Breaking news: Ethiopian Airlines flight has crashed on way to Nairobi

[Schwartz]

After the stab trim is deactivated (i.e. the trim cutout switches are put in the cutout position) the stabilizer doesn't move any more except, the report mentions, it moved barely 0.2 units nose-down in 2 minutes and 30 seconds. No mention of intermitency. I suspect this can be reduction of free play and flexibility in the mechanism and structure as the speed kept increasing and hence the aerodynamic forces on the stabilizer kept increasing.


I think it is quite clear. They were desperately trying to keep the nose from going down. The captain asks for help from the FO to pull up and the FO helps but the captain says that the pitch is not enough. They desperately needed to trim up and they had already tried the trim wheel manually only to find it impossible to move. They needed to revert to the trim switch. For me the real unanswered question is, why didn't they revert to the trim switch then, after re-engaging the trim cutout switches? They payed for that mistake with their lives.

I agree. Ironically, they were focused on flying the plane, not trying to reverse engineer a fatally flawed system design.

Looking at the numbers and the slope on the graphs, it does seem like the Trim UP is slower than Trim DOWN based, presumably because even the motor is affected by the forces acting on the stabilizer. The more I consider this situation the more obvious how poorly designed this system is. In ~10-15 seconds the plane puts the pilots in a position where they have to physically struggle to prevent the plane from nosing into the ground. Execution of the procedure they were given doesn't work because they can't manually trim against the aerodynamic forces let alone deal with all the other important aspects of flying the plane.

The pilots actually have a clue as to what needs to be done, but 5-9 more seconds of inattention to one very narrow control among hundreds -- with controls shaking, instruments not corresponding, alarms sounding -- dooms the plane.

I am now aligning with one of Evan's original sentiments, that any basic safety analysis of this subsystem would have exposed these flaws. This system isn't even safe enough for a test pilot if something happens to that AoA sensor.

[Gabriel]

Gabriel, I think the assumptions you are making are based on the fact that you believe the MCAS was working as intended - in regard to inputs and sensors. However, I personally believe the findings will be that the mcas did NOT work as intended (allowing for the erroneous sensor inputs) - I believe this is where the problem is primarily at fault. I cannot, for one second, believe that the pilots would re-engage - as a last attempt - the trim motors only to give a brief press- nonsensical !. Personally, I believe the system overrode these inputs. That when the mcas was initialised (at trim cutout reselect - that it acted in a controlling and over-riding way. Yes, pure speculation, but based on common sense from the reports (otherwise at this moment no reason to explain the brief inputs unless the system the (Make Corpses And SPLAT) was over-riding - perhaps on startup 'reboot' from a trim cutout event. it simply makes no sense.
I also believe pilots may well try to apply thrust in the even of a non (apparent to them - or non controllable event) in the MAX due to its propensity to pitch up during power application due to the engine positions - - a sort of 'power on and let the engines bring the damn thing up!' - which would happen as it is inherently unstable in pitch and power, butm known that due to the placement of the thrust vector a pitch up would normally occur. Obviously it did not do enough to save things due to a final overriding downward force from the stab. However, as said, it is not unreasonable to apply power - dramatic power, in a MAX if you simply cannot correct the downward pitch.
I commend you listing the possible unknown aspects, however, system override and intercept from a rebooted or re-engaged MCAS - or simply - am out of spec (bugged) mcas action is also readily apparent.
I can only hypothesise that on re-engaging the pitch trim that the reason is was so brief was simply that the MCAS had control and not the trim switches - hence brief and immediate abandonment of that manoeuvre. Speculation ? of course. Am I wrong, of course I could be, but ................... you well placed post raises more frightening questions than it answers in my very humble opinion. As I opined before, I really believe there is a major bug in the MCAS that allows it to override the pilot trim - it may only occur on restart from trim cutout - who knows ? - but there is definitely something very very amiss.
We could ALL be totally wrong, however..... when will we see what actually happened and not the sanitised version ?

