Boeing Built Deadly Assumptions into 737 Max, Blind to a Late Design Change

Re:Boeing Built Deadly Assumptions into 737 Max, Blind to a ... by na85 on Saturday June 01, 2019 @08:22PM (#20072653)

>the airplane did not have stable flight characteristics because of its physical design.

This is a gross oversimplification of the problem. In most of the flight envelope the aircraft is stable.

At high alpha the aircraft has pitch problems.

There are myriad ways to address this, and MCAS was one (bad) choice of many available to Boeing.

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Re:Boeing Built Deadly Assumptions into 737 Max, Blind to a ... by leoc on Saturday June 01, 2019 @08:42PM (#20072731)

That's the devilish thing, I think. Making the plane unstable then patching things up with MCAS, or something else, isn't a fault in any straightforward way. But it is taking a risk, and the source of risk isn't simply the risk that eg. MCAS will fail on any given flight, it's also the higher-order risk that eg. the MCAS system will have a faulty design. (A bit like rewriting code in C for performance, or keeping on generally unloved code to satisfy a paying customer, presumably.) I assume that makes the ethical and safety decisions a lot more murky for the engineers than having a specific fault to point to, especially in an organisation afflicted with go fever.

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Re:Boeing Built Deadly Assumptions into 737 Max, Blind to a ... by sokoloff on Saturday June 01, 2019 @08:43PM (#20072735)

I believe the airplane is aerodynamically stable even at high alpha. What it fails in certification is the requirement to have continually increasing pitch feedback forces. I believe the pitch feedback forces are still in the stable region, just too low. This is not a flying wing or intentionally unstable airplane (as the F-16).

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Re:Boeing Built Deadly Assumptions into 737 Max, Blind to a ... by inferiorhuman on Saturday June 01, 2019 @09:27PM (#20072892)

I believe the airplane is aerodynamically stable even at high alpha.

That would put you at odds with Boeing's test pilots.

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Re:Boeing Built Deadly Assumptions into 737 Max, Blind to a ... by sokoloff on Sunday June 02, 2019 @04:27AM (#20074222)

No it wouldn't (or "citation needed" if so).

The issue is not that the airplane shows negative or neutral aerodynamic pitch stability, it's that it does not exhibit an increasing stick force gradient, as required by certification rules.

https://airfactsjournal.com/2019/03/can-boeing-trust-pilots/

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Re:Boeing Built Deadly Assumptions into 737 Max, Blind to a ... by leoc on Saturday June 01, 2019 @08:53PM (#20072772)

>> [...] In most of the flight envelope the aircraft is stable.

>> At high alpha the aircraft has pitch problems.

> I believe the airplane is aerodynamically stable even at high alpha. [...] This is not a flying wing or intentionally unstable airplane (as the F-16).

In some ways that's likely worse news than an airplane that's inherently unstable in general, no? A corner case, and one that evidently isn't actually all that uncommon. If you're building something like an F-16 you know that you absolutely have to make the fly-by-wire correct and robust, and the ground crews similarly know that if anything affects its performance the plane isn't fit to fly.

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