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  #21  
Old 13 March 2019, 11:36 PM
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I am having a hard time dealing with this. Though I've never worked for Boeing, my dad, brother and his wife, both their kids and respective spouses, and other assorted family and friends (like Seaboe) did or still do. We live within walking distance of the Renton Boeing plant where I believe most of the assembly on the Max 8 is done. Looking out our front window, we can see the new jets take off. I'm a big fan of Boeing, and believe in the quality of the planes they build.

I won't say I was hoping it turned out to be terrorism or pilot error that caused this most recent crash. I won't say I am hoping if there's a problem in the plane, that it was one of the pieces that came from a subcontractor and not actually built by Boeing. I just want the planes to be good, and work the way they're meant to work. And I am very sorry for the lives lost.
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  #22  
Old 13 March 2019, 11:46 PM
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Tootsie, I agree with your sentiment that I want thinks to work properly. However, in reading about this, it would appear that the company let marketing get ahead of engineering. However, speaking as an engineer, if a project was left until every engineer was 100% satisfied, nothing would ever be finished.
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  #23  
Old 14 March 2019, 12:27 AM
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Quote:
Originally Posted by Tootsie Plunkette View Post
I won't say I was hoping it turned out to be terrorism or pilot error that caused this most recent crash. I won't say I am hoping if there's a problem in the plane, that it was one of the pieces that came from a subcontractor and not actually built by Boeing. I just want the planes to be good, and work the way they're meant to work. And I am very sorry for the lives lost.
I suspect that, even if the crashes are linked, it will be a little more nuanced than an either/or proposition of human error vs. design flaw.

I suspect it will be more along the lines of:

1) a redundant system failed in a predictable way, as redundant systems occasionally do
2) the aircraft responded as expected when said system failed (poorly)
3) humans did not respond to symptoms as expected, but then humans often don’t in emergencies, hence the need to account for human failings in advanced designs (ie: even though just following the checklist ought to be enough, assume humans might overlook certain conditions if they aren’t used to dealing with them, so go ahead and throw in a warning light to help highlight that condition being in place)
4) Boeing did not adequately account for foreseeable, albeit inappropriate, human responses to symptoms of a problem, thereby making for a design flaw

A few years ago I was directed to a video lecture on YouTube* (part of a series on commercial flight training for the American Airlines' Flight Academy), which has since been taken down, called "Children of Magenta." It’s discussed, in part, here:

Quote:
In 1997, American Airlines captain Warren Van Der Burgh said that the industry has turned pilots into “Children of the Magenta” who are too dependent on the guiding magenta-colored lines on their screens.
It’s not just about magenta-colored lines, but the relationship between automation, situational awareness, and how an over-reliance on automation can result in task saturation at critical points in the flight (which can lead to catastrophie if anomalies arise which affect automated systems or automated systems are inadvertently secured by human error).

Anyway, the human-machine interface is a thing, and a failure to reliably predict how humans might fail with regard to the machine is a failure of design nonetheless. But it is also a failure in the human (and/or their training and/or industry culture).

*If you’re really interested in seeing the video (which deals with levels in automation and how bad things happen when you end up in one level but think you’re in another) you can find it on Vimeo: Children of the Magenta Line.
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  #24  
Old 14 March 2019, 12:48 AM
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Originally Posted by erwins View Post
The FAA finally stepped in and issued an emergency order grounding them in US airspace, after Canada had done so, and saying it was based on new data seemingly linking this crash to the Lion Air crash.

I would be interested to know if Boeing's move had any significance other than PR at the point when they made it. It looked to me like they had already been grounded around the world when they joined in to "support" the FAA's order, and claim they had grounded their own planes worldwide.
I was somewhat confused as to the order of events, as I saw conflicting articles, some saying the FAA grounded them, others saying it was Boeing. So I wasn't sure if Boeing issued the order on their own or if they were just going along with what the FAA was doing.

