FAA is Investigating New Incident Involving a Boeing 737 Max 8 Jet in Midair (npr.org) 51
New submitter wgoodman writes: A Boeing 737 Max 8 jet experienced a rare but potentially serious problem recently known as a Dutch roll before landing safely. The Federal Aviation Administration is investigating the cause of the incident during a Southwest Airlines flight last month. Less than an hour after taking off from Phoenix on May 25th, the plane experienced an uncontrolled side-to-side yawing motion known as a Dutch roll while cruising at 32,000 feet. The pilots of Southwest flight 746 were able to regain control and the plane landed safely in Oakland, according to a preliminary report from the FAA.
[...] The Boeing 737 Max 8 jet involved in the Dutch roll incident is less than two years old. According to the FAA, a post-flight inspection revealed damage to a backup power control unit, known as a PCU. That system controls rudder movements on the plane's tail. The plane remained in Oakland until June 6th, when it flew to Everett, Wash., where one of Southwest's maintenance vendors is based. Boeing has been working to rebuild the trust of federal regulators and the flying public since a pair of Boeing 737 Max 8 jets crashed in 2018 and 2019, killing 346 people. Earlier versions of the 737 were involved in several accidents and crashes during the 1990s that were ultimately blamed on problems with the tail rudder.
[...] The Boeing 737 Max 8 jet involved in the Dutch roll incident is less than two years old. According to the FAA, a post-flight inspection revealed damage to a backup power control unit, known as a PCU. That system controls rudder movements on the plane's tail. The plane remained in Oakland until June 6th, when it flew to Everett, Wash., where one of Southwest's maintenance vendors is based. Boeing has been working to rebuild the trust of federal regulators and the flying public since a pair of Boeing 737 Max 8 jets crashed in 2018 and 2019, killing 346 people. Earlier versions of the 737 were involved in several accidents and crashes during the 1990s that were ultimately blamed on problems with the tail rudder.
Just the beginning (Score:3, Insightful)
Boeing cut corners to maximize profits and now this cost cutting may not have been apparent at first but it's going to get worse before it gets better.
structural failure can result (Score:2)
Lots of false information in this reply (Score:5, Informative)
Nearly every claim in this post is factually wrong. This person apparently knows nearly nothing about aircraft flying characteristics, other than buzzwords.
I am a degreed aerospace engineer working in flight test for over 30 years and I have tested large commercial/passenger-class aircraft, including deliberately-induced Dutch rolls for test purposes. I have sat in the cockpit behind pilots executing these Dutch roll maneuvers intentionally. I personally joined a flight test team that had a crash a few years before, due to a Dutch roll event during flight test in the early 1990s. I also edited the US Naval Test Pilot School handbook FTM-103 "Fixed-Wing Stability and Control Theory and Flight Test Techniques" in 2019-2021. So I'm working with definitive expertise acknowledged in my field.
Some facts.
1) The proper term is "Dutch roll", uppercase, not lowercase, just like "American flag" not "american flag."
2) Dutch roll has absolutely NOTHING to do with the wings alternately stalling. Zero. Nada. Its cause is more subtle and would take a few pages to explain; go look up section 5.2.2.3 of the USNTPS FTM-103 flight test manual (which I edited) if you want the math. A wing stall MIGHT occur AS A RESULT of Dutch roll if you cause such a very large Dutch roll at a very low speed, but I've never seen that happen in hundreds of flight test events, some of which were done with me in the airplane. And even if the wing DOES stall, it's not a big deal most of the time; I've also done many stall tests. We're careful and we know what will happen, but most stalls are immediately recoverable (because all airplanes are carefully designed to recover quickly and gracefully from an inadvertent stall).
3) There is no "triplet" input to "get out of" Dutch roll. It is a natural oscillatory motion and will persist until a "yaw damper" is engaged to counter it automatically; it's almost impossible to manually damp out because it will simply recur naturally. Even if you put in a complicated input to damp it out, it'll start again just due to small gusts. No pilot wants to spend all their time fighting Dutch roll; that's why aircraft have yaw damping systems.
4) Dutch roll absolutely CAN shear off the vertical tail if it becomes large enough. Look up the crash of American Airlines AA587 in 2001. And I personally worked on a program that crashed a Navy S-3B test airplane in 1991 from Dutch roll testing when the vertical tail failed due to bad test technique (deliberately overdriving the Dutch roll mode beyond the limits of the vertical tail strength, due to miscalculation of the tail strength limits). I personally have on my desk the control stick that was recovered by wreckage divers from the bottom of the Chesapeake Bay to remind me of that failure. That crash still informs Navy flight testing practices today.
