing for all we know, but placing a large order during this terrible time for the airlines is a bet on the future of MAX as well as the industry recovery.
[0] - https://www.cnbc.com/2021/03/29/southwest-airlines-adds-100-...
Meta note, this relatively frequent aircraft incident gets a lot of votes here on HN, yet the Southwest's order falls off the crack. Objectivity is as scarce on HN as on any other media frequently criticized here.
> They may get a great deal from Boeing for all we know, but placing a large order during this terrible time for the airlines is a bet on the future of MAX as well as the industry recovery.
Is this supposed to mean anything? To me it reads like an airline managed to get a massive discount on inventory that a struggling aircraft manufacturer hasn't been able to move for about a year due to their repeated problems with safety and accountability, which led the whole world to drop their orders.
For starters they can reiterate what has been said here, that a common error occurred and not the original MCAS problem.
Not being open about it will have the opposite effect.
Speaking of which, I have a friend that still runs a Note7
weren't those banned from flying on 737MAX's? (and all other aircraft)
With respect to the 737-8 MAX though, although in this case it's nothing to do with MCAS, doesn't the 737-8 MAX have smaller radius trim wheels than previous models (so less leverage)?
So in theory, trimming might be more difficult on the MAX than previous 737 models, especially at higher speeds (where there's more force on the control surfaces that would need to be counteracted in the case of runaway trim).
The trim wheel on the 737 MAX is identical, down to the part number, to the trim wheel on the 737 NG, which has been in service since 1997. The trim wheel on the 737 NG was reduced in diameter by approx 1/8 of an inch compared to the 737 Classic, which has been in service since 1982, in order to give adequate clearance to the “new” CDU (data entry keyboard for the flight management system). Since the trim wheel is around 10” in diameter, a 1/8” change would have a negligible effect on trim forces.
Why re 767 or A320? (i'm guessing because they're not recently in the news.)
737 max had two fatal crashes due to automated trimming issues (MCAS) and the fleet had been grounded until very recently.
It's a new aircraft not one 20years in service like your average 767 or A320!
That makes it less surprising, not more.
Component failures follow a bathtub curve. Mid-life is the lowest failure rate.
As I understand it the aircraft has a quite complex relationship with trim because of fundamental aerodynamic flaws (engines are too far forward). Am I right in saying other aircraft e.g. an A320 would handle this sort of failure without as much risk to the plane?
MCAS was only installed to cover up aerodynamic changes (not flaws) that would have required greater recertification and retraining of pilots. To save that expense, they covered it up with MCAS so they could say "See, it's just another 737!" which caused all the issues we know so much about.
So you’re saying without MCAS the plane flys just as safely but differently which would have required retraining. That’s interesting, thanks!
Yes @andy_ppp that's what I'm saying :)
No, the plane does not fly safely without MCAS. Without the MCAS there the aircraft has a tendency to pitch up, resulting in a stall situation.
That's incorrect. All planes have a relationship with thrust and pitch based on multiple factors (size, weight, speed, wing configuration, altitude, etc). The aircraft was perfectly sound.
The problem was software designed to alter the flight profile automatically to minimize the differences and new training required (and was allowed to override manual inputs). Any pilot with full training of this specific plane without MCAS would have no problem flying it.
The planes didn't crash because they pitched up but because bad software mistakenly, and forcibly, pitched them down.
What the poster was more likely referring to was the uncertifiable behavior that would occur without MCAS during a wind-up turm or during descent whereby stick control forces would slacken on the way to stall instead of requiring steadily increasing pressure on the control column to bring the plane to a stall due to extra lift from the forward nacelles. While technically a pilot could deal with it, aircraft that demonstrate said behavior cannot be certified as civil transport aircraft without appropriate mitigations.
It seems to me that the folks here arguing that the 737 Max is safe have a definition of "safe" that would satisfy a military test pilot. I'm sure that even without MCAS a top-notch pilot could fly the Max without incident, but when it comes to passenger aircraft safety, the bar is considerably higher.
