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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

#161

Post by quink »

CydeWeys wrote: post #81
Causality1 wrote: post #57

Earlier quoted context omitted.

Indeed. The article makes it sound like a foul-up late in the design process, but this plane was corrupt from the very beginning when Boeing set out to dodge the requirement for re-certifying the airframe.

The FAA needs to grow a pair and declare this type certification and all other certifications older than ~30 years EOLed. That doesn't mean you can't continue operating those planes, it just means you can't retrofit some changes onto a deeply legacy model and still call it the same type.

Say what now? It sounds like you want the FAA to revoke the A320 type certificate?

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

#162

Post by deanCommie »

LoSboccacc wrote: post #158
GoToRO wrote: post #118

Earlier quoted context omitted.

engineers overseeing this work There the thing: nobody wants to pay engineers on par with managers. Maybe one can not manage something he/she can not understand.

> There the thing: nobody wants to pay engineers on par with managers I used to think like that but I learned in time that the core issue is that engineers rarely know how to present their job in terms of monetary benefit during salary negotiations. i.e. as an automation engineer I led an initiative that saved a previous employer more than 60k€ yearly using automation and optimizing other validation workflows. as pri…

I assume these must be small examples on a long list of accomplishments, because 30k/year doesn't seem like it's enough to offset your salary. I have to imagine the impact of a principal engineer should be measured in the 10-100x of their salary?

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

#163

Post by WalterBright »

ulfw wrote: post #149
WalterBright wrote: post #123

Earlier quoted context omitted.

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

It has:

https://en.wikipedia.org/wiki/Dutch_roll#Accidents

http://code7700.com/accident_kc-135r_63-8877.htm

http://www.failure-interactions.com/boeing---19-oct-1959.htm...

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

#164

Post by burfog »

nopzor wrote: post #130
cmurf wrote: post #114

Earlier quoted context omitted.

Citation needed. FAR 25 applies to all transport category aircraft. The section on stability (§§ 25.171 - 25.181). In exactly what manner is the airplane not stable, with or without MCAS?

i haven’t looked at the fars in quite a few years, but i’m pretty sure there would be stuff in there that references stuff like pitch stability (which is how i’d define the “hardware problem”), is that not the case? i’m afk atm. i still maintain my macro point, either way. making the airframe on a pax airliner aerodynamically stable during normal takeoff and landing operations seems like basic “good engineering” to m…

I'm not so sure that it is good engineering to be inherently stable during normal takeoff and landing operations.

Modern fighter planes are inherently unstable because this is required for better maneuverability. Passenger planes can certainly benefit from that too.

Consider gusty crosswinds during a landing. With an inherently unstable aircraft, there is greater capability to compensate. You can have a computer stabilize the plane, preventing the tail or wing tips from striking the ground. When wake turbulence threatens to flip the plane or when a microburst threatens to pound the aircraft into the ground, a fast response is possible. Stability would deaden the performance of the needed response.

The extreme example is probably wings that are low-mounted anhedral and forward-swept, with the bending controlled by rapidly actuated aerodynamic surfaces near the tips.

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

#165

Post by zenzen »

djsumdog wrote: post #76
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…

The sad thing is that we'll probably see this plane fly again by the end of the year, because the millions of dollars in retrofits will still be cheaper than having to scrap all existing planes. We have no idea what other potentially lethal corners have been cut. What if they go back into service, after several months of retrofitting all of them at Boeing maintenance hangers, and then the following year there are two…

I had forgotten about the rudder problems! Worth a read: https://imgur.com/a/5wcFx8M

> Perhaps the single most complex, insidious, and long-lasting mechanical problem in the history of commercial aviation was the mysterious rudder issue that plagued the Boeing 737 throughout the 1990s. Although it had long been rumoured to exist, the defect was suddenly thrust into the spotlight when United Airlines flight 585 crashed on approach to Colorado Springs on the third of March, 1991, killing all 25 people on board. The crash resulted in the longest investigation in NTSB history, years of arduous litigation, and a battle with Boeing over the safety of its most popular plane.

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

#166

Post by spockz »

bowmessage wrote: post #159
tomglynch wrote: post #148

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 ou…

Interesting that there are two angle of attack sensor readings in the black box image when the major issue with MCAS seems to be that it was relying on only a single sensor?

MCAS use(s/d) one sensor at a time, rotating which one is used.

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

#167

Post by cmurf »

inferiorhuman wrote: post #152
cmurf wrote: post #114

Earlier quoted context omitted.

Citation needed. FAR 25 applies to all transport category aircraft. The section on stability (§§ 25.171 - 25.181). In exactly what manner is the airplane not stable, with or without MCAS?

From TFA But a few weeks later, Mr. Wilson and his co-pilot began noticing that something was off, according to a person with direct knowledge of the flights. The Max wasn’t handling well when nearing stalls at low speeds.

Insufficient. Stability requirements in FARs are clear, and not handling well might mean "substantially different from prior 737s" not unstable.

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

#168

Post by darkpuma »

phkahler wrote: post #42
mikeash wrote: post #24

Earlier quoted context omitted.

Airspeed is required for safe flight. The failure on that flight was detected immediately, it just couldn’t be handled. AoA on a 737 MAX is not required for safe flight and the system just needs to refrain from taking any action if it fails.

But MCAS was added because the plane doesn't handle well in some situations.

It handles fine, except it doesn't handle like a Classic/NG 737. This is a problem because pilots were trained to expect it to handle like a Classic/NG. The discrepancy between reality and pilot expectations is the gap MCAS was meant to fill, such that it wasn't necessary to correct pilot expectations.

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

#169

Post by burfog »

2Ccltvcm wrote: post #68
mnw21cam wrote: post #67

Earlier quoted context omitted.

If all you are using is ground-based position/speed, then you are ignoring the very real possibility that the air you are flying through is not stationary relative to the ground. In actual fact, especially at high altitudes, the air can be moving very fast, and the difference between ground speed and airspeed can be the difference between flying and stalling. Also, your GPS measurements give you position, direction,…

Can a near-stall condition be detected solely with some combination of GPS, accelerometer, and barometer?

You'll need the air speed and direction.

Normally, speed is from a tube aimed into the air. Normally, direction is from a little fin that can spin.

There are lots of alternatives:

Direction can be via multiple tubes aimed into the air, each with slightly different direction.

Speed can be from a hot wire. Weather stations sometimes use this.

You can get both via lidar. You just need to make it sensitive enough to pick up a response from minute particles of dust or ice.

I think I just invented a new way: do a short-duration high-power pulse of an electron source or an EUV laser, causing the air to fluoresce at enough distance from the aircraft to be clear of the boundary layer. Track the motion of the fluorescing air with multiple cameras.

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

#170

Post by darkpuma »

mikeash wrote: post #4
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…

The problem isn’t failure, but detecting failure. If the sensor had just stopped responding, there wouldn’t have been any problem. The planes would keep flying, the sensors would get replaced, and everyone would be fine. What happened was that the sensor gave erroneous readings. The MCAS system reacted to those erroneous reading and crashes the plane. With two sensors, you can detect failure. It’s very unlikely that…

> " it’s very unlikely that both would provide the same erroneous readings. "

You're assuming that faulty sensors will tend to have random output. But since we're talking about a real life mechanism, it seems likely it has some erroneous states that are more likely to occur than others. For instance if the mechanism often fails up against one of it's mechanical limits, the sensor might erroneously read out the limit position every time.

You can't actually say anything about the distribution of failure states for a sensor without evaluating that particular sensor.

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