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Ethiopian airliner down in Africa

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Ethiopian airliner down in Africa

Old 4th Apr 2019, 14:16
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Originally Posted by gmx
Also fair point. Maybe instead of "novel concept" I should have said "undesirable". Similar things are certainly not happening week to week. I'm not out to sink the boot into anyone at this stage. I'm keen to see the report and draw my own conclusions. My point at this stage is that the crew were obviously under stress, and the aircraft was working against them.
I think it is also important to note that both MAX crashes happened during day/VMC flight. I cannot imagine what it might be like to experience the same symptoms at night in IMC conditions.

Originally Posted by gmx
That's fair. I'll chase up a reference. Regardless, your characterisation of the FDR (that pilot-trim-up was involved in a losing tug-of-war with MCAS-trim-down) is incorrect. It is only the final 4 MCAS-commanded-nose-down trim commands that result in increasing nose-down attitude. The previous 21 such MCAS-commanded-nose-down trim commands are fully counteracted by the flight crew resulting in essentially level flight at 5000 feet for 6 continuous minutes.
Your overall description of JT610 is correct, but the airspeed was relatively low, so it may be premature to judge if electric trim would have had the same effects at speeds > 250kts, when both speed trim and horizontal stabiliser loading come into play.

FDR trace:



gmx The transition from captain to co-pilot is when the last four nose-up trim commands become short blips, instead of the long activation earlier in the FDR.

Last edited by GordonR_Cape; 4th Apr 2019 at 14:32.
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Old 4th Apr 2019, 14:23
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Originally Posted by GordonR_Cape
Your overall description of JT610 is correct, but the airspeed was relatively low, so it may be premature to judge if electric trim would have had the same effects at speeds > 250kts, when both speed trim and horizontal stabiliser loading come into play.

FDR trace:

Thanks Gordon. Any help on the transfer of control from PF to FO at the time the aircraft attitude starts to go south ?
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Old 4th Apr 2019, 14:24
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Last year my first ever real in-flight incident was in my CAP-10, flying downwind 1000ft AGL in the circuit. The electric trim ran away to the end stop and suddenly I was pointing at the ground, After pooing myself, I worked out what it was quite quickly and returned the trim to neutral, where it promptly ran away to the end stop again. So I recentralised it, and disabled it. Problem solved, although had to land without flaps.
Gave me a real heart thumping moment until it was sorted.
The stick forces even in my small plane were quite high.
At the next opportunity I went up to 5000 ft and had a practice while slowly moving the trim to its end stops to see if the plane was controllable, which it was. Uncomfortable, but controllable.

I don't think anybody should second guess what the pilots should and should not have done, or did and didn't do, until the full report is made public and we can see the facts.

I think Boeing will have a lot to answer to with explanations and money before these planes are certified for flight again. And then you have the public relations problem of getting bums on seats again.
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Old 4th Apr 2019, 14:40
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Originally Posted by michaelbinary
Last year my first ever real in-flight incident was in my CAP-10, flying downwind 1000ft AGL in the circuit. The electric trim ran away to the end stop and suddenly I was pointing at the ground, After pooing myself, I worked out what it was quite quickly and returned the trim to neutral, where it promptly ran away to the end stop again. So I recentralised it, and disabled it. Problem solved, although had to land without flaps.
Gave me a real heart thumping moment until it was sorted.
The stick forces even in my small plane were quite high.
At the next opportunity I went up to 5000 ft and had a practice while slowly moving the trim to its end stops to see if the plane was controllable, which it was. Uncomfortable, but controllable.

I don't think anybody should second guess what the pilots should and should not have done, or did and didn't do, until the full report is made public and we can see the facts.

I think Boeing will have a lot to answer to with explanations and money before these planes are certified for flight again. And then you have the public relations problem of getting bums on seats again.
Nobody is questioning that what they faced was a challenging situation. But these aren't recreational pilots out on a Sunday afternoon. These are professional revenue pilots, in theory trained to a very high standard. I agree, let's wait for the report, but you can't say "let's wait for the report, and Boeing is going to have a lot to answer for." I will bet anything that if we get a fair, complete report, it will cite design problems, single point of failure issues, yes - BUT I will eat my shoes if pilot training, adherence to standard procedures, maintenance practices, and even possibly parts sourcing and environmental factors (sand, high humidity, etc.) aren't all factors. I fully expect the end result to be a smorgasbord of issues. It usually is.
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Old 4th Apr 2019, 14:47
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Originally Posted by ecto1
Disregarding your choice of words, which I believe is unfortunate, we all agree that you need both things to fail (engineering and training) for most accidents to happen.