And of course Trump had to announce the grounding himself in an attempt to get credit for it. Did Jimmy Carter make a special announcement when the DC-10 was grounded? Somehow I don't think so.
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  #25  
Old 14 March 2019, 01:11 AM
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The plane was only in the air for 360 seconds, and on another forum I read (I have not verified) that the shortest checklist you can run through (on a completely unrelated thing) takes at least 50 seconds. So another question is whether Boeing's claims that running through the applicable checklist would have prevented the crashes is actually true and feasible. Also, in the same forum, it was said that the MCAS doesn't operate when flaps are extended. So the time between the MCAS kicking in and pointing the nose down (i.e., giving signs of the problem) and the crash happening is even shorter than 6 minutes since the plane had just taken off so had flaps extended for part of the time.
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  #26  
Old 14 March 2019, 01:25 AM
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It depends on how far down the checklist "flip stabilizer trim cutout switch" is, I would think.
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  #27  
Old 14 March 2019, 04:52 AM
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This article suggests that the initial reaction of pilots is likely to be an action that normally counters a similar problem, and that the immediate action required to offset the MCAS inputs may be counterintuitive. https://leehamnews.com/2018/11/14/bo...to-the-pilots/

Quote:
It can be stopped by the Pilot counter-trimming on the Yoke or by him hitting the CUTOUT switches on the center pedestal. It’s not stopped by the Pilot pulling the Yoke, which for normal trim from the autopilot or runaway manual trim triggers trim hold sensors. This would negate why MCAS was implemented, the Pilot pulling so hard on the Yoke that the aircraft is flying close to stall.
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  #28  
Old 14 March 2019, 02:59 PM
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If that's the case, then it sounds like Boeing was negligent (possibly even criminally so) in not requiring additional training to the pilots on the new system. Anything that the pilot cannot override with control inputs should include training specific to recognizing the condition and enough simulator training that overriding the system is something they can do without having to refer to a manual.

I wonder why the MCAS wasn't added to the stall warning system instead*? That shouldn't have required additional training either and would have allowed the pilots to use their existing training.

* Usually a two part warning. The audio "Stall! Stall!" warning you hear on voice recorders and a system that shakes the pilots' sticks to alert them to the potential stall condition.
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  #29  
Old 15 March 2019, 03:39 PM
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Default A set of stairs may have never caused so much trouble in an aircraft.

How a 50-year design came back to haunt Boeing with its troubled 737 Max jet

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First introduced in West Germany as a short-hop commuter jet in the early Cold War, the Boeing 737-100 had folding metal stairs attached to the fuselage that passengers climbed to board before airports had jetways. Ground crews hand-lifted heavy luggage into the cargo holds in those days, long before motorized belt loaders were widely available.

That low-to-the-ground design was a plus in 1968, but it has proved to be a constraint that engineers modernizing the 737 have had to work around ever since. The compromises required to push forward a more fuel-efficient version of the plane with larger engines and altered aerodynamics led to the complex flight control software system that is now under investigation in two fatal crashes over the last five months.
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  #30  
Old 15 March 2019, 04:34 PM
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But the decision to continue modernizing the jet, rather than starting at some point with a clean design, resulted in engineering challenges that created unforeseen risks.
IIRC, Boeing was considering a "clean sheet" design to replace the 737 until Airbus announced their A320-NEO family (their more fuel efficient re-engined version of the A320). Designing a completely new plane from scratch takes more time, and probably wouldn't be flying until the middle of the next decade. This meant that in the short term Boeing wouldn't have anything that was really competitive with Airbus, and airlines were telling Boeing they didn't want to wait that long for new planes*. So instead of a new design Boeing instead went with yet another update to the 737 so they could offer their customers something sooner, even if it was something of a compromise.

*Particularly Southwest and American, who had large fleets of older 737s and MD-80s that needed to be replaced soon.

