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

seattletimes.com

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

#41

Post by nutjob2 »

ptidhomme wrote: post #40

What I fail to understand is why do they not design an overriding scheme to MCAS, such as an "above-threshold" pull on the stick by the pilot. I can recall that this was a classic design by Boeing. Whatever the number of AoA sensors, the system should be easy and straightforward to disable. Those logics of "let's guess automatically if that sensor is failing" are just pushing the problem further. The real problem is…

The problem isn't too much reliance on automatic systems, it's that the systems are a half baked combination of the two.

The MCAS system is an example of that. As you say that overriding design is typical in Boeing planes, but MCAS purposefully overrides it, that is, pushing the controls hard, which overrides other automatic functions, has no effect on MCAS.

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

#42

Post by nutjob2 »

hairytrog wrote: post #26

The only way to be 100% safe and 100% fool proof is to not fly. For a mechanical system as complex as an airplane, triple redundancy with a good pilot is pretty much the best you can hope for.

A plane can still fall out of the sky and kill you.

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

#43

Post by 4sak3n »

4sak3n wrote: post #29

"Two is one and one is none." That's pretty much been aeronautical gospel since dinosaurs strapped cardboard to their stubby arms and dreamed of soaring.

To elaborate, I'm pointing out that redundancy has been an integral part of aeronautical engineering for ages so to ignore it in any situation, never mind in one where the pilots are kept out of the decision making loop, is criminally negligent.

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

#44

Post by ishan1121 »

ptidhomme wrote: post #40

What I fail to understand is why do they not design an overriding scheme to MCAS, such as an "above-threshold" pull on the stick by the pilot. I can recall that this was a classic design by Boeing. Whatever the number of AoA sensors, the system should be easy and straightforward to disable. Those logics of "let's guess automatically if that sensor is failing" are just pushing the problem further. The real problem is…

The airline manufacturers have to push for automatic systems as they are the one of the features that sells.

One of a close friend of mine who works at Airbus said that the company believes the next gen aircrafts would only require a single person in the cockpit, and everything will be handled through automations.

Airbus aircrafts are more automated than Boeing. If Boeing does not work on the automation part, it could loose to Airbus. Airbus faced AoA problem back in 2009, when Quantas flight suddenly dropped from the air. But they were able to patch it up within a month and no reported case has come up since then.

So I believe Boeing working on Automation is a good thing, and they should be able to fix it up.

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

#45

Post by ptidhomme »

nutjob2 wrote: post #41
ptidhomme wrote: post #40

What I fail to understand is why do they not design an overriding scheme to MCAS, such as an "above-threshold" pull on the stick by the pilot. I can recall that this was a classic design by Boeing. Whatever the number of AoA sensors, the system should be easy and straightforward to disable. Those logics of "let's guess automatically if that sensor is failing" are just pushing the problem further. The real problem is…

The problem isn't too much reliance on automatic systems, it's that the systems are a half baked combination of the two. The MCAS system is an example of that. As you say that overriding design is typical in Boeing planes, but MCAS purposefully overrides it, that is, pushing the controls hard, which overrides other automatic functions, has no effect on MCAS.

I'd say this is why they are half-baked : human integration was not thouroughly thought of in the design. When I speak of overriding, I mean human overriding.

This is something I think Boeing had got right with its manual overrides : when you design critical systems, you need human backup schemes, but you can go further and make these backup tightly integrated with the rest of the (highly automated) system.

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

#46

Post by jacquesm »

leggomylibro wrote: post #10
js2 wrote: post #2

Despite the headline, the article ends with: That triple-sensor system isn’t foolproof, however. In 2008, on a customer-acceptance flight of an Airbus A320, two of the angle-of-attack sensors froze and those two sensors then outvoted the third. When the pilots went to demonstrate the stall-prevention system, they were not aware of the malfunctioning sensors. The plane crashed, killing the seven people on board. The s…

Triple-redundancy isn't 100% foolproof, but it is a lot better than two potentially-faulty sensors. I know this isn't a great example, but triple redundancy is enough of a design cornerstone that Arthur C. Clarke made it one of the defining features of Rendezvous With Rama , a classic sci-fi story about an Oumuamua-like object that people manage to land on: >It was now strikingly apparent that the "city", like so muc…

That's science fiction, not science. Clarke used three to push your brain past our sense of left/right symmetry not because of some idea related to redundancy.

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

#47

Post by bdonlan »

AareyBaba wrote: post #32
cletus wrote: post #20

Earlier quoted context omitted.

Yep, 3 sensors can fail too. Less often however. These sensors exist to solve a problem with the MAX design. Changing and moving the engines increased the likelihood of a stall when the engines could push the nose up (as I understand it). Fine. But here's the kicker: this should be something that pilots should be trained on. They should be aware of how the MAX is different to the previous 737s and know what to do to…

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.

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

#48

Post by WalterBright »

Haga wrote: post #39
WalterBright wrote: post #18

Earlier quoted context omitted.

I once had a discussion with a scifi author about how to design a starship to last a long time. I suggested that it being repairable would be of paramount importance. To that end, the various systems should use interchangeable parts. Starting with the obvious like nuts&bolts should be standardized, extend that to things like computer boards and components, motors, etc. For example, if you had a linux machine running…

I had a similar discussion once, and the result was very biology cells inspired. Any subsystem must be able to repair itself, and must state its defunct state on repair needed state. If that times out the subsystem must destroy itself "deactivation". Dependant on importance other subsystems must pick up the load and create a replacement under strain over time. In a plane, the aoa could be replaced by sensor fusion of…

The difference with a plane, however, is it isn't necessary to fix it. It's just necessary to get it on the ground safely.

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

#49

Post by netsharc »

ishan1121 wrote: post #44
ptidhomme wrote: post #40

What I fail to understand is why do they not design an overriding scheme to MCAS, such as an "above-threshold" pull on the stick by the pilot. I can recall that this was a classic design by Boeing. Whatever the number of AoA sensors, the system should be easy and straightforward to disable. Those logics of "let's guess automatically if that sensor is failing" are just pushing the problem further. The real problem is…

The airline manufacturers have to push for automatic systems as they are the one of the features that sells. One of a close friend of mine who works at Airbus said that the company believes the next gen aircrafts would only require a single person in the cockpit, and everything will be handled through automations. Airbus aircrafts are more automated than Boeing. If Boeing does not work on the automation part, it coul…

> 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...

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

#50

Post by j16sdiz »

ptidhomme wrote: post #40

What I fail to understand is why do they not design an overriding scheme to MCAS, such as an "above-threshold" pull on the stick by the pilot. I can recall that this was a classic design by Boeing. Whatever the number of AoA sensors, the system should be easy and straightforward to disable. Those logics of "let's guess automatically if that sensor is failing" are just pushing the problem further. The real problem is…

New overriding scheme means more training. The selling point of 737MAX is any 737 pilot can fly on it without new training.
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