I also believe that the adequate level of engineering in this particular problem would have been a lot cheaper to achieve than adequate level of training for pilots. I mean, which is more understandable to you:

1) Assume that the new plane is not going to try to kill you (pilot) in a new way nobody explained you beforehand, (that was pilot error)
2) Assume that no crew is going to be "too easily overwhelmed" if the new system you designed, which is susceptible to failure as every other thing in the world, tries to kill them in a brand new way that you decide not to explain or mitigate beforehand. (that was boeing error)
Fair point, I should have written crews were overwhelmed instead of too easily overwhelmed. Nonetheless, despite all the stress and confusion that was surely occuring, the "only thing" that was happening is that the airplane was trimming nose down. According to Boeing this can be overriden with the electric trim switch and I have not seen any proof yet that this isn't the case. As I already wrote in an earlier post it is just very puzzling to me why a pilot would let his/her aircraft get to an extreme nose down state if it is possible to counter this with electric trimming. We obviously need more information to be able to understand what truly happened.
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Old 4th Apr 2019, 15:02
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Originally Posted by mryan75

If you're not a pilot, why are you posting on a professional pilot's website?
I would suggest that his input has been far more valuable that yours...

Ultimately, this crash will come down to design and engineering so, letís not be too precious about pilot only input into this forum.
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Old 4th Apr 2019, 15:34
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Anyone consider the old "pitch for airspeed" and how counter intuitive slowing down might have seemed?
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Old 4th Apr 2019, 15:36
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Originally Posted by GordonR_Cape
There were actually two failures on the MAX: The faulty AOA sensor data which triggered a whole range of spurious warnings, put the pilots in a high workload situation, which on its own was hazardous. Then MCAS comes along, and administers the coup-de-grace while the pilots are busy trying to make sense of the aircraft and their checklists.
This^^^.

Not one word more is necessary. Thanks.
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Old 4th Apr 2019, 15:40
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Originally Posted by 737mgm
Nonetheless, despite all the stress and confusion that was surely occuring, the "only thing" that was happening is that the airplane was trimming nose down.
Not quite the only thing - also Stick Shaker, elevator feel shift, IAS disagree and ALT disagree to deal with.

Regardless, there is a simple way of proving whether an average crew will be overwhelmed - test it in the sim. During the likely extent of the MAX grounding there must be enough NG/MAX crew getting a sim check anyway to give you a large dataset to be sure.

If the average crew is overwhelmed, either the system isn't safe or the training isn't good enough, or both. If the average crews cope just fine, then these crashes are just pilot error, nothing to fix, move along...

Of course, the industry can't do that because sims that can replicate mcas are rare as rocking horse sh*t outside of Boeing itself, because they aren't needed, because you can learn all you need to know about the MAX from an NG sim. All except how not to crash.
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Old 4th Apr 2019, 16:05
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Referring to the same post
And perhaps you could remind us how US crews were somehow able to fly this dangerously designed airplane for two full years without a single MCAS activation.
Isn't there a report by an AA pilot concerning MCAS causing problems in the safety reporting database (can't remember the name of it just now)?
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Old 4th Apr 2019, 16:11
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Originally Posted by FakePilot
Anyone consider the old "pitch for airspeed" and how counter intuitive slowing down might have seemed?
I have repeatedly suggested that excessive airspeed may have played a role, particularly based on the ADS-B data for the ET302 crash. Given the simultaneous stick shaker and other warnings, reducing speed may not have been the first choice, and was certainly not on any checklists.

The downside of reducing thrust with underslung engines, is that this reduction produces a slight nose down pitch. It is unlikely that a reduction in speed would have been sufficient in the time available, given the low altitude and 'point of no return' reached by ET302

Last edited by GordonR_Cape; 4th Apr 2019 at 19:03.
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Old 4th Apr 2019, 16:23
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Sim pilots also put Sully plane back on a runway.

