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Ethiopian airliner down in Africa

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Ethiopian airliner down in Africa

Old 30th Mar 2019, 01:05
  #2761 (permalink)  
fdr
 
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Elephants

The details on the trigger event have blocked out the major issue in these events, that is, why the crew were unsuccessful in coping with the problems that they encountered?

Note: MCAS is not a stall prevention system, it is a system to achieve compliance with a static stability criteria for a part of the envelope.
The deficiency in the natural stability could lead to excessive g loading or inadvertent stalls etc as a consequence as attitude maintenance tasks need greater monitoring than with a compliant system. The rules themselves are not necessarily as relevant as they were in the days of early attitude displays, and with shorter body aircraft. The flight crew in a modern aircraft will notice the response on their coffee cup as they pull a bit harder on the prong, which is not simulated well in current 6-DOF FFS.

Two crews had issues that presented in such a way that what is obvious post fact was not at the time. Why? That is the question. While Bill Boeing needs to sort out his system that appears to have been based on various assumptions of response that did not occur as expected, the fundamental case remains that all conceivable failure modes of the total aircraft as a system are unlikely to be run down prior to experiencing the same in the air, and the crew response needs to be able to recover from unknown symptoms in a time critical period.

Lion Air is poignant where it appears the pilot during the fault finding attempted to apply human factor training concepts, and in doing so control was finally lost. Every time we push on a balloon it reshapes the balloon... actions have consequences. The fundamental tenets of priorities have not changed, nor does human factor training expect to do so, but on the day, the intervention that was holding ground and keeping the flight path managed was lost with the transfer of control. The transfer was undertaken to give the pilot more cognitive capacity to deal with the issue, however the preventive action was not maintained by the FO...

Control reversion with true FBW aircraft, alternate modes on Boeing FBW aircraft are quite different to Airbus, however as Boeing always uses a speed trim input from the trim switches, the reversion from full FBW to none on the Boeing is not a significant change. On the Airbus, the degradation of modes results in the introduced requirement to use manual trim, which is also displayed on the ECAM, however history shows that the crews in a high work load and stress environment do not always respond with manual trim inputs, resulting in loss of control.

AOA gauges are great, and indexers of any type are good tools in achieving stable approaches. HUD's are also great, but neither of them is an absolute necessity to the safe flight of the aircraft. Given adequate funding, they are the first equipment on the options list to ask for. For these cases, the symptom of the problem was the out of trim case, and the inability to simply re-trim and cure the out of trim case. The trim system on any aircraft is not a Möbius loop, it will end at some point, and the continued demand to re-trim was inconsistent with normal operation of the trim on any aircraft.

Somewhere in the design architecture decision making, the necessity of a correct crew response to a fault was either not considered, or was considered and assumed that the crew would readily identify the problem symptom as a trim runaway, and intervene using the method that has been incorporated for more than 50 years. That a crew would not be able to recognise and respond appropriately shows that human factors are alive and well in the design and certification process. It is the human that may make an incorrect assumption on a design or certification matter who also intervenes and ensures that other matters that would not be caught purely by compliance with preexisting rules are mitigated. To err is human, but removing humans from decision making is a high risk game.
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Old 30th Mar 2019, 01:15
  #2762 (permalink)  
 
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Originally Posted by Water pilot View Post
It is likely that everything runs in the same memory space (especially if it is a 286) and looks like one large interrupt driven program. They probably have some sort of minimal 'frame' so they can compile together the various developer's work
Thanks.

Oops too short pprunepadding.
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Old 30th Mar 2019, 02:39
  #2763 (permalink)  
 
