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Twisties

Air Travel Safety and the 737 Max 8?

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Twisties

Educate me.

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Joe Frickin' Friday
19 minutes ago, Twisties said:

Educate me.

waddyawannaknow?

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Twisties

Grounding justified, or no?  Summary of evidence, summary of response to Lion Air, summary of criteria for grounding decision, perspective on overall air safety trends (are planes too complex to fly, or are automated systems improving safety), whatever else may be important....  we have a bunch of experienced pilots here... just thought maybe we could have some relatively informed debate...

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Joe Frickin' Friday

I'm not a pilot of any sort, but I'll throw in my two cents.

 

Most commercial passenger jets will warn the pilot of an impending stall with a yoke-shaking  mechanism, designed to mimic the buffeting behavior typically seen on smaller straight-wing aircraft.  If the situation continues, the plane will actually push the yoke forward, forcing the nose of the plane to pitch down in a controlled manner.  The important thing to note is that the yoke-pusher is weak enough that the pilot can physically overpower it if he consciously chooses to.  So if the yoke-pusher is acting based on an erroneous stall warning, there's no special action that needs to be taken: the pilot just pulls back hard on the yoke and defeats the yoke-pusher.

 

On the 737 MAX 8, instead of pushing the yoke forward, the system adjusts the pitch angle of the entire rear stabilizer.  If the pilot believes the impending stall isn't real,  he can pull back on the yoke, and it'll move the elevator tabs, but those elevator tabs are meaningless against the control authority of that entire stabilizer.  And that's pretty much how the Lion Air situation started: a faulty airspeed sensor convinced the computer that a stall was imminent when in fact everything was fine, and so the computer insisted on pitching the nose down repeatedly.  On the 737 MAX 8, there's a button the pilot has to press to override this system, and it sounds like the Lion Air pilots either weren't told about this unique feature, or didn't remember it.  So they fought and fought with this thing until the computer finally won and flew the plane pretty much straight down into the ocean.  The way to prevent this particular type of crash from happening again is to ensure that the pilots are fully trained on the peculiarities of the MAX 8, including this unique stall management system and how to get around it if necessary.

 

While the Ethiopian Airlines flight was also flying erratically and eventually came pretty much straight down into the ground, eyewitnesses are claiming that the plane was emitting smoke, debris, and odd noises well before it crashed, which suggests a problem other than the pitch control issue that the Lion Air flight had. 

 

So even though there have been two crashes of the same aircraft type in less than a year, and both aircraft were very new, I think that's where the similarities end.  Absent any other information (e.g. something particular they've discovered about the MAX 8 that hasn't been made public yet), I'd say that grounding all MAX 8 aircraft is unwarranted, and that the decision(s) to do so are about bowing to public pressure rather than technical data.  

 

As it happens, there was a statement from the FAA this afternoon about "new evidence" from the Ethiopian Airlines crash site that helps justify the grounding, but they haven't yet said what it is.  Waiting to see...

 

 

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Paul De
54 minutes ago, Joe Frickin' Friday said:

I'd say that grounding all MAX 8 aircraft is unwarranted, and that the decision(s) to do so are about bowing to public pressure rather than technical data.  

 

I understand Ethiopia Air grounding its fleet, but I was suspicious about the EU grounding 737 MAX. I gave that announcement a bit of a side eye given the level of financial support that the Eurozone gives to Airbus. The US grounding seems like a giving into public pressure and the perception that the FAA is overly influenced by Boeing and the airlines.

 

Boeing didn't help itself as I understand it.  When the MAX series was released the new engines tended to make the plane want to nose up more than the previous generation of the 737 and at some point they programed in some additional nose down bias  to compensate and uploaded the software to the global fleet but didn't either communicate it well or maybe did it with no notification at all.  I believe this information came out in the Lion Air investigation, and while it could in reality be entirely unrelated the coincidental timing w/o full disclosure of the change fed the narrative that Boeing was covering up a major flaw in the MAX series.

 

Jumping to conclusion is a natural thing for humans and in an information vacuum speculation as conclusion can spin out of control. I am sure a lot of Boeing engineers are now going with little sleep and a bottle of Tums on their desks frustrated that the data they need isn't in hand yet to make an informative decision on the action to take.

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Skywagon

It will take some time to sort out what new info the FAA has. If it were my decision, would I ground the US Fleet?  Yes....without any hesitation.  Why?  The recent crashed are too similar.  It could be mechanical, training, or a combination of both.  As the investigation/research continues if there is a common cause, it will be found just like the hard over rudder of 737's a few years ago.  Do we wait for one more and say ok that's enough, or do we take caution now?

 

Yes it will create some hardship for traveler, airlines, and some economic issues....but if your call and one more went down causing the loss of life, how would you feel about that decision to wait and see.

 

Boeing issued and emergency software patch this week to address the Lion crash.  Did they find a fault or just adding more safety.  They didn't really publicly say what that patch was for.  

 

For me as a pilot I would hope you would be happy I leaned forward on safety and a little less concerned over stats and financials.  I was never asked to pilot a plane with ops saying I think it is ok :)

 

 

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John Ranalletta

See blancoliro for commercial pilot's take.