Quote:
But some aspects of the legacy 737 design are vintage headaches, such as the ground clearance designed to allow a staircase that’s now obsolete.
As an aside, Boeing actually still offers a built-in staircase as an option on the 737. I'm guessing it's not a particular popular option, but Ryanair does have them on theirs, since they use airports that don't have jet bridges.
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  #31  
Old 15 March 2019, 04:51 PM
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I wish there was more official information about how MCAS works. On at least 3 other sites, it has been mentioned that if a pilot overrides MCAS trim adjustments by using the trim switches on the stick (not the stabilizer cutout switches) MCAS will pause for 5 seconds, and then resume. So you would get a behavior of nose down, manual correction, 5s pause, nose down, manual correction, 5s pause, ..... If that is accurate, that does not match the "condition" stated for the runaway trim checklist for at least the 737 NG. That condition is defined in terms of uncommanded trim that is "continuous."

To be clear, it seems like there could be many factors involved, so it may not be exclusively about MCAS, its implementation, and its documentation and training. But I am very interested in how chains of decision - making like this happen, as well as how automation - connected failures are often blamed on the humans involved not reacting "correctly," when that itself is an indication of a failure in the automation design and testing. (Or possibly training, but I think that's usually a very late in the game correction for a faulty design.)

ETA Another piece of the puzzle is that apparently pulling back on the yoke should be enough to counter the stabilizer trim. It can take a lot of force to counter full trim, though. So, theoretically, a pilot can counter even full nose down trim by pulling back on the controls, and should be able to achieve level flight. Correcting the trim manually will then just relieve the back pressure on the controls. I think I read that full nose down trim might add something like 40 kg of "weight" to the controls, though. So the pilot flying would have his or her hands very full just physically wrestling with the controls to keep level flight once trim was significantly nose down. So, the non-flying pilot would have to run through the checklist actions.

Last edited by erwins; 15 March 2019 at 05:07 PM.
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  #32  
Old 18 March 2019, 04:38 PM
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Airplane Flawed analysis, failed oversight: How Boeing, FAA certified the suspect 737 MAX flig

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Federal Aviation Administration managers pushed its engineers to delegate wide responsibility for assessing the safety of the 737 MAX to Boeing itself. But safety engineers familiar with the documents shared details that show the analysis included crucial flaws.
https://www.seattletimes.com/busines...ion-air-crash/
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  #33  
Old 18 March 2019, 05:20 PM
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That's quite an article. I wonder how it affects liability that Boeing did so much of its own safety reviews. And, of course, changed some of the details after the approvals.

I also wanted to correct something from my previous post. I've now read that pulling back on the stick may not be enough to counter the full nose down stabilizer trim. The elevators on the back of the stabilizer lose some of their effectiveness as the stabilizer moves the opposite way. So once it reached full nose down, it may not have been possible to hold level flight until the stabilizer trim was corrected.

I've also read the preliminary report on the lion air crash. It's available in PDF. There are some interesting graphs, and a lot of interesting information.
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  #34  
Old 18 March 2019, 05:30 PM
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The elevators are supposed to be able to counteract the stabilizer, but the 737 design where that was certified on was probably well before the MAX version came out, possibly even back in the -300 era. Since the new MAX was even more nose heavy, it may be that there is no longer enough elevator to counteract the trim when the trim is in full nose-down position.

Also, there is a big difference between counteract and overcome. And even if they could overcome the trim, could they do so with enough "left over" nose-up control to pull back to level flight they were already at low altitude?
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  #35  
Old 18 March 2019, 06:53 PM
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Good points. It's looking like the Ethiopian plane may never have climbed above about 3,000 feet above the ground. And part of the time, it was much lower -- under minimum safe height. Not a lot of room to recover from a dive, even if you could overcome it.

The unofficial data also says it sped up at times -- to as much as 400 knots, compared to a usual speed around half that (200-250). I wonder if either another control system was also involved, or if the pilots reacted to the stall warnings by speeding up. It had not been clear to me before reading the preliminary report on the Lion air crash that the stick shaker and stall warnings did activate in that crash.