In this and many other scenarios, figuring out what to do is a lot more challenge than doing it. That sim test is worth nothing if you know which specific failure is going to happen at your specific flight.
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Old 4th Apr 2019, 16:26
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Preliminary Report

http://www.ecaa.gov.et/documents/204...8-d7af1ee17f3e

- GY
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Old 4th Apr 2019, 16:32
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CNN say they have a copy of the preliminary Report - see their website - and have quoted some interesting facts.
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Old 4th Apr 2019, 16:34
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Hi Gordon,
Your post surprises me a bit. I can't see that I suggested a checklist for AoA disagree here...
I did say that the much touted so called "correct" checklist for Stab trim runaway was unsuitable for the rogue MCAS cases which have occurred and that a dedicated checklist should be made for that.But there can't be checklist, study or training until Boeing has the final (final...) design.
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Old 4th Apr 2019, 16:56
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FDR ET302


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Old 4th Apr 2019, 16:58
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Originally Posted by gmx
You might have to explain that further. The LionAir crash FDR clearly shows short bursts of uncommanded nose-down trim (from MCAS), each one counteracted by PF-commanded nose-up electric trim, maintaining level flight at 5000 feet for roughly six minutes. The uncommanded nose-down trim is never coincident with the PF's nose-up electric trim. They are clearly interleaved, which is exactly the MCAS behaviour described by the updated advice.

The erroneous AoA / AP disconnect / MCAS response chain may have manifested differently on the EA flight, but we'll have to wait for the FDR / CVR data in the report to know one way or the other.
Quite simply the LionAir data does not establish that it is possible to win the battle between Electric Trim and MCAS (particularly if time is of the essence). With combined opposing authority it may only have have a marginal effect on trim. While that may be sufficient to maintain control if the trim is close to optimum it may not be enough if the trim is already way off. Like you say, the data on Ethiopian has not been released yet. However, the published information on the LionAir incidents is not sufficient to draw firm conclusions. I will concede that in the LionAir incident it would appear to be the case that the situation could have been resolved by acting sooner; as in the previous flight. It is not clear that the same is true in the Ethiopian accident. It also may be of some importance that the situation developed at a later stage in the previous LionAir flight. Despite reading most of what is available, I still have more questions than there are answers. In the LionAir incident (crash) stick-shaker started at the beginning of the take-off roll... it is a stage that puts particular stress on the crew to properly interpret and react.
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Old 4th Apr 2019, 17:03
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Preliminary report and FDR data are out.

It appears MCAS did in fact make several Stab Nose-down inputs.

Pilots trimmed back up and selected switches to CUTOUT. But the stab remained in a nose down angle. Crew seen pulling back on elevator continuously. They decide to re-energize the stab cutouts so as to trim nose up again (only slightly). It is then when MCAS goes "I've had enough" and adds another 2,5degs nose down. Airplane dives.

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Old 4th Apr 2019, 17:04
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Originally Posted by 737mgm
Fair point, I should have written crews were overwhelmed instead of too easily overwhelmed. Nonetheless, despite all the stress and confusion that was surely occurring, the "only thing" that was happening is that the airplane was trimming nose down. According to Boeing this can be overriden with the electric trim switch and I have not seen any proof yet that this isn't the case. As I already wrote in an earlier post it is just very puzzling to me why a pilot would let his/her aircraft get to an extreme nose down state if it is possible to counter this with electric trimming. We obviously need more information to be able to understand what truly happened.
"Simulation has demonstrated that the thumb switch trim does not have enough authority to completely trim the aircraft longitudinally in certain corners of the flight envelope, e.g. gear up/flaps up, aft center of gravity, near Vmo/Mmo corner, and gear down/flaps up, at speeds above 230 kts.
In those cases, longitudinal trim is achieved by using the manual stabilizer trim wheel to position the stabilizer. The trim wheel can be used to trim the airplane throughout the entire flight envelope.
In addition, the autopilot has the authority to trim the airplane in these conditions.
The reference regulation and policy do not specify the method of trim, nor do they state that when multiple pilot trim control paths exist that they must each independently be able to trim the airplane
throughout the flight envelope."
Reference: Explanatory Note to TCDS IM.A.120 - Boeing 737 Issue 10 page 15 [Ref 1]. My reading of this, and the preceding paragraph in the referenced document, plus an equivalent safety issue on the 747-8 / -8F [Ref 2], is that the aisle stand trim switches can be use throughout the flight envelope, but the yoke trim switches cannot.

Ref 1 - http://www.easa.europa.eu/sites/defa...20ISS%2010.pdf
Ref 2 - http://www.easa.europa.eu/sites/defa...ESF%20B-13.pdf

Last edited by Semreh; 4th Apr 2019 at 17:43.
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Old 4th Apr 2019, 17:09
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"The crew performed all the procedures repeatedly provided by the manufacturer, but was not able to control the aircraft," said Ethiopian Transport Minister Dagmawit Moges, unveiling results of the preliminary probe into the crash.
Presumably Moges refers to "STAB TRIM CUT OUT switches (both) ... CUT OUT" on the Runaway Stabilizer Checklist.
Does the ET302 Preliminary FDR data support the assertion that the crew did this, and if so, when?
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