 

 

 

 

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Joe Frickin' Friday
7 hours ago, John Ranalletta said:

 

Porpoising, AKA phugoid flight, is associated with a complete lack of pitch control input, from either the pilot or the autopilot.  The Lion Air flight was quite the opposite: the computer pushed the nose over until it was satisfied the stall condition was eliminated, and then it let the pilots pull the nose back up, then the cycle of control inputs began again.  Given the similar aspects of the flight path for both planes, it's possible the same thing was happening, but eyewitnesses reported smoke and noise from the plane before impact, suggesting some other sort of failure.  Maybe they were misinformed about what they saw/heard, or maybe there was a failure that was caused by the wild flight.  Will be interested to see what comes out of all this.  

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Skywagon

porpoising will almost always be pilot induced as the servos can not act fast enough to create porpoising. It may be purely by the pilot with no input from the plane itself or it most likely caused by the trim on the elevator running one way and the pilot pushing or pulling the other. Trim on elevators move slowly.  If they didn't it would nearly impossible to level the plane.  Manual input can happen as slow or rapidly as you want.  What caused this oscillation?  Don't know but time will tell.  It could be the new program commanding one way and pilot manually overriding, TCAS working, or a number of things....time will tell.  

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Skywagon

It's hard to say what that will mean.  Remember there are really 3 parts of climb and descend ( 4 if you count thrust).  The stabilizer, the elevator, and trim.  If I remember correctly the autopilot can be overpowered with roughly 25 lbs of force.  Not a real big deal, but this new MCAS as I'm told, senses stall and rolls the stabilizer to the stops full down.  With the stabilizer pointed that far down, if that is what happened, even if the pilots were to pull back full on the yoke it is unlikely they have enough surface in elevator and trim to overcome the effects of nose down on the stabilizer.  I don't know any more than the next person what happened yet, but smells like MCAS in some way.  Maybe they were trained on it, maybe not...even if trained did it lock the stabilizer against the stops which  would not have given the pilots the ability to create climb by simply pulling back?  As a last result did the pilots go to take off power to create climb?  Don't know...but possible.  Killing the autopilot is something pilots do multiple times in any flight by just pressing the disengage switch on the yoke...so autopilot unlikely the issue... I'll do some research but I think the stabilizer is hydraulic.

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Joe Frickin' Friday
11 hours ago, Skywagon said:

If I remember correctly the autopilot can be overpowered with roughly 25 lbs of force.  

 

Unrelated to the current 737 MAX crashes, but Aeroflot 593 was an interesting crash that involved such a manual override of the autopilot:

Quote

With the autopilot active, Kudrinsky, against regulations, let the children sit at the controls. First, his daughter Yana took the pilot's left front seat. Kudrinsky adjusted the autopilot's heading to give her the impression that she was turning the plane, though she actually had no control of the aircraft. Shortly thereafter, Kudrinsky's son Eldar occupied the pilot's seat.[2] Unlike his sister, Eldar applied enough force to the control column to contradict the autopilot for 30 seconds. This caused the flight computer to switch the plane's ailerons to manual control while maintaining control over the other flight systems. A silent indicator light came on to alert the pilots to this partial disengagement. The pilots, who had previously flown Russian-designed planes which had audible warning signals, apparently failed to notice it.

 

Animation with CVR audio is here.

 

 

 

 

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Skywagon

if you are interested here is a link to some info on mcas   

https://www.avweb.com/

 

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Joe Frickin' Friday

The news this morning reported that the day before the Lion Air plane crashed, it experienced the same MCAS activation problem, but an off-duty pilot happened to be in the cockpit and showed the crew how to override that system with the previously mentioned button.   It was of course a different crew on the day of the actual crash, and so they were not aware of that MCAS override button - but one would have thought the incident on the day prior to the actual crash would have been reported so that the plane could be taken out of service and repaired.  

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Paul De

The how of these two flights crashing are now well into the investigation process, and the why of these crashes are now beginning to be brought to light. Early on the MCAS system and training jumped out as a first why.  The next why coming to light appears to be that the FAA may have not had the expertise and resources to adequately certify the 737 MAX ceding much of the certification process and systems review to Boeing engineers.  While I support a collaborative process between the private and public sectors to keep any certification process from turning into a bureaucratic mess it seems that Boeing may have had too much sway in the go gate decisions.  While I believe that no one at Boeing was intentionally covering up a fatal flaw in this aircraft's design and systems it is also can't be ignored that the FAA ceding this amount of authority to certify to Boeing exposed the process to make a No-Go decision with those with a greater conflict of interest to say No-Go.  This is a dilemma  for the US now as It seems the pendulum of government over-site and regulation has maybe swung too far to hands off and safety is beginning to suffer...and not just in aeronautics, we see signs of this in our food and water resources as well.

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John Ranalletta

Similar (IMO) to events leading to Challenger gasket failure.  There's lots of direct and indirect political and financial pressures to get these programs off the ground, so to say.

 

Boeing and other mfgs and operators exist in a zero defect world.  Too much caution is not enough until stockholders start grousing.

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Bud

My wife, daughter and grand daughter are due to fly back from SF in a couple of weeks on a Max 8. I'm personally happy to see them grounded until there is more info. When lives are at stake, error on the side of caution is the right thing to do.

 

Stockholders will start grousing when the price per share starts dropping as a result of these accidents. Someone one, somewhere made a decision that will not be cheap or easy to overcome. I doubt it was a "rogue, low level engineer" no more so than in the VW emissions fixing scandal.

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John Ranalletta

Southwest pilots had flown 41,000 flights with the Max w/o incident, so, that's reassuring.  

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