I wasn't sure they did, because I wasn't sure they would activate from just one sensor, and I didn't remember hearing if they had. But from rotation (the lifting up of the nose of the plane at take off), the left stick shaker activated on the Lion Air flight, and it stayed active for all or nearly all of that plane's time in the air. I read a study that showed that pilots sometimes initially choose the wrong checklist when there's a problem. Sometimes, they might realize it's wrong partway through, or choose the right one after completing the first one. This issue does not fit the "condition" for the runaway stabilizer exactly, and it also would have disagreeing sensor warnings and stall warnings.

Boeing and some others like to point out that the same problem occurred on the second to last flight of the Lion Air plane, but after a short time, the pilot hit the stabilizer cutout switches and ultimately landed safely. But one crew recognizing the problem and correcting it the right way does not mean that all crews can or should have, or that they will have time to. (It's also worth noting that the preliminary report says the AoA sensor that was acting up on the previous flight was replaced and the new sensor tested on the ground before the final flight took off. So, again, there may be something beyond just MCAS that went wrong.)

Last edited by erwins; 18 March 2019 at 07:18 PM.
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  #36  
Old 18 March 2019, 07:23 PM
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Without other data, I would assume that the aircraft was speeding up simply from the dive. The speed vs altitude charts for the Lion flight shows that the airspeed increases as the altitude decreases (which is the expected behavior if the thrust of the engines isn't changed). And I wouldn't expect the pilots to alter the thrust settings. After takeoff, the engines are going to be somewhere around 80% max thrust. Increasing thrust wouldn't do much if it is "stalling" at those settings. Also, turbine engines take time to increase thrust so the pilots are going to focus on the most immediate ways to prevent a stall (or recover when the plane thinks it is stalling).

ETA: I used the Lion's flight because I've not found an article that includes both speed and altitude charts for the Ethiopian flight. But multiple articles say that the flight profiles are remarkably similar.
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  #37  
Old 18 March 2019, 08:01 PM
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Quote:
Originally Posted by erwins View Post
That's quite an article.
Especially coming from the Seattle Times, which I've seen criticized in the past for going too easy on Boeing.
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  #38  
Old 19 March 2019, 07:53 PM
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A pilot at the engineering forum discussing this (https://www.eng-tips.com/viewthread.cfm?qid=450258) gave an explanation of something I'd been wondering about. Once you flip the stabilizer cutout switches, you have to manually crank a wheel in the cockpit to turn the jackscrew that adjusts the stabilizer. The pilot said that, from the full nose down position, it would take minutes to crank it back to where you need it, likely losing between 6000 to 10k feet in the process. (Basically depending on fitness.)

So, it seems like, when the problem occurs at low altitudes (which is mostly when it would*) to have a chance of recovering, the flight crew would have to recognize the problem early, or at least have been mostly or fully countering it with the electric trim switches before flipping the cutout switches, so that the plane could still be flown while the trim is manually adjusted.

I've noticed that MCAS is being described in different ways -- a stall protection system, an adjustment to handling "feel" that provides crucial feedback to pilots, an adjustment to handling to make it match the 737 NG, and an adjustment to make up for an inherent instability under certain circumstances. It can, of course, be all of those, but there may be different implications for some of them. I'm wndering how it was presented to, and understood by, regulators here and in other countries.

* MCAS is not supposed to be active when autopilot is engaged.
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  #39  
Old 20 March 2019, 04:03 PM
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One thing that I'm curious about is how the 737-MAX was certified outside the US. Canada usually accepts US certification (and vice versa) by agreement, but I haven't seen if such an agreement is in place for the EASA.

I would image that most other countries follow the FAA or EASA's guidance in certification, especially for US and European made aircraft.
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  #40  
Old 21 March 2019, 07:57 AM
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The Guardian reports that the Lion Air pilots were looking at the flight manual when their plan crashed.

https://www.theguardian.com/world/20...-plane-crashed
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