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Ethiopian airliner down in Africa

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Ethiopian airliner down in Africa

Old 4th Apr 2019, 16:50
  #3121 (permalink)  
 
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I owe the first officer, Ahmed Nur Mohammod, a true and heartfelt apology. He called the stab trim cutout and performed admirably. Two-hundred hours or not, he did his job well.
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Old 4th Apr 2019, 16:55
  #3122 (permalink)  
 
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Originally Posted by GordonR_Cape View Post
Some very strange error messages, not just AOA offset:
And in the maint log too - and like Lion all were tested using BITE and found "ok".

I can't see that it is confirmed anywhere that they re-engaged electric trim
- FO called for stab trim cutout, and in the narrative it is after they trimmed up (anyone going to change their appraisal of him? edit: seems someone did, good)
- one period of MCAS AND has no effect (so cutouts worked)
- later two manual elec trim inputs seem to be ineffective, maybe they did turn back on but too short to see the effect?
- Another MCAS input and this time the stab goes down
Given the info we have, it seems that both "switches were re-activated" and "switches failed to stop MCAS" are plausible.

And then there is the AP - they got the AP to engage (left-side, despite dud AOA, WTF?) but it tripped out 33 secs later. The AP appears to have been trimming nose down too, and failing to climb, and then we have:
Six seconds after the autopilot engagement, there were small amplitude roll oscillations accompanied by lateral acceleration, rudder oscillations and slight heading changes. These oscillations continued also after the autopilot was disengaged.
First impressions are that this ain't just a software fix, yes MCAS dumped them in the ground but even without that this was a brand new plane that was seriously sick.

All from one dud AOA sensor? - or something in the vicinity of the (left) ADIRU?
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Old 4th Apr 2019, 16:56
  #3123 (permalink)  
 
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Originally Posted by sooty655 View Post
The left AOA also appears to correct itself (very briefly) at 05:43:25, and immediately go haywire again. Very strange.
Wire chafe? Something got pinched or partially shorted (changing resistance) and briefly released? I have no idea how one would prove that given how little of the planes are left. A misrouted wiring harness on a new plane kind of fits the bill but there are a lot of other possibilities. Do they take detailed production photos?
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Old 4th Apr 2019, 17:01
  #3124 (permalink)  
 
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Originally Posted by GarageYears View Post
Had they trimmed sufficiently and hit the cutouts, we'd not be have this exact discussion.
But they trimmed repeatedly and did hit the cutouts. From the preliminary report:

Originally Posted by Airbubba View Post
At 05:40:35, the First-Officer called out “stab trim cut-out” two times. Captain agreed and FirstOfficer confirmed stab trim cut-out.

At 05:40:41, approximately five seconds after the end of the ANU stabilizer motion, a third instance of AND automatic trim command occurred without any corresponding motion of the stabilizer, which is consistent with the stabilizer trim cutout switches were in the ‘’cutout’’ position
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Old 4th Apr 2019, 17:04
  #3125 (permalink)  
 
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Originally Posted by LaissezPasser View Post
But they trimmed repeatedly and did hit the cutouts. From the preliminary report:
I suggest you look at the FDR traces and then tell me what you think. I did...

- GY
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Old 4th Apr 2019, 17:05
  #3126 (permalink)  
 
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Why no mention of the fact that they reengaged the stab trim cutout switches at 5:43:11? Seems to me as though they reengaged the system, applied nose up trim via the electric trim switches and left the stab trim cutout switches engaged thus allowing MCAS to activate again once they stopped trimming.
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Old 4th Apr 2019, 17:06
  #3127 (permalink)  
 
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Taken from ET-AVJ Preliminary Accident Report PP 26-27:


..

