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Ethiopian airliner down in Africa

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Ethiopian airliner down in Africa

Old 4th Apr 2019, 22:10
  #3181 (permalink)  
 
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Originally Posted by BluSdUp View Post
Just a few observations.
I have read a few hundred Accident reports and this one is one of the scariest!
Why did this Cpt select AP on, with stickshaker going?
Why did he retract flaps when he knew there was a 50/50 chance the MCAS would go off.
Why did he not set a reasonable pwr setting so as to not accelerate out of control?

Must have been confusing for him?

As for Boeing Max
It will never fly again without serious modifications!
Cpt B
It appears he tried to engage the left autopilot a fourth time, near the end at 05:43:30.

That's the only explanation to the AP Warning they got there.

It appears they
  • restored the stab trim cutout switches
  • made two quick manual ANU inputs
  • hit the autopilot engange button, hoping the autopilot would solve the situation for them
Instead MCAS kicked in again...
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Old 4th Apr 2019, 22:14
  #3182 (permalink)  
 
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Originally Posted by Brosa View Post
It appears he tried to engage the left autopilot a fourth time, near the end at 05:43:30.

That's the only explanation to the AP Warning they got there.

It appears they
  • restored the stab trim cutout switches
  • made two quick manual ANU imputs
  • hit the autopilot engange button, hoping the autopilot would solve the situation for them
Instead MCAS kicked in again...
The pilot may have recalled that MCAS is disabled when AP is enabled. Perhaps engaging AP seemed like a good idea at that point?
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Old 4th Apr 2019, 22:27
  #3183 (permalink)  
 
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so now the spin begins, "they followed all the rules and it still crashed"...well, not quite, how did the elec/auto stab trim find itself functioning again, or did it turn itself back on?
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Old 4th Apr 2019, 22:28
  #3184 (permalink)  
 
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Originally Posted by OldnGrounded View Post
Why would he "know" that?
Because Boeing stated MCAS inoperative with flaps extended. If crew extended flaps before reengaging electric stabilizer they could have prevented MCAS from operating. That would have allowed them to easily trim plane electrically. With known MCAS issue retracting flaps at 1000 agl seems too soon to me. At that altitude MCAS engagement more difficult to control.
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Old 4th Apr 2019, 22:37
  #3185 (permalink)  
 
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I'm still baffled by the speed they reached. Having control issues I'd think one would instinctively try to maintain some reasonable power level. It is almost if they flew TOGA till the ground...
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Old 4th Apr 2019, 22:39
  #3186 (permalink)  
 
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''About four minutes into the flight, the pilots gave up on the manual stabilizer wheel and switched the electric power to the tail back on, then used the thumb switches on the control column to pitch the nose back up.

But just five seconds later, MCAS kicked in again and once more pushed the nose sharply down.

Just 35 seconds later, six minutes after take-off, the plane rolled over before plowing into the earth in a “high energy impact” at a speed of approximately 575 miles per hour."


Checkmate - they were damned if they did (use trim cutout switches) and damned if they didn't. Seems that at the point they shut of the system the AND trim was more than the elevators could overcome and with ever increasing speed in the dive manual trim was not an option. what would you do? try flying inverted (as with the air Alaska accident )? May explain the last minute roll .

What a mess.


​​​​
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Old 4th Apr 2019, 22:41
  #3187 (permalink)  
 
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So why has the CEO/President of Boeing, tonight, said that he now own responsibility for what happened in that cockpit as a result of the MCAS debacle thrown up by the preliminary report?
He went on to state that Boeing had a 'fix' which will/is being implemented as he speaks.
Do you honestly believe a man of this stature is going to make a carefully crafted statement such as this - without advice.

Boeing is in for some serious pain for years to come, over this. Law suits have already been lined up.

The pilots 'appear' to have been cleared of any malpractice, it seems to me.......
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Old 4th Apr 2019, 22:50
  #3188 (permalink)  
 
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to add a non-pilot (burn him, burn him, but sometimes the ignorant can ask relevant questions..) question to the mix.

Could the reason that on both fatal flights that we saw unexpectedly brief presses to the "trim up" pickle switch be :

because that the pilot would have expected that his pressing of the switch to cause the immediate cacophony of noise of the trim wheels spinning , and maybe they didn't due to aerodynamic loads currently on them due to the lack of authority of the electric motor due to increasing speed so they quickly released the switch ("It's not working") . This would have been then followed up by MCAS throwing in it's "i'm OK to go again jack" logic of another bucketload of nose down. And the same side effect of increasing speed could cause the inability to wind back manually leading to the desperate measure of turning the electronic back on.

