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Ethiopian airliner down in Africa

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Ethiopian airliner down in Africa

Old 22nd Apr 2019, 20:48
  #4221 (permalink)  
 
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Originally Posted by Turbine70 View Post

The problem here is precisely that the combination of so many individually trained failures was too numerous to encourage and support successful timely diagnosis.

I don’t see a “combination of individual failures”. The failure of the Angle of Attack was only ONE failure. The crew did not correctly deal with that failure and made things worse for themselves.
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Old 22nd Apr 2019, 20:50
  #4222 (permalink)  
 
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Originally Posted by Lost in Saigon View Post



I don’t see a “combination of individual failures”. The failure of the Angle of Attack was only ONE failure. The crew did not correctly deal with that failure and made things worse for themselves.
Angle of Attack failures weren't even on the list of problems presented to the crew.

Last edited by Turbine70; 22nd Apr 2019 at 23:34.
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Old 22nd Apr 2019, 22:03
  #4223 (permalink)  
 
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So what simulator exercises would you incorporate to reflect the differences in the MAX, specifically the MCAS? How about an uncommanded nose down trimming? That is already incorporated in a conventional stab trim runaway, a basic requirement of getting a type rating on any B737.
Scenario 1: In the simulator, doing a “runaway trim exercise”. There you are at 6,000’ straight and level, 220kts, nothing happening. Oh look, the trim has started moving on its own, can’t stop it, I wonder if this is right? No? OK, do the runaway checklist. Sim passed! Easy, this trim runaway.

Scenario 2: In the aeroplane, cleaning up. Trim starts moving forward, then stops. Is that MCAS gone wrong (or even possibly functioning correctly), is it STS doing its job or is it the other guy who’s flying it trimming the aircraft? Hmmm. There goes the trim again...

Scenario 3: All the above plus continuous stick shaker, aural warnings and UAS symptoms.

Honestly, I’m not quite sure how you would train an MCAS runaway in the sim, if disconnecting the trim when there wasn’t an actual runaway = fail. It’s easy to say “they should have done the trim runaway checklist” but how do you tell NORMAL operation of MCAS/STS from ABNORMAL in a very limited timeframe? If you disconnect the trim every time it moves, you’re going to be doing lots of very short flights...
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Old 22nd Apr 2019, 23:23
  #4224 (permalink)  
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That last paragraph has been said before, but seems to be forgotten time and time again. IMHO, it is the crux of the matter.

Getting into the mind of an average pilot, whatever that might be these days. One thing's for sure, it's not one that's had his senses sharpened by months of focussed discussion on this specific crisis, and not necessarily comparable to some of the pilots on here that have a wealth of experience on a wide range of Boeing products.
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Old 23rd Apr 2019, 00:43
  #4225 (permalink)  
 
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Originally Posted by L39 Guy View Post
So what simulator exercises would you incorporate to reflect the differences in the MAX, specifically the MCAS? In other words, there is nothing so uniquely different with the MAX that justifies a new simulator let alone MAX (MCAS) specific training.
The only uniquely different thing is that the MAX could not meet certification requirements without MCAS (or other major changes)- that is a basic fact and not been disputed. No other 737 has MCAS that is a unique feature.

MCAS version 1 had different training requirements as it had a lot of authority and travel (far great was required than design plans) - but it did meet certification requirements with this authority.

MCAS version 2 has a large number of cut out features and is limited to a once of small movement. This puts the question as to have now can it still meet the certification requirements? My guess is it technically can depending on how grey you wish to read the data.

So my opinion is that it is not only possible, but very likely that the MAX will operate in the zone that fails certification limits. Reason is it either will not engage when "required", not input enough travel or be accidentally shut down prematurely.

I would expect that it be appropriate to have simulator training that included the actual stick forces encountered when MCAS did not active or only partially activated - my reasons for this is that this lack of feel is not evident in the previous aircraft and given MCAS involvement will be reduced, there is a greater possibility pilots will be exposed to this insufficient feel that does not meet certification levels.

Most people would find it reasonable to expect a pilot to have experienced flight conditions in the area outside the certification limits, if it is reasonably probable that the aircraft will be in this condition. With the proposed changes to MCAS there are now many conditions that will stop it from operating or only give partial operation, so a far greater possibility of flight outside the certified limit.

One would also assume it very handy to experience the MCAS experience just after takeoff operating normally, then again when it fails to disengage and turns into a runaway.

Might help to get the high AOA on a flapless landing.

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Old 23rd Apr 2019, 02:57
  #4226 (permalink)  
 
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Some decades ago I spent several sessions in a Viscount simulator (with a variety of abilities in the other seat) run by a serial killer who diligently added failures until a simulated smoking hole was commonly produced. You learned prioritization or got snuffed.

These days it seems simulator time is too expensive for crews to really get to know the airplane.

And now we see Boeing trying to put out a model that earlier model crew can step into without any simulator time.

I am reminded of the time as a 12 year old on my bike racing another kid downhill on a suburban street. Kids were playing jump rope on the other side. Half the street was clear. No problem. Then a kid began running across our side of the street. He'd be across the street by the time we got there. No problem. Then the kid stopped when he saw us. Lots of room between him and the curb. No problem.

Then the kid started running again when I was maybe ten feet away

It turned out he had a history of getting hit by bikes and the odd car.

The start / stop cycles of MCAS remind me of this kid. The crews got painted into a corner. Stick shaker and airspeed disagree distracted them from the real problem until it was too late. It definitely didn't help that the underfloor trim cutout switch no longer blocked automatic trim.

There's still an open question on the ergonomics of the control wheel trim switches when the stick shaker is operating. I suspect that the electrical contact has to be maintained for a minimum period (perhaps sub-second) for the relay to begin driving the trim motor. How much pressure is required to sustain the electric contact when stick shaker is operating?
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Old 23rd Apr 2019, 07:28
  #4227 (permalink)  
 
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FullWings,

Never a 737 pilot and now long out of date. But I believe your post sums up the problem pretty accurately. How many of us would have diagnosed the problem correctly in the time available?
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Old 23rd Apr 2019, 10:33
  #4228 (permalink)  
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RatherBeFlying #2447

There's still an open question on the ergonomics of the control wheel trim switches when the stick shaker is operating. I suspect that the electrical contact has to be maintained for a minimum period (perhaps sub-second) for the relay to begin driving the trim motor. How much pressure is required to sustain the electric contact when stick shaker is operating?
Quite. Could I be boring and again point to the switch 'noise' just on the centreline of the graph. I've always felt it might say far more than is being allotted to it in our discussions but have no knowledge of this graph's validity.
Lionair Upper: manual trim middle: automatic trim
is a tad confusing but blue surely must be thumb switch inputs. If so, where did this microscopic data come from?

It's from spornrad # 4076


Ethiopian airliner down in Africa
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Old 23rd Apr 2019, 11:34
  #4229 (permalink)  
 
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Trim Wheel

came across this thread, relevant quote from it below. Obviously no way of knowing if genuine or not, but given what else has been posted on the difficulty of operating the manual trim wheel, it does sound plausible.


Shutdown caused Boeing crash. - Page 4 - International Skeptics Forum

Quote...

"I agree it's a flawed design. And I used to work there. I'm glad I don't now.

Regarding the trim wheels: When the NG was being introduced, I happened to be the Lead Engineer in charge of them and a whole lot of other stuff. There were some issues. The new display system created a pinch point between the dash and the wheel. We had to make the wheel smaller. And the new trim motor resulted in the wheel, which is directly connected to the stabilizer by a long cable, springing back when electric trim was used. It was an undamped mass on the end of a spring. We had to add a damper.
Result: Depending on the flight conditions, the force to manually trim can be extremely high. We set up a test rig and a very fit female pilot could barely move it.
As I said, I'm glad I'm no longer there."

Alchad
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Old 23rd Apr 2019, 11:48
  #4230 (permalink)  
 
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Originally Posted by Alchad View Post
came across this thread, relevant quote from it below. Obviously no way of knowing if genuine or not, but given what else has been posted on the difficulty of operating the manual trim wheel, it does sound plausible.


Shutdown caused Boeing crash. - Page 4 - International Skeptics Forum

Quote...

"I agree it's a flawed design. And I used to work there. I'm glad I don't now.

Regarding the trim wheels: When the NG was being introduced, I happened to be the Lead Engineer in charge of them and a whole lot of other stuff. There were some issues. The new display system created a pinch point between the dash and the wheel. We had to make the wheel smaller. And the new trim motor resulted in the wheel, which is directly connected to the stabilizer by a long cable, springing back when electric trim was used. It was an undamped mass on the end of a spring. We had to add a damper.
Result: Depending on the flight conditions, the force to manually trim can be extremely high. We set up a test rig and a very fit female pilot could barely move it.
As I said, I'm glad I'm no longer there."

Alchad
Posted a few (hundred?) pages back in this thread: https://www.pprune.org/rumours-news/619272-ethiopian-airliner-down-africa-post10438165.html
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Old 23rd Apr 2019, 11:51
  #4231 (permalink)  
 
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Originally Posted by Alchad View Post
We set up a test rig and a very fit female pilot could barely move it.
Accepting that beauty is in the eye of the beholder, surely how much one fancies a lady has little if any bearing upon her ability to trim the 737 manually...
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Old 23rd Apr 2019, 12:13
  #4232 (permalink)  
 
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Originally Posted by FullWings View Post
Scenario 1: In the simulator, doing a “runaway trim exercise”. There you are at 6,000’ straight and level, 220kts, nothing happening. Oh look, the trim has started moving on its own, can’t stop it, I wonder if this is right? No? OK, do the runaway checklist. Sim passed! Easy, this trim runaway.

Scenario 2: In the aeroplane, cleaning up. Trim starts moving forward, then stops. Is that MCAS gone wrong (or even possibly functioning correctly), is it STS doing its job or is it the other guy who’s flying it trimming the aircraft? Hmmm. There goes the trim again...

Scenario 3: All the above plus continuous stick shaker, aural warnings and UAS symptoms.

Honestly, I’m not quite sure how you would train an MCAS runaway in the sim, if disconnecting the trim when there wasn’t an actual runaway = fail. It’s easy to say “they should have done the trim runaway checklist” but how do you tell NORMAL operation of MCAS/STS from ABNORMAL in a very limited timeframe? If you disconnect the trim every time it moves, you’re going to be doing lots of very short flights...
I understand what you are trying to say, but let me make this observation.

We know that the MCAS input stops if any pilot puts in manual electric trim. It then restarts after a 5 second delay. If a pilot is regularly responding to the changing trim pressures by inputting nose up trim (MCAS trims some nose down, pilot trims some nose up, MCAS trim nose down, pilot trims nose up, repeat), then yes, it looks a lot different than a classic runaway trim.

In the case of ET302, however, the MCAS input lasted 9 continuous seconds which equates to around 37 spins of the manual trim wheel. The entire time, the Captain has the yoke in his hands and the control pressures increase dramatically. This happened at least twice. What about this does not scream runaway trim?
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Old 23rd Apr 2019, 13:31
  #4233 (permalink)  
 
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Originally Posted by 737 Driver View Post
In the case of ET302, however, the MCAS input lasted 9 continuous seconds which equates to around 37 spins of the manual trim wheel. The entire time, the Captain has the yoke in his hands and the control pressures increase dramatically. This happened at least twice. What about this does not scream runaway trim?
I agree that’s a bit more obvious but we are now in the “end game” where the goose is close to being irreversibly cooked. What it screams to me is that the pilot(s) were so overloaded by control forces / stick shake / aural and visual warnings / general confusion that they had reverted to “pull back to make the houses look smaller” and had fixated on this due to saturation of their input channels. The trim running could well be the gorilla in the room, if you’ve seen the video.

As many have worked out, the stabiliser is a very powerful pitch control on the 737 and the elevator is just a trim, really. I’m not sure how much emphasis is put on that in training these days.
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Old 23rd Apr 2019, 13:48
  #4234 (permalink)  
 
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Originally Posted by Loose rivets View Post
RatherBeFlying #2447
is a tad confusing but blue surely must be thumb switch inputs. If so, where did this microscopic data come from?
It is just a magnified screen shot from the prelim. report of the Lionair crash

Reason I posted this is the weird question of the ET captain to the FO to help him with the electric, manual trim, plus the (way too) short trim blips late in the traces of ET as well as the too short trim blips late in the Lionair traces. I was simply wondering if there could be a hint here to a common ergonomic problem due to artificial feel stick force and shaker.

