The Ethiopian 737 crash in cold and concise terms

[Centaurus]

https://www.skybrary.aero/index.php/B38M,_en-route_south_east_of_Addis_Ababa_Ethiopia,_2019?utm_source=SK Ybrary&utm_campaign=b612ce0882-614_Alarming_Story_31_12_2018_COPY_01&utm_medium=email&utm_term=0_e405169b04-b612ce0882-276530305

So much has been written in other Pprune forums of the Boeing 737-800 MAX disasters that it is all too easy to switch off. . The above link to the latest gen from www.skybrary is a concise and sobering description of the Ethiopian Airlines accident.

[Dora-9]

Sounds horrible.

What are "manual electric trim inputs"? The implication, though I didn't find it, is that the trim cut-out switches were re-instated.

[KRUSTY 34]

https://www.skybrary.aero/index.php/B38M,_en-route_south_east_of_Addis_Ababa_Ethiopia,_2019?utm_source=SK Ybrary&utm_campaign=b612ce0882-614_Alarming_Story_31_12_2018_COPY_01&utm_medium=email&utm_term=0_e405169b04-b612ce0882-276530305

So much has been written in other Pprune forums of the Boeing 737-800 MAX disasters that it is all too easy to switch off. . The above link to the latest gen from www.skybrary (https://www.pprune.org/www.skybrary) is a concise and sobering description of the Ethiopian Airlines accident.

Easy to switch off indeed Centaurus.

When LionAir went down there was almost bewildering onslaught of input from Technophiles of just about every description. “This how this system works”, “This is what they should have done”, lot’s of defense of Boeing. Stuff like that.

Hiding in plain sight among all this clutter was the real problem.

[RHSandLovingIt]

What are "manual electric trim inputs"? The implication, though I didn't find it, is that the trim cut-out switches were re-instated.
I believe that refers to the trim switches on the control column (that activate the electric trim servos)... as opposed to the trim wheel.

I think what you're looking for is in the summary in the top right:

On 10 March 2019, left air data system faults on a Boeing 737-MAX 8 soon after departing Addis Ababa were followed by autopilot disconnection, left stick shaker activation and two successive periods of automatic nose down stabiliser causing EGPWS ‘DON’T SINK’ alerts. Recovery was achieved using manual stabiliser trim but prior to a third automatic pitch down, the trim system was switched off as per the runaway stabiliser drill but briefly reinstated to help recover from it. Recovery from a fourth automatic pitch down was not achieved and a high speed dive led to terrain impact six minutes after takeoff.



The text itself doesn't say as much, but I agree that it seems to imply that at some point, the stab trim was turned back on in an effort to apply ANU trim... which unfortunately, let the MCAS kick in 5 seconds later and trim AND to 1.0 :(
For approximately the next 2½ minutes, the stabiliser position moved in the AND direction from 2.3 to 2.1 units whilst “aft force was being applied to both control columns which remained aft of (the) neutral position”. The crew confirmed to each other that after disconnecting the stabiliser trim, they could no longer control it (although there was no mention on the CVR of whether this was attempted using the control column switches or the pitch trim wheel). During this time, the right side (correct) indicated airspeed increased from approximately 305 KIAS through Vmo (340 KIAS) and the right side overspeed aural warning was activated and remained active thereafter. The left side displayed airspeed remained up to 25 knots less than that on the right side. During this time, the Captain asked the First Officer to request radar vectors to return to the airport and the flight was given a right turn onto 260°. Towards the end of this 2½ minute period, both pilots were recorded as calling out “left alpha vane” and the Captain announced that “pitch is not enough” shortly before “two momentary manual electric trim inputs in the ANU direction were recorded”. These inputs resulted in pitch trim (stabiliser) position moving in the ANU direction from 2.1 units to 2.3 units.

Approximately five seconds after this final manual electric pitch trim input, a fourth period of AND automatic pitch trim command occurred and the pitch trim (stabiliser) position moved in the AND direction from 2.3 to 1.0 units over approximately 5 seconds. Despite the pilots’ added and simultaneous aft control column input throughout the remainder of the flight, the aircraft nose down pitch attitude continued to increase, eventually reaching 40° nose down with the recorded pitch trim (stabiliser) position varying between 1.1 and 0.8 units.

[Icarus2001]

Hiding in plain sight among all this clutter was the real problem.


Yes but trying to get two pilots to agree what that is may be difficult.

(hint: they could have used the electric trim to stop MCAS)

[machtuk]

Yes but trying to get two pilots to agree what that is may be difficult.

(hint: they could have used the electric trim to stop MCAS)


If it where that simple then why all the furore over this? The grounding of the type, the cancelation of orders and the reduction of production means there must be a LOT more than simply turning off a couple of switches!

Two lost airframes, lots of dead people, I hope they get to the bottom of it, the effects will be long lasting I'd say!

[Sunfish]

The conundrum seems to be how you install a primary safety system with massive control authority- MCAS, make sure it can’t be accidentally disabled, while passing off the Max as “just another B737” to Boeing’s customers.

