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Lack of redundancies on Boeing 737 MAX baffles some involved in developing it

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Re: Lack of redundancies on Boeing 737 MAX baffles some involved in developing it

#121

Post by Xixi »

sixothree wrote: post #118
crocal wrote: post #61

I am a designer and implementor of vital speed and distance measurement systems, with triply modular redundancy, used in mass transit application. I cannot even imagine what the designers of this thing are going through now. It must be terrible. To make it worse, it's a confusing topic. There are two pillars to the design of such system. 1. Faulty sensor must be detected with a very high probability. The typical way…

Are AOA sensors really so prone to failure that they caused the downing of two airplanes?

Like all sensors out there in the atmosphere, icing is an issue. So not only are they error prone, but failures are sometimes not independent. Airbus planes from the A320 family have three such sensors, but it so happened that on November 5th, 2014, an A321 had two sensors freeze in the wrong position during flight. Two sensors against one win, so the flight envelope protection system kicked in and the aircraft started to nose dive. It lost 4000 feet in altitude before the crew regained control...

Details of the flight if you want to do some research: Lufthansa Airbus A321-200, registration D-AIDP, performing flight LH-1829 from Bilbao, SP (Spain) to Munich (Germany) on November 5th, 2014.

Re: Lack of redundancies on Boeing 737 MAX baffles some involved in developing it

#122

Post by ams6110 »

sixothree wrote: post #118
crocal wrote: post #61

I am a designer and implementor of vital speed and distance measurement systems, with triply modular redundancy, used in mass transit application. I cannot even imagine what the designers of this thing are going through now. It must be terrible. To make it worse, it's a confusing topic. There are two pillars to the design of such system. 1. Faulty sensor must be detected with a very high probability. The typical way…

Are AOA sensors really so prone to failure that they caused the downing of two airplanes?

Normally no, from what I have read they are very reliable. And the sensors are the same ones used on all 737s. So it seems that there is some other problem with the MAX that is leading to the a false "nose high" indication.

Re: Lack of redundancies on Boeing 737 MAX baffles some involved in developing it

#123

Post by hbarka »

crocal wrote: post #61

I am a designer and implementor of vital speed and distance measurement systems, with triply modular redundancy, used in mass transit application. I cannot even imagine what the designers of this thing are going through now. It must be terrible. To make it worse, it's a confusing topic. There are two pillars to the design of such system. 1. Faulty sensor must be detected with a very high probability. The typical way…

I enjoyed your comment because I’m particularly interested in Tesla’s Autopilot system and your mention of “graceful degradation and clean handover” sounds like it should apply to driving autonomy levels as well.

Re: Lack of redundancies on Boeing 737 MAX baffles some involved in developing it

#124

Post by ams6110 »

sollibro wrote: post #13
argd678 wrote: post #4

Earlier quoted context omitted.

It does seem like a primitive system to use the wind for AoA, seems like there should be better and more reliable ways to determine it. Update: AoA not AoT

Is there another method to measure wind direction, that doesn't involve a small physical winglet?

It can be derived using static ports that measure air pressure at several locations.

Re: Lack of redundancies on Boeing 737 MAX baffles some involved in developing it

#125

Post by ams6110 »

cm2187 wrote: post #51
netsharc wrote: post #49

Earlier quoted context omitted.

> the next gen aircrafts would only require a single person in the cockpit, and everything will be handled through automations. Hasn't that myth been around for years, along with "Planes can take off and land by themselves?" https://www.askthepilot.com/questionanswers/automation-myths...

He may be right for the state of what has actually been wired up in today’s cockpits, but conceptually I don’t see why you couldn’t fully automate a plane. Even in emergency situations, pilots are required to follow established procedures and check lists, not become creative. The pilot mentions the example of an aborted take off, I can’t think of any reason an auto pilot wouldn’t be able to perform one. And of course…

Combinatorial complextity. It's impossible to foresee every possible combination of failures. There are checklists for the ones that can be foreseen (and these have often been written in the blood of those who discovered them) and maybe in theory most of those could be automated. But they cannot be exhaustive. So when all else fails, you rely on human intelligence guided by experience and training as the last line of defense. It doesn't always work, but until we have an AI that performs better, it's the best option we have.

