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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

#121

Post by yardie »

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

I wouldn't hold fighter jets up as an example of safety. They spend more time broken then they do operational. Require a an entire team of engineers for each airframe, and the number of pilot deaths/flight time is pretty atrocious. But since it's 1-2 pilot deaths rather than >100 passengers we put up with it.

A well designed aircraft should not have a single point of failure, including the software.

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

#122

Post by mhandley »

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:…

I think that would open up a different safety issue. Suppose you're in a tight turn for some reason, pulling back hard on the yoke, as you have to do in a tight turn. The aircraft is at fairly high angle of attack, but not yet quite enough to enable MCAS. You've got quite a high column load, and you blip the trim upwards to relieve it a bit. If you blip the trim just as MCAS kicks in, and it disables, then you're now flying at high AoA without MCAS protection. You've not trained for that, and your chances of an accelerated stall just went up significantly as the plane no longer flies quite like you trained.

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

#123

Post by Rooster61 »

VBprogrammer wrote: post #118
Rooster61 wrote: post #111

Earlier quoted context omitted.

> Theoretically they could have flown indefinitely while they debugged the problem. Not true. From what I have read, MCAS runs in 10 second intervals, with the amount of trim added increasing with each successive run. Once the trim has reached a certain point, it over-powers the amount of control the pilot has by putting pressure on the yoke (this controls elevators, which have less overall influence on the aircraft…

The pilot can run the trim in the other direction using the normal switches on the yoke. You can see that if you look at the trim position graph in the Lion Air accident. For some reason before the crash the pattern of repeatedly correcting changes, possibly because he handed control to the first officer.

"The undated EASA certification document, available online, was issued in February 2016, an agency spokesman said.

It specifically noted that at speeds greater than 230 knots (265mph, 425kph) with flaps retracted, pilots might have to use the wheel in the cockpit’s center console rather than an electric thumb switch on the control yoke. "

So, yes and no. It gives SOME control over the trim, but if the trim keeps getting bumpped progressively higher by the MCAS, it will eventually outstrip the yoke control.

My guess is that that change you mentioned is the threshold at which their yoke trim control became insufficient.

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

#124

Post by linuxftw »

salawat wrote: post #103
MockObject wrote: post #99

Earlier quoted context omitted.

> Without MCAS these accidents would not have happened. Without MCAS, wouldn't there be accidents caused by the nonlinear pitch though?

No, because the air frame would not have been certified for airworthyness.

That's my understanding. So a simple 'oh we'll just disable it if the readings disagree' seems like a faulty fix. MCAS is required for safe flight. While it may be possible to operate a Max 800 successfully without it, that's not how it was designed to be flown.

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

#125

Post by linuxftw »

upofadown wrote: post #30
mysterydip wrote: post #3

"Instead of relying on a single sensor indicating the angle of the plane’s nose, MCAS will rely on data from both of the plane’s sensors" Why wouldn't you design it that way from the beginning? This isn't Boeing's first plane.

It brings up the question of what it means for the two sensors to disagree. How much do they have to disagree? For how long? How many times? The atmosphere is full of weird effects that can transiently make the two sensors be different. How much and for how long do you get to disable the MCAS system until you can't claim it as a protection? If you can disable it whenever things get strange then why have it at all? Th…

> There is a tendency to fixate on the bug that caused a crash to the extent that you introduce new more new bugs than you had before.

Exactly this. It can't be both required for safe flight and disabled at a moments notice during the most dangerous portion of a flight (takeoff).

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

#126

Post by cmurf »

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:…

Pilot pulling back on the control column does not disengage the autopilot; pilot changing throttle lever settings doesn't disengage the autothrottle. And also, these things can have different behaviors in different modes (or laws, referring to airplane computer control not legal), which vary from make and model of aircraft hence part of the reason for type ratings.

The problem with articles thus far: there's a lot of confusion whether MCAS exists to meet a FAR 25 requirement (aircraft airworthiness for transport category aircraft)[1], or FAR 61 requirement (pilot certification and ratings)[2].

I still don't know the answer to that, but either way it seems problematic to have an ostensibly required function that can be disabled and either have an instantly decertified (not airworthy) airplane, or an instantly decertified (not type rated) pilot, or both.

