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Ethiopian airliner down in Africa

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Ethiopian airliner down in Africa

Old 22nd Mar 2019, 22:24
  #2361 (permalink)  
fdr
 
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Originally Posted by infrequentflyer789 View Post
Yup. From that same data source (and wishing vbulletin did tables):
737 NG: >20 years, >7000 built*, 20 hull losses, 591 dead
737 MAX: <3 years, ~350 built, 2 hull losses, 346 dead
So, if it's the crews or the airlines and not a problem with the plane, how do you explain the (order of magnitude at least) difference in crash rate?
On the surface that is an interesting observation, however it is the result of working with unequal population sizes and looking at temporal processes. Safety of a system is judged by exceptional events, losses in aviation. overall, historically loss rate has loosely followed a curve similar to long term average costs in economics, a broad U shape. initially there is a potential elevated risk from unknowns in a new system (airline, aircraft, route, operation etc..) which is mitigated by the control loop of the system. After an extended period of time new factors will come into play, which may elevate risk, loss of corporate knowledge, structural fatigue, ageing effects, apathy etc. these are also affected by the overall system response which should improve over time, and it does to an extent, SSID, SMS etc, but the underlying issues are non linear, and the system response is also non linear. Responses hardly ever are exactly correct and without new risks and unintended consequences.

Pretty much, systems are non linear. Estimates based on largely different samples are only correct in say QA sampling, and even then it comes with interesting maths due to uncertainties.

The NG didn't make headlines on safety with its introduction, however there were considerable fatalities from the start for various issues, and the fatality rate then reduced. The losses occurred in the noise of other events, and did not raise eyebrows. in more recent time, we continue to see over runs, loss of control, and similar crew related matters increase on the NG. The A320 started with a lousy run of losses, most due to knowledge issues with the crew related to the automation functions. the A320 loss rate continued to be managed, but there are still wild card events that occur to this day, including loss of control, CFIT and other odd events.

Both of the airlines involved with the most recent events have considerable track records with accidents, all of them raising questions on system integrity. For the regions that they operate in, at least in Africa, ET is one of the better performers. In Indonesia, safety records are always of concern, and JT has had its share of events and losses, which given its size of operation is probably not far from the average in the country. Indonesia like Africa has elevated operational risk factors, that even if comparative operational standards exist would probably lead to more incidents of the type that are most common there, overruns and offs of the runway. Loss of control events have occurred with various aircraft types in the region, for a multitude of reasons, crew turning off the attitude platforms, severe weather encounters...

The question on the Max is why did apparently trained crew not recognise and action a simple procedure in the events. Stab cut out has been fitted since the 40's, when stabs were the solution to high speed flight trim changes. Cutout is not a new device, nor is the problem of uncommanded stabiliser trim changes. So with the Max, what is the reason the crew didn't recognise the need to do a simple action to save the day? The concurrent stall warning would appear to have had a strong influence on the cognitive capabilities of the crew on the day. The revised event information of the JT aircrafts prior flight suggest that on the day that crew also needed additional input to successfully undertake corrective action. The CVR info on JT610 starts to suggest that the crew did attempt to manage the event in a calm manner, but with that process, the hand over of the flying duties from the capt to the copilot had a down side, the captain had been responding to the uncommanded trim, the copilot was not successful in doing the same and the flight path was promptly affected. It is indeed unfortunate that the captain following CRM best practice training principles takes action that appears to have had severe consequences. If the captain had recognised the trim problem consciously, cutout would have been an appropriate action. The copilot was handed an aircraft with the problem, and it is quite possible (unknown at the moment) that the captains successful reactions to the trim problem were subconscious, and that it was being managed so was not communicated at the time of the transfer to the copilot. That point is going to need consideration for any real longterm improvement in problem cueing, where the comprehension of the crew of the actual status is critical. Crew SA is paramount, and what appears to be 3 cases so far had problems in this area.

I don't think that these operators are unique in the issue of SA at all.