Both incorrect. The stability system to correct pitch to avoid training is only one side of the story. The other side is there wasn't a linear relationship between pitch, aoa and stick forces, and that would not have passed the faa certification.
LOTS of aircraft have a tendency to pitch up or down based on throttle. This isn't unique to the 737 MAX.
A quick google on "thrust line pitch moment" gave me this: https://www.homebuiltairplanes.com/forums/threads/thrust-ang...
" I want to adjust the thrust angle from where it was (0° with respect to the chord line) to reduce the downward pitching moment when thrust is added (or more importantly the upward pitch moment when thrust is reduced)"Not many passenger aircraft have a tendency to pitch up to the point of stalling, though.
It does not just pitch up randomly. It does pitch more than other 737s due to engine size and placement, but that's just the specific behavior of this plane.
Stalls are not a serious problem, they're basically the first thing pilots learn to solve. And there are plenty of aircraft that are more challenging to fly. That's what training is for.
The real issue is that pilots should have full understanding of the behaviors of the airframe instead of relying on software to change it. Especially when they don't have full understanding of the software either, and the system can both override manual inputs while being susceptible to faulty sensors.
> Stalls are not a serious problem
They account for 25% of fatal accidents [1]
[1] https://www.aopa.org/-/media/Files/AOPA/Home/Pilot-Resources...
Seems like the vast majority of cases there are personal aircraft not piloted by ATPs. General aviation is what it is. Certainly there are airline pilots that don't recover from stalls successfully (Colgan Air Flight 3407's crew), but there are confounding factors like sleep deprivation. Personally, I worry a lot more about sleep deprivation than particular subsystems of jetliners. You can easily kill two airliners worth of people in a few seconds when you read back "hold short of runway 31R" and then just barel onto it because you're not alert.
The source says "the overwhelming majority of unintended stalls occur on personal flights in day visual meterological conditions (VMC) under light winds". And the commercial flights are mostly part 137 (aerial application like agriculture and fire fighting).
So to add context, stalls under commercial part 135 flights are extremely rare and even less fatal. There's almost always some other compounding issue that led to the stall instead of just basic flight maneuvering.
Neither does the 737 MAX.
No, they are legit flaws. https://www.business-standard.com/article/international/boei...
I respectfully disagree. A news article calling them flaws does not make them a flaw. Here's the issue: At lower speeds such as you'd see during a landing approach, the throttle setting of the 737 Max directly affects its pitch. If the pilot were to suddenly reduce throttle, the nose would pitch up. This is due to the engine's more forward position.
The forward position of the engines was done so that they wouldn't have to re-engineer half the plane to fit the larger engines. High bypass turbo fans are big, and they couldn't maintain ground clearance without either moving the engines up higher or making the landing gear longer. To move the engines higher they had to move them forward. So they did.
The new behavior of the aircraft required retraining and making sure pilots knew how the throttle and pitch were related. Mind you, a lot of aircraft have such relationships, so this is not in itself a flaw.
The real flaw came when they decided to replace training with software, and then conveniently forgot to tell anybody about the robo-pilot that they put in the cockpit. THAT was the failure. The airplane itself, even without MCAS at all, would be a bit more of a handful to fly, but nothing terrible. With a properly functioning MCAS, and proper training about how to disable it in case of a problem, the issue is solved. And that's what the FAA believed happened when they recertified the 737 MAX to fly again. But by now the reputation has been tarnished so badly that we're hearing news about unrelated failures because it happened on a 737 MAX.
So you can see the real failure isn't aerodynamic, its pretty much everything else.
If I got any details wrong, I apologize. I'm flying by the seat of my pants on this layman's analysis after a long day.
>At lower speeds such as you'd see during a landing a approach, the throttle setting of the 737 Max directly affects its pitch.
Any conventional airliner has this "flaw". If you are at low airspeed and you push the throttles forward, an A320 will exhibit nose-up pitch, too. It's a direct consequence of having giant engines slung kinda-sorta-underneath the wings of a low-wing monoplane.
That's my point. The engine positioning is not an aerodynamic flaw, it's just a design change that makes the aircraft behave differently than the 737-shaped planes that came before it.
