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Ethiopian airliner down in Africa

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Ethiopian airliner down in Africa

Old 4th Apr 2019, 06:58
  #3041 (permalink)  
 
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I have a simple question:
What happens if the trim cutoff switches are in on position (electrical trim possible), MCAS wan’t to trim the stabiliser nose down while the pilot holds his dual trim switches on the colom for nose up?

Who wins?

According to water_pilot the PF win’s but is it verified?

With the outcome of ET302 I have my doubts.
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Old 4th Apr 2019, 07:15
  #3042 (permalink)  
 
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Originally Posted by RatherBeFlying View Post
It appears that MCAS can in ten seconds move the stab whenever it's in the mood, but the pilots need considerably longer to bring back the stab with dozens of cranks of manual trim - provided that airload allows them to move the trim.

Very much an unequal contest.

​​​​​​MCAS really shouldn't be putting in more trim than can be corrected by the crew in the interval before it reactivates.

But then, limiting MCAS authority might fail to achieve required stick force increase approaching stall. The software will have to get even fancier to satisfy 10E-9 reliability.

I'm with gums. Dump MCAS and fix the nacelle aerodynamics.
Me too, and I would be willing to bet quite a few Boeing engineers long before anyone else ever heard of it.
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Old 4th Apr 2019, 07:49
  #3043 (permalink)  
 
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Originally Posted by EDLB View Post
I have a simple question:
What happens if the trim cutoff switches are in on position (electrical trim possible), MCAS wan’t to trim the stabiliser nose down while the pilot holds his dual trim switches on the colom for nose up?

Who wins?

According to water_pilot the PF win’s but is it verified?

With the outcome of ET302 I have my doubts.
PF wins, see FDR traces.

On a different topic, failure of control column deflection cutoff override to always closed would mean that if the trim thumb button is pressed nose down, or fails to that position, it will not be cut if the pilot pulls.

Very rare coincidence, but previous posters are right in that periodical check would be needed.

It is in my eyes as dangerous and as rare as the control column defection switches failing to always open, and they installed an override for that (before mcas)
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Old 4th Apr 2019, 08:05
  #3044 (permalink)  
 
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Apart from Boeing the FAA will be left holding the legal responsibility here.

Trying to get the Max back in the air and fully certified will not be easy.

This is not a quick fix and rubber stamp job.

Added to that the passenger viewpoint of an old design past its sell by date and clearly not safe and you have a whole bundle of problems for the manufacturer.
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Old 4th Apr 2019, 08:27
  #3045 (permalink)  
Pegase Driver
 
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I was talking this week end with a senior from one of the European airline affected, they had last week decided stop training on the Max, transfer all the pilots to their other types for upgrade and strike out the type from their summer schedule. Whether the airline will survive this financially is in the balance now as the Summer season is where the money is made... this will have rippling effect on the industry well beyond Boeing..
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Old 4th Apr 2019, 08:38
  #3046 (permalink)  
 
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So the prelim report, issued by the Ethiopian government says the crew "repeatedly followed procedures recommended by Boeing.."
https://www.bbc.co.uk/news/business-47812225
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Old 4th Apr 2019, 08:46
  #3047 (permalink)  
 
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Repeatedly?! How is that possible?
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Old 4th Apr 2019, 08:48
  #3048 (permalink)  
 
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Interesting. When it appears in print and is verified, I await all those that said that "sub standard training was the cause", and that "it would never have happened in the US" to say they were wrong.
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Old 4th Apr 2019, 08:49
  #3049 (permalink)  
 
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From the Ethiopian Airlines press release,
"The preliminary report clearly showed that the Ethiopian Airlines Pilots who were commanding FlightET 302/10 March have followed the Boeing recommended and FAA approved emergency procedures to handle the most difficult emergency situation created on the airplane. Despite their hard work and full compliance with the emergency procedures, it was very unfortunate that they could not recover the airplane from the persistence of nose diving"
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Old 4th Apr 2019, 09:01
  #3050 (permalink)  
 
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Wall Street Journal article

The Wall Street Journal, relying on sources who have seen the flight data recorder readout, reported that the pilots, upon experiencing uncommanded nose-down trim, used the 737’s stabilizer trim cutout switches. And while the 737 MAX 8 retains the manual trim wheels it has had from day one, it’s not known if they used these to re-trim the aircraft. The sources told the Journal that the pilots appeared to have reengaged the stabilizer trim cutout switches, which would have re-enabled the MCAS stall protection system.

