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

nytimes.com

191–200 of 280 posts

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

#191
post #149

Earlier quoted context omitted.

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...

Fun fact. The original 737 actually had two yaw dampeners because they expected it to have diverging yaw stability. Just by chance the airframe is actually positively stable so can operate safely with no yaw dampeners so one was removed.

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

#192
post #138
post #106

Earlier quoted context omitted.

it’s reputation has been destroyed in the international aviation community. which is extremely sad because it was really hard won. classic story of gutting a gov organization, and regulatory capture. i know some really good people at faa and the situ makes their blood boil. mine too.

I haven't seen commentary from international pilots who are worried about flying Boeing planes. Even with the two MAX planes that went down, fatal crashes are enormously rare (for Airbus/Boeing/CRJs/ERJs). This one is only getting so much attention because it was that extraordinarily rare "design defect" rather than a maintenance issue or pilot issue.

Now better?

> https://www.thedailybeast.com/pilots-complained-to-feds-abou...

More specifically, the complaints reportedly referenced issues pertaining to a takeoff “autopilot system” and situations where the plane is “nose-down” while trying to gain altitude. One pilot reportedly wrote that it was “unconscionable” that Boeing and federal authorities allowed pilots to fly the planes without fully describing how the 737 Max 8 was different than other planes. “The fact that this airplane requires such jury-rigging to fly is a red flag,” the same pilot wrote.

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

#193
post #43
post #27

I really see this as a failure of the Systems Engineering process. With so many people unaware of the impacts of the changes, it’s up to the systems types to have the big picture view and make sure these sorts of things are taken into account. Especially if as the article says a failure of the AOA sensor on the system would be Hazardous (looks like it was Catastrophic when paired with MCAS in retrospect), that would…

Thinking about this a little more, I also see a failure here in terms of naming things, which I have noticed in my career can be scoffed at but is so important. As the article says, the function of MCAS changed and its operational envelope was greatly expanded. What if, internally at least, the new system was referred to as MCAS2? This is somewhere that things can get political, as was exactly the case with the Max,…

This is so true. Naming to me is one of the most important decisions. When I see someone who frets over naming decisions for hours, or will sit down with me and really think through what we're going to name something - I know they get the gravity of the situation. I trust those kinds of people much more for big picture architectural or project lead decisions.

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

#194

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…

Direct link to image bypassing imgur’s awful interface: https://i.imgur.com/WJuhjlO_d.jpg?maxwidth=1640&shape=thumb&...

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

#195
post #184

Great article. But for me there's a huge question being left unanswered, like the elephant in the room: Why did exactly did the engineers/test pilots feel the need to "enhance" the original MCAS with the new, more powerful version that worked at lower speeds? What did they know? I doubt they did it for the hell of it. And therefore, what has changed that that enhanced functionality is now no longer necessary, and it'…

The answer to why they wanted to “enhance” MCAS is that they wanted it to be certified as a 737 like all previous versions, which means pilots need to be able to fly it exactly like previous 737s without additional training, and a technical hack which “corrects” pilots' actions facilitates that.

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

#196

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…

If the pilots were putting that much force on the yoke it is pretty apparent that the pilots really truly wanted the plan to do what they asked of it. I am curious what scenarios the designers of the plan drove then to not trust that the human in the seat really has no idea what they are doing. Was the ignoring the wishes of the pilot and attempt to prevent a crazed irresponsible and unlicensed idiot from doing somet…

You make it sound like the plane has some kind of agency. Though a plane is very complicated, the treacherous MCAS system is actually very simple.

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

#197
post #120

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…

Engines were mounted to make a stable configuration inherently unstable in not so uncommon circumstances. The pitch was used to control the the most critical axis of the plane - something done normally with the rudder. This gave an automated system the authority to override the pilot with a wide margin. The behavior of the plane differs wildly from the old 737 as soon as the surprising narrow corridor of normal flight situation is exceeded.

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

#198
post #65

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.

To be fair, it's not like this isn't standard industry practice. Airframe evolve and change, with incremental changes typically only affecting limited areas of impact. OTOH seeking a non aerodynamic solution to a significant stability degrading airframe modification was IMHO a bridge too far. If the pitch stability (not the pitch feel) problems couldn't be dealt with aerodymancally without busting type certification,…

Re-engineering the rudder may also have helped avoiding employing pitch control (with it's inherent delay and hard to undo actions). But that would have made it obvious that this is a different plane...

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

#200
I've never understood why they make planes with 1-2 sensors for a crucial reading like airspeed.

Why not have 20 airspeed sensors of 5 different types? It's an obvious failure mode that your one sensor will fail and then the pilots and the computer will be left in a state of dangerous uncertainty about the situation.

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