7 ms·

That's not really what happened here. If you know what's going on, MCAS is quite safe - there are two highly visible switches that kill electric trim completel

• CodeSheikh 8y ago
  Because Boeing refused to provide them additional training that was needed to make these decisions. Boeing wanted to sell it as an add-on package. And the basic mandatory training they provided was on an iPad instead of simulator.
  • village-idiot 8y ago
    You’ve got it confused. Boeing did not want to sell the training as an add on package, they didn’t want more training at all. This reduces the cost to purchase the 737 Max, because existing 737 pilots can fly the max without recertification. What was sold as an add on was the system to detect the two AoA indicators disagreeing. This would help, but it probably would have been less effective than MCAS training would have been. Better still would have MCAS read both sensors and disengage when they disagree, with an alarm.
• GiorgioG 8y ago
  > MCAS is quite safe A few hundred people who died as a result of MCAS would disagree. MCAS is not safe as currently implemented, or the 737 Max would still be flying.
  • admax88q 8y ago
    MACS is safe but its not zero delta training as Boeing advertised. Pilots who were trained on it properly are able to recognize the problem and fix it when it occurs.
    • jfk13 8y ago
      A problem of such potential severity should not be happening with anywhere remotely like the frequency we've seen.
      • admax88q 8y ago
        I think you'd be surprised how often small problems can occur on planes. They all have _potentially_ huge severity, but none of them have huge consequences because they are expected problems that pilots are trained to respond to.
    • bekman 8y ago
      If it’s needed to be fixed then it’s not safe.
    • drcross 8y ago
      MCAS is safe in its current implementation like nuclear power is safe- it works well when you know exactly what you're doing at all times.
      • CydeWeys 8y ago
        I disagree; modern nuclear power is way safer, and is a result of decades of continuous improvement. MCAS on the other hand is basically a bad hack that was necessary for business reasons. It's a serious step backwards in safety from previous iterations, which has not happened with modern nukes.
        • theluketaylor 8y ago
          I'd say MCAS is a predictable business hack that resulted from terrible regulatory pressure. Airplane certification is expensive for both manufacturer and airlines that might want to fly it. So there is a quicker process if you just make minor revisions, a reasonable compromise on the surface. Certification is so expensive and not having to retrain pilots is such a huge selling feature it creates a pressure to make planes that meet the same type requirements rather than design new airframes. Boeing is all set to design a new airframe to replace the 737 that will be more fuel efficient and be built for today's point to point flights. Along comes airbus with the a320neo (new engine option) that kills the 737-800 on fuel efficiency and Boeing panics. They scrap 2020 plans for a 737 replacement and design the MAX. Now the problems mount. Fuel efficiency needs turbines that spin slower but have more surface area and are therefore larger. 737 is a low slung plane, dating back to hub and spoke flight concepts where the 737 might land places that don't have jetways. Since the plane is so close to the ground, Boeing has to move the engines forward so they can raise them. This generates more lift than previous 737s, but to meet same type requirements the plan has to be the same. Not meeting same type means they can't sell to airlines like southwest who only fly a single type and any airlines who do commit will have to spend training dollars, raising the total cost of operation without adding anything to the bill of materials. Enter MCAS, a system designed to meet the same type regulation with disastrous unintended side effects. Side effects made much worse by the fact pilots don't know the system even exists since this plane is the same as every other 737 as far as they know. I don't think the same type regulation should be scrapped since it would stop things like fuel efficiency gains during an airframe's lifespan, but there needs to be a same type minimum training and documentation that has to be done even if the only thing you change is thickness of the paint. If anything the definition of what meets same type should be slightly expanded allowing more flexibility in what can be changed. Combined with mandatory training for all subtypes (but still much shorter than different type training) the perverse incentive to make the plane behave exactly the same is removed. That leaves room for the better technical fix to win the day rather than the one that will meet the regulation. Training costs will go up some, but less than full different type certification.
• raverbashing 8y ago
  > one has to question why the pilots did not take this simple corrective action. If that was the only issue, the plane would have not been grounded. But it seems here on HN there's this persistent idea that it's just fine for the plane to start misbehaving and it's "only" a matter of the pilots fixing it. Sure, why not, let's all run a cronjob that gets a random number, then beeps and wipes your computer every 1/100 times. But hey, it will beep and you'll have 1 second to fix it, sounds good, right? This attitude killed 300 people
  • salawat 8y ago
    That is nominally the purpose of a pilot. To safely operate the machine within the envelope for which it is engineered. There is always a trade-off with these types of decisions, and like it or not, every airframe certified airworthy has the potential to kill everyone on board without proper piloting. I'm not saying that I'm letting Boeing off the hook personally, but as someone who has an avid interest in engineering things, I do understand the optimization points they were going for with the MAX, they found a physical design that could accommodate those optimizations, but they skimped or didn't put enough emphasis on communicating changes to pilots. The pilots are the single most versatile safety system on the plane. Hiding or keeping from them the information they would need to form a checklist to handle this type of failure is the major failing here (given we assume there were no other physical configurations that could have been grandfathered in that wouldn't have involved an MCAS like system for certification). The root cause of that omission though may be traced to the minimal retraining requirement, which was absurd in the first place.