5) But in normal operation with a properly-functioning control system and absent extreme pilot inputs, Dutch roll will never become large enough to cause a failure; all aircraft are designed with sufficient stability to not reach this point without a control system input (either deliberate or due to a hardover rudder input). It is, however often a nuisance residual motion which can be annoying or nauseating.
6) Dutch rolls not exactly a "very slow" oscillation. Slow, but not VERY slow. In most large aircraft, its period is about 5-6 seconds per cycle. Smaller aircraft have faster oscillations, maybe 2-3 seconds. It's easy to observe, and quite annoying.
See my root-level post here with more information about Dutch roll in general, and the actual issues in this event.
Re: Lots of false information in this reply (Score:2)
Re: Lots of false information in this reply (Score:4, Interesting)
Not surprising - given the accident description, the pilots dramatically exceeded the structural limits of the airplane by dramatically exceeding the posted limits of safe operation.
Here's the report of the event:
https://asn.flightsafety.org/a... [flightsafety.org]
It reads to me as if the (co)pilot deliberately amplified the Dutch roll motion (which is a simple lateral/directional dynamic characteristic of aerodynamics of ALL aircraft, whether or not it's operationally significant) until reaching such a large motion (probably a combination of simultaneous roll and yaw rate) that it exceeded the strength of the engine pylons.
In particular, it's possible to overstress the aircraft by putting in large OPPOSING inputs in an attempt to stop to the Dutch roll motion too quickly. It's quite possible that if they'd simply gone hands/feet off the controls, it would have damped out naturally with no damage. The failure of AA587 is an example of this: the pilot's large rudder input against the yaw motion (which was due to a yaw excursion due to unexpected turbulence) is exactly what caused the tail to snap.
Re:structural failure can result (Score:4, Insightful)
The worst single-plane crash in history, Japan Airlines Flight 123, was caused in part by Dutch roll after a hydraulics failure which ripped off most of the vertical stabilizer. 520 dead, only 4 survivors.
https://en.wikipedia.org/wiki/... [wikipedia.org]
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that airplane lost hydraulics after a unsatisfactory repair cause the tail to separate, emptied all 4 hydraulic systems, and decompressed the aircraft. With hypoxic pilots, a missing primary flight control structure, and minimal controls...dutch rolls were inevitable, but not the proximate cause of the crash.
Re:Just the beginning (Score:5, Informative)
They cut corners at a critical time when Boeing was moving towards more automation and fly-by-wire.
One of the biggest differences between Airbus and Boeing is that Airbus aircraft are fully fly-by-wire. When the pilot moves the controls, they are telling the computer that they want to do something, and the computer figures out how to do it within the programmed limits for roll, pitch, engine power and so forth. There are some "direct" modes where the controls directly affect the control surfaces and engines, but those are only used in emergencies and even then there is still no direct connection, it's fly-by-wire.
Boeing do have autopilot and some elements of computer control, but are more hands on in that the controls are connected to control surfaces and engines via hydraulics. The computers involved move the physical controls to achieve the effect they want. Some people prefer it because they can see and feel what the computer is doing very easily, where as in an Airbus you have to look at the displays to see what is going on and it might differ from what the controls are commanding.
The problem is that now Boeing is introducing more and more Airbus style fly-by-wire, in part to try to make aircraft fly a certain way that doesn't require pilot retraining. Boeing lacks the experience, and pilots don't understand when it creates discontinuity between the controls and what is actually happening. Airbus had to put a huge amount of expensive engineering effort into their system, and a lot of pilot training. Boeing just doesn't seem willing to do what is needed to make it safe.
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If it's anything like the MCAS system, they don't properly require a quorum of sensor data before performing an action automatically.
Though if Dutch roll is natural due to wind and pressure changes with the aircraft movement, it's probably the lack of automatic action that's the problem here. The closest thing I can think of is that it lost that backup power control unit and didn't account for still having primary power and disabled the automatic adjustments altogether. It just seems in line with Boeing'
Looks a bit like a dutch angle in midair (Score:2)
https://www.google.com/search?... [google.com]
Re:Looks a bit like a dutch angle in midair (Score:5, Funny)
You can fix that using the dutch rudder technique https://www.urbandictionary.co... [urbandictionary.com]
A "Dutch Roll" (Score:2)
...known in the Netherlands as a "Stroopwaffel".