Most airliners have the engines under the wings (and therefore under the CG). Thus, most airliners will pitch up when thrust is applied. The 737 Max has a higher thrust line (which means closer to the CG) than prior 737s. The nose will pitch up less than other 737s when applying power. The problem isn't pitching up when applying power.
The problem is that at high angles of attack, the nacelles start to produce lift, and with the more forward position, they cause a greater pitch up force than previous versions.
This sounds very plausible, but I haven't heard this before. Do you have a reference? I'm genuinely curious- not calling you out, so to speak.
So I actually went and found this fabled 245-page report :
https://transportation.house.gov/imo/media/doc/2020.09.15%20...
And this, I think, is where the whole faulty/flawed thing gets introduced :
> Faulty Design and Performance Assumptions.
> Boeing made fundamentally faulty assumptions about critical technologies on the 737 MAX, most notably with MCAS. Based on these faulty assumptions, Boeing permitted MCAS—software designed to automatically[...] It also expected that pilots, who were largely unaware that the system existed, would be able to mitigate any potential malfunction. Boeing also failed to classify MCAS as a safety-critical system, which would have attracted greater FAA scrutiny during the certification process.[...]
So, I would agree that Boeing's design flaw here was not alerting the pilot with a huge red warning light (and being cheeky about re-certification). But I don't think that this report goes so far as to say that the airframe was flawed and therefore necessitated MCAS.
Yup never flying Boeing again. Airbus all the way.
It's a feature, not a bug.
>As I understand it the aircraft has a quite complex relationship with trim because of fundamental aerodynamic flaws (engines are too far forward).
That's not really correct. The engines being in a different position means the aircraft doesn't meet a very specific criterion of the FARs (positive stick force gradient). The 737 Max has the exact same relationship with trim as any other airliner.
>Am I right in saying other aircraft e.g. an A320 would handle this sort of failure without as much risk to the plane?
No. TFA explicitly states this issue was not related to MCAS. It's likely an analogous failure on an A320 or a 737NG would still have necessitated aborting the flight.
One thing that has always bothered me about how MCAS was implemented - if it truly was a stick force gradient issue, why not make the change in the Elevator Differential Feel Computer, which already manipulates the stick force gradient during approach to stall, rather than physically moving a control surface? Aside note, the elevator feel computer is a mechanical / non-electronic computer that is stuffed full of aneroids and solenoids and cams and followers and servovalves. Straight out of the 1950’s.
Where have you been all through the 737 Max debacle! It's refreshing to read someone who genuinely understands this issue.
And for what it's worth I've pondered that before and my only conclusion was as others have said here, probably a lack of detailed organisational knowledge on the design of the pitch feel computer. Perhaps there are confounding factors, it has its own pitot tube but not a AoA vane for example. Or perhaps changing it may have triggered more regulatory oversight than MCAS did (unfortunate given events which followed).
>Aside note, the elevator feel computer is a mechanical / non-electronic computer that is stuffed full of aneroids and solenoids and cams and followers and servovalves. Straight out of the 1950’s.
That's likely why they didn't. That type of change is hard to conceal and far more difficult to keep out of the documentation. A software change could potentially be handwaved. Full on revamping of said system would probably have edged a regulator enough to have raised an objection or a deeper dive into the nature of the reconfiguration.
A software change could potentially be handwaved
This to me seems a much greater process failure.
Maybe that's why, I don't blame engineers who didn't want to touch it...
I sympathize with the engineers there.
It's like a bug that will not go away in some software. You think you've fixed it and all seems well and you get a good nights sleep with the gleam of satisfaction in your eyes.
But the next day your manager says "That bug is still there".
You incredulously do not believe that bug report and go to replicate it yourself.
And surely, under some edge weird case scenario, it really happened.
You put the fix in and uneasily sleep the next night. You actually dreamed about the issue. And wake the morning with no reports.
Over the next weeks and months, its all good. No new reports. and your mind has turned to some new projects. Surely that bug has been squashed.
