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Maybe someone can illuminate this. This comment seems to say that Boeing has recently implemented a bunch of fixes to prevent MCAS from activating in various s

Maybe someone can illuminate this. This comment seems to say that Boeing has recently implemented a bunch of fixes to prevent MCAS from activating in various scenarios, which allegedly make MCAS safety a non-issue: https://philip.greenspun.com/blog/2019/04/08/boeing-737-max-crash-and-the-rejection-of-ridiculous-data/#comment-325105 https://philip.greenspun.com/blog/2019/04/08/boeing-737-max-... I'm not knowledgeable on planes, but some parts of this make me wonder if these fixes will cause the opposite problem. For example if the two sensors disagree then MCAS now won't activate. How long until a crash happens because of that new behaviour? Either MCAS is necessary safety equipment, in which case this sounds dangerous, or it isn't, in which case why bother?

Zak 8y ago
> Either MCAS is necessary safety equipment, in which case this sounds dangerous, or it isn't, in which case why bother? The situation is more subtle than that. A simple analogy is that MCAS is like ABS on a car. ABS is not required to drive a car safely and does not activate during normal driving. ABS activating when it should not can cause a crash. Likewise, the intended scenario in which MCAS activates is abnormal and requires a combination of conditions that are unlikely without several errors in judgement by the pilot. There's another layer though: it's possible to get the 737 MAX into a situation where the standard stall recovery for other 737s, which starts with lowering the nose using the elevator is insufficient. Instead, both the trim and the elevator are required; MCAS does the trim part automatically.
salawat 8y ago
You are correct. The rather humorous aspect is that they really can't stick to the "no retraining" claim or really the claim the plane is airworthy because the plane is only certifiably airworthy when MCAS is operating. So in short, yes. Their fix is introducing problems elsewhere. This characteristic is what has many thinking their was a series of grievous process, business, and regulatory errors layered on top of the known poor engineering decisions that came together to set the stage for these catastrophes.

Zak 8y ago

> Either MCAS is necessary safety equipment, in which case this sounds dangerous, or it isn't, in which case why bother? The situation is more subtle than that. A simple analogy is that MCAS is like ABS on a car. ABS is not required to drive a car safely and does not activate during normal driving. ABS activating when it should not can cause a crash. Likewise, the intended scenario in which MCAS activates is abnormal and requires a combination of conditions that are unlikely without several errors in judgement by the pilot. There's another layer though: it's possible to get the 737 MAX into a situation where the standard stall recovery for other 737s, which starts with lowering the nose using the elevator is insufficient. Instead, both the trim and the elevator are required; MCAS does the trim part automatically.

salawat 8y ago

You are correct. The rather humorous aspect is that they really can't stick to the "no retraining" claim or really the claim the plane is airworthy because the plane is only certifiably airworthy when MCAS is operating. So in short, yes. Their fix is introducing problems elsewhere. This characteristic is what has many thinking their was a series of grievous process, business, and regulatory errors layered on top of the known poor engineering decisions that came together to set the stage for these catastrophes.