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Old 22nd Mar 2019, 23:02
  #2362 (permalink)  
 
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Originally Posted by Ian W View Post
---snipped--
Would you really let trim carry on monotonically trim down 2.5 units every 5secs and not switch it off? l can only assume that you would. It is really immaterial why the trim was operating it could be a now dead rodent chewing through an electric cable, you just want the trim to stop and two switches that have been there forever allow you to do that. I am sure that Boeing is aghast that their NNCs for trim runaway were being read in such a contracts lawyer fashion. Perhaps they should review the semantics of all memory items and NNCs/checklists and any training that reinforces those limiting semantics.
The Lion Air crews DID NOT KNOW how many units or even how long this goblin would trim. They didn't even have 10 seconds to observe the trim wheel amidst all the warning. To them, what happened to AC was exactly like what was reported/read in the pre-flight briefing: "STS running the wrong direction due to speed difference". As reported on the Lion Air's A-SHOR:


The conflicting data's [ALL INDICATORS were out of whack - previous flight at least the SIC's indicators were still valid, but not this one], perhaps observing the surrounding, rummaging through the QRH, communicating with the ATC, etc..., were all conspiring to overload their mental faculties and sensory perception. And, to top things off, they didn't have the luxury of having a dead head sitting on the jump seat helping to observe and analyze what's going on.

On the preliminary report, CAPT and/or FO of the previous flight apparently had failed to mention the stick-shaker condition and the NNC for runaway trim they'd performed to overcome what thought to be the STS trim going the wrong way. The last few facts are very much what makes the hole in the Swiss cheese lined up.

Last edited by patplan; 22nd Mar 2019 at 23:07. Reason: clarity
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Old 22nd Mar 2019, 23:07
  #2363 (permalink)  
 
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I'm thinking that the JT610 P1 retrimmed completely from each MCAS excursion, but P2 did not allowing the nose down trim excursions from MCAS to accumulate while P1 was head down in the manual - which had no information on MCAS.

​​​​​​Will the CVR, once released, show whether P1 communicated to P2 what P1 was doing with trim before handing over control?

Remember also that stick shaker was adding workload.

We now know that a faulty AoA will both trigger shaker and MCAS once at a safe height where flaps are normally retracted and more thorough diagnosis of the situation can begin, but then they were handed a new problem.

​​​​​
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Old 22nd Mar 2019, 23:21
  #2364 (permalink)  
 
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Originally Posted by Ian W View Post
How about the NNCs in all 737s for Runaway Trim? oh of course it is not 'runaway' as it is only repeated (reads from dictionary) nose down trim, so I will let the Stab Trim fly me into the ground rather than switch it off.

Would you really let trim carry on monotonically trim down 2.5 units every 5secs and not switch it off? l can only assume that you would. It is really immaterial why the trim was operating it could be a now dead rodent chewing through an electric cable, you just want the trim to stop and two switches that have been there forever allow you to do that. I am sure that Boeing is aghast that their NNCs for trim runaway were being read in such a contracts lawyer fashion. Perhaps they should review the semantics of all memory items and NNCs/checklists and any training that reinforces those limiting semantics.

Yes recognizing the trim issue is the heart of the matter. That was exactly my point. You cannot make this into "switch off the AP and fly the plane"-scenario. A pilot with poor manual flying skills but being able to identify the issue does much better than a skilled flier who isn't able to identify the issue.

It doesn't help you to switch off AP and AT and stabilize things by flying "power and pitch". You can't because you don't achieve a stable pitch.

So hence my real point, the challenge: Show me that up until six months ago anyone suggested making "stab trim cutout" part of a "disengage auto and fly the plane" if you don't have a clue what the issue is.

The "should they have been able to catch on to the trim issue?" discussion has been done ad nauseam. In my personal opinion the only way to hypothetically get the truth there would be if you could find 20 average pilots who had been in coma for the last six months and put them through a surprise sim scenario replicating an actual MCAS-misfire.
Then we would know how the average pilot would have done.What people with all the facts are now convinced they would have done is not relevant evidence to me.

I bet that if you asked the average px if they were confident that they'd get a life jacket on in case of a water landing landing the vast majority would say yes. They've seen the briefing a gazzillion times. How hard can it be?

Yet we know how many out of a 150 px in the "Sully flight" actually managed to put on a life jacket properly waist strap and all. Was it a three digit number? Was it a two digit number?
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Old 22nd Mar 2019, 23:24
  #2365 (permalink)  
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Having read every post since the first crash I'm at a loss as to how we're not, for the most part, progressing logical thought.