Re: A "Dutch Roll" (Score:2)
I love the joke. But here, let me ruin it. Stroopwafels are flat. I think itâ(TM)s actually known as a saucijzenbroodje. Both quite tasty.
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Loves me some stroopwafels.
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Air safety investigations are focused on safety and finding root causes, not assigning blame, to prevent incidents. This is how air travel became so safe. These boring "it could have been horrible, but pilots did their job and nothing actually happened" stories need to have better context: they are incredibly routine and not specific to any manufacturer.
Except they seem to be showing up a lot with Boeing.
Air safety incidents are usually constantly reported and reviewed and it is all very routine and generally boring. And the two MAX incidents which were explicitly included in the summary are indeed indicative of real need for constant vigilance and review, but those were mainly pilot training and certification issues which are the result of complex considerations of what airlines want.
No, they were mainly issues with a terrible design decision, proper pilot training could have saved the day but Boeing obscured the need for that training so they could make the plane look more attractive.
The MAX exists because airlines wanted something their existing pilots could fly without much additional training expenses, while benefiting from newer engines and systems, which resulted in a compromised design and a solution which perhaps should have been treated as a significant change and triggered exactly what the airlines did not want: extensive certification and training costs before existing 737 pilots could fly the actually quite different plane when it came to very particular systems.
The MAX exists because Boeing was too cheap to start designing a replacement for the 737 and delayed until Airbus released the A320neo. Now Boeing was losing sales so they did the quickest/cheapest thing that could, stuck giant engines on the 737 and call
Re:Boeing is Boring (Score:4, Informative)
Air safety investigations are focused on safety and finding root causes, not assigning blame, to prevent incidents. This is how air travel became so safe. These boring "it could have been horrible, but pilots did their job and nothing actually happened" stories need to have better context: they are incredibly routine and not specific to any manufacturer.
Except they seem to be showing up a lot with Boeing.
Especially rudders.
That wouldn't be so bad if the previous 737 series hadn't also been plagued by a series of rudder failures initially.
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What Boeing did that resulted in the crashes of those planes was to lay off all its experienced (and more expensive) staff and give the MCAS contract to a company which normally wrote software for financial companies because it was cheaper. The reason why the airlines didn't train pilots what to do when an AoA sensor went bad and hosed the MCAS is because Boeing didn't tell their customers that the issue even existed.
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Except they seem to be showing up a lot with Boeing.
Seem? It can be quantified by going to the source, rather than relying on individual selective reports on investigations.
I agree there could be a bias in media talking about Boeing incidents more, but I don't really know how to test that out.
Certainly, the door issue would have made the news regardless of manufacturer.
The MAX exists because Boeing was too cheap to start designing a replacement for the 737 and delayed until Airbus released the A320neo. Now Boeing was losing sales so they did the quickest/cheapest thing that could, stuck giant engines on the 737 and called it MAX.
It is commercial aviation. Boeing and Airbus try to build what airline operators want to buy, and that meant a compromised design. Boeing did not drive this market: airlines did. Boeing as a business wants to build what they can sell and airlines want to buy what they can use for a profitable business and customers will only pay for what they want. Economics drives the industry from top to bottom.
Yes, Boeing did go to far with the redesign and there were lapses in training pilots on new systems that were greatly different, but if Boeing could have made a brand new plane with all new systems to all work with the least compromises, they certainly would have done it, but there is no market for that and therefore it is not commercially viable. So a review of the processes involved in Boeing and in the regulatory bodies is definitely warranted and reforms are definitely needed to ensure that there is more oversight over everybody, including the regulatory bodies.
The problem with this attempt to pass the buck is that as the manufacturer it's Boeing's responsibility to make a well-designed safe airplane. The airlines and pilots were in no position to realize that Boeing was cashing in on its previous reputation and had started cutting corners.
Regulators should have done m
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Yes, and there was a single action that a pilot could have taken which would have prevented that.
GTFO of here trying to put this on the crew of those aircraft. Yes, "pull the breaker to the trim tab motor" is a single, simple action, and at least one pilot was good/smart/lucky enough to figure that out before the plane succeeded in killing him, his crew, and his passengers, but he shouldn't have had to be.
Kind of hard to take corrective action to fix a system that you were specifically, purposefully, not told the existence of much less trained on.
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While I appreciate this line of argument; to me the buck stops with Boeing.
