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How do you know the airframe is fundamentally flawed? ("the engines are too big" is not an answer).

Like the hundreds of other comments on here mentioning how the engines were too far forward. The 737 was originally designed to be low to the ground, and rather than raising the jet and placing engines where they are on other similar planes (meaning it could no longer be classified as a 737 and requiring new manuals/training/certification), they moved them forward and adjusted for the new unexpected handling with the MCAS.

Raising the jet requires a wider body for the landing gear to fold up into

The 757 sits a good 4 feet higher with the same fuselage diameter.

If I remember correctly, the 737 either doesn't have the space for longer landing gear, or there's an issue with the longer landing gear, or both. Citation needed, of course, as this is off of memory.

It was designed lower to be easier to work with ground handling and servicing. This lead to a few different designs of plane-deployed airstairs and made it popular with Alaska Air and other airlines serving small airports.

https://en.wikipedia.org/wiki/Boeing_737#Background

The 757 has a wingspan 30 feet wider than the 737. If you look at a picture of the airplane, you can see that the landing gear is part of the wing.

https://qph.fs.quoracdn.net/main-qimg-0f650e809408f3962a1ed0...

Yes, but you said body and not wing.

We know because hundreds of people died in the airframe. We know the MCAS was a workaround to an aerodynamics problem. Boeing has admitted this both directly and indirectly. Airframes shouldn't need software fixes to accommodate for a design failure and design failures shouldn't be allowed to fly after killing hundreds of people.

How do you argue what they did and are continuing to do is just in this situation?

Uncrashable airplanes don't exist. The question isn't whether there were crashes (nobody disputes that). It's whether the problem can be fixed so that pilots can fly it safely. Given all the times the plane flew without incident (other than the two crashes), it seems this should be possible?

Yeah, it was perfectly safe except for two crashes. But that's two crashes more than I can tolerate.

The problem is now the lack of public trust in their work. They might fix the software, but how to prove they're not lying again?

The same way you prove Airbus isn't lying?

Presumably Airbus is still being watched by a regulator or two. Unlike Boeing which has not been watched as the FAA has clearly been gutted.

The 737 MAX will be watched by all regulators world-wide. So it will be checked as carefuly, or actually even way more carefully than any competing aircraft.

We must remember that repeated checking does not make a bad design good. It’s completely clear now what Boeing’s priorities and methods were.

The 737 is a very successful design and it is clear with practical experience, what its strengths and weaknesses are.

Boeing build processes that build aeroplanes. Those processes swiftly mutilated and killed hundreds of people when the product was unleashed. The response from Boeing was 100% sociopathic.

You may find that OK, if you wish. You may choose to do nothing.

We don’t, and won’t.

Which NOONE bothered to do before millions of people were made to fly in them. THAT is the very issue at hand.

The plane still crashed twice which is many many times higher than the non-purely-human-cause crash rate of other airplane types. Probably even then 737 MAX is still safer overall than cars, but airplanes have a higher safety expectation than cars do.

But it crashed 2 times for the same reason. Take away that reason and you have a completely different situation to estimate its reliability.

The crash rate is zero if you ignore the crashes, it's true.

It is not about ignoring the crashes. But as both crashes were caused by MCAS, you cannot make a safety statement about a 737 without MCAS or rather with a fixed one.

Yes you can. Clearly Boeing Is suffering serious process failure, especially in letting two crash before responding properly.

Is the MCAS the only place they messed up? Will this fix truly be 100%? Remember that their first attempt at a fix was rejected.

When you see one bug, that’s often an indication that more are nearby.

You clearly have absolutely no background in aerospace engineering. The 737 airframe is actually relatively stable compared to many other things that fly ... for instance, many high-performance jets will literally begin to oscillate and tear themselves apart without help from their flight computers. The flight computer is a part of the airframe, and it is perfectly valid for the flight computer to contribute to the airframe's handling characteristics. Boeing's mistake was in underestimating the burden placed on the pilots in a runaway trim situation, and assuming that pilots could execute a recovery procedure correctly that remained unchanged from prior iterations but that had also been rarely needed on prior iterations (vs. the MAX, where MCAS failures were common enough that an average pilot might actually need to execute the procedure).

People like to bring up the instability of high performance jets, but I'd like to point out that they generally have ejection seats and don't carry passengers.

Airbus jets carry passengers and have been fly-by-wire for decades. Cables and hydraulics have been replaced with software and computers. Like it or not, the software and hardware that make up the flight computer are an integral part of the airframe on most newly produced passenger jets, regardless of who makes them.