What is going to hurt Boeing, speaking as a former employee of a Boeing customer, is the breach of trust implicit in what Boeing has done before during and now after these incidents. Up until now I always thought of Boeing as the most trustworthy name in aviation.

[industry insider]

If I turned something off for a reason, I wouldn’t turn it back on again unless it was part of a staged checklist reinstatement sequence.

But this was all very confused and they didn’t have the luxury of altitude to assess and deal with the issue. I’m sure there is lots they “could’ have done differently, speed, throttle etc. but It’s always easy to be a crew room troubleshooter.

[Icarus2001]

If it where that simple then why all the furore over this? There are many reasons, some valid others less so but I will let someone else draw that conclusion. What I can say, without fear of contradiction, is that the crew who flew the aircraft prior to the Lionair crash dealt with the situation using electric trim and cut out switches and they landed safely, writing up the defect.
Draw from that your own conclusion.

The use of the electric trim stops MCAS trimming and then there is a five second pause. This is without using the cutouts. Again, draw your own conclusion.

[Tankengine]

There are many reasons, some valid others less so but I will let someone else draw that conclusion. What I can say, without fear of contradiction, is that the crew who flew the aircraft prior to the Lionair crash dealt with the situation using electric trim and cut out switches and they landed safely, writing up the defect.
Draw from that your own conclusion.

The use of the electric trim stops MCAS trimming and then there is a five second pause. This is without using the cutouts. Again, draw your own conclusion.
- Assuming MCAS works like you say.
I reckon it is a **** system designed by engineers who think pilots cannot make up their own mind.
Any system that winds on trim countering pilot input (while pilots are trying yo sort out another failure giving unreliable speed and constant stick shaker) needs to be disabled from all aircraft.
Dealing with multiple failures at low level while trim forces both on the control column and trim wheels become impossible?
Even dealing with this with full knowledge and hindsight would be a challenge.
If the basic design of the max is now so bad that it cannot be certified without MCAS then maybe it should not continue.

[RubberDogPoop]

Any system that winds on trim countering pilot input...


But does it? Is that really what it does? In each case the FDR trace seems to show cessation of MCAS input for 5 secs after a "manual" (read electric or hand wheel trim). In both accident aircraft there is evidence that the Stab cutout worked as suggested as well - in the case of Lion, the day before the accident, and with ET302 in that the MCAS ceased to move the stab from the point of "cutoff" being selected, and only resumed as they reversed (perhaps understandably) their actions.
Be careful with the fundamental attribution error...

[Sunfish]

The lion air crew had the benefit of a jump seat pilot who I understand helped fix the problem. Blaming the crews for failing to deal with a problem caused by a system they didn’t even know about is just vile.

[RubberDogPoop]

The lion air crew had the benefit of a jump seat pilot who I understand helped fix the problem.
Correct.
Blaming the crews for failing to deal with a problem caused by a system they didn’t even know about is just vile.
Agreed. (Though Ethiopian were aware of the recently issued bulletin, and the preliminary findings of Lion Air).

So what is your point?

[Atlas Shrugged]

Any system that winds on trim countering pilot input (while pilots are trying yo sort out another failure giving unreliable speed and constant stick shaker) needs to be disabled from all aircraft.

Spot on! .

[neville_nobody]

I reckon it is a **** system designed by engineers who think pilots cannot make up their own mind.

From what the whistle blowers are saying the engineering team were not in favour of MCAS. It was management that wanted to push it through, and not tell anybody because they were under a company design mandate of no extra pilot training.

Now whether this is just people trying to cover their butt, or this is what really happened is yet to be determined. Boeing are already throwing mud at the whistleblowers so who knows where the truth lies.

[RubberDogPoop]

Spot on! .

Is it?? It doesn't oppose the pilot input (at the time).
Those that have flown the 737, did STS do counter-intuitive trimming after take-off also?

[Icarus2001]

The lion air crew had the benefit of a jump seat pilot who I understand helped fix the problem. Yes indeed and the crew of the Ethiopian aircraft had benefit from knowledge of the Lionair crash and information provided by Boeing. Sunfish I enjoy your input on this forum but with the greatest respect, unless you are a professional pilot who goes to the sim every few months to be trained and checked and experience what this entails and what is expected of us then you cannot possibly understand the subtlety of the crews actions. I don't feel qualified to post on legal forums or medical forums so I don't.

Any system that winds on trim countering pilot input (while pilots are trying yo sort out another failure giving unreliable speed and constant stick shaker) needs to be disabled from all aircraft.

Do you know what a tail-strike avoidance system is? Should they be disabled?

[27/09]

I might have got this information wrong, but I understand they had the stick shaker going almost immediately after takeoff, yet they retracted flap. Why would you you retract flap in this situation?

I understand MCAS is inhibited with flap extended.

[Senior Pilot]

Gents, this is the Dunnunda GA forum.

Please take your thoughts and posts to one of the existing 737 Max threads, thanks :ok: