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Comment by asynchronous13 | Hacker News Reader

> This software wasn't even a critical feature.

There are two crashes directly related to this feature. So, it doesn't make sense to claim it wasn't critical.

In Boeing's own hazard analysis, they rated the feature "Hazardous", which is the second most critical rating. Obviously, it should have been rated "Catastrophic". But even with their own policy, anything rated hazardous is not allowed to have single-sensor failure. By their own policy, this should have had at least two sensors. There were multiple failures that let this slip through to production.

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Sorry, I meant to write crucial (similar word, quite a different meaning..)

I believe the reason for MCAS was because the had to lower and move the engines forward. So at lower power, the forward engines make the plane nose-heavy. When the engines are near full power, the lower engines push the nose up. Compounding the difference in handling compared to the older models.

Here's the safety bulletin Boeing issued after the first crash. Even when you know what you're looking for it's hard to spot: "runaway stabilizer". It does seem they downplayed how serious the failure is, but they couldn't know how common it could be. That raises another question: Other pilots must have experienced the runaway event, but managed to gain control. What happened to those reports?

There will be lessons learnt from these crashes, in a number of fields.

[https://theaircurrent.com/aviation-safety/boeing-nearing-737...]

> I believe the reason for MCAS was because the had to lower and move the engines forward. So at lower power, the forward engines make the plane nose-heavy. When the engines are near full power, the lower engines push the nose up. Compounding the difference in handling compared to the older models.

Wrong. If the power of the engines mattered, it'd have been an input to MCAS. Moving the engines forward changed how the nacelles created lift at high angles of attack, causing a pitch up effect from the nacelles, reducing (but not eliminating) the stick forces required to maintain the high angle of attack.

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