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"Instead of relying on a single sensor indicating the angle of the plane’s nose, MCAS will rely on data from both of the plane’s sensors" Why wouldn't you desi
by mysterydip 8y ago
"Instead of relying on a single sensor indicating the angle of the plane’s nose, MCAS will rely on data from both of the plane’s sensors"
Why wouldn't you design it that way from the beginning? This isn't Boeing's first plane.
- kristofferR 8y agoThey did, but the redundancy was a premium add-on feature.
- Moru 8y agoNo, the extra sensor was add-on feature. It still wasn't redundant for the MCAS, just an indicator for the pilots.
- kristofferR 8y agoWow, that's even worse...
- mhandley 8y agoAll 737s have two AoA sensors - they're used for several purposes, not just MCAS. Originally MCAS used only one of the two sensors, though it alternated which one with each flight. The optional features were an AoA disagree indicator, and the AoA data itself being displayed on the cockpit displays. Having either optional feature didn't change the fact that MCAS only used one sensor.
- mhandley 8y agoBecause if you did that, you'd have to alert the pilots when the AoA sensors disagree and MCAS has been disabled. And you can't do that without training them on what that means, notably how the plane will now fly differently with what you might call "relaxed stability" at high angles of attack. And Boeing really really wanted to avoid retraining of pilots because apparently they had a contract with SouthWest that would cost then $1M per plane if retraining was required.
- isolli 8y agoRelated question: how does regulatory approval of planes work, worldwide? I read a few times that the FAA had approved the new plane too quickly, but don't other regulators have their word?
- Svip 8y agoFAA have (or had) such a good record, that other regulators, like EASA, simply trusted a FAA certification. In the same way, FAA trusts an EASA certification for an Airbus plane.
- peeters 8y agoBilateral certification agreements. Canada and U.S. have one as well (it goes both ways): https://www.tc.gc.ca/eng/civilaviation/standards/int-baa-usa-2000-3676.htm https://www.tc.gc.ca/eng/civilaviation/standards/int-baa-usa.... It's good in theory (cutting down on a giant amount of repeat work), as long as both certifying bodies maintain their standards and don't get politicized.
- SilasX 8y agoWell, they're working hard to change that, I guess...
- ricardobeat 8y agoNot only that, but apparently they also delegated most of the certification duties to Boeing itself.
- theelous3 8y agoBuy toilet duck.
- VBprogrammer 8y agoIt's worth noting that there are other more engineering reasons it could be tricky to use both. An aircraft in a side slip will show different reading on the left and right sensors. Also, there are failures which are likely to impact both at much the same time, icing being a big one.
- sergiosgc 8y agoWorse. Why don't they do it with three sensors and a voting system? By using two sensors, when they disagree, MCAS will have to be disabled. It seems the plane is unstable without MCAS, due to the forward positioning of the engines, requiring specific training and abilities from pilots.
- deleted 8y ago[deleted]
- zaxomi 8y agoNo, it is not unstable without MCAS. MCAS is only designed to change the trim if the airplane is hand flown in flaps-retracted, low-speed, nose-up flight. This is something almost everyone is missing: A normal flight should not encounter this.
- acqq 8y agoThe way you describe it the faulty sensor would have not caused two crashes. If the code would check all these preconditions it would still ignore the AoA sensor. It’s obvious that the code was executed during the regular flight conditions which means it has to be applied even then. The motors simply push the plane nose up too much compared to the previous models, threating the plane to enter the stall. Once in the stall the plane is just not controllable. MCAS was there to hide that. And now that the problem is known to the world either will Boeing provide the proper solution, no matter the cost, or there will be a third crash and that will be too much. Boring still tries to present all that as “business as usual.” It’s wrong.
- phkahler 8y ago>> This is something almost everyone is missing: A normal flight should not encounter this. Nobody said there was anything abnormal about the two flights that crashed. It really doesn't matter since the root problem is the plane doing things without telling anyone and then doing it wrongly. Without MCAS these accidents would not have happened.
- 8y ago
- upofadown 8y agoIt brings up the question of what it means for the two sensors to disagree. How much do they have to disagree? For how long? How many times? The atmosphere is full of weird effects that can transiently make the two sensors be different. How much and for how long do you get to disable the MCAS system until you can't claim it as a protection? If you can disable it whenever things get strange then why have it at all? There is a tendency to fixate on the bug that caused a crash to the extent that you introduce new more new bugs than you had before.
- linuxftw 8y ago> There is a tendency to fixate on the bug that caused a crash to the extent that you introduce new more new bugs than you had before. Exactly this. It can't be both required for safe flight and disabled at a moments notice during the most dangerous portion of a flight (takeoff).
- tzs 8y agoI think the sensors are on the side of the nose, about as far forward as the pilots. It looks like one is on the left and one is on the right. These things are essentially just wind vanes that read the direction that the air is moving past them. Short of the plane flying obliquely into a tornado, I can't think of any atmospheric effect that could lead to a disagreement. You'd need an atmospheric effect that causes a significant difference in wind direction between two points that are maybe 3 m apart and the difference that atmospheric effect is trying to cause would have to be noticeable when superimposed on the wind vector due to the plane's velocity.
- ptero 8y agoIt is possible that it was clear from the start that this is the right way to go, but a modern plane is a very complex and highly regulated piece of equipment. Even minor changes could have a long tail of ramifications for operation (some of those have been noted, such as likely very different performance when crabbing at crosswinds). I am not saying that Boeing did not try to cut corners (I just do not know), but the current media circus painting Boeing as a bunch of [idiot engineers | greedy execs | lazy testers] is likely far from reality or at least a major oversimplification. Boeing planes (including 737 max) are still very safe (compare to cars). Mistakes should be calmly assessed and fixed and making a public circus of this simply pushes engineers to avoid everything but uber-conservative, uber-safe solutions, which has major costs in itself. My 2c.
- CaptainZapp 8y agoWhat I think they're absolutely and criminally guilty of is to not ground the plane after the first crash. Instead they wasted time and resources to smear the airline and the pilots. And that's inexcusable.
- ams6110 8y agoSo any time there's a crash now, we're going to ground the worldwide fleet of that model of aircraft until we have a final report on the cause?
- CaptainZapp 8y agoIf it happens to a brand new plane? I'd say: Yes; that's reasonable. At least until the cause is known. Edit : Some clarification
- ams6110 8y agoCause is always complicated in an air crash. We don't officially know the cause of either of these crashes. When MCAS was established to be a likely factor in the first crash, Boeing issued an emergency airworthiness directive to all operators of the 737 Max, alerting pilots to the possibility of undesired nose down trim, and reminding them that the runaway trim procedure would disable it.