* The airlines said they wanted an aircraft that did not require pilots to re-certify ... and more ... and more efficent ... and ..
Sure customers ask for a lot of things
* The regulators and Boeing said it would be easier if corporate could do their own certifications..
Indeed things are usually easier with fewer parties.
Nobody at Boeing said, well that sounds like a great ask but we can't reasonably deliver on that. Nobody at Boeing s
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To be fair, it wasn't JUST luck, it was also design. And it's the design that's being investigated to see if it needs improvement. (Based on recent history, I'm pretty sure it does.)
Luck and design will always both be involved. But you want to minimize the need for luck.
Open Beta Test almost Over (Score:3)
Air safety investigations are focused on safety and finding root causes, not assigning blame, to prevent incidents.
Exactly. People are clearly being too hard on Boeing. They seem to have managed to fix the software and training problem that caused their planes to fall out of the sky and the doors no longer appear to fall off, they have a workaround for the software glitch that cut the plane's power on takeoff and I'm sure they'll be able to patch this rudder problem with enough duct tape and PR.
Indeed, if they keep up this proactive, positive approach of patching all the problems then their planes should soon be mov
Dutch roll (Score:2)
No thanks the Swiss make the best rolls. If they can't serve that, they should stick to airline pretzels.
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I don't think you've had a KLM breakfast. Dutch pastries are excellent.
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damage that was not detected ?? (Score:3, Insightful)
a post-flight inspection revealed damage to a backup power control unit, known as a PCU.
ok. That could have been damaged accidentally during maintenance or something.
But if it was , why they heck wasn't there a warning or some other indication that it was damaged ? Those systems must have self-test/checks, especially a power supply which is trivial to monitor and check.
Or it was fine at take off and then was damage _during_ the flight. That would be very concerning...
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It's a BACKUP! The primary was probably just fine. While I'm sure that having one of the two failing should show an alert to someone, it shouldn't be disabling critical flight stability systems. Probably it was fine at takeoff and determined by the computer system to have failed when it didn't respond correctly at some point. But it sounds like the the aircraft deemed the lack of backup power as critical, ignoring the working primary power for the rudders, and disabled roll correction while also NOT ale
"The pilot is in control" doctrine (Score:5, Insightful)
Boeing had long distinguished itself with the mantra that the "pilot is in control".
Their planes avoided using software control to limit pilot actions like Airbus did. Software safety experts like MIT's Dr. Nancy Leveson (the founder of the field of Software Safety) praised this doctrine because it meant that safety was not dependent on software but rather hardware limitations.
With the MAX Boeing backtracked on its conservative attitude about pilot control. And when doing so, they seem to have done it in a way that seems far less safe than Airbus' approach.
Note that Airbus also had control problems due to "mode confusion" in the past that led to serious incidents, which is less spoken of today.
Boeing should go back to their old doctrine and leave software out of the critical safety loop. But most of all they need to get rid of those MBAs that are ruining the company and hand it back to the Engineers that know what they're doing. If such people are even still with the company.
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We agree but Boeing will "Solve it with AI" instead.
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The bottom line is that McDonnell Douglas ruined Boeing. Go back to the 777, the last aircraft Boeing designed as Boeing and without the taint of MickeyD's, and you find a plane that was and still is fantastic. All of the cost and quality cutting and the aircraft problems resulting from it happened after the merger and with the aircraft designed and built after the merger. Before McD, Boeing was that engineer-driven company. After... that's where the MBAs came in.
What they need to do is undo McDonnell D
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In a lot of accidents the automation would have saved the day if the pilots would let it do its job instead of being "in control". It performs better than the pilots five nines percent of the time.
the 737 Max (Score:1)
Re: the 737 Max (Score:2)
Some factual information about Dutch roll (Score:5, Informative)
I have a few observations about this incident, because I see some false information in this thread.
I am a degreed aerospace engineer working in flight test for over 30 years and I have tested large commercial/passenger-class aircraft, including deliberately-induced Dutch rolls for test purposes. I have sat in the cockpit behind pilots executing these Dutch roll maneuvers intentionally. I also edited the US Naval Test Pilot School handbook FTM-103 "Fixed-Wing Stability and Control Theory and Flight Test Techniques" in 2019-2021. So I'm working with definitive expertise acknowledged in my field.
Some facts.
First, the proper term is "Dutch roll", uppercase not lowercase, just like "American flag" not "american flag." Basic respect for Holland and all that.