The underline is mine. Why would a pilot reengage a failed system? If they wanted to control the stab trim after turning of the electric stab trim switches, why did they not use the manual trim wheel?
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Old 4th Apr 2019, 09:02
  #3051 (permalink)  
 
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No “foreign object damage” or “structural design problem” identified

That’s likely to be a significant finding
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Old 4th Apr 2019, 09:08
  #3052 (permalink)  
 
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Originally Posted by compressor stall View Post
Interesting. When it appears in print and is verified, I await all those that said that "sub standard training was the cause", and that "it would never have happened in the US" to say they were wrong.
I think it would be wise to wait for the report. If the aircraft wasn't put in trim using the switches as per Boeing recommendation before placing them to cutout and it turns out that the switches were then turned back on, again contrary to guidance, the press release from Ethiopian is misleading to say the least.

​​​​​​
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Old 4th Apr 2019, 09:09
  #3053 (permalink)  
 
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Why would a pilot reengage a failed system? If they wanted to control the stab trim after turning of the electric stab trim switches, why did they not use the manual trim wheel?
Maybe because the control loadings at the speed they were doing made it difficult/impossible to manually trim, so they tried the electric trim again? If you’ve got both (or even four) hands on the control column trying to stop the aircraft pitching down, there’s not many hands left for the manual trim...
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Old 4th Apr 2019, 09:12
  #3054 (permalink)  
 
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Originally Posted by warbirdfinder View Post
Why would a pilot reengage a failed system? If they wanted to control the stab trim after turning of the electric stab trim switches, why did they not use the manual trim wheel?
Speculatively with both pilots hauling back on the control column and no electric trim, the moment any of them lets go to give the wheel a try the nose would dip down again. Additionally, at nose low and high speed with stab overloaded the wheel might have been much too stiff to both move and do so enough times to make an impact.
I hate to speculate on this but it points to proper action by crew finding themselves unable to bring nose up with manual means and reactivating the cutouts to regain electric trim capability. (Which should come back and if used should stop MCAS either way, unless...)
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Old 4th Apr 2019, 09:24
  #3055 (permalink)  
 
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Originally Posted by Albino View Post
I think it would be wise to wait for the report. If the aircraft wasn't put in trim using the switches as per Boeing recommendation before placing them to cutout and it turns out that the switches were then turned back on, again contrary to guidance, the press release from Ethiopian is misleading to say the least.

​​​​​​
The Boeing NNC regarding runaway trim, or MCAS, has never told us to trim to neutral before placing the switches to cut off. It tells us to stop the trim with the switches if the trim doesn’t stop after disconnecting the autopilot. Then use manual trim. Period.

The armchair experts have now moved from «They should just have placed the cut off switches to off and contained the problem» to «They should just have trimmed neutral and then used cut out switches and contained the problem».
Congratulations! It took only a few weeks to come to this conclusion.
The Lion Air and Ethiopian pilots only had a few minutes.
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Old 4th Apr 2019, 09:33
  #3056 (permalink)  
kwh
 
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Originally Posted by jagema View Post
Speculatively with both pilots hauling back on the control column and no electric trim, the moment any of them lets go to give the wheel a try the nose would dip down again. Additionally, at nose low and high speed with stab overloaded the wheel might have been much too stiff to both move and do so enough times to make an impact.
I hate to speculate on this but it points to proper action by crew finding themselves unable to bring nose up with manual means and reactivating the cutouts to regain electric trim capability. (Which should come back and if used should stop MCAS either way, unless...)
If this turns out to be correct, could it be because the Boeing recommended response to the unwelcome MCAS activation was developed in a simulator incapable of generating the forces that the real world can generate, so the pilots developing & “testing” the protocol could pull back the sim yoke with one hand, while rotating the easy to spin manual trim wheel with the other? “Don’t worry, this is easy to get out of if we just add a page to the manual to tell people what to do, watch...”. Also “Flight test the fix on a real aircraft? Sounds like a lot of work, dude... let’s not, OK?”

No, well spotted, I’m not a pilot, but I assume that not every control in a simulator for an aircraft where the force felt through the controls relates to the forces the control surfaces they connect to are experiencing [i.e. a non-fully-FBW plane] will be 100% accurate?
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Old 4th Apr 2019, 09:41
  #3057 (permalink)  
 
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Originally Posted by ManaAdaSystem View Post


The Boeing NNC regarding runaway trim, or MCAS, has never told us to trim to neutral before placing the switches to cut off. It tells us to stop the trim with the switches if the trim doesn’t stop after disconnecting the autopilot. Then use manual trim. Period.