I commend you for the extremely well presented and researched (and knowledge based) posts.
SA.

I don't think so. In both crashes the MCAS was working as expected, stopping every time that the pilots used the trim switch and restarting exactly 5 seconds later. Why would it be different in the last seconds of the flights?

[brianw999]

The Trump Factor.
What all here need to realise as well, is the idiot factor in the final 'solution' if it ever gets there - that is Don the Con..

Not, how he 'announced' the grounding (not because his personal pilot would not be accepted for the head honcho FAA job ????!!!) - he wanted to 'own it' as he wants to own everything. He is of dubious IQ - low by all signs - a pathological liar, a con man, a cheat and an illiterate numbskull. .. now, when this starts to make sense (the whole MAX fiasco) then Don the Con will try to make it anyone elses issue apart from his own - or in this case - boeing !. that intransigence will simply make respected and intelligent leader of the free world refuse to accept his lies and promises. The saga will go on BECAUSE of trump interfering in things that have jack shit to do with him.
He is likely to drive a stake into boeing's heart in his attempt to override all actual facts and say that it is safe with one line of code and a bandaid. The guy is an utter moron!!!, yet, will play a key roll on all this, as he is genetically deformed enough to do so.
Instead of correcting and managing (spinning even!) a tragedy, he will simply lie and attempt to con. The REAL leaders of the world who are FULLY aware of this idiot's silly games and will not let it go. --- I mean ? wasn't Boeing actually Born (created) in Germany (sic) - like his racist father ? lol .////

It brings a whole new dimension to improving safety when you have a narcissistic pathological liar MAKING himself in charge - even after he sacks his patsy..... You ain't seen nothing yet boys and girls, the Don the Con show will go into full gear soon. - Dont buy more MAX's - ???? we will add TARIFFS !!! F&*ING MORON.

Are you related to LH-B744 by any chance ?

[3WE]

...Ironically, they were focused on flying the plane, not trying to reverse engineer a fatally flawed system design...but 5-9 more seconds...inattention...controls shaking, instruments not corresponding, alarms sounding...

Your post on the trim behavior and your comments really nail it.

You used the word inattention- it's correct, but contrast that (as you did) with what they WERE diligently paying attention to.

[SmoothAir]

I don't think so. In both crashes the MCAS was working as expected, stopping every time that the pilots used the trim switch and restarting exactly 5 seconds later. Why would it be different in the last seconds of the flights?

Exactly ! - that is my concern as the brief trim up is nonsensical with the limited data we know. Why did they stop the trim up ? - I postulate another reason - exactly what ? dunno ? however, it 'may' indicate that was #supposed# to happen to the trim did not, which is very very worrying.

[SmoothAir]

Are you related to LH-B744 by any chance ?

lol, no, just anti 'Don the Con' and the influence of a pathological liar on the outcome of an extremely important and sensitive investigation Brian.

[brianw999]

lol, no, just anti 'Don the Con' and the influence of a pathological liar on the outcome of an extremely important and sensitive investigation Brian.

Phew, thank God for that. !

[brianw999]

Ethiopean authorities release statement saying pilots acted according to Boeing instructions.....

https://www.nytimes.com/2019/04/04/world/asia/ethiopia-crash-boeing.html

[BoeingBobby]

Ethiopean authorities release statement saying pilots acted according to Boeing instructions.....

https://www.nytimes.com/2019/04/04/w...sh-boeing.html

I personally don't believe it. After talking to two different MAX Captain's that I have known for years. According them, if you turn off both stab trim cut out switches, the system is no longer powered.

[Evan]

I personally don't believe it. After talking to two different MAX Captain's that I have known for years. According them, if you turn off both stab trim cut out switches, the system is no longer powered.

MCAS is just software. The cutout switches supposedly remove power to the stab motor. I can't imagine how anything could activate the trim motors if they were cut off.