Dutch roll, according to the US Naval Test Pilot School handbook FTM-103 "Fixed-Wing Stability and Control Theory and Flight Test Techniques", is defined as a second-order oscillatory lateral/directional mode of oscillation, sometimes referred to as a nuisance or annoyance motion. It is characterized by an oscillation back and forth between roll and yaw (sideslip); if you look out the side of the aircraft you'll see the wingtip trace a small circle or oval path. Nearly every airplane will exhibit Dutch roll - it's baked into the aerodynamics - the only question being how susceptible it is, and how well it naturally is damped.
So every airplane ever flown is deliberately tested for lateral/directional stability including deliberately inducing Dutch roll to check for its damping characteristics: will it naturally die out or is the "yaw damper" needed to reduce it, and how fast is it reduced by that system.
Dutch roll testing is actually one of the more benign types of flight tests. We are careful to avoid exceeding the sideslip limit of the airplane, so we build up to the larger test points, but it's generally quite safe.
You can see a sample plot of relatively representative Dutch roll motion here: https://www.researchgate.net/p... [researchgate.net]
My read of the article and other information I can find about this incident is that it wasn't a Dutch roll that *caused* the problem. "Dutch roll" is simply a natural mode of oscillation present in any airplane, and won't lead to any aircraft damage unless something else went badly wrong. In this incident, it's likely that the rudder power control unit (PCU) had a "hardover" or oscillatory failure and drove the tail to swing sideways (either once or oscillatory) far enough to cause physical damage to the tail (the FAA preliminary report says "substantial" damage), which I presume manifested as popped rivets and visible sheet metal buckling (I've personally seen these before after flight test events that went a bit too far). So the failure was not Dutch roll itself. Presumably the pilots immediately turned off the Dutch roll damping system (the "yaw damper") and maybe even the rudder PCU itself. The resulting residual motion after such a failure, without the yaw damper reducing the oscillation, might be characterized by a sustained yaw/roll oscillation which WOULD be a Dutch roll mode of oscillation, but that was the effect, NOT the cause.
Dutch roll is not inherently dangerous. What *is* dangerous is when it is excited (by pilot input, by control system failure, or by wind gusts) and becomes large enough to cause structural damage, usually to the vertical tail due to side loads on the tail. The crash of American Airlines AA587 in 2001 is an example of what happens when the vertical tail fails due to overstress; the pilot encountered an wind-gust disturbance and used too much rudder to try to correct the motion, and literally sheared off the vertical tail. So modern aircraft include rudder limiting systems to prevent large inputs at high speeds.
In this incident this week, the rudder PCU apparently malfunctioned and caused a huge yaw input, leading to (probably) vertical tail damage.
AFTER the real failure and any damage that occurred, because of the failure of the PCU, it's likely that the rudder couldn't properly damp the Dutch roll during the rest of the flight, so there would also have been a sustained but small oscillation which can cause people to get nauseous or worse due to motion sickness.
If you want to learn more about Dutch roll, here is an older public-domain copy of FTM-103 (the new version I edited is not being released publicly) and you'll find the relevant information in section 5.2.2.2.3.
https://usntpsalumni.wildapric... [wildapricot.org]
Finally, is this a symptom of Boeing design = bad? No, I don't think so. Every aircraft has a ton of parts which must be well maintained. Servos (PCUs) fail due to wear and tear. Aircraft maintenance practices are designed to spot failing or worn parts such as PCUs and replace them before this happens, but sometimes it still happens. That has nothing to do with the fundamental design. And as I have tried to convey above, Dutch roll is inherent to every airplane. The only question is how good are the systems to limit and damp it out, and how good is the servo design to not cause it. Since this and thousands of other 737 aircraft generally have no problems like this, it's not a design flaw; it's a worn-out-parts flaw. So if anything, I'd pin this as most likely due to maintenance not catching a worn part, but maybe just bad luck.
Dutch Roll vs Danish Roll? (Score:2)
Both can kill you if experienced in excess? ;-)
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Pilot comment: Swiss Cheese model (Score:1)
The Swiss Cheese model of accident reconstruction goes something like this:
- Toss a piece of Swiss Cheese on a plate. There is cheese. There are holes.
- Toss another piece on top of that. A hole or two may line up.
- Repeat for a few more slices. If all the holes in one spot or more line up, there's your accident/incident aircraft.
That means at any point in the laying of the slices of Swiss Cheese, someone could have said "Oh hey look, there's a hole there."
At any point thereafter they could have said "O
Just no. (Score:1)