And then one day...
I feel their pain. It's not the same, because lives and reputations are at stake. It's so much worse.But I feel their pain.
Aerospace engineer here.
From TFA:
>A component of the main electric trim system became inoperative. Our pilots ran the appropriate checklist, which included manually trimming the aircraft. They returned to MIA and landed uneventfully. The issue was not related to MCAS.
That statement is from the airline, not from Boeing, so I'm more inclined to trust it. Additionally, if the airline lies and it turns up on an airworthiness audit (air maintenance organizations are subject to regular audits) then the penalties are quite severe.
In any case, per the airline's statement it was an issue unrelated to MCAS. Aircraft break literally every day in a myriad of ways that are often invisible/imperceptible to people riding on that very aircraft. In this particular case it was some unspecified component of the electric trim system.
You can look up the Master Minimum Equipment List for the B737[0] and see for yourself just how granular the approved maintenance program gets for aircraft like this. Everything on the MMEL is essentially an item that can be broken and the aircraft can still take off legally. Note that this is a different (and more rigorous) standard than "can be broken and aircraft can take off/operate safely".
I don't know exactly what broke here but I suspect it is a part that has broken on 737s hundreds if not thousands of times in the past, with similar outcomes.
I merely dabble in software but to further your analogy: This situation is when you've been dreaming about that bug for weeks and you get the call from the boss thinking it has recurred but instead it turns out it was a similar-smelling failure caused by some intern's microservice not failing gracefully when confronted with a network outage that brought down the system anyways.
Flight instructor here. This person knows what they're talking about.
But this doesn't feed the machine that is the 24-hour news cycle. I fully expect cable news to try to declare "more trouble for troubled plane," even though it appears to be a garden variety failure.
I think that attempts to whitewash the fact that Boeing have managed to burn the trust it spent decades building on the space of 2 or 3 years. This is the natural outcome -- until time proves otherwise again, every failure will be under a lens
> until time proves otherwise again, every failure will be under a lens
But it's really not every failure. There were 2 other failures on Boeing airliners yesterday alone and nobody posted the other two.
American B38M near Nassau on Mar 29th 2021, pitch trim issue/failure (OP's article)
Southwest B737 at Denver on Mar 30th 2021, speedbrake arming issue
United B739 at Denver on Mar 30th 2021, flaps problem
Day before
Batik B739 at Semarang on Mar 28th 2021, hydraulic fault
Aeroflot B738 at Krasnodar on Mar 28th 2021, flaps problems
Day before that
ANA B773 over Pacific on Mar 28th 2021, engine shut down in flight
iAero B734 near Evansville on Mar 27th 2021, loss of cabin pressure
Here's a 737-800 with a similar electrical trim issue recently https://www.youtube.com/watch?v=nLonztIXXWQ You probably didn't hear about that one
Like others said these aircraft fail every single day. People who read about them don't post them on HN because they're so common.
Not to mention that the 737 series of planes is the most produced passenger plane in history.
The odds of none of them having issues on a given day is slim.
These common imperceptible failures... Do they involve the aircraft turning around and flying an hour back to the departure airport?
Yes, if the destination isn't a maintenance base that stocks the part that fails. It's happened to me - 45 minutes into a 1 hour flight they decided to turn around and return to our departure airport. It's very annoying.
The problem is that some failures mean the plan can't fly again until the part is replaced, and sometimes it's cheaper to turn around than to have the plan sit idle until they can get the replacement part out to it along with someone certified to repair it.
Yes, they do. I suggest that you set avherald.com as your homepage for a week, and learn how common air turnbacks and diversions are.
Fun comment section on that site
> This girl is one of a few 757s that Delta uses exclusively for charters. Lower cycles on them. 31.5 years old and still chopping up birds. Love it. Long live the 757!!
One "silly" reason why minor failures result in flying back to the original airport is sometimes that the original airport is some sort of hub for the airline with plenty of equipment and personnel for maintenance, which makes it cheaper for the airline to repair the plane specifically there compared to another airport. If you follow avherald.com even a little bit, you will notice a lot of incidents result in exactly that.
