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Preliminary conclusion MCAS misfired in Ethiopian's 737 max crash

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Re: Preliminary conclusion MCAS misfired in Ethiopian's 737 max crash

#91

Post by wp381640 »

tomnm wrote: post #74

Physics cannot be fixed by software. The necessity of MCAS means the airframe has fatal flaws. I would avoid 737 Max by all means, no matter whatever software revisions Boeing releases. Previous discussions: https://news.ycombinator.com/item?id=19509618

most modern fighter jets would drop out of the sky like a rock without software

they'll eventually get this right - they just need to step back and recognise that the MAX is a completely new type of aircraft and stop taking shortcuts on certification and training

what saves them is that Airbus is at production capacity on the neo

Re: Preliminary conclusion MCAS misfired in Ethiopian's 737 max crash

#92

Post by just_steve_h »

Here's the design decision that puzzles me the most: MCAS commands nose-down trim. The pilot uses the trim button on the yoke to command nose-up trim. Why isn't that enough to disable MCAS and cause an audible alert?

Think of an analogy: when the autopilot commands a nose-down elevator input, and the pilot pulls back on the control column, that's enough to disengage the autopilot.

Or think of cruise control in a car: if the computer commands acceleration, and the driver steps on the brake, cruise control disengages.

The necessity of MCAS is to meet regulatory requirements for similarity in handling characteristics to achieve a common type rating. It's not strictly an engineering requirement, nor is it a safety-assisting technology. It's an attempt to mask the actual aerodynamic characteristics of the aircraft being flown. That is a conflicting mission if you will.

Re: Preliminary conclusion MCAS misfired in Ethiopian's 737 max crash

#93

Post by fooqux »

tomnm wrote: post #74

Physics cannot be fixed by software. The necessity of MCAS means the airframe has fatal flaws. I would avoid 737 Max by all means, no matter whatever software revisions Boeing releases. Previous discussions: https://news.ycombinator.com/item?id=19509618

You realize that many modern aircraft are all fly-by-wire, right?

Re: Preliminary conclusion MCAS misfired in Ethiopian's 737 max crash

#94

Post by wp381640 »

bunderbunder wrote: post #82
saiya-jin wrote: post #61

Earlier quoted context omitted.

If those victims would be primarily from western country, especially US, there would be almost immediate class action lawsuit against Boeing from families (US citizens seem more trigger-happy to fire lawsuits when feeling wronged, at least from my perspective). But I guess Ethiopian/Indonesian cries for some sort of compensation/justice would have to go very viral in western media to force a corporation like Boeing i…

Most countries don't have such a thing as class action, and even among the countries that have it, it's only commonly used in the one that invented the idea, and multi-national class action isn't really a thing. So I think you'd find that, far from "especially in the US," you should only expect a class action lawsuit like that for a flight that is either to or from (or both) a US airport. With lots of of passengers o…

First Ethiopia lawsuit was filed today in Chicago

MH370 was a multi-national class-action lawsuit filed in SC that was only dismissed because the circumstances of the disappearance were not clear and nothing to do with it being multi-national

https://www.documentcloud.org/documents/3512628-16319045179....

With the Lion Air crash the settlements the Indonesian government had passengers sign included waiving any right to sue Boeing in the USA

https://www.nytimes.com/2019/03/21/world/asia/lion-air-crash...

The fault being with Boeing in this case seems a lot more clear-cut

Re: Preliminary conclusion MCAS misfired in Ethiopian's 737 max crash

#95

Post by bobowzki »

wp381640 wrote: post #91
tomnm wrote: post #74

Physics cannot be fixed by software. The necessity of MCAS means the airframe has fatal flaws. I would avoid 737 Max by all means, no matter whatever software revisions Boeing releases. Previous discussions: https://news.ycombinator.com/item?id=19509618

most modern fighter jets would drop out of the sky like a rock without software they'll eventually get this right - they just need to step back and recognise that the MAX is a completely new type of aircraft and stop taking shortcuts on certification and training what saves them is that Airbus is at production capacity on the neo

While it's true that fighter jets have been aerodynamically unstable for decades, they're not built for transportation and have ejection seats.

