patrickjp93
Posts: 425
Joined: Thu Aug 22, 2019 12:00 pm

Re: Why are they still medling with MCAS, and not looking for other options?

Wed Oct 09, 2019 5:50 pm

Armadillo1 wrote:
patrickjp93 wrote:

I'm using integers for simplicity


AoA 1 ---- AoA 2
8 ___________ 8
8 ___________ 8
8 ___________ 8
8 ___________ 8
8 ___________ 8
8 ___________ 4 <--- Disagreement detected, could be a fluke, such as a heavy drop of water ramming into the foil of the sensor
8 ___________ 4 <--- Disagreement continues, depending on polling rate, may still be fluke
8 ___________ 4 <--- Disagreement still continues, log as a sensor disagreement mid-flight and proceed to test
7 ___________ 4 <--- Vertical stabilizer manipulated, only one sensor changed, and in the expected direction
9 ___________ 4 <--- Vertical stabilizer manipulated, only one sensor changed, and in the expected direction, confirming AoA 2 defect. AoA 2 inputs to systems disabled
8 ___________ 4 <--- Vertical stabilizer manipulated, only one sensor changed, original flight angle restored, pilot control resumed.

And if you want the other 7 failure modes, I can go through those too.

Edits: manipulation of the spacing and underscores to get the data table to line up.

good try, but this will not work so good and simple in dynamic situation while AoA (and speed) still changing.


It will still work (it's actually failure mode 8 of 8 and the admittedly ugliest one to cover all ground on). Again, I chose integers and a single degree of freedom to make it easy to explain the first case, but here's an example where AoA is increasing, speed is increasing, and a disagree occurs. Bear in mind that without some fancy graphing tools, accounting for dilation of time in raw data would take a lengthy table, but that's still a well-understood process across multiple dimensions of change (or fitting partial derivative curves).

AoA 1 - S1 ---- AoA 2 - S2
8 _____4_________ 8_____4
9 _____5_________ 9_____5
10 ____6_________ 10_____6
11 ____7_________ 11_____7
12 ____8_________12_____8
13 ____9_________11____7 <--- Disagreement detected, could be a fluke
14 ____10_______10____6 <--- Disagreement continues, depending on polling rate, may still be fluke, but widening
15 ____11________9_____5 <--- Disagreement still continues, log as a sensor disagreement mid-flight and proceed to test
18 ____10________9_____5 <--- Vert. Stab. set for nose up, AoA1 changes more than historical record in expected direction. AoA2 stays level or falls? Suggests AoA2 fault.
15 ____11________8_____6 <--- Vert. Stab. set for nose down, AoA1 changes expectedly. AoA2 changes in expected direction but not to AoA1's magnitude.

Now, at this point it's a bit messier, because a diagnostic test for this scenario would rely on data from the last few pilot inputs, sensors on the control surfaces, engines for accurate thrust changes to gauge which AoA has proper speed readings (and can be double-checked against other sensors and satellite data), whether the vertical stabilizer has had a hardware fault, whether flaps/spoilers are deployed/extending/retracting, but there are limited sub cases in this scenario to close out the diagnostic to prove AoA 2 has had a fault and not AoA 1 with pretty much zero chance of error except in a multi-system failure, at which point the pilots need to be flying manually anyway and MCAS should just be disabled if a disagreement is detected at all.

And the software to run this diagnostic needs to be robust enough to, of course, not change pitch in the direction of danger (too high = stall, too low = crash) unless physical obstacles are incoming (like a mountain on climb suggests pitch down is a bad idea), and in that case limit scope of change to what is within half the range of safe deviation in either case.
 
patrickjp93
Posts: 425
Joined: Thu Aug 22, 2019 12:00 pm

Re: Why are they still medling with MCAS, and not looking for other options?

Wed Oct 09, 2019 6:11 pm

asdf wrote:
patrickjp93 wrote:
....The Boeing engineers right now addressing the 737 MAX MCAS' shortcomings ..... should only care that the 2.0 design meets the requirement that, in the future, 0 people die.


its pretty showing that you FIRST mentioned the requierments, and after that the "0 people die"

if one would be a psychologist he/she could tell you a whole story where your premises really are ...


They'd say I think like an engineer and am good at compartmentalizing. That zero people die is not a functional requirement. It's a non-functional requirement and really is just a side-effect of good engineering. If the functional requirements are sound and are met, no one will die. The death toll is merely a consequence of the underlying requirements of design and engineering. It is not a requirement unto itself.

To put it another way, a requirement of MCAS should be that it does not cause a plane to crash itself except in an "Act of God" scenario (let's say we're on takeoff, and suddenly the AoA sensors all suddenly are suggesting far too high a pitch and the altitude sensor is fried and claims you're at 10,000 feet instead of 200 feet. Good luck recovering. And even that you can probably put a time-based failsafe in so MCAS can't activate for at least the first 5-10 minutes of flight.). If that requirement is met, no one dies because of MCAS. Boeing's engineering effectively does not and should not care about the lives on board, because for the plane to keep bringing Boeing revenue, it needs to have as long a service life as possible, require as few repairs as possible, and give the best fuel consumption performance in-class.

To meet the public's "wish" of zero deaths by crash merely requires meeting good functional requirements that, at the end of the day, really have absolutely nothing to do with passengers. Death by asphyxiation is covered by pressurization (for the passengers), death by entrapment upon landing is covered by evacuation (for the passengers), and death by crash itself is covered by making sure the plane is solidly built (takes off, flies, and lands durably and easily for pilots). Passengers and human lives essentially have nothing to do with that third one.
 
Sokes
Posts: 438
Joined: Sat Mar 09, 2019 4:48 pm

Re: Why are they still medling with MCAS, and not looking for other options?

Fri Nov 15, 2019 1:08 am

patrickjp93 wrote:

Engineering is a psychopathic field, but only to those people too attached to their emotions to stick to the facts.


A neurosurgeon will have people dying under his scalpel weekly. Empathy would prevent him from functioning properly.
Ask somebody with anxiety disorder if he/ she considers engineering to be a psychopathic field.
One could however argue that not grounding the Max after the first crash indicates that management is a psychopathic field.
Why can't the world be a little bit more autistic?

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