[1] There's are many behavioral requirements in FAR 25, I'm cherry picking two:

§ 25.203 Stall characteristics. (my emphasis on paragraph a.)

https://www.law.cornell.edu/cfr/text/14/25.203

§ 25.173 Static longitudinal stability. (my emphasis on paragraph c. and d.)

https://www.law.cornell.edu/cfr/text/14/25.173

[2] The pilot must have a type rating, 61.31 a(3) for aircraft the FAA says must have a type certificate

https://www.law.cornell.edu/cfr/text/14/61.31

which then points to this section which has all kinds of ins and outs

https://www.law.cornell.edu/cfr/text/14/part-21/subpart-B

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

#127

Post by rubinelli »

Rooster61 wrote: post #116
rubinelli wrote: post #113

Earlier quoted context omitted.

I wish there was a law to nationalize a company that was found guilty of gross negligence, to subsequently pay damages and re-sell them in the market. Make shareholders accountable, instead of sending a couple of middle managers to jail and keeping the same incentives that caused the first tragedy in place.

> instead of sending a couple of middle managers to jail So you want to turn the company over to the same governmental body that lets companies get off by firing a few middle managers? The same body that possibly allowed this lapse in safety to get through regulations in the first place?

Temporarily, yes. It doesn't have to be the same government agency, and the aim would be to divest as fast as possible, so hopefully less short-sighted and more responsible shareholders would control it in the end.

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

#128

Post by VBprogrammer »

Rooster61 wrote: post #123
VBprogrammer wrote: post #118

Earlier quoted context omitted.

The pilot can run the trim in the other direction using the normal switches on the yoke. You can see that if you look at the trim position graph in the Lion Air accident. For some reason before the crash the pattern of repeatedly correcting changes, possibly because he handed control to the first officer.

"The undated EASA certification document, available online, was issued in February 2016, an agency spokesman said. It specifically noted that at speeds greater than 230 knots (265mph, 425kph) with flaps retracted, pilots might have to use the wheel in the cockpit’s center console rather than an electric thumb switch on the control yoke. " So, yes and no. It gives SOME control over the trim, but if the trim keeps gett…

This appears to be a reference to https://www.easa.europa.eu/sites/default/files/dfu/IM.A.120%... issue 10.

They are saying there that near Vmo (maximum operating speed) with an aft centre of gravity (the aircraft loaded in a specific way) there might not be enough nose down trim authority available within the limits of the electric trim to completely trim the aircraft (allow the pilot to relax the forward pressure on the yoke).

In the crashes there was too much nose down trim and MCAS kept adding it more. They are trying to move it in the other direction.

Pants reporting but nothing to see here.

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

#129

Post by dingaling »

bredren wrote: post #43
yg6ht5 wrote: post #39

Earlier quoted context omitted.

$1M sounds like pocket change after all that has happened.

Market cap loss since crash of flight 303 is $27 billion. https://ycharts.com/companies/BA/market_cap

None of which matters to Boeing as an entity. Market cap is not liquidity.

Outstanding Max order backlog is $600 billion at list price. That is what matters.

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

#130

Post by tzs »

upofadown wrote: post #30
mysterydip wrote: post #3

"Instead of relying on a single sensor indicating the angle of the plane’s nose, MCAS will rely on data from both of the plane’s sensors" Why wouldn't you design it that way from the beginning? This isn't Boeing's first plane.

It brings up the question of what it means for the two sensors to disagree. How much do they have to disagree? For how long? How many times? The atmosphere is full of weird effects that can transiently make the two sensors be different. How much and for how long do you get to disable the MCAS system until you can't claim it as a protection? If you can disable it whenever things get strange then why have it at all? Th…

I think the sensors are on the side of the nose, about as far forward as the pilots. It looks like one is on the left and one is on the right.

These things are essentially just wind vanes that read the direction that the air is moving past them.

Short of the plane flying obliquely into a tornado, I can't think of any atmospheric effect that could lead to a disagreement.

You'd need an atmospheric effect that causes a significant difference in wind direction between two points that are maybe 3 m apart and the difference that atmospheric effect is trying to cause would have to be noticeable when superimposed on the wind vector due to the plane's velocity.

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