I strongly disagree with this one being a real link in the chain.
OK, we put bigger engines on. The 737 is kinda already sporty and easy to get the nose too high on departure. Now it's a little worse with bigger engines.
This is part and parcel for what happens when you stretch planes, adapt new engines, etc; there are minor, associated design changes you need to make to improve handling, etc. Software is a reasonable way to do it.
The criticality of this was badly misunderstood and mis-characterized.
You disagree with the statement that roughly the urge to avoid recertifying pilots caused Boeing to not mention MCAS even in manuals, leading directly to these deaths? Because from my pov, Boeing introduced a new failure mode (MCAS failure leading to intermittent forcing of the nose down) without any warning to the pilots.
Now maybe the pilots' standard training should have compensated, and there are obviously maintenance or training deficiencies, but Boeing also knew good and well they were selling planes to pilots with these existing training deficiencies. And should have designed a plane to be operated by real world pilots.
I disagree that deciding to stretch the 737 is fundamentally bad engineering. Yes, it realistically requires some control augmentation (and maybe earlier 737's should really have had something like MCAS, too). Yes, bigger engines and heavier 737's have the problem worse, but it isn't unreasonable to fix this with systems.
I think there were failures across the board. The fundamental analysis of MCAS was flawed: it was much less reliable than was thought, and failures of it provided a much more difficult situation for pilots than anticipated.
I suspect the analysis boiled down to "MCAS provides a little defense against getting the nose excessively high on departure; it shouldn't be necessary so no big deal if it fails. And the worst failure we can think of is like stabilator trim runaway, which everyone knows how to deal with."
This was compounded by the fact that many developing countries do not require pilots to demonstrate they can deal with runaway trim as part of a checkride and recurring training.
Not disclosing information about the system made the problem even worse-- and this is harder to attribute purely to being part of bad initial analysis.
I do not understand some of the aircrew actions, even in retrospect. If I am fighting pulling the yoke back-- I am going to have my finger on the trim switch to try and get rid of those control forces, even before I am thinking about the problem. This would have inhibited MCAS and retrimmed the plane. I think that Boeing assumed that this would happen. I am lazy and would rather not have to tug the yoke so I use trim a lot. :P
I don't have any technically knowledgeable comments to make, but I think if you don't fully understand what happened, there's no excuse for doggedly insisting one group of people involved should be given the benefit of the doubt and the other not. It's reasonable to assume we lack something when it comes to the crew's POV.
Actually, I have one thing to contribute, that I often think of whenever I read about an air disaster. Experts frequently say "why didn't the operators do logical thing X?", and I think there is a practically universal answer. Whenever something unusual goes wrong, it is likely to upset your existing logical model. You know either your logic is faulty or the inputs to your model are wrong, but which is it and how?
It's easy to say "just do A, B, and C as trained", but once jolted out of your mental context, you probably can't regain it in a few seconds or minutes before crashing. The impossible task is not to know the necessary actions according to the book, but regaining the trust that they are the right ones in the face of something unexpectedly violating your assumptions.
Developing a new logical model for reality is very difficult even for highly trained people, particularly under time constraints and life-or-death pressure. Or, even the meta-problem of knowing whether it is time to develop a new model of reality.
I really don't understand many of the responses to what I'm saying.
I have already stated that MCAS was a horrible screwup and failure in analysis and regulation. Any system that routinely puts people to the test requiring high performance to avoid death is bad.
That doesn't mean one should ignore the other weaknesses. Given that both the countries with crashes didn't require pilots to demonstrate coping with stab trim runaway as part of type training... and pilot understanding of the stab trim system under stress seems lacking... maybe that should be addressed too.
Yup, I agree completely. There's some people who say that because the longer 737 is less stable in pitch it should have never been built, and I think that's over the top.
> There's some people who say that because the longer 737 is less stable in pitch it should have never been built, and I think that's over the top.
I know that aerodynamic instability requiring continuous correction by fly-by-wire systems has become common on fighter jets because it's necessary to achieve some of the maneuvering characteristics necessary to make them competitive. These are, of course very different priorities from commercial passenger aircraft.
Has a jetliner been certified before the 737 MAX that is aerodynamically unstable in any of the tests that it's required to pass without control inputs made by the computer without direct input from the pilot, or in contravention of the pilot's input? I know Airbus is fond of its "do what I mean" system, but that in some circumstances, Airbus flight control systems revert to essentially emulating an analog airplane. Would their flight characteristics pass certification in that mode?
Concorde's Safety Flight System is in some ways similar to MCAS, in that it'll nudge elevons itself.
I don't know if Airbus would meet certification requirements in direct control law. I suspect not. Definitely not in mechanical control law.
Just like more conventional jetliners wouldn't meet certification guidelines without all of their control rigging, counterweights, and trim systems. It's just now tempting to make adjustments to those systems with software instead of fiddling with everything else.
