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Ethiopian airliner down in Africa

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Ethiopian airliner down in Africa

Old 4th Apr 2019, 17:25
  #3121 (permalink)  
 
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Originally Posted by GarageYears View Post
However, you might add, at no point was thrust reduced from 94% N1, which allowed the airspeed to reach around 375kts.... which at the final ND trim was unrecoverable.

None of the crew trim inputs at any point were sufficient to counter the MCAS ND trim events, which is really where things went wrong. Had they trimmed sufficiently and hit the cutouts, we'd not be have this exact discussion.

Also, the AOA was not offset for the entire flight, it appears to an event that occured some8 seconds after takeoff. Bird strike maybe?

- GY
The left AOA also appears to correct itself (very briefly) at 05:43:25, and immediately go haywire again. Very strange.
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Old 4th Apr 2019, 17:25
  #3122 (permalink)  
 
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Flaps UP at 05:39:45 but there appears to be two Automatic Trim Down commands prior to this which produced some Down Pitch Trim.
Is this STS, or MCAS operating when the flaps are down?
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Old 4th Apr 2019, 17:27
  #3123 (permalink)  
 
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I'm interested in this "bird (or other) strike." Where did that info come from? Is this a real event? How do we know that, CVR?
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Old 4th Apr 2019, 17:36
  #3124 (permalink)  
 
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Originally Posted by Avionista View Post
Flaps UP at 05:39:45 but there appears to be two Automatic Trim Down commands prior to this which produced some Down Pitch Trim.
Is this STS, or MCAS operating when the flaps are down?
Those both occur while the AP was engaged, which is a 'disable' input for MCAS, hence I think we can assume those are STS.

-GY
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Old 4th Apr 2019, 17:40
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Originally Posted by mryan75 View Post
Link to the preliminary report please...
Post #3187.
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Old 4th Apr 2019, 17:48
  #3126 (permalink)  
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I'll put it here again since the thread is moving at a nice clip:

Preliminary Report


Dear readers, please have a look at the Preliminary Report; it may answer some of your questions "up front." You'll probably have some questions that it does not answer.
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Old 4th Apr 2019, 17:48
  #3127 (permalink)  
 
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Originally Posted by Airbubba View Post
Narrative of the flight from the preliminary report:
Thanks for the tabulated data Bubba,
That puts it in pilot's perspective and makes terrible reading.
I hate to think what those poor fellows felt like.

Also opens up new questions which as usual we will guess at, until a reliable report emerges.
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Old 4th Apr 2019, 17:50
  #3128 (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, 17:55
  #3129 (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, 17:56
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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, 18:01
  #3131 (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, 18:04
  #3132 (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, 18:05
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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, 18:06
  #3134 (permalink)  
 
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Taken from ET-AVJ Preliminary Accident Report PP 26-27:


..

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Old 4th Apr 2019, 18:08
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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 18:24.
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Old 4th Apr 2019, 18:11
  #3136 (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, 18:14
  #3137 (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, 18:19
  #3138 (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, 18:21
  #3139 (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, 18:42
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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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