It's an interesting point. One of the reversion modes on Airbus is "direct law". Under that control mode the stick displacement is proportional to the control movements.

If, hypothetically, an Airbus had a problem in the same region of flight would it even be detected in flight testing? As far as I'm aware it wouldn't be as direct mode is a reversionary mode intended to get the aircraft safely on the ground.

One of the things that is regulated is stick control forces.

They cannot be greater than a set level (essentially, an average strength pilot), particularly when performing critical manuevers.

This was actually the whole reason MCAS was engineered in the first place: to lower the effective stick force required to within the acceptable limits in certain scenarios.

So presumably Airbus in direct mode could still have similar issues flagged in direct mode, if the plane behaved in such a way as to require unacceptably high stick force to move control elements (even if it was a 1:1 mapping).

Technically I'd say they introduced MCAS to increase the control force in certain scenarios (high power high angle of attack). But yes I mostly agree with you.

One thing I'm not sure about is whether Airbus would have to demonstrate proper controllability (i.e. adherence to control force regulations) in all phases of flight and corner conditions.

You could have a scenario where by they have a complete control reversal on the approach to stall but under normal law the pilot would be oblivious. This would obviously show up in direct law.

I'm tracking what you're saying now.

I'd hope they would have to demonstrate both things: (1) that a given mode can or cannot be active in a certain scenario, and (2) how the plane behaves in all tested scenarios under all modes potentially active.

Is there a reason this necessarily wouldn't be the case?

My guess is that it's considered so unlikely that they wouldn't be required to demonstrate the full range of behaviour. In the same way as I wouldn't expect them to demonstrate all of the edge cases of the flight envelope with a failed yaw dampener. I could well be wrong though, I haven't found any good references.

Your comment is absolutely deceptive. Fly by wire doesn’t mean that airbus planes are as unstable as jet fighters.

Fly-by-wire is not about airframe stability. High-performance jets are fly-by-wire because high-performance generally means you need to build an unstable airframe, and computer control is the only way to compensate for it.

But that's not commerical aviation - that's combat aviation. That's "you fly faster or the missile catches you and you die anyway" aviation.

Building intentionally unstable airframes for civilian aviation is a very different proposition. And unrelated to the use of fly-by-wire.

How is

> Airbus jets carry passengers and have been fly-by-wire for decades

a response to

> instability of high performance jets

They also crash incredibly often by civil aviation standards.

> The 737 airframe is actually relatively stable compared to many other things that fly

Nice strawman. We are talking about the MAX not the 737 in general.

Why don't you explain why previous variants of the 737 didn't require MCAS?

Why don't you explain why previous 737 versions have a Mach trim to prevent Mach tuck, or why it had a speed trim system to control the pitch force response to speed changes.

For the same reasons it has control surfaces at all. Planes need to adjust their aerodynamic properties in order to adapt to various external and intrinsic factors. Trim in particular maintains aerodynamic stability in the presence of some conflux of the two.

The trim equivalent of MCAS would be some elevator trim that ensures the excess AOA potential of the MAX could not occur, if set correctly. That is how a stable aircraft behaves. MCAS is a computer override to compensate for a condition that should not really occur in the first place.

If passenger planes had the failure rate of high performance jets we’d all be using boats and trains. The fact that high performance jets have ejection seats while passenger planes do not should clue you in that failure is anticipated.

High speed jet fighters flying above Mach speed doesn’t really compare with a chubby airliner flying 900km/h?

> The 737 airframe is actually relatively stable compared to many other things that fly.

I agree, so where is your comparison of 737 Max and non-Max airframe? Because we have real data, including death toll, that shows one airframe is not like the other.

> Boeing's mistake was in underestimating the burden placed on the pilots in a runaway trim situation, and assuming that pilots could execute a recovery procedure correctly that remained unchanged from prior iterations but that had also been rarely needed on prior iterations (vs. the MAX, where MCAS failures were common enough that an average pilot might actually need to execute the procedure).

This is not the whole truth as we know in this situation MCAS 1.0 was a critical flight system with a non-redundant data source. The "burden" placed on pilots was that the system did not have sufficient and trustworthy information to prevent a faulty and inadequately designed system (MCAS) from crashing the airplane. Furthermore since MCAS is not required, again, on non-Max airframe it seems your assertion that you have background in aerospace engineering is egregious because you should understand all 737 Max are currently grounded because the 737 Max is not a 737 airframe and should be recertified as such.

..."relatively stable compared to many other things that fly"...

Balloons, paper jets...

Please list all passenger airframes that would “tear themselves apart”. Should be easy for you to do considering your background in aerospace engineering.