The main reason they are unstable is to increase agility. Is this necessary or even wanted in passenger aviation? I don't know but I'd guess not. Probably safety, comfort and fuel economy are far more important and can (should?) be achieved with a stable airframe.

Re: Preliminary conclusion MCAS misfired in Ethiopian's 737 max crash

#96

Post by wp381640 »

just_steve_h wrote: post #92

Here's the design decision that puzzles me the most: MCAS commands nose-down trim. The pilot uses the trim button on the yoke to command nose-up trim. Why isn't that enough to disable MCAS and cause an audible alert? Think of an analogy: when the autopilot commands a nose-down elevator input, and the pilot pulls back on the control column, that's enough to disengage the autopilot. Or think of cruise control in a car:…

> Why isn't that enough to disable MCAS

From what I understand it did but it would reengage again. It's the reason why the Lion Air flight lasted longer in the air than Ethiopian, because the pilots in that case kept hitting the trim and buying themselves 40-60 seconds each time

Re: Preliminary conclusion MCAS misfired in Ethiopian's 737 max crash

#97

Post by petschge »

fooqux wrote: post #93
tomnm wrote: post #74

Physics cannot be fixed by software. The necessity of MCAS means the airframe has fatal flaws. I would avoid 737 Max by all means, no matter whatever software revisions Boeing releases. Previous discussions: https://news.ycombinator.com/item?id=19509618

You realize that many modern aircraft are all fly-by-wire, right?

Fly-by-wire does not necessarily imply that there is software interfering. You can have a very linear system that just translates yoke input into control surface deflection, but uses software and cables instead of hydraulic lines.

Re: Preliminary conclusion MCAS misfired in Ethiopian's 737 max crash

#98

Post by wp381640 »

bobowzki wrote: post #95
wp381640 wrote: post #91

Earlier quoted context omitted.

most modern fighter jets would drop out of the sky like a rock without software they'll eventually get this right - they just need to step back and recognise that the MAX is a completely new type of aircraft and stop taking shortcuts on certification and training what saves them is that Airbus is at production capacity on the neo

While it's true that fighter jets have been aerodynamically unstable for decades, they're not built for transportation and have ejection seats. The main reason they are unstable is to increase agility. Is this necessary or even wanted in passenger aviation? I don't know but I'd guess not. Probably safety, comfort and fuel economy are far more important and can (should?) be achieved with a stable airframe.

fighter jets are the more extreme and established example, it also applies to most modern airliners which have software systems in place to prevent human controls from exceeding the aircraft flight envelope

fuel efficiency in these modern aircraft has been gained with swept back wings, larger intake engines etc. which with direct control and no software would be almost impossible to keep flying

discarding all of these systems because of a problem with one would set airline safety and efficiency back decades

Re: Preliminary conclusion MCAS misfired in Ethiopian's 737 max crash

#99

Post by MockObject »

phkahler wrote: post #28
zaxomi wrote: post #22

Earlier quoted context omitted.

No, it is not unstable without MCAS. MCAS is only designed to change the trim if the airplane is hand flown in flaps-retracted, low-speed, nose-up flight. This is something almost everyone is missing: A normal flight should not encounter this.

>> This is something almost everyone is missing: A normal flight should not encounter this. Nobody said there was anything abnormal about the two flights that crashed. It really doesn't matter since the root problem is the plane doing things without telling anyone and then doing it wrongly. Without MCAS these accidents would not have happened.

> Without MCAS these accidents would not have happened.

Without MCAS, wouldn't there be accidents caused by the nonlinear pitch though?

Re: Preliminary conclusion MCAS misfired in Ethiopian's 737 max crash

#100

Post by peeters »

Svip wrote: post #19
isolli wrote: post #13

Earlier quoted context omitted.

Related question: how does regulatory approval of planes work, worldwide? I read a few times that the FAA had approved the new plane too quickly, but don't other regulators have their word?

FAA have (or had) such a good record, that other regulators, like EASA, simply trusted a FAA certification. In the same way, FAA trusts an EASA certification for an Airbus plane.

Bilateral certification agreements. Canada and U.S. have one as well (it goes both ways): https://www.tc.gc.ca/eng/civilaviation/standards/int-baa-usa.... It's good in theory (cutting down on a giant amount of repeat work), as long as both certifying bodies maintain their standards and don't get politicized.
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