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Old 4th Apr 2019, 17:08
  #3128 (permalink)  
 
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From the outside, after looking carefully at the Ethiopian crash flight recorder plot:

Systems should nowadays be able to detect faulty AOA sensor (or every other sensor) output automatically by checking whether it is congruent with the set of information available. Flight parameters are not independent of each other.
To be more specific, a correctly detected sudden increase in the AOA can have a limited number of causes:
a) very strong upward winds - very improbable, and if, only possible for a couple of seconds. Anyway, even then there has to be a corresponding spike in upward acceleration to be detected.
b) corresponding increase in longitudinal pitch
c) corresponding hefty decrease in airspeed
As none of those were present, a sensor failure should have been detected, the pilots informed and the sensor input to other systems blocked.
A similar reasoning can be set up for airspeed sensors.

If the pilots had consistently nullified the automatic downwards trim by manual upwards trim, they would have made it. So clearly they did not identify the chain of problems (wrong AOA, MCAS reacting) correctly. The stick shaker certainly didn't help here for a clear analysis.

Last edited by dlen; 4th Apr 2019 at 17:24.
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Old 4th Apr 2019, 17:11
  #3129 (permalink)  
 
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Originally Posted by Report, page 11 of 33, near bottom
At 05:41:46, the Captain asked the First-Officer if the trim is functional. The First-Officer has replied that the trim was not working and asked if he could try it manually. The Captain told him to try. *
At 05:41:54, the First-Officer replied that it is not working
This is a puzzling excerpt from the CVR. It appears that the FO had the right idea, in terms of getting control of the trim back via manual. By "not working" - I wonder what he meant.
(As I look at the Airspeed value, I keep thinking, will ask another question in a bit ...
The left indicated airspeed increased from approximately 305 kt to approximately 340 kt (VMO). The right indicated airspeed was approximately 20-25 kt higher than the left.
At 05:41:20, the right overspeed clacker was recorded on CVR. It remained active until the end of the recording.)

*As I read this, they had already put stab trim cut out.
At 05:40:35, the First-Officer called out “stab trim cut-out” two times. Captain agreed and First- Officer confirmed stab trim cut-out.
At 05:40:41, approximately five seconds after the end of the ANU stabilizer motion, a third instance of AND automatic trim command occurred without any corresponding motion of the stabilizer, which is consistent with the stabilizer trim cutout switches were in the ‘’cutout’’ position
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Old 4th Apr 2019, 17:14
  #3130 (permalink)  
 
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Originally Posted by GarageYears View Post
I suggest you look at the FDR traces and then tell me what you think. I did...

- GY
The callout box with the arrow pointing to the aqua blue line where it says "Automatic Trim Command With No Change In The Pitch Trim" indicates to me (and apparently to the investigators) that the cutout switches were in the "cut out" position.

I'm thinking wiring issue.
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Old 4th Apr 2019, 17:19
  #3131 (permalink)  
 
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Originally Posted by Lonewolf_50 View Post
This is a puzzling excerpt from the CVR. It appears that the FO had the right idea, in terms of getting control of the trim back via manual. By "not working" - I wonder what he meant.
​​​​​​​(As I look at the Airspeed value, I keep thinking, will ask another question in a bit ...)
It's a shame that Mentour Pilot took his video down, I think it showed exactly what he meant (physically unable to move trim wheel), I also think their sim session was lower airspeed (310?).
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Old 4th Apr 2019, 17:21
  #3132 (permalink)  
 
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Originally Posted by mryan75 View Post
I'm a real pilot, too. The one thing that really stands out to me in the prelim is that they didn't reduce power. I just took a nice big bite of humble pie regarding the first officer, so I'm not going to sling any more mud, but one could reasonably have assumed they would have done so, wouldn't you say? While trying to fight a nose-down situation? Unusual attitude recovery 101.
They probably thought they did: "At 05:39:42, Level Change mode was engaged. The selected altitude was 32000 ft. Shortly after the mode change, the selected airspeed was set to 238 kt."

