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Boeing Built Deadly Assumptions into 737 Max, Blind to a Late Design Change

nytimes.com

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Re: Boeing Built Deadly Assumptions into 737 Max, Blind to a Late Design Change

#141

Post by lugg »

lutorm wrote: post #120
ficklepickle wrote: post #52

This whole plane sounds like any ugly hack. They slapped very different engines on an existing airframe. Then, when it inevitability exhibited undesirable behaviour, they tried to paper over the cracks. Then they hid this information from their customers, regulatory agencies and the pilots. It makes me wonder if there are other issues with the Max that the public doesn't know about yet. I hope a thorough review of Bo…

I think this is false thinking. The 737 is by now a very well tested airframe. Yes, you change some things and there are unexpected results, but the core is sound. Starting over on a completely new design, everything has to be debugged from scratch. This reasoning reminds me of the tendency to argue "this code needs to be thrown out and rewritten from scratch" among software engineers. It's easy to see the flaws, but…

Please, no. This is not the same thing at all.

This is like taking your MySQL app and running it against MongoDB with a bunch of hacks to translate the SQL into mongo calls.

And then claiming you did all this so you could "avoid a rewrite".

Some architectural decisions are far reaching and leaky. This is not the ideal but it often is the ideal trade off. The alternative is decoupling to the nth degree resulting in a hunk of junk impossible to change that won't get off the ground.

Re: Boeing Built Deadly Assumptions into 737 Max, Blind to a Late Design Change

#142

Post by kdazzle »

> It never tested a malfunctioning sensor, according to the three officials.

That one popped out to me. Man. Lots to learn.

> Boeing continued to defend MCAS and its reliance on a single sensor after the first crash, involving Indonesia’s Lion Air.

Also...how? So many non safety critical services use a load balancer and at least a couple of servers because who can trust just one thing working perfectly all the time?

Re: Boeing Built Deadly Assumptions into 737 Max, Blind to a Late Design Change

#143

Post by jngreenlee »

lugg wrote: post #141
lutorm wrote: post #120

Earlier quoted context omitted.

I think this is false thinking. The 737 is by now a very well tested airframe. Yes, you change some things and there are unexpected results, but the core is sound. Starting over on a completely new design, everything has to be debugged from scratch. This reasoning reminds me of the tendency to argue "this code needs to be thrown out and rewritten from scratch" among software engineers. It's easy to see the flaws, but…

Please, no. This is not the same thing at all. This is like taking your MySQL app and running it against MongoDB with a bunch of hacks to translate the SQL into mongo calls. And then claiming you did all this so you could "avoid a rewrite". Some architectural decisions are far reaching and leaky. This is not the ideal but it often is the ideal trade off. The alternative is decoupling to the nth degree resulting in a…

I dont think its corelous (is that a word?). It's not really a lift and shift to new platform.

However the analogy to "rewrite all this" politics is good I think. Often you could walk into a building and say "all this needs to go" but truely the costs of doing so and starting from scratch are hidden in code and engineering design that's survived a trial period.

No matter how nice and neat everything might look, that's only because it doesn't yet account for 10,000 other edge cases you're not able to simultaneously consider...a system as complex as a commercial plane is still going to care about these.

Re: Boeing Built Deadly Assumptions into 737 Max, Blind to a Late Design Change

#144

Post by jngreenlee »

WalterBright wrote: post #123
nopzor wrote: post #104

Earlier quoted context omitted.

the airplane did not have stable flight characteristics because of its physical design. that’s a hardware problem. MCAS only exists because of that hardware problem. the fact that boeing also did not train or tell pilots about MCAS, in order to make the airplane more financially appealing by retaining the 737 type rating, is a separate (also bad) issue.

All jetliners are unstable at altitude in cruise, and require augmentation. https://en.wikipedia.org/wiki/Yaw_damper Aircraft design is a giant bag of compromises between desirable characteristics, most which are in conflict with each other.

Best-stated comment so far. We seem to forget that this whole problem exists in an edge domain only.

Re: Boeing Built Deadly Assumptions into 737 Max, Blind to a Late Design Change

#145

Post by Merad »

2Ccltvcm wrote: post #63
aivisol wrote: post #2

Is this only me, or all this one-vs-two AoA sensor talk seems some kind of diversion from the real problem with this plane. I mean, if one-sensor based MCAS failed twice so early in the life span of the plane model, what is the probability that a two-sensor model will fail pretty soon as well? The math should be simple, we have all data needed: combined hours flown by all planes of the type and number of failures (at…

I want to know why the Boeing flight computer needs pitot tube input at all. Modern ublox GPSes can easily obtain 3D lock on multiple satellite constellations within a minute of booting. Several of these in parallel for redundancy if you are paranoid. Flight controllers on fixed wings don't even need a magnetometer to stabilize. Just GPS path heading. If all else fails, solid state accelerometers are very reliable. A…

Unless you limit yourself to flying very near the ground and very near sea level, the speed of an aircraft is more complex than a single number. In fact four different speed numbers are commonly used: indicated airspeed, calibrated airspeed, true airspeed, and ground speed.