To see this 'Why didn't they fly the plane'. chanted out again and again is beyond offensive. The congressman has "been in contact with . . ." etc., etc. I'm sure he would have handled the MAX like a Warbird, and saved the day.

For the first time in many, many years on PPRuNe, I'm allowing myself to really bristle at some of the posts.

There are so many factors coming out of the woodwork. The Seattle Times was the first to spell out some of the home truths. The technical article today left me astonished. The rear switch (in the column) removed, and the function of the left and right Stabilizer cut out switches changed in the MAX. ??? Have I missed these points? Are they not correct? They're major factors.

'gums' has a lot of experience and his considered thoughts today about being in the hot seat for those first moments says a lot. Mostly, the problem was NOT bloody obvious, it was, insidious - proceeding in a gradual, subtle way, but with very harmful effects. A word I chose carefully in one of my earlier posts.
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Old 22nd Mar 2019, 23:28
  #2366 (permalink)  
 
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Originally Posted by RatherBeFlying View Post
I'm thinking that the JT610 P1 retrimmed completely from each MCAS excursion, but P2 did not allowing the nose down trim excursions from MCAS to accumulate while P1 was head down in the manual - which had no information on MCAS.

​​​​​​Will the CVR, once released, show whether P1 communicated to P2 what P1 was doing with trim before handing over control?

Remember also that stick shaker was adding workload.

We now know that a faulty AoA will both trigger shaker and MCAS once at a safe height where flaps are normally retracted and more thorough diagnosis of the situation can begin, but then they were handed a new problem.

​​​​​
The LEFT/CAPT shaker was triggered immediately, IAS/ALT disagreed as well. Meanwhile, MCAS trim was activated after the AC was flap up.
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Old 23rd Mar 2019, 00:07
  #2367 (permalink)  
 
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Salute!

Apparently the Chuck Yeager cadre here lives on....
So today we see other examples:
That one is esay [sic], you cross check the 3 airspeed indicators, thrust, performance and attitude to determine if the stickshaker is real or false.
errrr, sir? What's with the airspeed and altitude warning lights ? "No problem, pilgrim, I can tell our speed is O.K. by how fast the trees are going by and the ground ain't getting a lot bigger"

stick shaker is on one side only, it is an AOA failure & not a valid stall warning.
errrr, sir, my stick ain't shakling, therefore, it must not be a valid stall warning, right.? I guess the airspeed and altitude and feel difference lights must also be false, ya think? "trust me, dweeb, I know a stall when I feel one"
Beam me up.

Gums sends...
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Old 23rd Mar 2019, 00:14
  #2368 (permalink)  

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Originally Posted by Loose rivets View Post
Having read every post since the first crash I'm at a loss as to how we're not, for the most part, progressing logical thought.

To see this 'Why didn't they fly the plane'. chanted out again and again is beyond offensive. The congressman has "been in contact with . . ." etc., etc. I'm sure he would have handled the MAX like a Warbird, and saved the day.

For the first time in many, many years on PPRuNe, I'm allowing myself to really bristle at some of the posts.

There are so many factors coming out of the woodwork. The Seattle Times was the first to spell out some of the home truths. The technical article today left me astonished. The rear switch (in the column) removed, and the function of the left and right Stabilizer cut out switches changed in the MAX. ??? Have I missed these points? Are they not correct? They're major factors.

'gums' has a lot of experience and his considered thoughts today about being in the hot seat for those first moments says a lot. Mostly, the problem was NOT bloody obvious, it was, insidious - proceeding in a gradual, subtle way, but with very harmful effects. A word I chose carefully in one of my earlier posts.
Scratching my head now: If the cause of these two accidents was an MCAS event due to a faulty sensor, then the solution would be to click off those two Stab Trim Cutoff switches, then fly the airplane, make a landing, then go to the hotel and have a beer.
I have been practicing the Stab Trim-Run away on Boeing’s in various simulators for over 30 years and I would Hopefully remember these 2 switches if it happened in real life.
If this is beyond what is to expected of airline pilots these days, then I will take the train.
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Old 23rd Mar 2019, 00:14
  #2369 (permalink)  
 
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Originally Posted by safetypee View Post
[LEFT]Alchad, #2365,
there is merit in your linked reference. https://www.satcom.guru/2019/03/ethi...lion.html#more
It's said that angle of attack disagree was 22°5 (at least on Lion Air). But the AoA vane does not directly measure angle of attack, but angle of airflow around the fuselage, which is higher - about twice the angle of attack - due to aerodynamics around a long body

That means the error at the Angle of Airflow vane was not 22°5 but about 45°, which correspond to the angle between AoA screws.
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Old 23rd Mar 2019, 00:19
  #2370 (permalink)  
 
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"Much like tapping the brake pedal in a car to disengage cruise control, a sharp tug on the controls of older models of Boeing Co’s 737 used to shut off an automatic trim system that keeps the plane flying level, giving the pilot control.