> We know because hundreds of people died in the airframe.

Since both crashes were caused by malfunctioning software, this doesn't tell you anything about the fundamental soundness of the airframe.

> We know the MCAS was a workaround to an aerodynamics problem

MCAS was a workaround to make the plane handle more like a 737. The existing handling was fine by itself (not 'fundamentally flawed'), it just didn't match the 737.

> How do you argue what they did and are continuing to do is just in this situation?

I don't see where I did that. I just don't think there is any evidence that the airframe is actually fundamentally unsafe.

The software is a fundamental part of the airframe. You can’t separate the two and still have an airplane rated for flight.

> Keep talking about the software. Make it about the software, so no one knows the airframe is fundamentally flawed.

It's pretty clear that the author of the comment I originally responded to was not considering software.

Their point was about the way Boeing is trying (and mostly succeeding) in steering media coverage about the MAX-8. (If Boeing keeps discussion on the micro issues, maybe they won't have to publicly address a macro problem). Their comment doesn't take a position on whether software is a fundamental part of the airframe or not. Yours does.

Because MCAS is required, unlike every other aerodynamically stable airplane that came before it.

https://en.m.wikipedia.org/wiki/Qantas_Flight_72

Qantas Flight 72 is probably a good demonstration of why using MCAS as a band-aid for the 737 MAX's stability issues is a bad idea. One of the key reasons that fault didn't lead to a crash that killed everyone on board is that Airbus placed much safer limits on the amount of control authority their flight envelope protections had and the altitude at which they could operate.

Airbus does it too. They have several control laws that are used to provide flight envelope protection. It was the pilot's failure to understand his plane's software that caused AF447 to crash. Essentially he didn't realize that the flight control software had changed modes, that it wasn't providing the normal handling augmentations, and that his inputs were putting the aircraft into a stall, which caused the crash.

See: https://en.wikipedia.org/wiki/Air_France_Flight_447

https://aviation.stackexchange.com/questions/62338/why-did-a...

Build unstable airframes? Not outside of forward canard jet fighters.

And that pilot crashed a perfectly fine airliner after he lost situational awareness and then did the one thing you should never do - pull the steering column back in a mad panic until the plane stalls.

No, in normal flight regimes, MCAS is not required. For example, it is disabled at any time, the flaps are extended, that is during starts and landings. It is only required (by law) at high angle of attacks. In these kind of flight regimes, most other airplanes also have systems to ensure their "stability". The 737 MAX isn't fundamentally more unstable than competitor airplanes with large engines.

The wings are too low?

Keeps crashing into the ocean

The plane was built in the 50s, it was low to the ground. But Boeing wanted to fit bigger/newer/better engines on it, but they wont fit since you can't make the landing gear longer. They had to move the engines higher and much more forward.

Isn’t the engines being not mountable at a well balanced point a big part of the answer? Which isn’t down to only the size of the engine but also the height of the wings. So yes it’s complicated but the engine is part of the picture. Although not being in the industry, I don’t know, is a strap-on engine added to a design that wasn’t intended to accommodate it technically considered part of the airframe?

Basically no jet engine at any airliner are mounted at a point which is well-balanced in all flight situations. At level flight, the 737 MAX is also well balanced. That is just a matter of weight distribution in the machine. The problem appears at high angle of attacks, that means the force vector isn't pointing vertically down as it were only due to gravity. In this situation, the balance of every aircraft which has large engines hanging down from the wings does shift and needs to be compensated for in some way in the control systems.

If the airframe isn’t flawed, fly it without MCAS. With Boeing management onboard. Surely you don’t need to dynamically adjust flight dynamics without the pilot’s input or knowledge if the airframe is sound.

It’s realistic to build aircraft where software is required to fly said aircraft depending on the flight dynamics, and the pilot(s) are fully aware of what’s running. But that changes the type rating and blows Boeing’s regulatory sidestep out of the sky.

God it's frustrating seeing people here talk about aviation.

Flight computers are a fundamental part of normal aeronautical design.

Asking Boeing to fly a Max without MCAS would be like asking you to write a bug free C++ program... with a compiler with no error messages or validation.

[removed] Other sibling comments are of higher quality.

Better not ever fly on an Airbus then, either.

https://en.wikipedia.org/wiki/Air_France_Flight_296

https://www.telegraph.co.uk/technology/9231855/Air-France-Fl...

The MCAS was a workaround implemented as a stopgap, no? How does this fall under the broad category of a flight computer as you've stated? What other airliners have been retrofitted with similar systems? Why doesn't a non-Max 737 need MCAS?