While attempting to sort out the trim situation, they didn't see that the airspeed kept increasing.
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Old 4th Apr 2019, 17:42
  #3133 (permalink)  
 
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Originally Posted by Organfreak View Post
I've read the entire report and still see no mention of a bird (or other foreign object) strike to the left AoA sensor. Where did that tantalizing hint come from??? CVR?
Also, the media coverage (and even posts here) keep harping on the idea that all Boeing recovery procedures were followed, and yet they turned the trim cutout switches back ON in their desperation, which was certainly NOT part of the prescribed procedures. Seems as if that is some serious "dumbing-down" of the info.
The press conference statement was 'no foreign object' as a I recall. This is not the same as conclusively denying a bird strike.
The FDR data supports a sudden event on the AoA system with at least 2 hints that it was at the sensor:

1: Sudden jump to extreme non changing value until late in flight with partial freeing near end. Bird guts blew off?
2: Master caution anti ice caution and 'Primary AOA heat L' to off coincident with above. This is consistent with significant physical damage to AoA sensor causing an open in heater circuit.

I suspect there may be internal disagreement on the possible cause of this so they left it out but a bird strike is a strong contender in my view.
Could be the initial bird strike reports followed the above reasoning but may not be a way to dis/prove the theory.


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Old 4th Apr 2019, 17:45
  #3134 (permalink)  
 
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ET-AVJ Preliminary Accident Report
Maintenance Log pp. 20-21


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Old 4th Apr 2019, 17:50
  #3135 (permalink)  
 
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Originally Posted by mryan75 View Post
I'm a real pilot, too. The one thing that really stands out to me in the prelim is that they didn't reduce power. I just took a nice big bite of humble pie regarding the first officer, so I'm not going to sling any more mud, but one could reasonably have assumed they would have done so, wouldn't you say? While trying to fight a nose-down situation? Unusual attitude recovery 101.
I've been suggesting that speed was a factor in not being able to trim up, which is probably true. However a careful look at the FDR shows that everything was stable for several minutes, provided no speed/thrust or trim changes were made. The aircraft certainly could not land safely in that configuration.

The high speed alone was not the direct cause of the crash, though it may have severely limited their options. In theory speed could have been reduced gradually, though it is not known what effect the reduction of engine thrust would have on pitch.

IMO the combination of speed, and the final MCAS activation of nose down trim was fatal. Conversely, MCAS activation at low speed earlier in the flight was recoverable, because they could trim up manually. The fault-tree is complex...

Edit: pilotmike If I remove the word slight will that make you happy?

Edit: In retrospect I stand by my statement for muiltiple reasons:
1. Pilots are not the only people who know about aerodynamics.
2. The discussion is around flight close to VMO, at which speed the aerodynamic forces far outweigh the pitch moment of the engine thrust.
3. Most discussion of engine pitch up moment is close to VMC, in which case the aerodynamic forces are proportionately small.
4. Most discussion of underslung engines centers around TOGA thrust, which could not be further from this flight regime.
Nobody has come up with any hard numbers, so these factors may remain an unknown.

Edit: Similar mention of speed/thrust from justthisonce

Last edited by GordonR_Cape; 4th Apr 2019 at 20:56.
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Old 4th Apr 2019, 17:51
  #3136 (permalink)  
 
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The biggest issue that I see from the data so far is the massive authority that MCAS has and how small the authority of the STS/ pickle switch is. Two massive MCAS AND trim adjustments in the space of 29 secs sealed the fate of the flight. If is not clear if it was possible to manually trim given the airspeed but unlikely due to control pressure. The ground proximity probably precluded thrust reduction or runaway trim recovery procedure.

The crew would have had to correctly diagnose the problem and flicked the trim disconnect switches in just over 60s from stick-shaker to unwanted MCAS AND. It seems the crew did not make all the right choices but hardly reckless driving either. I suspect that the overall picture is that that Boeing are asking way too much of their customers to fly this aircraft. It is an accident waiting to happen. Broadly speaking the data shows a horrible control system that does not work properly and could have been much more safely and better designed. It also shows that pilots may not always make all the best decisions when under high levels of stress.

Being a little flippant... a logical solution is to automatically disconnect electric trim if there is a left side stick-shaker condition... or instead of alpha vane disagree indication it could automatically disconnect MCAS (slightly more serious solution). Behind the systemic problems is the question of why the AOA sensors failed... is this a freak, or is there something more fundamental at work?
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Old 4th Apr 2019, 18:02
  #3137 (permalink)  
 
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First Lawsuit

COTCHETT, PITRE & McCARTHY, LL
https://www.cpmlegal.com/media/news/..._Complaint.pdf

IN THE UNITED STATES DISTRICT COURT FOR THE NORTHERN DISTRICT OF ILLINOIS EASTERN DIVISION

MICHAEL STUMO and NADIA MILLERON, as Personal Representatives of the Estate of SAMYA STUMO, deceased,
Plaintiffs,
v.
THE BOEING COMPANY, a Delaware corporation;
ETHIOPIAN AIRLINES, a foreign corporation;
ETHIOPIAN AIRLINES ENTERPRISE;
ETHIOPIAN AIRLINES GROUP, INC.;
and
ROSEMOUNT AEROSPACE, INC., a Delaware corporation;
Defendants.

A Claim against the FAA has also been filed by the same partners, ahead of a possible suit.
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Old 4th Apr 2019, 18:14
  #3138 (permalink)  
 
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The autopilot behaviour differed considerably from the Boeing documents:

By 05:38:45 the left AoA sensor was reporting (but not displaying) over 74deg AoA, yet the LH AP was engaged successfully some 37 seconds later and remained engaged until time 05:39:55. By that time MCAS had completed 3 discrete pitch-down trim inputs before the AP actually disengaged.

George the autopilot wants to go up whilst HAL the MCAS wants to go down.

Eeek.
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Old 4th Apr 2019, 19:01
  #3139 (permalink)  
 
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One common pattern between the Lion air and Ethopian air crash is, that the later/last manual trim up commanded from the coloum switches are in both cases only short blips, followed by 5 second trim down from the MCAS system.

I find it hard to believe that both pilots clinging on the control coloums for their dare life to get nose up do not try harder/longer on the electric trim as long as engaged and not cut out.

I assume that there is more to the story.
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Old 4th Apr 2019, 19:06
  #3140 (permalink)  
 
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Originally Posted by Just This Once... View Post
The autopilot behaviour differed considerably from the Boeing documents:

By 05:38:45 the left AoA sensor was reporting (but not displaying) over 74deg AoA, yet the LH AP was engaged successfully some 37 seconds later and remained engaged until time 05:39:55. By that time MCAS had completed 3 discrete pitch-down trim inputs before the AP actually disengaged.

George the autopilot wants to go up whilst HAL the MCAS wants to go down.

Eeek.
Really?

Aside from why the AP was successfully engaged, the three trim ND FCC commands (and one NU for good measure), DURING autopilot engagement are brief and likely STS driven - not MCAS. That comes after the AP is disconnected.

The first MCAS ND command occurs on deselection of the AP, and runs for 10 seconds as the system is expected to do. You can clearly see that in the FDR traces.

The crew then input a shorter NU pickle switch trim input (which did not equal the MCAS ND demaind).

MCAS reset and 5 seconds after the crew ceased their input, it runs again for less than 10 seconds this time, since the crew again provided NU pickle switch trim, which shut off MCAS for another 5 seconds, at which point the crew had selected the cutoff switches.

MCAS ran again (since it was reset) but had no effect, since it was disabled by the cutoffs.

At this point the aircraft was roughly pitch trim of 2.5 units (so ND). The crew then tried to use manual trim (which failed) and then hauled back on the column and tried to control the aircraft via the yoke.

Later two very short pickle switch inputs NU were input indicating the crew re-engaged the electric trim, but they were very short and had a very small effect on trim.

5 seconds later MCAS, having been reset by the crew electric trim input, and now being active again, ran for less than 10 seconds and seems to have been interrupted by the Left AOA value changing.

Unfortunately at this point the aircraft was very fast >375kts and the ND input was too much to overcome.

- GY


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