I thought of a much better answer to your question:
Many airplanes require functional (electronic) yaw damping to be safe in various flight conditions, because of dutch roll. There are also e.g. electronic control feel systems in some aircraft that must be operational to exceed certain speeds and/or altitudes and not be excessively vulnerable to PIO, etc.
My understanding of dutch roll (from watching a few flying videos on youtube and reading the wikipedia article) makes it seem like dealing with it is basic flight control coordination that shouldn't give a pilot experienced in a given aircraft any trouble.
Is it harder than I'm imagining in big jets, or in specific aircraft due to peculiarities of their handling characteristics?
Dutch roll is an oscillatory mode resulting from delayed cross-axis coupling and different axis stability. There's not really much a pilot can do about it other than trying to avoid exciting it.
Aircraft with swept, low wings exhibit dutch roll worse than other types (e.g. airliners). It's also worse at high speeds and high altitudes.
Yaw dampers vary based on aircraft and flight regime to "attenuating somewhat that annoying-bouncing-back-and-forth-feeling in the back of an airliner during cruise (imagine how bad it would be without active damping!)" to "preventing an oscillation from building in 2-3 cycles to a point where it will cause structural failure".
I think some of my confusion here was related to some notable youtubers misusing the term to mean a roll-on-heading exercise. When I wrote my last question, I was thinking "there's too much, or an unpredictable amount of adverse yaw", but I now understand the problem as "the aircraft enters a self-reinforcing oscillation in response to certain poorly coordinated control inputs", which doesn't sound like a good thing at all.
Thanks for all your input in this discussion. I find both flight in general and the case of the 737 MAX fascinating. Previously the implementation of MCAS sounded absolutely insane to me, but I can mostly understand how they got there after reading your comments.
Sure, but 737's have crashed before from crews getting the nose too high on departure, so... arguably the entire 737 fleet would benefit from a "proper" MCAS.
The people who built MCAS thought they were taming a 737 handling weakness that was worsened by the new engines. Again-- a normal kind of thing to have to work on when stretching jets.
Not stalling on takeoff is pilot 101. If an aircraft is prone to it I personally do not want layers of software hiding the issue. It's practically a law of nature that software is full of bugs.
Better avoid Airbus, then, because there's a massive control law between the pilots and the actuators to create a "do what I mean" interface with envelope protection and all kinds of characteristics tamed.
Thanks. I couldnt agree more. It would make sense if the bar was higher for adding control software than training pilots. To me it seems like the type cert problem was backwards.
In fairness, we've added a whole lot of automation since 1970, and most people think that increased automation has been a key factor in why aviation is so much safer overall. (Along with crew resource management).
Automation definitely has directly killed people, though, too.
Boeing was proven wrong by the two crashes but it's not a priori obvious that pilots wouldn't know to manually trim the stabilizer and then pull the cutout after MCAS kept kicking in.
They were following Boeing's advice! Boeing said if MCAS misbehaves then pull the cutout. They did that but then they couldn't move the manual trim wheel because of the forces on the stabilizer. So they reenabled the electric trim, at which point MCAS jumped in again and everybody died.
They couldn't move the manual trim wheel because the plane had been allowed to overspeed.
It was climbing at Vmo; they could have pulled back the power to not let the plane overspeed, rather than exceeding Vmo.
Hopefully at Vmo they could move the trim wheel, but if not, they could wait until they had a few thousand feet more height, aerodynamically unloaded and trimmed.
> So they reenabled the electric trim, at which point MCAS jumped in again and everybody died.
They re-enabled the electric trim, and touched the electric trim switch a couple of times but left the plane far out of trim. I can't figure this out-- there's even an indicator that makes it obvious you're out of trim. Why re-enable electric trim and not really use it?
Then after a timeout after they pushed the trim switch, MCAS jumped in again and everyone died.
That's what you would do, you weren't there though, they were. Confronting a system whose implementation details were not well known, already two potential memory item checklists into the flight to the ground.
It's easy now to point the finger and say "Airmanship" when you know the innards of the damn thing. They had one airworthyness directive, and maybe a grand total of five paragraphs in the entire manual, plus a memory item checklist that didn't accurately reflect the detail of an MCAS failure. An MCAS failure is not continuous uncommanded trim. It's discrete pulses,
I appreciate the detail and effort, and you certainly speak as an experienced member of the industry; but pushing this off to the pilot's when there is so much that had to happen before the plane left the factory for them to be in that position is a bit much.
There is whistleblower testimony that the decision to not implement a multi-sensor MCAS was intentional to avoid the financial consequences of having to have pilots put in simulator time.
You can't sit here and say the pilots weren't good enough when the manufacturer went out of their way to make sure they could skulk a plane by regulators with the least amount of training humanly possible, safety be damned. To do so is not just mad, it's unconscionable. It's the very thing of insanity. A Catch-22 if I've ever heard one.
OK, so you're here to ad hom and mock (in your other post) and then not actually speak to the question asked here (when your plane is climbing, why would you re-enable electric trim, and then not even bother to significantly retrim the plane?)
This is not the behavior I expect from someone whom I'll voluntarily talk to.
