7 ms·
They should be forced to add the 3-sensor config on the plane and have that supported by the MCAS for all planes. A single sensor failing and causing unlimited
by r00fus 7y ago
They should be forced to add the 3-sensor config on the plane and have that supported by the MCAS for all planes.
A single sensor failing and causing unlimited automatic shifts in pitch is a nightmare I will not fly on.
- qaq 7y agoIt's no longer unlimited
- hetspookjee 7y agoWell, that's a relief.
- platz 7y agoSo if that software fix relieves you, wouldnt you have to admit that it was the software the was the most direct reason for the crashes? HN folks here seem hesitant to say this. But without the dumb ability to do repeated activations it would've been a much less severe problem.
- hu3 7y agoThe software did exactly what it was told to do. The error was in the specification.
- platz 7y agoHah, wow
- thombat 7y agoLet's suppose that the entire control logic for MCAS was now re-implemented with vacuum tubes. Would you now argue that the aircraft crashes indicate a hardware problem? Or would you agree that the real problem is in the system design, since any conforming implementation of it will produce the jeopardy?
- platz 7y agoIf it was implemented with vacuum tubes, that would indicate a hardware problem as well as a system design problem. So in this situation, the claim is that braindead contractors mechanically implemented something to spec by force of law? Sure, then whoever designed the logic is accountable. In 99.9% other environments, the distinction is collapsed because the implementor typically has responsibility to design sub-component level logic correctly, to high-level requirements, but also to overall business need and in service to even higher level project goals, and the team that designed the logic is also implemented by the same team.
- bdavis__ 7y agonope, all of the vacum tubes would be working as designed. not a hardware problem, a system design problem. thus the invention of a discipline called 'systems engineering'.. i would say in 100% of engineering development, the design is done as a system, and specific requirements are allocated to design elements (like MCAS software). Each of these elements is tested against the requirements. aeronautical engineering is a very specific skill. so is aircraft controls. so is airworthiness. a software engineer is an expert in software, not these other disciplines.
- platz 7y agoAt the level of specification you've laid out here, the act of 'software development' is reduced to almost nothing, and you have re-categorized the entire effort as systems engineering.
- zaroth 7y agoHaving a specification for how a system should behave in response to various input signals is not at all the same as actually having the functioning software for achieving that system. In fact, achieving a functional and fully correct piece of software based on such a specification is not at all a trivial task, as experienced software engineers will well appreciate. Because while the specification may describe a certain sequence of inputs that should result in a certain sequence of outputs, it probably does not prescribe the exact data structures, memory layout, logic flow, and computational steps required to guarantee the correct output is always produced from a given set of inputs. And the people being paid to create the necessary data structures, algorithms, calculations and control logic in order to implement the design specification... those developers are specifically not in a position to make systems design engineering changes to the underlying specification itself.
- comex 7y agoAnd it’s now 2-sensor.
- cameldrv 7y agoThe fix means MCAS doesn't activate unless two sensors roughly agree, and it only activates once, which means that the plane is still controllable with just the yoke after MCAS activation. MCAS will also deactivate if the yoke is pulled back (questionable IMO, since it is supposed to compensate for mishandling), and you can leave the electric trim on and undo what MCAS did without fear of it activating again. IMO the risk of a mistaken activation that leads to an accident is extremely remote with these changes.
- peteradio 7y agoI thought the MCAS would typically be activated while the pilot would already be pulling pack on the yoke. So I'm a little confused under what circumstances MCAS would ever activate. Does it activate while yoke is pulled back but the pilot can additionally yank harder to deactivate?
- cameldrv 7y agoYes, it typically would. There's something called an aft column cutout switch which deactivates nose down trim if you're pulling back on the yoke with a certain amount of force. They're proposing to use this switch to deactivate MCAS. I'm unsure how much force it takes to activate this switch, but it seems to me that this makes MCAS less useful for its intended purpose, and that's why I said this decision was questionable.
- phire 7y agoThe new software has been updated to use both sensors. It won't activate when sensors disagree by more than 5.5 degrees. The new software now only does a single stabilizer movement. They have eliminated all known failure conditions which might cause multiple movements. With only a single movement, the pilots will be able to counteract the force. Two sensors is not quite as good as three sensors. It can't know which sensor is bad. But it can disable itself and prevent unintended activations. The new software, when combined with adequate pilot simulator training to both disable MCAS when it encounters an issue, and to fly the plane in with MCAS disabled makes things safe enough.
- vkou 7y agoSo, this fixes the MCAS problem (Where the plane plunges nose-first into the ground, despite the best attempt by the pilots to pull the stick up)... But how does this fix the problem that MCAS was supposed to be a band-aid over (That the plane is aerodynamically unstable during take-off, and pulling too much on the stick will cause the plane to easily stall)..? The new MCAS sounds like it will only protect against this instability once - and, if overriden, will not do anything to protect against a stall?
- tzs 7y ago> But how does this fix the problem that MCAS was supposed to be a band-aid over (That the plane is aerodynamically unstable during take-off, and pulling too much on the stick will cause the plane to easily stall)..? MCAS is not even enabled during take-off, which makes it hard to see how it could be meant to address supposed stability problems during take-off. It can't come on until the flaps are retracted.
- sokoloff 7y agoThe 737-Max is not “aerodynamically unstable”. (It does not exhibit negative longitudinal stability.)
- phire 7y agoI mean, that's true of every plane. You pull back too much, it will stall. It's not that the MAX stalls super easily, It's not an instability. It's just that the controls feel wrong when approaching stall. The FAA have pretty precise regulations about how much backpressure the pilots should feel when approaching stall. In normal flight, the plane is never anywhere near stalling, so MCAS never activates. Nor do the pilots encounter this weird stall. The combined chances of both MCAS being disabled AND the pilot not recognizing the stall is pretty low. But this is why the simulator training is important, so the pilots are familiar with the new feel as the plane approaches stall.
- o-__-o 7y agocouldn't make it 3 sensor that would change the certification (obviously they can now) but I wonder what this means for Southwest Air. The whole reason the MAX exists is because of Southwest. If southwest didn't throw their weight around and loudly announce they were considering Airbus, the MAX would likely exist in a non-737 configuration right now.
- r00fus 7y ago> If southwest didn't throw their weight around So wait, it's a customer's fault that the supplier cheated the regulations?