No. It was a software fix put in place to satisfy a regulatory requirement under specific, known flight conditions.

The following planes (among others) all translate flight inputs. Airbus A320, A330, A340, A350, A380; Boeing 777. https://en.m.wikipedia.org/wiki/Flight_control_modes

A non-Max 737 doesn't need MCAS because it already behaves like a 737.

Essentially, most replies on this boil down to people being shocked (shocked!) that computers are currently helping all planes fly. I'm not sure how they thought AEs were getting efficiency gains while physics stayed the same...

The replies do not all boil down to people being shocked that computers help planes fly. That is a willfully distorted charicature.

Hundreds of people were killed due to a bad implementation of a deeply irresponsible and insensible approach to make money by skirting flight safety regulation. The bad implementation was in part software, but nobody is confusing that aspect with the whole picture.

The 737 MAX does not need MCAS. Nothing needs MCAS. Boeing executives wanted the money that MCAS made them.

Is it really?

If that were the case, then you'd see people debating the relative merits of SDLC approaches and organizational blinders to letting bugs slip through.

In reality, that's only about 20% of any Boeing discussion.

80% is outrage about how Boeing could have released such an "obviously flawed" airplane that required flight computer adjustments. And misunderstanding that Boeing pivoted from a clean sheet design to instead build exactly what the carriers asked them to.

Generally, HN comments are pretty good, but the amount of kneejerking in Boeing threads in lieu of informed discussion is terrible.

Edit: Although reading through new replies this morning, it's nice to see voting mostly sorted the technical wheat from the chaff.

> A non-Max 737 doesn't need MCAS because it already behaves like a 737.

If I read this correctly you're implying a 737 Max doesn't behave, aerodynamically, as that a non-Max 737 does? And if we follow that line of thinking since non-Max 737 don't require MCAS to behave appropriately then the 737 Max is not a 737 airframe and it should be recertified as something else, no?

I'm in no way "shocked" computers fly and/or help fly airplanes. I am shocked so many comments defend the gross negligence by Boeing, however.

Remember that in all of the needless death the 737 Max is attributed with absolutely zero deaths were because of a flight computer. The real root cause of the 737 Max crashes are Boeing executives and FAA personnel making cognizant choices to allow process to be skipped in the vain of profits and loss avoidance. I believe we'll see this, at some point, no different than the commonly referenced Challenger failure [0].

[0] https://www.breakingthewheel.com/root-cause-analysis-five-wh...

You're wrong.

Sophisticated flight computers are only necessary for aircrafts that are inheritenly unstable (fighter jets) that require special flight characteristics.

Safe commercial, and private aircraft are built to be inheritenly stable. It's less complexity.

Sure we've added fly by wire, or dynamic power controls. But those are relatively straight forward.

Changing the center of gravity of the plane and therefore introducing different (dangerous, risky, and unsafe) flight charectierstics is a major issue.

Define "necessary".

Depending on how exactly you define it, pilot error is either the #1 or #2 cause of commercial plane crashes. FBW systems seek to reduce or eliminate that.

That's not true for Boeing aircraft. They are designed to be flyable manually, unlike Airbuses, which are fly by wire.

The 777, 787, 747-8, and 737 Max are all fly by wire.

The Max is not fly by wire, that's the problem. It's a hydraulic/mechanical control. That's why pilots aren't able to pull it out of dives or re-trim it, the aerodynamic forces are too much for the crew to fight against.

Right. If this was a fly by wire aircraft, it would have to have triple or quadruple redundant control systems and redundant air data sensors. But because the auto-trim system wasn't considered primary flight control, it didn't get evaluated like a fly by wire system.

Auto-trim has been around for years, and failures are usually more annoying than serious. But the 737 MAX's auto-trim had far too much control authority, and was being used to compensate for bad handling characteristics, making it a flight critical system.

And if they hadn't opted for secrecy, properly put it in the manual instead of hoping that the outcome of bad sensor readings would appear like that of a fried switch, someone might have realized what a perfect trap they had built while writing "engage trim cut-out, then work the manual trim wheel until you regain control or hit the ground, whatever comes first".

Neither is the 747-8. Half of his examples were made up.

Not fully, but spoilers and ailerons in the -8 are FBW.

The other three are but the 737 Max is most definitely not fly by wire.

"God it's frustrating seeing people here talk about aviation"

Google the 'Murray Gell-Mann Amnesia effect'.

Edit: https://en.m.wikipedia.org/wiki/Gell-Mann_amnesia_effect

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