I guess the question is - is there a combination of speed and nose down trim that can mean that neither the electronic trim nor the hand wind trim can counteract it. And of course if you re-enable the electronic trim to try, having manual trim try and failed, then MCAS gives you an extra dose of "nose hard down"...

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Old 4th Apr 2019, 22:55
  #3189 (permalink)  
 
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Rananim

Fair summary.
But it is not criminal to be one level above Your Competency Level.
It IS criminal to make such a shit aircraft and certify and sell it like Boeing does!
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Old 4th Apr 2019, 22:57
  #3190 (permalink)  
 
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Originally Posted by Rananim View Post
Prelim report is perplexing.At face value it appears that the crew did cutout
the required switches(only after 2 bursts of MCAS ) with stabilizer at 2.1
units but FO couldnt get the manual trim working.FO has 200 hours
so this is not surprising.
...
...
Agree with many of your points, esp on failure to react to ever increasing speed. The report mentions setting a speed target at some point, perhaps they thought auto throttle was working?

That said do disagree with statements on manual trim, pretty strong evidence that at the speed and trim they were in it would be physically very hard or impossible to trim manually without unloading maneuvers that the did not have the altitude for and/or knowledge/training of.
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Old 4th Apr 2019, 23:01
  #3191 (permalink)  
 
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Originally Posted by ironbutt57 View Post
so now the spin begins, "they followed all the rules and it still crashed"...well, not quite, how did the elec/auto stab trim find itself functioning again, or did it turn itself back on?
I don't believe it is spin on the part of The Media. It's just too complicated to process all this information into something understandable and digestible for the public.
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Old 4th Apr 2019, 23:03
  #3192 (permalink)  
 
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When all is said and done, the one common indicator is the AoA reading on the Cap's side. Debate everything else till your heart's content.

Why did it flip to ~75deg at 150kn? More interestingly, why did it flip back to "normal" for a moment just before end of flight before flipping back to error?

I assume the slowly diverging altitude readings relate to the AoA stuck at 75 while pitot static reads ok...

Boeing's proposed fix includes shutting off the "required" MCAS when AoA disagrees so this is kind of important.

Whisky Tango Foxtrot guys? What's happening to that vane or the electrons/code behind it?
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Old 4th Apr 2019, 23:08
  #3193 (permalink)  
 
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Originally Posted by ktcanuck View Post
When all is said and done, the one common indicator is the AoA reading on the Cap's side. Debate everything else till your heart's content.

Why did it flip to ~75deg at 150kn? More interestingly, why did it flip back to "normal" for a moment just before end of flight before flipping back to error?

I assume the slowly diverging altitude readings relate to the AoA stuck at 75 while pitot static reads ok...

Boeing's proposed fix includes shutting off the "required" MCAS when AoA disagrees so this is kind of important.

Whisky Tango Foxtrot guys? What's happening to that vane or the electrons/code behind it?
Maybe it is just simple plain old grounding also why the other sensor messed up , combined with a very bad qa at boeing trying to push more and more of the planes out of the factory more mistakes made
Both incident planes had issues within months of delivery i would love to see the issues on the other 380 they had delivered
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Old 4th Apr 2019, 23:21
  #3194 (permalink)  
 
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There is something seriously wrong with this design.
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Old 4th Apr 2019, 23:32
  #3195 (permalink)  
 
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Originally Posted by AVAT View Post


Because Boeing stated MCAS inoperative with flaps extended. If crew extended flaps before reengaging electric stabilizer they could have prevented MCAS from operating. That would have allowed them to easily trim plane electrically. With known MCAS issue retracting flaps at 1000 agl seems too soon to me. At that altitude MCAS engagement more difficult to control.
Totally agree that, if the crew actually understood MCAS, and understood that they had a sensor or sensor signal failure that might cause it to activate, they would not have cleaned up when they did. I honestly don't think that the ET crew, or the vast majority of crews at that time, had anything like the understanding of MCAS that we have now, notwithstanding the Lion crash and the subsequent Boeing and FAA notices. At this point, I can't remember airspeed, etc. at the point they reengaged electric trim. I think it may have been high enough that extending flaps would not have come naturally to mind, but I'll have to look at the data again.
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Old 4th Apr 2019, 23:52
  #3196 (permalink)  
 
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More about the newly-disclosed 'minor' issue with safety-critical software, from the Washington Post:

Additional software problem detected in Boeing 737 Max flight control system, officials say

But later Thursday, Boeing confirmed to The Washington Post that it had found a second software problem that the Federal Aviation Administration has ordered fixed — separate from the anti-stall system that is under investigation in the two crashes and is involved in the worldwide grounding of the aircraft.

That additional problem pertains to software affecting flaps and other flight-control hardware and is therefore classified as critical to flight safety, said two officials who spoke on the condition of anonymity to discuss the probe.

