Well, yes: the plane is inherently unstable. That's why the MCAS system is there. The system itself is mostly fine, it does what it's intended to under ordinary conditions. The problem was that Boeing, in order to avoid costs to the buyer, declared that pilots did not require training on it and made the instrumentation that manages the system woefully inadequate to the task of handling malfunctions (plus the system relying on a single sensor is pretty brittle but adequate malfunction handling instruments would've mitigated that).
Is it unstable? I thought the problem was that they didn't want to require retraining so they built in a flight control system that made it seem like the previous generation plane from a flight dynamics pov. That system would only take inputs from a single sensor on any given flight. If that sensor had issues then the flight control system would misbehave. If they had gone the retraining route and not included MCAS, then the plane would be fine. At least that was my understanding.
the airplane did not have stable flight characteristics because of its physical design.
that’s a hardware problem.
MCAS only exists because of that hardware problem.
the fact that boeing also did not train or tell pilots about MCAS, in order to make the airplane more financially appealing by retaining the 737 type rating, is a separate (also bad) issue.
The plane cannot be certified without MCAS or some other stability augmentation. This is not unusual in itself, almost every jet aircraft has some kind of instability. The problem was that MCAS is not reliable and doesn’t fail safe. The fix they’re testing actually makes it less reliable, but when it fails it will disable itself instead of making a smoking hole in the ground.
You're missing OP's point. MCAS was flawed, but the plane would have been fine if they hadn't added MCAS. It would just have required pilot retraining (which Boeing desperately wanted to avoid). I have never seen a reliable source for the claim that the handling characteristics without MCAS would fail to meet airworthiness requirements.
That is due to the mistrim situation that a perturbed MCAS had already put the plane into. Proposing that without MCAS (from the outset) the aircraft is inherently unstable is what I'm questioning.
The aircraft did not have stability issues. The purpose of MCAS was about providing the right resistance profile to the controls. The aircraft was still stable from an aeronautical perspective.
The flaw was fixed with MCAS. The problem that caused the two crashes was that pilots weren't trained on the new system because Boeing wanted to act like it was the same plane. The pilots didn't know what was going on or how to disable MCAS when it started misbehaving because of bad sensor.
With training, improved systems, and redundant sensors, MCAS should be safe. There are other planes that have similar systems. And there procedures for disabling bad sensors or misbehaving sensors.
I'm not sure if MCAS is necessary, there is some indication it is only there to mimic older 737 and plane would be safe without it and with training.
MCAS only exists to paper over a small handling deficiency. Apparently nobody (at least nobody with the power to force a change) thought that it could pose a safety problem. It’s not safety critical, so who cares if it fails? Except that it can fail in a way that crashes the plane.
@HPsquared “.. The plane is perfectly stable without MCAS ..”
NO, no, no it isn't .. doesn't matter how many different ways you re-arrange the word salad. MCAS is a software kludge to compensate for an unstable airframe
This is a bit of an urban myth that keeps flying around. The plane is perfectly stable without MCAS, but would have had different handling characteristics than the previous version. The purpose of MCAS was to modify the handling to match the previous plane, so pilots' type ratings would carry over with minimal retraining.
At its heart, it was a (poorly implemented) kludge in an attempt to sidestep a lot of paperwork.
MCAS is a band-aid trying to fix the inherent stability of the 737 max. Add in the fact that a single faulty pitch sensor could bring down a plane and blam. Finally, fail to properly train pilots on how the system actually worked and how to override it and here we are today. Software is a part of it but overall I don't see it as a software issue.
MCAS in itself doesn't seem to have been the problem. The fact that MCAS relied on a single sensor (no idea how that got certified in the first place) and that pilot were not aware of MCAS and how it worked were the problems. The latter was due to Boeing trying to avoid re-training and re-certification of air crew.
It’s not like the plane was uncontrollable without MCAS, it’s more that it did not fly like a 737-NG, and so would have required extra pilot training to compensate, which would have made the plane less attractive to airlines.
Yes but this is not a huge problem with the airframe itself. The tendencies without MCAS are fine. The pilots just need to be trained for them.
The problem was that airlines want to skimp on the training.
The same thing happened with the engine management. Boeing doesn't want to introduce an engine warning system because it would mean pilots have to be retrained. A lot of these barriers aren't part of the physical design but the industry as a whole being extremely wary of training. Probably as a result of cheap low-cost carriers emerging.
Not saying Boeing is a great manufacturer but it's not the only issue at play.
Sure there is. If the design was as inept as widely reported, there’s plenty of reason to be suspicious.
Then there’s the hackiness of MCAS itself. Boeing tried to cut corners and put bigger engines on an ancient plane design that couldn’t accommodate them without deleterious aerodynamic effects.
Then, to help airlines cut corners, they slapped MCAS on it to suppress those effects and obviate the need for pilot training.
Of course, the big “problem” should be easily manageable by any pilot: an upward-pitching tendency under heavy power. If you don’t notice or can’t easily correct for that, you have no business flying a plane.
It crashed because the system that was making it behave that way failed. The MCAS did not get correct data, did not react well, was not easily deduced to be the problem, and was not easily disabled.
Training and technical improvements can resolve these problems and it's ready to fly. If that's still deemed too risky then Boeing can remove the behavior modifications with training and certification as a completely new design. It was this cost that they were trying to avoid through emulation but clearly not done in a safe enough manner.
Yet four highly trained pilots plowed this "inherently stable aircraft" into the ground.
This had nothing to do with the aircraft being unstable, but that MCAS had introduced a huge downwards trim as consequence of the sensor malfunction. Had MCAS not been active, none of the accidents had happened.
I think we're talking past each other. MCAS is stability control which a lot of planes have and is allowable to pass certifications.
However MCAS also makes the MAX behave like the older design which specifically led to the gap in training and controls over the system. If they just had stability control but without the emulation of behavior then there would be new training and certification, which is something they wanted to avoid but would've prevented these accidents.
Great video. But he says the exact same thing I did. The MCAS is necessary because of the different engine placement. So the airplane cannot recover from a stall without it. That, to me, makes the entire airplane unstable and improper for commercial flights as this is an expected condition at times that the plane should be able to recover from. The airplane cannot function without a deeply flawed software system no one understands and no one knows how to operate. Changing the software doesn't change any of these things.
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