That would strain the definition of "imperceptible", wouldn't it?
My point is that aircraft break all the time. Once in a while they break in such a way that they need to return to base. This wasn't an MCAS failure.
Your wording was problematic. "In this case" strongly implied you were putting this incident in the same category.
Perhaps my wording was careless; I can't go back and edit it now.
The fact it wasn’t MCAS really isn’t important. What is important is that Boeing has completely botched the development of this aircraft and this continues to be revealed to us in new ways over and over again. It’s a management issue through and through.
the good old programming testing rule: the number of bugs you will find in a piece of software is proportional to the number of bugs you already found
Lol so true.
FTA: "The issue was not related to MCAS"
It's not the engineers pain, as it wasn't an engineering decision to mount the engines higher and forward of the wing. Precipiting a pronounced nose-up aspect. All the same, I admire your attempt to deflect blame from the management at boeing.
> I admire your attempt to deflect blame from the management at boeing.
Bah, what a vile comment. He didn't contest that at all.
It's the engineers who will have to go through this exercise of fixing it, and he identified something most of us can probably relate to.
It's definitely the engineers pain. It's clear that management is the cause of all this shit, but the problem now lies in the engineers lap. So who has to solve it? Right, the engineers.
They're the ones that accepted and designed an unsafe aircraft ( a single sensor known for failure feeding a critical system that can crash an airplane? And they hid it from the FAA? They absolutely knew what they were doing and should rot in jail for at least a few years).
Boeing has lost the public trust not only in the US, but internationally.
Inherent instability aside, fact remains the general perception is that Boeing retrofitted engines too large for 50yr plane design necessitating structural modifications which compromised its flight worthiness. As a result, software had to be written to compensate for this, which unbelievably, relied on input from a single sensor--iow, single point of failure.
The lost of trust is further exacerbated by the fact that Boeing/FAA knew there was high probability of another crash after the first catastrophic incident but refused to ground the planes continuing to let them fly while issuing deceptive public statements regarding the planes safety.
Boeing's largest market is China, which justifiably, will not allow the 737 to fly within their territory.
Boeing did not get into this position overnight. After the massive cost and schedule overruns on the 787 program, they were far too cash-poor to fund the development of a clean-sheet design, hence the re-warmed 737. The 787 itself was a huge experiment in outsourcing both the costs and risks of aircraft development. It turns out you can outsource cost, but the prime contractor always owns the risk. Dr. John Hart-Smith published an excellent white paper warning of this while the precursor to the 787 was still in development, shortly after the Boeing-McDonnell Douglass merger.
https://www.google.com/search?q=Outsourced+Profits+%E2%80%93...
What has really ruined my trust for Boeing is not necessarily the incidents with the 737 MAX model specifically, but more the change in that company's culture that these incidents have made me aware of. I can recommend this video[1], but the short of it seems to be that Boeing over a period of decades has replaced its previous "engineering first" culture with what I can only describe, for lack of better wording, as the "suits taking over", with predictable results.
- A component of the main electric trim system became inoperative. Our pilots ran the appropriate checklist, which included manually trimming the aircraft. They returned to MIA and landed uneventfully. The issue was not related to MCAS.
I'm refusing to fly the MAX, period! The plane is flawed by design...
I have no opinion about flying on this particular plane.
It's not so much MCAS, electric trim, this, or that.
The bigger issue is it's too complicated, has too many features, and the FAA can't adequately oversee testing and certification all the way down the engineering stack. Furthermore, because of pressures to save a buck, Boeing is willing to cut corners and sacrifice safety by slapping a plane together without properly engineering or testing it. Because of this behavior, it's difficult to know how many other problems are lurking around like in the 787.
This is every commercial plane, though. We've traded more frequent crashes due to human error for fewer, more spectacular crashes due to how complex planes have become.
False equivalency and hasty generalization that equivocates every plane as having the same risks when they clearly don't, and ignoring testing and training process improvements. Also, an oversimplification that somehow fundamentals of aviation are shifted as a finite resource over to automation when that's clearly not the case.