• linuxftw 8y ago
  How many aircraft that we know had an MCAS malfunction are currently not destroyed from a crash? 0. So far, aircraft with malfunctioning MCAS has resulted in 100% loss of aircraft.
  • ams6110 8y ago
    Wrong, the flight preceeding the Lion Air crash had the same issue, and the pilots managed it, by switching off the stab trim system as per the runaway trim checklist.
    • deleted 8y ago
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    • linuxftw 8y ago
      You'll note I said 'aircraft' versus 'flight'. That particular aircraft is no longer in service because it was destroyed in a catastrophic crash caused directly by the faulty MCAS system. At first, everyone asserted it was 'faulty sensor reading,' but later it came out that there's also faulty programming and the MCAS system has way more authority than originally specified to the FAA.
      • ams6110 8y ago
        And the pilots mismanaged it.
        • birdiesanders 8y ago
          Because they were provided with zero additional training on the "unseen" MCAS system.
          • ams6110 8y ago
            They had training on runaway trim. All they needed to do was follow the memory items.
• phire 8y ago
  While the same checklist fixes both runaway trim and faulty MCAS, pilots haven't been trained to recognize MCAS problems. The two problems present themselves differently enough that it's confusing pilots (runaway trim is continuous trim movement. MCAS is 5 seconds on, 10 second off). This is a systematic training issue. Pilots have been trained to recognize runaway trim but not faulty MCAS. The only real solution is extensive simulator training until pilots reliably diagnose MCAS activations and start the correct checklist, something which Boeing and airlines don't want to pay for.
• msbarnett 8y ago
  > If you know what's going on, MCAS is quite safe - there are two highly visible switches that kill electric trim completely (thus disengaging MCAS) and allow the pilots to take manual control. Activating these switches is a memory item (i.e. pilots have to memorize the checklist) for runaway trim and would be universal across 737 variants. > Unfortunately, it appears that both the Lion Air pilots and the Ethiopian Airlines pilots did not recognize that this was a runaway trim issue at all (or until it was too late). If the Ethiopian Airlines disaster turns out to have an identical cause to the Lion Air crash, one has to question why the pilots did not take this simple corrective action. Not quite: While the runaway trim checklist is a memory item, the symptoms that pilots train on in simulator presents runaway trim as a continuous event (the "classic" runaway trim being a relay becomes stuck and the trim just extends continuously). So while they've trained on the correct response to save the plane, they've never actually been exposed to the symptoms that an "MCAS runaway" presents (stick shaker on the AOA too steep side when the plane is patently not in stall combined with speed warnings and an uncommanded nose-down that goes away for several seconds when the stick is pulled back). The "backs off" part is critical when combined with the speed warning alerts and lack of continuous trim, because this makes the nose down easy to interpret as coming from the 737's speed trim system, which has existed for decades, and the net result is that the combination of symptoms seems to overload/confuse the pilots. We have, now, at least 3 documented examples of "MCAS runaway" -- the two downed flights, and the prior Lion Air flight in which a deadheading pilot in the jump seat did suggest to cut the automatic trim, but ONLY AFTER several minutes of confusion in the cockpit. And even after disabling it, they re-enabled the auto trim initially and only re-cut it out when symptoms re-occured. Which all boils down to: The MCAS system is in no way "quite safe". Safety is not a single line of defence, and the fact that at least 3 sets of pilots have struggled to identify the correct response to the MCAS issue indicates that the design of the system is flawed, because no system is safe when its sole and only fallback relies on humans 100% providing the correct response to a never-before-seen set of symptoms.
  • cal5k 8y ago
    I understand, that's why I mentioned that the pilots didn't recognize that it was a runaway trim issue. After the Lion Air crash, however, this information was widely disseminated by the manufacturer. If the Ethiopian Airlines pilots were not properly trained on this new scenario then there was clearly a breakdown somewhere in the chain of communication.