Re: Lack of redundancies on Boeing 737 MAX baffles some involved in developing it

#126

Post by AceyMan »

bdonlan wrote: post #47
AareyBaba wrote: post #32

Earlier quoted context omitted.

I am puzzled by the apparent lack of a "this plane is heading straight into the ground" sensor that should have overridden the MCAS.

The MCAS is designed to prevent an aerodynamic stall; a situation where the plane is pointed too far up and as a result starts heading straight for the ground. It does do by detecting the plane pointing too far up, and pushing it back down. If it did not function when the plane was descending rapidly it would not be fit for its designed purpose.

> The MCAS is designed to prevent an aerodynamic stall [...]

This has become a trope and is flatly incorrect.

MCAS was cooked up to maintain the handling characteristics required by the certification specifications.

The standard requires stick resistance to increase as the critical (stall) angle of attack is approached. The MAX violated that requirement due to the aerodynamics of the new engine cowls, so MCAS was Boeing's (?crap) implementation of "artificial feel" to meet the spec.

Yes, while the spec exists presumably to prevent the pilots from themselves taking the ship into a stall, MCAS doesn't change wing or aircraft performance in a material way that would be meant by "prevent a stall."

Re: Lack of redundancies on Boeing 737 MAX baffles some involved in developing it

#127

Post by AceyMan »

ncallaway wrote: post #120
Cacti wrote: post #113

Earlier quoted context omitted.

My understanding is that the recovery scenario wasn’t supposed to be complicated at all, because in the event of a MCAS failure, it would always manifest as a runaway trim scenario, and that pilots are trained heavily on recognizing as correcting for that scenario, and that by following the standard runaway trim solution/checklist/process that this would necessarily involve disabling MCAS whether the pilots were awar…

One significant problem as I understand it was the assumption that a failing MCAS would present as runaway stabilizer trim. When, in actuality, it may not have looked much like runaway stabilizer trim to the pilots. My understanding is in a runaway stabilizer trim situation the trim wheel (a medium sized wheel near the pilot and co-pilots knees) spins continuously and makes a loud clacking noise as part of the spinni…

NB. It seems this moment news is breaking that the Ethiopia pilots indeed followed the checklist — yet they still lost the airplane.

This is getting worse for Boeing at every turn.

Re: Lack of redundancies on Boeing 737 MAX baffles some involved in developing it

#128

Post by [deleted] »

hbarka wrote: post #123
crocal wrote: post #61

I am a designer and implementor of vital speed and distance measurement systems, with triply modular redundancy, used in mass transit application. I cannot even imagine what the designers of this thing are going through now. It must be terrible. To make it worse, it's a confusing topic. There are two pillars to the design of such system. 1. Faulty sensor must be detected with a very high probability. The typical way…

I enjoyed your comment because I’m particularly interested in Tesla’s Autopilot system and your mention of “graceful degradation and clean handover” sounds like it should apply to driving autonomy levels as well.

[deleted]

Re: Lack of redundancies on Boeing 737 MAX baffles some involved in developing it

#129

Post by cjbprime »

HlessClaudesman wrote: post #90
cjbprime wrote: post #84

Earlier quoted context omitted.

For what it's worth, "take a punt on" means "avoid dealing with", which sounds like the opposite of your intent.

I was more going for the "make a general guess / bet" kind of meaning, which is how the phrase is used today in England / Australia / New Zealand. https://english.stackexchange.com/questions/20742/why-did-th... Thanks for the heads up tho, I will retire it from my rhetorical toolkit in favor of something more universally understood.

Oh, thanks for the info! Rare to see a phrase with antonymic regional differences ("I'll try it / I won't try it") survive in today's globalized world etc etc.

Re: Lack of redundancies on Boeing 737 MAX baffles some involved in developing it

#130

Post by [deleted] »

hbarka wrote: post #123
crocal wrote: post #61

I am a designer and implementor of vital speed and distance measurement systems, with triply modular redundancy, used in mass transit application. I cannot even imagine what the designers of this thing are going through now. It must be terrible. To make it worse, it's a confusing topic. There are two pillars to the design of such system. 1. Faulty sensor must be detected with a very high probability. The typical way…

I enjoyed your comment because I’m particularly interested in Tesla’s Autopilot system and your mention of “graceful degradation and clean handover” sounds like it should apply to driving autonomy levels as well.

[deleted]
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