737 classics are simpler and reliable.
The NG's randomly have hidden structural weaknesses exposed during runway overruns and hard landings when the fuselage breaks up because of Ducommun and Boeing negligence.
The MAX is a steaming pile that may be a white elephant around Boeing's neck.
The 787 is notoriously-bad.
The 777 is pretty good.
Airbus has had much more automation for years. Are they dropping out of the sky? Maybe they manage their complexity better than Boeing, who hires underpaid engineers to work on things that they're really not qualified to do.
As a passenger the 787 is a fabulous aircraft.
I have taken a similar stance myself (not that I'm flying anywhere these days) but, out of curiosity: do you also refuse to be a passenger in automobiles? The 737MAX is quite a bit safer than those.
The 737MAX is safer than a car per passenger mile, but saying that it's safer than "driving" is false unless you assume that both trips are the same distance. This isn't usually how it works. A Californian who refuses to vacation in New York to avoid the 737MAX usually does not drive to New York instead -- they drive to Point Reyes or something nearby, or just don't go at all.
This is true to some extent, although the difference in safety is so large that in the example you are still more likely to die from a car accident on your way to Point Reyes than your flight to New York.
Deaths from car accidents per 100 million miles driven: 1.33
Deaths from plane accidents per 100 million miles by plane: 0.0077
(Note above statistics are from the US)
In your example, California to New York would be approx 3k miles while point Reyes is approx 150-300 miles depending on where you start. A 10-20x longer journey via plane is still an order of magnitude safer.
Per mile, the car is about 200x more dangerous - in fact the usual statistic is that getting on a plane is safer than driving to the airport, not doing the whole distance in the car.
All of these statistics are too generalised to be useful.
People who fly in planes are generally not flying from every conceivable location on the globe to every other one in an even distribution and randomly using every type of plane available on every carrier. Neither are those driving cars driving from every possible destination to every other in every kind of vehicle etc.
Compare someone exclusively flying back and forth between one wealthy first world country to another on a Dreamliner run vs someone driving an 80's Ford Pinto regularly across treacherous mountain passes in the Andes.
Or the converse (use your imagination).
An important and useful statistic is that one particular, new model of aircraft is tremendously crashy considering the amount of time it's been in service.
It makes sense to avoid travelling on that aircraft, until it can be proven to have a flight-miles/crash ratio more in line with other models. (Which may take a number of years, or decades, especially if people are avoiding it...)
What you say is true but coarse statistics doesn't reflect actual situation. You would have to compare 737 MAX deaths per mile to OP car deaths per mile. Maybe taking into account that hopefully OP doesn't speed, drink, text, watch harry potter... Don't know if deaths includes pedestrian or bikes killed by cars, could be irrelevant if you only compare your odds to be alive after journey. I'd also expect a recent car with good safety to have a lower rate than average and maybe 737 MAX higher than average?
Apologies, I thought OP was just talking about flying in general rather than specifically the 737 max but I have re-read and it's clear. I think I just forgot as I was writing the response!
> Don't know if deaths includes pedestrian or bikes killed by cars, could be irrelevant if you only compare your odds to be alive after journey.
I agree this could be debated, but I don't think it's too useful to say "The journey was safer because rather than kill the person travelling it only killed a random pedestrian".
If I can chose between a 2021 Polestar or a 1956 Chevrolet, I may go with the Polestar for a long trip.
"- A component of the main electric trim system became inoperative. Our pilots ran the appropriate checklist, which included manually trimming the aircraft. They returned to MIA and landed uneventfully. The issue was not related to MCAS."
I don't get it. It is common for other airliners to rely systematically on trimming? Do other airliners have similar 'correcting' systems as MCAS?
Almost every airplane except the absolute most basic have trim controls for flight surfaces, especially the elevator. Even little two seat Cessnas get trim controls.
Trim is changed for each phase of flight. Electric trim is just a motor spinning the manual trim control.
Most airliners will be doing constant trim adjustment.
If you want a real change of pace check out Airbus’ control system. It does a lot more intervention than anything Boeing does. Depending on the state of the aircraft the control stick will respond to input in entirely different ways (3 ‘laws’ that contain no less than 5 submodes). Sometimes it will act as you would expect a stick to act, other times it will intentionally limit what the pilot is asking of the plane, sometimes it will average what the two pilots are asking. Confusion about how the system works has caused at least two crashes I can think of (AF447, QZ8501). It’s killed more people than the Max, but it was written off as pilot error since it was operating as designed in both cases. It just happens to be a design that will change the way the plane is controlled when things go wrong. A few of the modes do in fact include automatic trim adjustments.
AF447 was definitely pilot error, not realizing that the aircraft was stalling.
Predicated on their assumption that the flight control laws would prevent a nose-up control input from stalling the aircraft, and not realizing that the aircraft was in alternate law. Some of the last words on the CVR from the pilot flying were “But I’ve been at maxi nose-up for a while” while the computer was shouting STALL STALL STALL in the background.
You ever have the experience when you listen to someone speak with a strong accent, you don't quite catch the beginning of a word and the whole of what they say sounds like a foreign language?
I imagine that is how those poor pilots felt as their instruments screamed conflicting information at them as they tore through the skies above the mid-atlantic.
A huge problem with that incident is that as the plane got deeper into the stall, the computer decided it couldn't get an accurate idea of what was going on and STOPPED giving the stall warning. This lead to the crummy situation where pulling back on the stick made the warnings go away, despite being the exact opposite control input required.
This situation is 100% opposite of basic stall recovery, but I don't know how much that still works when you are panicking and no longer feel like you can trust your instruments or your plane
The phrase "the computer decided" gives way more agency to the computer than it deserves in this instance. In reality it was a simple airspeed threshold below which no one imagined the aircraft actually flying.
It was a really tragic accident with many lessons for anyone involved in the design of critical systems.
Yeap. The electric trim systems tend to be automatic with speed and altitude to approximate what the pilot wants via trim up/down controls. Without trim, planes would be pitching and diving all over the place, or at least require yoke/sidestick back-pressure to hold steady. Some planes can be trimmed through enormous deflections of the horizontal stabilizer. If configured incorrectly and under the wrong conditions, incorrect trim can lead to dangerous flight characteristics like pitching up or down beyond what the elevators can handle at full deflection. A broken jackscrew (part that moves the horizontal stabilizer for the trim commands) can cause this type of dangerous configuration or even worse.
Even gliders have trim. It's not technically considered a primary flight control because you can survive without it, but at the very least it's annoying not to have it.
So if the situation came, where the plane was at the edge of its flight envelope and needed to use MCAS (or whatever its called now), it wouldn't have been able to use it, causing the plane to stall? Thats a lot more serious then.
The plane doesn't really NEED to use MCAS. Systems like MCAS or Speed Trim and others do not make the planes flyable, they make them predictable. Aerodynamically, even the 747 or the A380 are normal planes operating on the same principles as the tiny Cessna 172, they're just much bigger, fly faster and react a lot slower.
Airliners are packed with systems that make them dull and predictable to fly, because things can break on a sunny day over Texas, but also at midnight in the rain over the Atlantic, and the last thing you want your pilots to care about when they're stressed out, disoriented and working through complicated checklists is whether this particular plane has a weird tendency to pitch up at these particular conditions.
Nope. “The EASA flight tests confirmed that MCAS was needed to provide full compliance but also that the loss of this function does not preclude the safe flight and landing of the aircraft; i.e. the 737 MAX remains stable following the loss of the MCAS function.”
https://www.easa.europa.eu/sites/default/files/dfu/B737_Max_...
Did this happen to be anywhere in the Bermuda triangle? :-)
Just a loose cord, ha!
I flew on one of the returned 737-max aircraft down to Houston about a month ago. Flight was uneventful and landed a few minutes early.
Thankfully, our standards for aviation safety are not low enough for an anecdote of a safe landing to be a valuable data point.
Anecdotal evidence but glad you survived.