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How Boeing, FAA certified the suspect 737 MAX flight control system

seattletimes.com

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Re: How Boeing, FAA certified the suspect 737 MAX flight control system

#81

Post by anamexis »

ajross wrote: post #65
tafda wrote: post #62

Earlier quoted context omitted.

Not true. https://www.seattletimes.com/business/boeing-aerospace/faile... Quote: The discrepancy over this number is magnified by another element in the System Safety Analysis: The limit of the system’s authority to move the tail applies each time MCAS is triggered. And it can be triggered multiple times, as it was on the Lion Air flight. One current FAA safety engineer said that every time the pilots on the Lion Air…

Yes true.[1] You're misunderstanding that quote. It's talking about "authority" in the sense of software's authorization to move the trim tab, not the aerodynamic authority of the tailplane. The 737 has a 60 year old, very conventional elevator with a trim tab. The tab changes the resting angle of the overall elevator, and thus the "center point" of tailplane force on the airframe. Being out of trim means that the ai…

A comment from a pilot citing the 737 flight manual [1] contradicts this:

"Excessive air loads on the stabilizer may require effort by both pilots to correct mis-trim. In extreme cases it may be necessary to aerodynamically relieve the air loads to allow manual trimming. Accelerate or decelerate towards the in-trim speed while attempting to trim manually."

[1] https://news.ycombinator.com/item?id=19383756

Re: How Boeing, FAA certified the suspect 737 MAX flight control system

#82

Post by stcredzero »

Numberwang wrote: post #31
stcredzero wrote: post #22

There is a big difference between how you behave when you're calm, vs how you behave when you're under stress. Basically, you start hitting sub-sentient "defaults." You default to your training. You default to inherited flight or fight behaviors. Emergency procedures and training need to be designed with this in mind, or they will fail. (Presentation preparation is like this. My last presentation failed because by se…

How would you design presentation preparation with that in mind? Or anything for that matter?

How would you design presentation preparation with that in mind?

Rehearse. Repetition strengthens associations and so increases the chance that you will fall into the same behavior.

Or anything for that matter?

Masaad Ayoob revolutionized police gunfighting techniques by simplifying movements and changing techniques to more closely resemble the natural stance people take when in the "Fight or Flight" mode.

When an airplane is diving into the ground, the natural inclination for pilots is to pull back on the stick. Making the override resemble this would be a way of following this design principle. I think the situation which caused the accident is a bit more complicated and nuanced than just that idea, however.

Re: How Boeing, FAA certified the suspect 737 MAX flight control system

#83

Post by outworlder »

ajross wrote: post #55
mimixco wrote: post #10

Notable and disturbing here is the lack of Max simulators in existence. It looks like neither Lion Air nor Ethiopian nor any US airline had access to one. Also linked in this article is the original FAA table of differences between the Max and other 737 models. It makes no metion of MCAS.

Yeah. As much blame as Boeing and the FAA certification process seems to deserve here, it's worth pointing out how much of the cascade of failures is in the airlines and cockpits too. I mean, yes, the trim system was being driven by input from a single nonredundant sensor, which is a violation of the kind of engineering for failure process that airliners should be designed in. But at the same time that trim system is…

> But at the same time that trim system is, by design, not strong enough to overpower pilot input to the other control surfaces.

That is incorrect for the 737 and many airliners. Elevator input is way less strong than trim. Trim moves the entire surface, not just the elevator control surface.

I had the same misconception, my brain was translating GA aircraft knowledge to airliners.

Re: How Boeing, FAA certified the suspect 737 MAX flight control system

#84

Post by outworlder »

pdonis wrote: post #17
saluki wrote: post #13

Earlier quoted context omitted.

y, sounds like a change like this: The system, known as the Maneuvering Characteristics Augmentation System, or MCAS, was incorporated because the plane has larger engines placed further forward on the craft, and so has a chance of facing a stall at lower speeds than earlier 737 variations. Would require more training than a few hours.

> has a chance of facing a stall at lower speeds than earlier 737 variations No, that's not the issue. The issue is that, because of the pitch up moment created by the engines, at higher angles of attack the force required to move the yoke decreases instead of increasing. That's (a) a highly undesirable characteristic since the changing feedback confuses pilots and makes it hard for them to know when a stall is immin…

Thank you. MCAS is not an anti-stall mechanism and should not be confused with one. Yes, pitch the aircraft too much and you will stall. But MCAS would allow a stall regardless, it is not its job. The job, as you point out, is to keep the aircraft handling similar to existing models.

This is not just splitting hairs. These distinctions matter.

Re: How Boeing, FAA certified the suspect 737 MAX flight control system

#85

Post by rnbrady »

mimixco wrote: post #10

Notable and disturbing here is the lack of Max simulators in existence. It looks like neither Lion Air nor Ethiopian nor any US airline had access to one. Also linked in this article is the original FAA table of differences between the Max and other 737 models. It makes no metion of MCAS.

> It makes no metion of MCAS.

27 - FLIGHT CONTROLS STABILIZER TRIM: Stab Trim cutout switches panel

Re: How Boeing, FAA certified the suspect 737 MAX flight control system

#86

Post by maxxxxx »

johnsea wrote: post #39
ineedasername wrote: post #33

Earlier quoted context omitted.

Hopefully it will also fall in part on the FAA, which greenlit the thing for use without checks that might have caught this.

And will it also fall in part on the passengers who demand cheap and cheaper air fares? (Not only to the detriment of their own safety but also to further increasing ecological debts).

You can't put this on passengers. What are they supposed to do? Pay more voluntarily in the hope that the money goes to safety and not just towards a bigger bonus for the execs?

Re: How Boeing, FAA certified the suspect 737 MAX flight control system

#87

Post by linuxftw »

ineedasername wrote: post #57
linuxftw wrote: post #44

Earlier quoted context omitted.

The free market answer would be insurance. As an individual, you probably want some kind of life insurance in the event of catastrophe. Your insurance carrier may require you only ride in such and such certified aircraft (eg, an aircraft that is insured against loss of life). An aircraft may only obtain insurance if it meets certain requirements, etc. Unfortunately, we've got a regulatory body asleep at the wheel, te…

Looking back a hundred or more years when the market was more free, your vision of how things might work does not hold. There were no insurance markets for potential injury due to riding a horse, no private certification of stables that lent horses to ensure animals were fit and free of issues of temperament that might cause them to throw a rider. The free market is not a panacea that solves every problem. It does so…

Large ships did have insurance.

> There were no insurance markets for potential injury due to riding a horse, no private certification of stables that lent horses to ensure animals were fit and free of issues of temperament that might cause them to throw a rider.

Insurance markets have appeared for all manner of things now. This argument doesn't really make any sense.

> The free market is not a panacea that solves every problem. It does solve some problems.

I haven't heard of a problem it doesn't solve yet. How much safety regulation (via insurance) would an airline industry need? I don't know, but the market would surely tell us. It may decide that more or less safety is optimal, based on market inputs. Surely there are proponents of more regulation and surely there are proponents of less regulation, how do we decide who's right?

Re: How Boeing, FAA certified the suspect 737 MAX flight control system

#88

Post by outworlder »

azernik wrote: post #8

For those who were wondering why pilots didn't override the autopilot? Turns out that just made things worse: ================================================== The discrepancy over this number is magnified by another element in the System Safety Analysis: The limit of the system’s authority to move the tail applies each time MCAS is triggered. And it can be triggered multiple times, as it was on the Lion Air flight.…

> For those who were wondering why pilots didn't override the autopilot?

MCAS only works when autopilot is OFF (and flaps retracted).

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