• cmurf 8y ago
  >MCAS is quite safe FAA emergency airworthiness directive 2018-23-51 [1] We are issuing this AD because we evaluated all the relevant information and determined the unsafe condition described previously And what it describes previously is MCAS when receiving erroneous AOA sensor input. Also, your post basically says MCAS is safe when disabled, because in the very same sentence you claim it's safe you also claim the pilots are supposed to know how to (indirectly) disable it. That's almost comedy. >why the pilots did not take this simple corrective action It's a valid question why they didn't take corrective action; it's insulting and asinine editorializing to call it simple. [1] http://rgl.faa.gov/Regulatory_and_Guidance_Library/rgad.nsf/AOCADSearch/83EC7F95F3E5BFBD8625833E0070A070?OpenDocument http://rgl.faa.gov/Regulatory_and_Guidance_Library/rgad.nsf/...
• deleted 8y ago
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• jarym 8y ago
  Looking at one component and saying it’s safe (qualified with ‘if you know what’s going on’) misses the point. In fact it’s an engineering style response because it shows some myopia. Safety in an aircraft means getting passengers to their destination without injury or loss of life. Boeing failed here - blame lack of training, single sensor dependence or software if you like but there was certainly a failure. Now no one really cares if MCAS is problematic - any solution needs to resolve the underlying fault.
  • salawat 8y ago
    The underlying fault unfortunately isn't 100% a Boeing problem. There are airworthyness regulations that specify how a passenger plane is to behave near stall that have had a precedent set where non-compliance can be remedied through flight envelope driven interlocks. (See stick-pushers and other piloting aids). Engineeringwise, the airframe was still not compliant; the airframe would still manifest aberrant behavior, but the action on the controls combined with a type certified pilot was considered enough to mitigate the problematic aerodynamics. This practice, fortunately or unfortunately depending on who you ask, effectively normalized deviance, and short-circuited the protection offered by that airworthyness regulation. It went from being clearly spelled out to "or equivalent level of safety" which opens the door to all sorts of workarounds. The alpha vanes need to be a high-priority maintenance item. They may also need to be redesigned/augmented such that they can be hardened against typical failure states, or subjected to in-flight remediation/diagnostics and graceful failover. That isn't easy from my understanding. Doing something like hardening vs. freezing would require some form of heating element, which would potentially effect the calibration of the sensor while active, and increase maintenance complexity. Adding some sort of self contained calibration unit to the sensor could work too, however, the more complexity built into that, the more costly it becomes. There is a point of diminishing returns, and I do think the plane can be rendered safe with MCAS and pilot retraining. Unfortunately, that will still come bundled with an aircraft losing its airworthyness rating on Stab Trim cutout.
• inferiorhuman 8y ago
  If you know what's going on, MCAS is quite safe No, it's not, and most of the regulatory agencies around the world agree. Pilots that Boeing handpicked to test out MCAS fixes (and thus knew what it was, what to do, and expected a problem) agree. And that whole runaway stab trim checklist is a red herring especially after Boeing has come out and said MCAS is a part of STS — itself a system that trims the stabilizer in a counterintuitive manner on the NG. The stabilizer operates in a counterintuitive manner on the NG and MCAS runaway doesn't meet Boeing's definition of runaway trim. Full. Stop. https://www.nytimes.com/2019/03/25/business/boeing-simulation-error.html https://www.nytimes.com/2019/03/25/business/boeing-simulatio... Here's a relevant quote: Those involved in the testing hadn’t fully understood just how powerful the system was until they flew the plane on a 737 Max simulator, according to the two people.
• weaksauce 8y ago
  They had 40 seconds to avert the accident from what I read. the memory items for runaway trim take about 1 minute in a relatively calm simulator with a professional 37 pilot to get to that point where they flip the switch[0]. They still had an incorrectly trimmed aircraft when they got to that point. also of note was that the pilots in the sim were at 3000' AGL where the other ones that crashed were at about 1000' AGL. 0. https://youtu.be/xixM_cwSLcQ?t=1016 https://youtu.be/xixM_cwSLcQ?t=1016
  • maimeowmeow 8y ago
    To be frank, they shouldved went faster then. Emergency situation is no time to fool around. One of them was praying. Imagine if both people were trying at the same time. They could have finished two steps at a time.
    • weaksauce 8y ago
      Well, to be frank back, the steps are sequential not parallel. I haven't read anything about the CVR but if they were praying instead of flying that's a huge mistake. They didn't have much time though and they didn't have much altitude to work with(in fact, I just looked it up and they were 450' AGL when they started having some troubles but I couldn't find anything on the cvr transcript). the old adage of aviate, navigate, communicate in that order applies.