But Boeing disabled the “yoke jerk” function when it brought out the 737 MAX, the latest version of its top-selling jet - and many pilots were unaware of the change, aviation experts told Reuters....

...pilots would have needed to know that MCAS existed, that it had unusual power to force the plane down and that “a hard pull on the yoke” would no longer turn off the automatic trim that uses MCAS, John Hansman, an aeronautics professor at MIT, said in an interview.

“That wasn’t clear to the pilots flying the airplane,” Hansman said. “The training material was not clear on that.”"


https://www.reuters.com/article/us-e...-idUSKCN1R322M

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Old 23rd Mar 2019, 00:36
  #2371 (permalink)  
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Towhee:

So it seems that rear switch in the pole has been removed on the MAX.

That is a major difference. I wonder if it was mentioned in the few minutes of conversion notes.

TowerDog:

......If the cause of these two accidents was an MCAS event due to a faulty sensor, then the solution would be to click off those two Stab Trim Cutoff switches, then fly the airplane, make a landing, then go to the hotel and have a beer.
Well, that's the point. If. As in, If you know it's happening.

First and foremost: it's not a stab trim runaway in the usual sense. The inputs, resets and then re-datumizing is quite, quite different. Plus you're in a chaotic condition before 1000' and flaps up.

Remember, you observe the STS running on a daily basis, and the MCAS actions are so intermittent and subtle that you don't know there's something inputting into the Horizontal Stabilizer from that source. You're not going to be able to diagnose what's happening while under stress - especially if you've never been told there's a software system that's taking this mysterious action.
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Last edited by Loose rivets; 23rd Mar 2019 at 01:03.
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Old 23rd Mar 2019, 01:11
  #2372 (permalink)  
 
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Originally Posted by deltafox44 View Post
It's said that angle of attack disagree was 22°5 (at least on Lion Air). But the AoA vane does not directly measure angle of attack, but angle of airflow around the fuselage, which is higher - about twice the angle of attack - due to aerodynamics around a long body

That means the error at the Angle of Airflow vane was not 22°5 but about 45°, which correspond to the angle between AoA screws.
I don't believe I really get this point. It sounds OK if indeed the airflow was not parallel with the fuselage at some locations. But why wouldn't the streamline effects be well known beforehand from wind tunnel testing and the AOA vanes located at a point where the lines are truly parallel?
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Old 23rd Mar 2019, 01:24
  #2373 (permalink)  
 
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Originally Posted by deltafox44 View Post
That means the error at the Angle of Airflow vane was not 22°5 but about 45°, which correspond to the angle between AoA screws.
Are you suggesting the AOA sensor was installed 45° from the proper angle? Is that even possible? (No keyway or other locating method?)
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Old 23rd Mar 2019, 01:25
  #2374 (permalink)  
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So what's being said is, the AoA vane hub is rotated in error by one screw-hole place?

For it to be able to be so misaligned seems impossible - for the main casting to not be designed D shaped, or have a flat edge would be deeply worrying. But it is a compelling scenario since the output error is so consistent.

I'd personally discounted damage to the vane after the second crash, and would be mystified if it were to be a mechanical problem since the vanes are so strong. They look frail, but they're anything but.
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Last edited by Loose rivets; 23rd Mar 2019 at 01:47.
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Old 23rd Mar 2019, 01:30
  #2375 (permalink)  
 
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Originally Posted by Loose rivets View Post
So what's being said is, the AoA vane hub is rotated in error by one screw-hole place?