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I tossed in my commercial licence 40 years ago for a rewarding and exciting career in finance and IT but flying was always in my blood so I have always been interested in aviation. In this 737 Max crash issue something seems totally wrong to me. Both here in PPRuNe and in other media I have see a number of times where it has been inferred that this is pilot error as a MCAS fault is like trim runaway and fixing that is a memory item and takes 15 secs. However if I understand it correctly with runaway trim when you go to trim nose up the automation keeps on trimming more nose up even though the pilot has stopped trimming. In this situation it is the exact opposite the pilot trims up and the automation pushes the nose down. But I cannot see where people have focused on this critical difference. I would have thought in a crisis situation which was the case in these two crashes the last thing you would train your pilots to do would be tho take actions contrary (or in this case opposite to) to the symptoms being experienced. The people including some people presented in the media as experts who say that this is the same or similar to trim runaway seem to be missing the point that it is the exact opposite and therefore totally confusing. Who is missing the point here? Me or the experts?
And for those who wonder how I could give up flying for a business career. I am now long retired but I think I was unsuitable. I would have been totally bored as a pilot and therefore eventually potentially unsafe. I had a career where nearly every day was different, regular crisis to keep my attention, lots of mentally challenging problems to solve, and where I got to be the rule maker and breaker rather than the follower.
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Old 30th Mar 2019, 03:43
  #2764 (permalink)  
 
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I'm attaching 3 normal flights profiles, 1 normal speed and altitude data vs the profile of the crashed Ethiopian and its speed and altitude readings.
The difference between them is obvious.
Could it be that being, maybe, early and first flight of the day the cover of the pitot tubes where not removed? It has happened before. The latest happened to a MH in Brisbane Australia. Poor preflight checks by engineers and pilots. They both missed it.
This could explain the lack of speed and altitude during almost 2 minutes of the doomed plane. Then in very short time speed of 250-383kts.
During take off roll they were caught by surprise and missed* the 80 kts callout. First reaction of a ill trained crew to fly Airspeed Unreliable Speed NNC or junior crew ( *FO had,its being said, 200hrs) was to level off to gain speed. Once speed increases rapidly he retract flaps to avoid exceed VMO placard. Speed jumps very fast. To control it commander pulls abruptly to control speed and then a real high AOA of attack is reached. Having a problem he requests to turn back...
MCAS kicks in when: High angle of attack, manual flight, flaps up and in a turn.
Assuming pilots did all this in sequence, it might triggered the MCAS. And sadly in this case, it worked exactly the way it was designed to work. To avoid an upset triggered by a unreasonable maneuver by pilots or environment.
Then they kept fighting MCAS, why? Investigation will tell the probable cause...






its just a thought...
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Old 30th Mar 2019, 05:24
  #2765 (permalink)  
 
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NYT has made the Max its cover story today. And they're not friendly.
https://www.nytimes.com/2019/03/29/b...gtype=Homepage
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Old 30th Mar 2019, 06:40
  #2766 (permalink)  
 
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apologies if posted prior

MCAS the Achilles Heel of the Max that has the potential to end the 737 line.
Lets hope Boeing gets the fix right and the Max flies on as a great final version of the robust and venerable 737.



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Old 30th Mar 2019, 08:24
  #2767 (permalink)  
 
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Originally Posted by WingNut60 View Post
Because "it's not working properly".
Because "we don't have a spare".
Because they can!
I'm assuming you have never worked in an airline maintenance environment.
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Old 30th Mar 2019, 08:33
  #2768 (permalink)  
 
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Originally Posted by VONKLUFFEN View Post
I'm attaching 3 normal flights profiles, 1 normal speed and altitude data vs the profile of the crashed Ethiopian and its speed and altitude readings.
The difference between them is obvious.
Could it be that being, maybe, early and first flight of the day the cover of the pitot tubes where not removed? It has happened before. The latest happened to a MH in Brisbane Australia. Poor preflight checks by engineers and pilots. They both missed it.
This could explain the lack of speed and altitude during almost 2 minutes of the doomed plane. Then in very short time speed of 250-383kts.
During take off roll they were caught by surprise and missed* the 80 kts callout. First reaction of a ill trained crew to fly Airspeed Unreliable Speed NNC or junior crew ( *FO had,its being said, 200hrs) was to level off to gain speed. Once speed increases rapidly he retract flaps to avoid exceed VMO placard. Speed jumps very fast. To control it commander pulls abruptly to control speed and then a real high AOA of attack is reached. Having a problem he requests to turn back...
MCAS kicks in when: High angle of attack, manual flight, flaps up and in a turn.
Assuming pilots did all this in sequence, it might triggered the MCAS. And sadly in this case, it worked exactly the way it was designed to work. To avoid an upset triggered by a unreasonable maneuver by pilots or environment.
Then they kept fighting MCAS, why? Investigation will tell the probable cause...

its just a thought...
Do you mean that a blocked pitot caused erroneous AoA that in turn triggered repeated applications of MCAS ?