* IAS is the raw airspeed reading from the pitot tube.

* CAS is IAS corrected for instrument errors, e.g. if the plane is at an angle that disrupts air flow around the pitot tube.

* TAS is basically CAS adjusted for altitude and air pressure. It’s the aircraft’s speed relative to the air around it.

* Ground speed (or speed over the ground) is TAS adjusted for the wind. This is the number that GPS is going to give you.

IAS and CAS are particularly important for describing performance characteristics - if an aircraft stalls at 100 knots CAS, then it always stalls at that CAS. If you try to describe the stall speed in terms of TAS you go from a single data point to a graph of speed and altitude.

Re: Boeing Built Deadly Assumptions into 737 Max, Blind to a Late Design Change

#146

Post by brucemoose »

Brakenshire wrote: post #75
ficklepickle wrote: post #52

This whole plane sounds like any ugly hack. They slapped very different engines on an existing airframe. Then, when it inevitability exhibited undesirable behaviour, they tried to paper over the cracks. Then they hid this information from their customers, regulatory agencies and the pilots. It makes me wonder if there are other issues with the Max that the public doesn't know about yet. I hope a thorough review of Bo…

> This whole plane sounds like any ugly hack. They slapped very different engines on an existing airframe. Then, when it inevitability exhibited undesirable behaviour, they tried to paper over the cracks. Then they hid this information from their customers, regulatory agencies and the pilots. Don’t forget, the system they used to paper over the cracks had a single point of failure.

*One of the systems that we are aware of

Re: Boeing Built Deadly Assumptions into 737 Max, Blind to a Late Design Change

#147

Post by uptownfunk »

Whatever it's worth, this whole thing has traumatized me so much it makes me fearful of flying at all. But one thing's for sure, if I have any say, I'll probably never fly a 737 MAX again.

I'm sure there are many people who will do the same. In fact, every flight I do go on now, I check to make sure it is not a MAX.

I doubt there will be enough people who think this way that it would cause a problem economically for any airlines that carry this line, and I'm sure with time, people will forget, but I sure as hell will do my best not to.

Re: Boeing Built Deadly Assumptions into 737 Max, Blind to a Late Design Change

#148

Post by tomglynch »

I posted this as a comment the other day in another Boeing and MCAS discussion.

In my research into the topic the saddest bit of information I've seen is the image of the black box data for the flight (the first crash): https://i.imgur.com/WJuhjlO.png You can see from the graph that in the final minutes and seconds, the pilot put insane amounts of force on the control column (aka the yoke) to try to pull the plane out of the dive - to save the 189 people on board. But no, MCAS was overpowering and lacked the documentation for the pilot to try anything else.

Also interesting to see is the amount of times the pilots bring the nose up, only for MCAS to kick in and force the nose back down. 26 times.

All data from this Seattle Times article, which was written before the second crash occurred: [1] https://www.seattletimes.com/business/boeing-aerospace/black...

Re: Boeing Built Deadly Assumptions into 737 Max, Blind to a Late Design Change

#149

Post by ulfw »

WalterBright wrote: post #123
nopzor wrote: post #104

Earlier quoted context omitted.

the airplane did not have stable flight characteristics because of its physical design. that’s a hardware problem. MCAS only exists because of that hardware problem. the fact that boeing also did not train or tell pilots about MCAS, in order to make the airplane more financially appealing by retaining the 737 type rating, is a separate (also bad) issue.

All jetliners are unstable at altitude in cruise, and require augmentation. https://en.wikipedia.org/wiki/Yaw_damper Aircraft design is a giant bag of compromises between desirable characteristics, most which are in conflict with each other.

an INOP yaw damper doesn’t cause a hull loss crash

Re: Boeing Built Deadly Assumptions into 737 Max, Blind to a Late Design Change

#150

Post by ulfw »

danols wrote: post #103
ilaksh wrote: post #98

Earlier quoted context omitted.

I agree. I think the FAA failed in it's mission also.

Their credibility outside the US is shattered. Their word & opinion caries zero weight anymore since they have proven themselves to be morally corrupt.

They have outsourced certification (their job!) to the manufacturer (Boeing) since the 787. My confidence in that plane thus isn’t sky high either.
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