Unless, the cut out switches are upstream of the automation and only cut out the trim switches (where trim runaway shorts tend to occur).

Although Boeing tells us this works and I trust that Boeing at least knows how to read their own wiring diagrams.

[Gabriel]

Exactly ! - that is my concern as the brief trim up is nonsensical with the limited data we know. Why did they stop the trim up ? - I postulate another reason - exactly what ? dunno ? however, it 'may' indicate that was #supposed# to happen to the trim did not, which is very very worrying.

That we cannot understand why the pilots did something doesn't mean that they didn't do it. Air France and Colgan come to mind.
Your postulation has no basis whatsoever other that you don't want the pilots to have done what apparently they did.
My postulation matches 2 CVRs and the technical descriptions of the 737 trim and MAX's MCAS.

Am I necessarily right and you necessarily wrong? No, but I see my speculation more substantiated and hence more likely that yours. But it is perfectly possible that I am wrong and you are right. Let's wait and see.

[Gabriel]

I personally don't believe it. After talking to two different MAX Captain's that I have known for years. According them, if you turn off both stab trim cut out switches, the system is no longer powered.

BoingBobby, don't get mad at me, but have you been following the case? Did you read the report? Follow the latest news coverage? Watched the latest youtube videos on the matter? Read the interim report or the discussions about it here?

Let me summarize it for you. And this is FACTUAL (except where noted):
1- The pilots DID use the trim cutout switches.
2- That DID stop the MCAS.
3- But they were quite out of trim already and gaining speed (all the way to overspeed).
4- That meant that they had to apply increasing pull force on the yoke to keep the nose from going down, which was getting harder and harder.
5- By when they tried to move the trim wheel manually, the combination of too much nose-down trim, a lot of force and deflection on the elevator, and high speed, created very high forces on the jackscrew that made it impossible to turn the trim wheel manually. They tried, and couldn't. ***
6- They reconnected the cutout switches. Apparently, they did so as a last desperate resource to be able to use the thumb switch as the speed kept going up, the stick forces kept increasing, and they were starting to lose the battle.
7- For reasons that are not clear, they did just a couple of super brief clicks in the nose-up thumb switch.
8- 5 seconds after the last click, as per deign the MCAS kicked in and quickly put the plane in a -3G , -40 degrees pitch dive. It took only 20 seconds to go from 7000 ft AGL to their final destination. (you know how powerful just a little bit of trim is when you are overspeeding)


*** --- 5.a- The effect of stiffening trim wheel when there is a combination of significant out-of-trim situation and high speed is reportedly described in the 737 manual since ever and, reportedly (by a former Boeing engineer that worked in the first versions of the 737), there used to exist a procedure in the first versions, apparently removed in the -300, that explained how to deal with that situation. It was nicknamed the rollercoaster maneuver. Pitch up well above the horizon, unload the elevator letting the nose go down (that will unload the jakcscrew) and crank the trim wheel. When the nose goes below the horizon, pull up to well above the horizon again and repeat until the trim is not so out-of-trim that the wheel can be cranked without resorting to the rollercoaster. I proposed, if you have enough elevator authority and arm strength to pull up well above the horizon, why don't just pull up well above the horizon, reduce thrust and let the speed go down until the load in the jackscrew has reduced enough to manually crank the wheel. This is a characteristic of all the 737 line since the beginning, not just the MAX.

[Gabriel]

Q&A by Mentour. Among other things, he explains why he removed the video (and will never upload it again) and he also explains the rollercoaster maneuver.

https://www.youtube.com/watch?v=q17vykscK0w

[flashcrash]

[QUOTE=Gabriel;681729] there used to exist a procedure in the first versions, apparently removed in the -300, that explained how to deal with that situation. It was nicknamed the rollercoaster maneuver. /QUOTE]

Copy attached here for reference

[Gabriel]

Copy attached here for reference

Thanks!