Or that those were two independent, simultaneous failures ?

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Old 30th Mar 2019, 08:45
  #2769 (permalink)  
 
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Originally Posted by DaveReidUK View Post
Do you mean that a blocked pitot caused erroneous AoA that in turn triggered repeated applications of MCAS ?

Or that those were two independent, simultaneous failures ?
I think VONKLUFFEN is flogging a dead horse. That theory has been supersed by the leaked preliminary accident investigation report, which confirms that MCAS was activated in the Ethiopian crash. The rest of the explanation does not make sense in view of the known ADS-B speed and altitude data points.
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Old 30th Mar 2019, 09:03
  #2770 (permalink)  
 
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I'm assuming you have never worked in an airline maintenance environment.
I’ve worked in airline maintenance environments that were so cowboy by nature that my local car wrecker would blush if he saw some of the practices.
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Old 30th Mar 2019, 09:34
  #2771 (permalink)  
 
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Originally Posted by DaveReidUK View Post
I'm assuming you have never worked in an airline maintenance environment.
Correct. But I have worked in Indonesia for most of the last forty years.
You may think that what I suggested could not happen because of procedures, checks and balances.
I assure you that it can.

Just remember, it's the same environment that recently saw a PIC fly for an hour and a half on stick-shaker and not report it.

My query asks "is it possible to open the AoA vane unit body in the field."
If the answer is Yes, then don't discount the possibility that it could happen, overnight in Jakarta.
It is very possible.
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Old 30th Mar 2019, 09:50
  #2772 (permalink)  
 
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Originally Posted by WingNut60 View Post
My query asks "is it possible to open the AoA vane unit body in the field."
If the answer is Yes, then don't discount the possibility that it could happen, overnight in Jakarta.
It is very possible.
"Captain, would you mind testing our unauthorised, undocumented repair to the LH AoA sensor on the next sector?"

"No, we don't have an Overhaul Manual for it - it's not a field-serviceable item - but, hey, how hard can it be?"

"You might find that it reads a bit high (or possibly low) afterwards as we have no idea how to calibrate it, but we can tweak it again if necessary until it's reasonably accurate"

No, I don't think so.
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Old 30th Mar 2019, 10:11
  #2773 (permalink)  
 
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Originally Posted by DaveReidUK View Post
"Captain, would you mind testing our unauthorised, undocumented repair to the LH AoA sensor on the next sector?"

"No, we don't have an Overhaul Manual for it - it's not a field-serviceable item - but, hey, how hard can it be?"

"You might find that it reads a bit high (or possibly low) afterwards as we have no idea how to calibrate it, but we can tweak it again if necessary until it's reasonably accurate"

No, I don't think so.
Dave Reid, not possible in the UK. But we are talking Indonesia here.
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Old 30th Mar 2019, 10:15
  #2774 (permalink)  
 
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Originally Posted by DaveReidUK View Post

No, I don't think so.
While we will have to agree to disagree over the possibility, I would like to see EXACTLY what the techs said they did in each instance.
I know that there have been previous references but I can't find them now.

I am really interested in what was recorded as having been done.
Verbatim, in Bahasa Indonesia, would be best, if anyone has it.

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Old 30th Mar 2019, 10:29
  #2775 (permalink)  
 
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Originally Posted by marchino61 View Post
Dave Reid, not possible in the UK. But we are talking Indonesia here.
I concur. I live in Indonesia and there is almost zero safety culture. That's not to say this contributed in any way to the Lion crash. But some of the things you see here in regards to basic safety and risk analysis would certainly shock you.
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Old 30th Mar 2019, 10:48
  #2776 (permalink)  
 
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Dave, Have you ever worked in Indonesia ?
I have and I agree with the guys above. Its known as the midnight parts store !!
and contra to what you might think some of these guys are technically quite smart
We are not saying it happened but we are saying it can !!
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Old 30th Mar 2019, 10:57
  #2777 (permalink)  
 
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Consistency with data trace

I have read with interest all possible explanations suggested here fot the incorrect AOA readings.