The realization of a second software problem explains why the timeline that Boeing projected publicly last week for getting hundreds of the aircraft airborne again has slipped, the officials said.
Boeing initially said it planned to submit fixes for its stall-prevention system to the FAA for review last week. On Monday, an FAA spokesman said the agency instead expected to receive the final package of software “over the coming weeks.”

“Obviously, we ended up at a situation that in hindsight was not supposed to happen,” one of the officials familiar with the investigation told The Washington Post. “Now, you don’t want to be in a situation where there was one contributing factor to an accident, and then three weeks later you find another one.

In a statement, Boeing called the additional problem “relatively minor” but did not offer details of how it affects the plane’s flight-control system. “We are taking steps to thoroughly address this relatively minor issue and already have the solution in work to do that.”
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Old 5th Apr 2019, 00:42
  #3197 (permalink)  
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There is something seriously wrong with this design.
In all seriousness, I fear you're right.




We always used to say, if it looks right, it'll fly right, etc., but I can't recall ever having such an uneasy feeling about an aircraft's ground clearance. Remember, this is the core of the problem we're discussing.

Fuel, payload and a bit of the thumper will make it even more critical, and that's before a hefty cross wind.
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Old 5th Apr 2019, 00:46
  #3198 (permalink)  
 
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While it seems fair to say the crew made decisions that we, based on FDR plots and from the comfort of our homes, do not understand... I think it is also important to keep in mind the timespan and chaotic situation in the cockpit at the time. Pretty much in the time that it takes you to read the events as they happened, they had to analyze them and troubleshoot them with alarms going off. We can sit down with a cup of tea or coffee and take 10-15 minutes to think about it and decide what they should have done instead.

Pointing at the crew as the cause of this accident is not completely fair in my opinion. They may have made decisions that turn out to be questionable to the skygods here who have figured out exactly what they should have done. But... if they'd had a well designed plane without vague, ill designed and explained "safety" features one could also argue this accident would not have happened. Follow the problem down to the roots and you will IMHO always end up at Boeing and the design decisions made. The crew on this flight could be considered the last slice of the cliché swiss cheese with the hole lined up.
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Old 5th Apr 2019, 00:49
  #3199 (permalink)  
 
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Left side AoA sensor vs vertical acceleration (g)

I offer an explanation for the behaviour of the Left hand AoA indication throughout the flight.

If the vane had been lost the AoA sensor would become unbalanced about its usual axis of rotation. The internal balance weight** would then cause the axle to be subject to movement when the aircraft transitioned from +g to -g. +g would cause the indication of +AoA. (If I have got this the right way round

Looking at the FDR traces it can be seen that this appears to be the case. I have drawn four green vertical lines to indicate the transitions from +g to -g and vice versa. In each case they appear to align with a change in the direction of movement of the sensor in the correct sense. Remember that the data consists of discrete samples and we do not know the sample rate and I am assuming that any small discrepancies are due to errors introduced by the sampling.

I have (rather crudely) chopped out a period in the middle of the chart so that it is a bit narrower so that the scale markings can be easily seen. The horizontal blue line in the "g" section of the chart is coincidentally exactly on 0g.

It therefore seems quite likely that the vane was lost or perhaps damaged soon after take off, perhaps by a bird strike or otherwise. Note however that if the vane had been bent back its balance would be moved in the other direction and its aerodynamic influences would still have been felt so I think that the best conclusion consistent with the data is that the vane was lost.

** A post on PPRuNe regarding this incident showed an exploded view of the AoA sensor and it featured an internal balance weight. Unfortunately I cannot recall where it was now.




Last edited by jimjim1; 5th Apr 2019 at 02:15.
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Old 5th Apr 2019, 01:04
  #3200 (permalink)  
 
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Originally Posted by jimjim1 View Post
I offer an explanation for the behaviour of the Left hand AoA indication throughout the flight.

If the vane had been lost the AoA sensor would become unbalanced about its usual axis or rotation. The internal balance weight** would then cause the axle to be subject to movement when the aircraft transitioned from +g to -g. +g would cause the indication of +AoA. (If I have got this the right way round
Excellent post, the tracking is almost too perfect to be believed at first.

This fits with the AoA heater fault as well, whatever happened caused 2 symptoms that are hard to explain except as physical damage to the sensor since the heater supply is independent of the resolver.

Someone commented that the pilots would have heard a bird strike, given the lack of a full CVR transcript we don't know if anything was audible.
I would suspect that the press conference statement of 'no foreign object' would suggest but not prove none was audible.

Anyone know if a departing vane by itself would cause a heater open?

One other observation is that the flight deck actions seem to be mostly normal until the AP disconnect, almost as though the stick shaker was activated but not working or noticed.
If missing from CVR that probably would have been noted.



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