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Old 23rd Apr 2019, 14:04
  #4235 (permalink)  
 
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Originally Posted by Bergerie1 View Post
How many of us would have diagnosed the problem correctly in the time available?
At least three if these columns are anything to go by
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Old 23rd Apr 2019, 14:55
  #4236 (permalink)  
 
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Most people would find it reasonable to expect a pilot to have experienced flight conditions in the area outside the certification limits, if it is reasonably probable that the aircraft will be in this condition.
I don't find it reasonable at all. Unless you are a qualified test pilot, you should not be going outside the certification envelope.
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Old 23rd Apr 2019, 15:18
  #4237 (permalink)  
 
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In response to this:
Most people would find it reasonable to expect a pilot to have experienced flight conditions in the area outside the certification limits, if it is reasonably probable that the aircraft will be in this condition.
Fortissimo posted this:
Originally Posted by Fortissimo View Post
I don't find it reasonable at all. Unless you are a qualified test pilot, you should not be going outside the certification envelope.
That's fine, as long as non-test pilots can be reasonably confident that it is not "reasonably probable" that the aircraft will end up outside the envelope on any given flight.

Last edited by OldnGrounded; 23rd Apr 2019 at 15:19. Reason: Formatting (but I thought it was right the first time)
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Old 23rd Apr 2019, 15:43
  #4238 (permalink)  
 
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fizz,

It's very easy to sort these things out with hindsight and when sitting comfortably in an armchair!
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Old 23rd Apr 2019, 16:42
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Originally Posted by Bergerie1 View Post

How many of us would have diagnosed the problem correctly in the time available?
If any of the accident pilots had simply flown the aircraft and kept the aircraft in a reasonably in-trim state (the thumb switch will trump the automation every single time), then the time available would have been equal to the fuel available. There was no ticking time bomb here.

Last edited by 737 Driver; 23rd Apr 2019 at 18:34. Reason: typo
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Old 23rd Apr 2019, 17:14
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Originally Posted by FullWings View Post
What it screams to me is that the pilot(s) were so overloaded by control forces / stick shake / aural and visual warnings / general confusion that they had reverted to “pull back to make the houses look smaller” and had fixated on this due to saturation of their input channels. The trim running could well be the gorilla in the room, if you’ve seen the video.
Yes, I’ve seen the video, and yes I agree that it appears the Captain had achieved cognitive overload. Where I differ is that I feel the circumstances were not so extreme that cognitive overload would have been a reasonable expectation of a 737 type-rated Captain.

I used to do basic flight instruction, and I’ve seen many types of students. I would often tell them that flying an aircraft on a nice day really wasn’t that difficult once you had a little time under your belt, not too unlike learning to drive an automobile. The huge difference between a car and a plane, of course, is that you just can’t pull an aircraft over on the shoulder when things go wrong. You have to take whatever comes, work with whatever you have, and do your damnedest to get the aircraft safely back on the ground. I would tell my students that if they could not deal with that reality, then they should not become a pilot.

As professional pilots, we ought to meet an even much higher standard. When things started to go wrong, at least one of these pilots needed to look past the noise, place their hands firmly on the yoke and throttles, set the proper attitude and power settings, keep the aircraft in trim, and stay away from the rocks. That was all that was required. Everything else could have waited. The plane wasn’t on fire, the wing didn’t fall off, there were no bombs on board. This plane was flyable.

Yes, Boeing fracked up. Yes, the FAA and the airlines were culpable of going along with the fiction that the MAX wasn’t really that much different from the NG. But you know what? On any given day someone else could screw up and give us an aircraft that will malfunction in a unique and potentially dangerous way. And as always, the pilots are the last line of defense. We need to be mentally prepared for that reality or find another line of work.


Last edited by 737 Driver; 23rd Apr 2019 at 17:16. Reason: typo
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