My humble contribution would be to ask to all future posters to make any theory somehow match with the data trace.

It has a very specific behaviour: 10 or 12 degrees offset, higher on the left at power - up, fairly stable on both sides, then during taxi hardly any real movement at any side, but several (6 or 8) short instances of left AOA vane reading ramping up a few degrees at a time, not vertically (cliff) but at a slope, increasing the offset to about 25 deg, then at rotation the right one increases (normal) the left one decreases (abnormal) and then both set at 22 degrees offset and seem to measure quite faithfully to each other (apart from the offset) for the rest of the flight.

(numbers are very rough guess, trends are right though)

To me the only two explanations that so far match (loosely) are:

- a slipping shaft that slips with the bumps but sticks with aero forces (but two sensors in a row, I don't think so)
- a intermittent electrical connection outside of the probe somewhere in a encoder-like signal which is disturbed by the bumps of taxi and creates an offset. Perhaps at the control module or power to the probe.

I don't think any of them is very probable, though. There must be a better explanation. Although bit corruption or software bug doesn't fit any better to me.

edit: another plausible but quite crazy scenario would be a voltage reference for analog signals drifting up and the electronic box going for the higher value of the sin cos signals instead of simply ruling them unsuitable because the plausibility check failed.
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Old 30th Mar 2019, 11:07
  #2778 (permalink)  
 
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Originally Posted by marchino61 View Post
Dave Reid, not possible in the UK. But we are talking Indonesia here.
If the "replaced" AoA sensor at Denpasar had in fact been the same one that was removed, following an illicit repair, then by definition there would not be a U/S sensor on its way back to the manufacturer, nor any paperwork to show that a serviceable one had been drawn from stores.

Don't you think that the investigation would have established that at an early stage ? In fact, the report states the exact opposite.
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Old 30th Mar 2019, 11:12
  #2779 (permalink)  
 
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Originally Posted by ecto1 View Post
...............

It has a very specific behaviour: 10 or 12 degrees offset, higher on the left at power - up, fairly stable on both sides, then during taxi hardly any real movement at any side, but several (6 or 8) short instances of left AOA vane reading ramping up a few degrees at a time, not vertically (cliff) but at a slope, increasing the offset to about 25 deg, then at rotation the right one increases (normal) the left one decreases (abnormal) and then both set at 22 degrees offset and seem to measure quite faithfully to each other (apart from the offset) for the rest of the flight.
............

To me the only two explanations that so far match (loosely) are:

- a slipping shaft that slips with the bumps but sticks with aero forces (but two sensors in a row, I don't think so)
- a intermittent electrical connection outside of the probe somewhere in a encoder-like signal which is disturbed by the bumps of taxi and creates an offset. Perhaps at the control module or power to the probe.

I don't think any of them is very probable, though. There must be a better explanation. Although bit corruption or software bug doesn't fit any better to me.
One report that I have for JT says that, in Jakarta :

The technician cleansed the Air Data Module (ADM) pitot and the left static port to repair the IAS and ALT disagree along with operational tests on land with no results. Then the Technician cleaning the electrical connection at the Elevator Feel Computer is accompanied by an operational test with good results.
Who here knows what those "operational tests" might have involved?
Are there any such, approved operational tests?

What approved operational tests might have been carried out that could have shown "no fault" when a fault still existed?
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Old 30th Mar 2019, 11:18
  #2780 (permalink)  
 
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Originally Posted by DaveReidUK View Post
If the "replaced" AoA sensor at Denpasar had in fact been the same one that was removed, following an illicit repair, then by definition there would not be a U/S sensor on its way back to the manufacturer, nor any paperwork to show that a serviceable one had been drawn from stores.

Don't you think that the investigation would have established that at an early stage ? In fact, the report states the exact opposite.
The AoA sensor was reported as changed in DPS only, I think. Not Jakarta.
I'm talking about Jakarta.

Dave can you point me to the JT incident report please. I just can't find a link.

FYI - "Cleaning a connector...." is a really dangerous euphemism in Indonesia.
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