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Ethiopian airliner down in Africa

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Ethiopian airliner down in Africa

Old 1st Apr 2019, 15:13
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I find this particulary disconcerting ...
Ethiopian officials asked the French aviation accident investigation bureau BEA, which downloaded data from the black boxes, to permanently delete that information from its servers once it had been transmitted to Ethiopian authorities. The BEA has confirmed complying with the request.
If this a normal procedure, it still seems strange that the data should be deleted by BEA while investigations are still ongoing. Otherwise it would suggest the Ethiopian authorities are trying to conceal something,
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Old 1st Apr 2019, 15:17
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Smile

Actually Wee, it was Vilters who mentioned the rate - I just like the angular presentation in relation to an angular sensor.

Check out the 737 flap position indicator for instance. That could be done on a strip but it wouldnt be so obvious.

As you say, lets agree - to disagree.
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Old 1st Apr 2019, 15:26
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MPN11
Presumably the information is safely stored everywhere else except the servers?????
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Old 1st Apr 2019, 15:26
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Originally Posted by TTail
Now that the MCAS is being classified as a subsystem of the STS wouldn't the below paragraph - possibly without the EFS module part - read like something you'd find in a Boeing MAX AFM if the intent were to give a brief non-technical description of MCAS?

"As airspeed decreases towards stall speed, the speed trim system trims the stabilzer nose down and enables trim above stickshaker AOA. With this trim schedule the pilot must pull more aft column to stall the airplane. With the column aft, the amount of column force increase with the onset of EFS module is more pronounced."
No, because STS is triggered by change in airspeed (in either direction), and MCAS is triggered by angle of attack, and only by high, not by low values. So although they sit in the same box, and one may even be considered a subsystem of the other, their functions and activation criteria are fundamentally different.

STS doesn't even have anything to do with stall, or stick forces, but is about speed stability. Only the first sentence of the paragraph you quoted is about the STS, the rest is about the Elevator Feel Shift module.

The speed trim system (STS) is a speed stability augmentation system designed to improve flight characteristics [...]. The purpose of the STS is to return the airplane to a trimmed speed by commanding the stabilizer in a direction opposite the speed change.
And if someone didn't catch it the first time, it repeast a few lines later:

As the airplane speed increases or decreases [...], the stabilizer is commanded in the direction to return the airplane to the trimmed speed.
Nothing about stall at all. That it is also active close to a stall is mostly a side-effect of the speed stability augmentation.

Bernd
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Old 1st Apr 2019, 16:57
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Originally Posted by bsieker
STS doesn't even have anything to do with stall,
Careful, the function of STS is nothing to do with avoiding stall (ditto MCAS), but the implementation does have an AOA input and does behave differently at high AOA.

Copy/pasting from the AMM (my emphasis):

JPL 701-799, 803-899, 901-999 The stall detection circuit monitors the flap position and the angle of airflow. Near stall, the speed trim function trims the stabilizer to a nose down condition to allow for trim above the stickshaker AOA and idle thrust. The trim continues until the stabilizer gets to its limits or the aft column cutout position is exceeded.

If the roll angle from the ADIRU is more than 40 degrees, it opens an electronic switch and stops the speed trim signals.

JPL 801, 802 The stall detection circuit monitors the flap position and the angle of airflow. If it calculates that the airplane is near a stall condition, it opens a switch and stops the speed trim signals.

If the roll angle from the ADIRU is more than 40 degrees, it opens the same switch and stops the speed trim signals.
As I understand this, STS normally trims nose up when you add power (speed), on early revisions of the 737-800 this is prevented at AOA near stall (for obvious reasons). On later revisions this was modified so that near stall AOA, STS will trim down to allow it to then trim up if/when you add speed (and thus maintain speed stability). I believe I've seen rumours, maybe here, that this revision was needed to achieve EASA certification.

I think it is likely that the idea (and maybe some of the implementation) for MCAS came from this part of STS.

Last edited by infrequentflyer789; 1st Apr 2019 at 16:58. Reason: twypo
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Old 1st Apr 2019, 17:25
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Originally Posted by meleagertoo
There's national pride and reputations at stake here, and I don't mean in the US. Boeing are big enough to take whatever's coming on the chin an deal with it. Are Ethiopian/Ethiopian government?
As ever the two accidents will almost certainly come down to a relatively benign aircraft failure getting out of hand due to faulty human factors.

How did the ET pilots fail to recognise a failure that must heve been just about the sole topic of conversation in the crew room for the previous few weeks, analysed and discussed to death by everyone on the fleet? One that Boeing had published to all MAX operators with extreme urgency?`
What action did the ET training department take over it?
Surely that advice was passed on to the line pilots? If so how can it not have taken root? ...or was it?
Was the crew experience-mix even remotely suitable? Was it compatible with published company policy?

The facts from the recorders must have been known to and publishable by the authorities for a couple of weeks now - this delay is beginning to look like unwillingness to publish, not inabiity.

At this stage one can only surmise the whys and wherefores, but chances are there's stuff in there that the publisher either doesn't want publishing or hasn't included when the other interested parties believe it should be.
And that ain't good for the whole point of flight safety.

Ethiopia would do well to ensure total transparency here to reassure the rest of the world that they posess a responsible safety culture. Failure to do so will far outweigh any temporary saving of face if they do otherwise.
Sadly, having spent some time in the country I'm not holding my breath that face-saving won't turn out to be the order of the day, and some 'in charge' Colonel telling us they'll do it their way is hardly reassuring.
You nailed it. The first accident left no doubt what the problem was and what to do if it happened again. Top of mind for every Max driver on the planet. Where were those two? There appears to be much more to this than MCAS alone.
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Old 1st Apr 2019, 19:00
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Originally Posted by bsieker
No, because STS is triggered by change in airspeed (in either direction), and MCAS is triggered by angle of attack, and only by high, not by low values. So although they sit in the same box, and one may even be considered a subsystem of the other, their functions and activation criteria are fundamentally different.

STS doesn't even have anything to do with stall, or stick forces, but is about speed stability. Only the first sentence of the paragraph you quoted is about the STS, the rest is about the Elevator Feel Shift module.



And if someone didn't catch it the first time, it repeast a few lines later:



Nothing about stall at all. That it is also active close to a stall is mostly a side-effect of the speed stability augmentation.

Bernd
Hi Bernd.

Thanks for your input. I do not pretend to be anywhere close to fully understanding these systems although contributors in this thread have certainly inceased my knowledge tremendously.

It's funny that your quoted passages are the exact sames ones I have underlined in my manual! I'm still not convinced though, that your last sentence is 100% accurate :"That it is also active close to a stall is mostly a side-effect of the speed stability augmentation". The headline where my quoted paragraph is taken from, follows the section that gives the general explanation of the STS where your quotes are from, and it reads Stall Identification. The first sentence here says: "Stall identification and control is enhanced by the yaw damper, the Elevator Feel Shift (EFS) module and the speed trim system. These three systems work together to help the pilot identify and prevent further movement into a stall condition." There are no caveats in terms of CG position, weight or thrust condition for this to work so it is atleast possible to interpret this as something more than just a side effect of the STS.

But this is not really my main point. The thing is, Boeing has mentioned in several places in their manual that there is another system, in addition to the pilot and autopilot, that has the authority to run the THS in flight - the STS. If you consider this alongside the "Runaway Stabilzer" NNC and Boeing's opening statement that "....checklists cannot be created for all conceivable situations and are not intended to replace good judgement", it would not be too far fetched to see how Boeing could argue their case that any qualified crew should be able to handle the Lionair situation (and possibly the Ethiopean if it turns out the culprit is the same).

I'm not saying I agreee with this, in fact after having read on these pages how MCAS works, I'm in a state of shock and utter disbelief that a system like this could pass quality and safety checks. But no matter where in the chain the fault originates - from the AOA vane to the FCC - I think it will boil down to whether Boeing will find acceptance for their claim that the pilot should be the ultimate safety mechanism if something should go wrong in these scenarios. I do not think an AOA indicator or AOA DISAGREE lights would have made much difference - and the Boeings I flew had both. The major thing to me that sets these three flights apart (the two Lionair and the one Ethiopean) is the presence of a third crew member. This added mental capacity seems to have saved the day and the lives of many people. And I think this is what Boeing will argue. Not the introduction of a third pilot but the fact that experience, training, skills and knowledge of any two pilots in the cockpit of one of their airplanes should be able to free up enough capacity to deal with situations similar to those we are discussing.
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Old 1st Apr 2019, 19:15
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infrequentflyer789, TTail,

thanks a lot for your input. Food for thought.

It would appear that, even without MCAS, there is more to automated trimming on the 737 (even pre-MAX) than meets the eye. I'm quite experienced in reading and interpreting FCOMs and related material, but sometimes this feels like deliberate obfuscation.

I have a feeling Boeing's idea that the pilot has to save the day will fall short of regulators' approval. They can no longer maintain after two accidents (where in the second one the crew almost certainly knew about the first) that any pilot "without exceptional skill" (which is the regulatory requirement, and, if you think about it, is a lot less than "average") will be able to handle it.


Bernd
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Old 2nd Apr 2019, 01:25
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How did the ET pilots fail to recognise a failure that must heve been just about the sole topic of conversation in the crew room for the previous few weeks, analysed and discussed to death by everyone on the fleet?
Whats a crew room?
My comment is obviously facetious but it’s there to highlight that the way we share information has changed significantly over the last decade.
I now arrive at the gate 55 mins before departure to meet an F/O that I often have never met, we work together and then his/her name will ring a bell when it’s on my roster six months later but I can’t picture them.
I certainly don’t chat with other Captains as was the way when I joined up many years ago.
The safety related information we get sent can be pored over and dissected in an armchair and discussed online........or it can be deleted without reading between feeding the cat and putting the rubbish out. Nobody knows if the latter has occurred.

It is easy to become isolated from the company ‘safety culture’ even if it is a strong one.

Putting a Safety Notice out digitally is very very cheap. When faced with a training issue/problem, it is far more attractive commercially to take this route and regulators appear happy to allow companies to deal with most training issues in this manner. The person who decides whether to bring 500 pilots into the classroom/ simulator v’s firing off a digital memo is financially incentivised to choose the latter.

I will be interested to read how Ethiopian responded to the Lion crash. I will be analysing whether or not the head of their Safety Department knew, without doubt, that every one of their Max pilots was fully aware of how the MCAS event manifested itself, and had at least chair-flown their response regarding disconnecting the stab trim cut-out switches.
If their chosen strategy involved no method of confirmation that each pilot fully understood those things then it was insufficient.
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Old 2nd Apr 2019, 02:07
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I come from the past. We do things different there. If something like the Lion Air crash happened to any airplane I was flying, nothing would have stopped me from finding out every detail about it and having a plan for what to do if it happened to me. On my own. Before there was any internet.
I did not know anyone who thought otherwise.
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Old 2nd Apr 2019, 02:42
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Originally Posted by b1lanc
The Airbus strategy (as I recall which was about 4 decades back) was to deliver the code to 3 companies in three different countries, none of whom knew of the others existence. AB expected each would find some unique code exceptions by doing so.
Hi b1lanc,

It's also been a long time since I was in Uni (B.Eng Software Engineering) and my old Engineering/Reliability Prof. had us study the Airbus methodology. As I recall, you've got the gist - but I think some of the specifics have been mixed up in translation.

It wasn't three teams, it was two, and it as far as I can recall it wasn't contracted out to different companies - I believe it was all in-house. The reason for this was because we're talking roughly 1984-88, and at the time all of the techniques they were using were pretty much on the bleeding-edge of what had gone before - though built on tried-and-tested principles, all the way down to algebraic engineering expressions that hurt my head to this day. Also, while I can't be certain that this was a motivation, one of the overriding goals of developing the FBW system was to provide an unprecedented level of commonality within their product range - keeping things in-house reduced the risk of losing that potential competitive advantage.

Also, as I understood things, dissimilar/differential implementation wasn't a matter of "find[ing] code exceptions" as much as it was aimed at reducing the risks of implementation errors in the code (as opposed to specification and/or design problems with the underlying logic) causing flight control problems - as I recall the code from both teams underwent multiple reviews and if a single similarity was found, one of the teams was tasked with finding a different implementation of the logic. In effect this was an extra "belt and braces" level of redundancy in the code layer - and interestingly, Boeing did not follow suit in this manner when developing the B777 (and later FBW types). The unparalleled safety record of the B777 could be used to argue that while dissimilar implementation was completely necessary for a pioneering effort, it might have been less so once the concept was proven.
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Old 2nd Apr 2019, 02:56
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I come from the past. We do things different there. If something like the Lion Air crash happened to any airplane I was flying, nothing would have stopped me from finding out every detail about it and having a plan for what to do if it happened to me. On my own. Before there was any internet.
Thats great Ferry pilot, I’m in the same boat. That doesn’t change my point though, things are different now and there are always going to be pilots who have a different attitude to you or me so we need to look at the way we train, recruit, and disseminate information to mitigate against the pilot who doesn’t research and study like you do, the pilot who was on annual leave for three weeks and then didn’t read all the memos because he or she knows that most are garbage and nobody is watching anyway.
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Old 2nd Apr 2019, 03:29
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Originally Posted by Unhooked


Thanks for the reply but my comparison was never meant to be in in depth technical discussion. I have flown widebody and narrow bodied Airbus for over 10 years and Boeing's for even longer so the Airbus flight protection system's summary wasn't nessecary.

The simple point I was actually trying to make is the fact that the flight control inputs we as pilots make can be overridden by 'computers' in both the Airbus abnormal V alpha prot and the Boeing MCAS situation. This would not of happened before the advent of flight control computers and fly-by wire technology.
I certainly didn't want to get drawn into a deep technical comparison, it was not my intention.
I now remember why I stopped contributing to these forums. There is always some smart arse hiding behind his keyboard trying to show the rest of the world how brilliant they are.
Good morming. My comment was aimed to the people that donít have a so deep knowledge of the Airbus flight control system and not specifically to you. There are many people reading here that could simply make some general and wrong assumptions from your original post. About technology... I have flown a lot of second generation fighter bombers and first generation four engine jet transport aircraft... a lot of fun either way. I donít like when pilots are taken out of the picture but that is good for me...today most of my valid second-in-command cannot just make a proper landing with 20 knots crosswind. About the smart arse, you can always delight me with all the contributions and efforts you have profused in changing the actual industry situation during your long flight career.
Happy landings.
JF
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Old 2nd Apr 2019, 07:23
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infrequentflyer789 #2884,

Thank you for the interesting information.
A conclusion from this is that the vane output was corrupt, but perhaps without considering the wiring into ADIRU and thence to FCC.

There is still no explanation from investigations or Boeing as to how AoA could be corrupted.
As currently described, the Boeing modification limits the difference in AoA which MCAS uses, but presumably not so for other systems.
Thus if the AoA corruption is ‘new’ to the 737 Max, then other systems could suffer more frequent events after the modification because AoA corruption would still occur.

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Old 2nd Apr 2019, 08:04
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Originally Posted by 73qanda
Thats great Ferry pilot, Iím in the same boat. That doesnít change my point though, things are different now and there are always going to be pilots who have a different attitude to you or me so we need to look at the way we train, recruit, and disseminate information to mitigate against the pilot who doesnít research and study like you do, the pilot who was on annual leave for three weeks and then didnít read all the memos because he or she knows that most are garbage and nobody is watching anyway.
Also, time was when the piloting profession would commonly, and indeed was even expected to, hav their own thoughts and deep interest like this. Now it's not only dumbed down but all about just about compliance, fuel consumption league tables,and following what someone else has written down in SOPs. If they haven't envisaged it there, hey ho ...

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Old 2nd Apr 2019, 09:51
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Why superior pilot skill?

Originally Posted by bsieker
infrequentflyer789, TTail,

thanks a lot for your input. Food for thought.

It would appear that, even without MCAS, there is more to automated trimming on the 737 (even pre-MAX) than meets the eye. I'm quite experienced in reading and interpreting FCOMs and related material, but sometimes this feels like deliberate obfuscation.

I have a feeling Boeing's idea that the pilot has to save the day will fall short of regulators' approval. They can no longer maintain after two accidents (where in the second one the crew almost certainly knew about the first) that any pilot "without exceptional skill" (which is the regulatory requirement, and, if you think about it, is a lot less than "average") will be able to handle it.


Bernd
Dear Bernd,

Have a look at this video of American Airlines pilots talking about the MCAS system after experiencing it at Boeing's 737 MAX simulator:

Pilots talk to King 5 about 737 Max fix (You tube - I am not allowed to post URLs yet)

At 01:25 one of the pilots says, "the natural pilot reaction is to not allow the airplane to become uncontrollable."

Now I understand that having stick shaker on right after Takeoff, IAS disagree and so on is confusing and overwhelming. But there are airspeed unreliable memory items for that scenario and from what I have read in the preliminary report the crew did not carry those out, which would be the first issue already one could look at. Just food for thought: They could have carried out the airspeed unreliable memory items and then used the pitch and power values for flaps extended as there would not really have been a need to retract the flaps as one would want to return to the airfield with the problem at hand anyway. Under those circumstances MCAS would not have activated at all.

Instead they did retract the flaps 2:05 Minutes after Take off. By that time at least the intial surprise factor concerning the stick shaker going off should have been gone. Based on the faulty sensor signal MCAS moved the horizontal stabilizer creating a nose down movement. What happens in the cockpit at that time? The stabilizer trim wheels can be heard and seen as they are moving and the first time MCAS activated they moved for 10 seconds, which would already qualify as a criteria for a stab trim runaway. If understandably due to all the confusion the pilots didn't notice the trim wheels, the pilot flying will still feel on his control yoke that the force required to maintain the desired pitch attitude has become significantly greater. Coming back to the statement of the American Airlines pilot: what is the natural thing to do now? The pilot will pull a little more on the yoke and then he will trim via the electric trim switch to counter the forces felt. This is the most basic aspect of flying the aircraft and even a Cessna pilot will fly a plane in this way. It has nothing to do with superior skills. In fact this is exactly what the pilot flying did:

After the flaps reached 0, the DFDR recorded automatic aircraft nose down (AND) trim active for 10 seconds followed by flight crew commanded aircraft nose up (ANU) trim.

This actually went on for more than 30 times. Tragic to think about is the fact that even this procedure could have saved the plane. It isn't even necessary to think of the stab trim runaway memory items and set the cut out switches to cut out. The pilot can also just continue to counter the MCAS induced horizontal stab trim nose down movement with an equal horizontal stab trim nose up movement until the flaps are retracted again for landing which is when MCAS will stop operating. Nonetheless after 30 times trimming against the nose down trim movement, it is hard to understand why the pilots did not think to set the stab trim cut out switches to cut out. Every 737 pilot knows that doing this will disable any system to move the horizontal stabilizer if there is unwanted movement. Also does it matter if one knows that the MCAS is moving the stab trim wheels in the cockpit? If there is an engine fire -for example- it also doesn't matter what is causing the fire. All that matters is that I shut down the engine via the engine fire memory items. If my stab trim wheels continue to move even though I don't want them to, all that matters it that I stop this from happening via a procedure that all 737 pilots must know. What does this have to do with superior pilot skill?

We have to wait for the official results to come out and in the case of Ethiopian we really do not know yet what actually happened. Also I realize that it is easy to comment on the accident flight when I am sitting at home on my couch. In fact, as a pilot I have already experienced plenty of situations where I did not have the full situational awareness required and I have of course made plenty of mistakes already. Nonetheless, solely based on the official information that is available so far it seems as if the accident could have been prevented by the crew simply flying the aircraft in a way that comes natural to a pilot and by applying the memory items that they were trained for.
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Old 2nd Apr 2019, 09:54
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Originally Posted by ferry pilot
I come from the past. We do things different there. If something like the Lion Air crash happened to any airplane I was flying, nothing would have stopped me from finding out every detail about it and having a plan for what to do if it happened to me. On my own. Before there was any internet.
I did not know anyone who thought otherwise.
"...........and hear, hear to that !
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Old 2nd Apr 2019, 10:06
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Nonetheless, solely based on the official information that is available so far it seems as if the accident could have been prevented by the crew simply flying the aircraft in a way that comes natural to a pilot and by applying the memory items that they were trained for.
ďIn the way that comes naturalĒ..... I thought maximum use of automation was the call of the decade? Hand flying now days often takes significant cognitive effort because of the automation policies in place at most Airlines, and thatís without contradictory information being presented.
ďthat they were trained for.......Ē. .I suspect we are going to find out that the training received to transition to the Max was insufficient.
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Old 2nd Apr 2019, 10:14
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Originally Posted by 73qanda

“In the way that comes natural”..... I thought maximum use of automation was the call of the decade? Hand flying now days often takes significant cognitive effort because of the automation policies in place at most Airlines, and that’s without contradictory information being presented.
“that they were trained for.......”. .I suspect we are going to find out that the training received to transition to the Max was insufficient.
It may very well be that the pilots were used to relying on automation and I have thought of that being an issue as well. However, being able to maintain a certain pitch attitude and trimming out the forces felt as one is doing that... are you suggesting pilots have even forgotten to do that?

Furthermore they did counter the nose down trimming of the MCAS several times as I mentioned, which shows they were able to do it. The question is why did they stop. News reports suggest that the Captain was pilot flying at first. After a while he handed control to the first officer who then did not counter the MCAS induced nose down trimming sufficiently ( information cannot be verified though).

About the training aspect: airspeed unreliable memory items and stab trim runaway memory items aply to the 737 Classic and NG just like they do to the 737 MAX. I don't see how transition training has anything to do with it.
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Old 2nd Apr 2019, 10:23
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Originally Posted by DaveReidUK
That sounds like a description of a random failure, rather than something that would manifest itself over several consecutive flights, as was the case with Lion Air.
Depends on what causes the holes to line up. On a new system it is more likely to be random occurrence as it is just a case of a very low probability of event(s) that eventually just happens. On an old system that has had an additional piece of software bolted on (MCAS) it is more likely to be the new software that has now introduced a significant hole in the cheese. Obviously as a system starts up, if all of the external factors are the same, the processing sequence will be exactly the same, including which bit of code is interrupted by a specific interrupt. However, if something happened on both of the Lion Air flights just prior to take-off (purely as an example, such as detection of an IAS Disagree), the change to the processing sequence would be the same on both flights, which caused the software frailty and the colliding interrupt to create a corruption. All other flights without the special trigger would get away with it, perhaps forever, perhaps not.
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