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Comment by MaupitiBlue | Hacker News Reader

I'm sorry, but what does squeezing jobs have to do with:

1. Drive MCAS with only one AOA sensor.

2. Don't tell MCAS to look for (or even think about) bad AOA data or AOA disagreements.

3. Equip airplane with two AOA sensors as usual, but make the AOA disagree warning light a "value added option" that customers have to pay extra for.

4. Don't actually bother to tell pilots that they don't have AOA disagree warning lights.

5. Don't bother to tell pilots that MCAS exists at all.

6. Don't test MCAS subsystem to see what it actually does with bad AOA data.

7. Give MCAS a ridiculous amount of control authority, operating cumulatively over repeated applications to exceed what the pilot can manually override.

8. Change how the trib stab switch has been wired since 1966 and not tell pilots.

How any engineering team let this through is unfathomable. Don't blame the MBAs or the unions. Didn't these guys get the lecture about the Hyatt?

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In broad terms, I think the intent of the article is to point out the potential for quality to suffer when duties are outsourced, in part because an organization relinquishes some level of process control as a trade off to save money.

The same argument could be extended to the FAA oversight functions being “outsourced” to Boeing which may have had a direct impact on all those items you listed

You missed the big one that even made MCAS necessary:

0. Reposition the engine forward on the wing such that the airframe is inherently unstable and needs software for stabilization.

The airframe is not unstable. It exhibits positive longitudinal aerodynamic stability. It’s positively but insufficiently stable to meet certification requirements, which is what required them to add MCAS.

MCAS is nowhere near fast enough to compensate if the Max were actually unstable.

> insufficiently stable to meet certification requirements

Sounds like unstable to me. "I am not fat, I am just insufficiently thin".

It's stable. In aerodynamics, stability has a specific meaning and it's possible for two things to be stable, and for one of those things to be less stable than the other.

Picture a pendulum that is hinged on a greased axle vs one that is hinged on a high-friction axle.

Both will reach equilibrium eventually (they're stable) but one will do it faster/with fewer oscillations.

The 737 MAX is longitudinally stable, but it doesn't meet certain nuanced requirements of the Airworthiness regs.

Seems so. More info here: https://www.quora.com/Is-the-Boeing-737-MAX-aerodynamically-...

> what happens is that the stick force lessens as angle of attack increases at high AoA and low airspeed, whereas in order to be compliant with certification it has to gradually increase with increasing AoA, just like a 737–100.

There is so much doublespeak here. If it is less stable than required for airworthiness then it is not airworthy. Can we agree on that?

Sure, but that doesn't mean it's unstable.

If it is not stable enough then it is unstable. Where do you draw the bar on stability, if not airworthiness?

>If it is not stable enough then it is unstable.

Nope, sorry, that's not what stability and instability mean.

Stability means it will return to equilibrium if disturbed, but the issue with the MAX is that it requires a positive force gradient per the Part 25 Airworthiness Regulations, which the MAX does not exhibit in a specific part of the envelope.

Stability is not a binary condition. The MAX is longitudinally stable in every part of the flight envelope.

"Not airworthy" does not equate to "unstable". Those two terms are orthogonal.

What I’ve learned from these 737 discussions: Anyone who uses the term “inherently unstable” is an armchair aerospace engineer. It’s such a vague weasely term.

Would you prefer "insufficiently stable" instead? The kinds of mistakes Boeing made are so basic that even laypersons can immediately understand it. Like not having redundant sensors.

Like fixing a hardware problem using software. See this video about the plane's tendency to pitch up at low speed and full thrust. That's "insufficiently stable"! https://www.youtube.com/watch?v=6p5sboD2oO8

Plus if I remember they didn't mention the MCAS anywhere?

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