For it to be able to be so misaligned seems impossible - for the main casting to not be designed D shaped, or have a flat edge would be deeply worrying.
I think that it's been established elsewhere on the thread/s that there are lugs or something that means that they can only be installed in the correct orientation - but tdracer has said that he has seen them carefully machined off so that they can in fact be incorrectly fitted...
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Old 23rd Mar 2019, 02:32
  #2376 (permalink)  
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The only reason I can think of for doing that would be for one unit to be able to fit a new aircraft. Hmmm . . . now let me think.

'We could make those NG vanes fit the MAX if we shaved the lug a little.'
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Old 23rd Mar 2019, 03:23
  #2377 (permalink)  
 
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Since it has not been disclosed the conditions and settings where the engine nacelles provide extra lift and nose up the ac (if/when MCAS kicks in)...an AoA sensor is meaningless.

The UT AoA sensors have an offset bolt pattern to insure correct installation.


Last edited by Smythe; 23rd Mar 2019 at 03:39.
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Old 23rd Mar 2019, 03:39
  #2378 (permalink)  
 
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Operational useof angle of attack - boeing

Does this help

OPERATIONAL USEOF ANGLE OF ATTACK
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Old 23rd Mar 2019, 03:39
  #2379 (permalink)  
 
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A nuance that I have not seen stated here previously, one well worth considering as people go back and forth arguing over whether or not the pilots should have saved the day:

MCAS introduced a single point of failure that without pilot intervention in a highly specific way results 100 percent of the time in the aircraft flying itself into the ground. Either the pilot nails the answer to the question while all hell is breaking loose and g-loads are all over the place (about a system which they had no awareness existed), and they do it within a very very short period of time, or the airplane will 100 percent fly itself into the ground. Straight into the ground BTW.

I cannot recall any other instance of a single point of failure system or sensor (or any system for that matter) on a commercial airplane which places the airplane in a state where the only chance for survival is a single action by the pilot, without which the airplane will crash. Once the AOA failed in Indonesia the airplane was essentially trying to fly itself into the ground. The Capt. kept that from happening for a bit, then it succeeded when he handed the airplane to the FO to grab the book and look for an answer that was not in fact there.

I can recall tons of technical issues that resulted in incidents and accidents, in fact I’ve survived a few on my own, but none where the failure of a single sensor meant that a perfectly good airplane was literally trying to kill everyone on board.

We can go round and round about whether or not the flight crew should have been able to aviate their way out of the circumstance they found themselves in, but if the penalty for failure to act quickly enough and perfectly enough on any given in-flight issue on a single sensor and a system about which you knew nothing was immediate death for you and your passengers would you still choose to fly?? Are you that certain of your perfection in the air??

If you knew that there might be a system on your airplane that you knew nothing about and that had the power to command the airplane to try to kill you, would you fly in that airplane, or god forbid take command of it with a couple hundred people in your care??

That is exactly what Boeing did to every MAX crew that flew the airplane. And whether with ill-intent or not they did it knowingly and deliberately. We don’t know them now, but Boeing is filled with smart people. Someone(s) knew exactly what Boeing was doing putting MCAS into service in the clandestine way they did, and I presume it was done that way for an (as yet unknown) reason. Those people will speak up at some point, or I hope they will anyway because it was no accident that MCAS anonymously arrived in the MAX without flight crews being made aware of its presence.

We can argue that the Lion Air crews who successfully survived an otherwise fatal experience should have alerted the airline, and we can argue a ton of other things too.

What we cannot argue, for one moment, is that the regulatory system that allowed Boeing to self-certify safety of the 737 MAX functioned as intended.

What we cannot argue is that Boeing and the regulatory system produced a safe airplane.

Quite to the contrary they produced an airplane that with the right type of single sensor failure would immediately try to kill everyone on board, with only the immediate and correct intervention of the pilots, who had no idea that the system trying to kill them even existed, to prevent that outcome.

The surprising thing isn’t that it happened, it’s that it took so long to happen.

Regards-
dce
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Old 23rd Mar 2019, 03:40
  #2380 (permalink)  
 
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Originally Posted by GH5 View Post
There is a Boeing document made around year 2000 regarding how Boeing defines AOA I cannot post the link but the cover sheet label is
" operational use of angle of attack on modern commercial airplanes "

Aero 10 Flight operations
John cashman director
brian d kelley technical fellow

can be downloaded as a pdf or viewed in html
Here is your link: OPERATIONAL USE OF ANGLE OF ATTACK (pdf)
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