The armchair experts have now moved from «They should just have placed the cut off switches to off and contained the problem» to «They should just have trimmed neutral and then used cut out switches and contained the problem».
Congratulations! It took only a few weeks to come to this conclusion.
The Lion Air and Ethiopian pilots only had a few minutes.
And that highlights a big difference between runaway stab. and MCAS unwanted operation:

With runaway stab you can’t catch it by trimming - it is running away...

With MCAS unwanted (for want of a better description) operation you can theoretically catch (reverse) it by trimming.

Another difference is that in an AoA fault caused unwanted MCAS operation other factors also come into play - even before MCAS operation on flap retraction:

Autothrottle, Instrument anomaly, Stall warning etc. which can cause:

Unwanted rise in speed, initial pilot input nose down response, cockpit confusion.

Therefore the standard drill for stab runaway does not necessarily apply. Trimming to neutral and ATS disconnect might well have priority over stab trim cutoff operation.

Of course we didn’t know this, the poor crews didn’t know it and it is a scenario which Boeing will be looking at hard before submitting a suitable procedure for recertification, I am sure.

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Old 4th Apr 2019, 09:49
  #3058 (permalink)  
 
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[QUOTE=bill fly;10438384]
Originally Posted by ManaAdaSystem View Post


The Boeing NNC regarding runaway trim, or MCAS, has never told us to trim to neutral before placing the switches to cut off. It tells us to stop the trim with the switches if the trim doesn’t stop after disconnecting the autopilot. Then use manual trim. Period.

The armchair experts have now moved from «They should just have placed the cut off switches to off and contained the problem» to «They should just have trimmed neutral and then used cut out switches and contained the problem».
Congratulations! It took only a few weeks to come to this conclusion.
The Lion Air and Ethiopian pilots only had a few minutes.
[/QOTE]
And that highlights a big difference between runaway stab. and MCAS unwanted operation:

With runaway stab you can’t catch it by trimming - it is running away...

With MCAS unwanted (for want of a better description) operation you can theoretically catch (reverse) it by trimming.

Another difference is that in an AoA fault caused unwanted MCAS operation other factors also come into play - even before MCAS operation on flap retraction:

Autothrottle, Instrument anomaly, Stall warning etc. which can cause:

Unwanted rise in speed, initial pilot input nose down response, cockpit confusion.

Therefore the standard drill for stab runaway does not necessarily apply. Trimming to neutral and ATS disconnect might well have priority over stab trim cutoff operation.

Of course we didn’t know this, the poor crews didn’t know it and it is a scenario which Boeing will be looking at hard before submitting a suitable procedure for recertification, I am sure.
You are both right. But Boing introduced a very "clever" sentence in the AD:

"Electric estabilizer trim can be used to neutralize control column pitch forces before moving the stab trim cutout switches to cutout"

Can: means that if you do it and you crash, they would say they didn't tell you to do it, but if you don't do it and you crash they will say that they mentioned it for something.

Not that any amount of words is going to change the fact that they are responsible. If only they were as clever in the design as they are with legal-related documents.
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Old 4th Apr 2019, 09:49
  #3059 (permalink)  
 
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They should've kept airframe and hydraulics (99% of them, just a touch here and there)
DO you have any idea of how much of the 737 does not meet the modern day safety standards and is grandfathered? That's probably worthy of a thread of its own.

Nearly 25 years ago Airbus complained to JAA about Boeing's grandfather rights that were letting the 737 get away with nearly half a dozen more seats than a comparable newly certified airliner could, all being equal.
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Old 4th Apr 2019, 09:52
  #3060 (permalink)  
 
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Originally Posted by ManaAdaSystem View Post


The Boeing NNC regarding runaway trim, or MCAS, has never told us to trim to neutral before placing the switches to cut off. It tells us to stop the trim with the switches if the trim doesn’t stop after disconnecting the autopilot. Then use manual trim. Period.

The armchair experts have now moved from «They should just have placed the cut off switches to off and contained the problem» to «They should just have trimmed neutral and then used cut out switches and contained the problem».
Congratulations! It took only a few weeks to come to this conclusion.
The Lion Air and Ethiopian pilots only had a few minutes.
Have you read the Boeing bulletin?

​​​​​​Under operating instructions
'Electric stabilizer trim can be used to neutralise control column pitch forces before moving the stab trim switches to cutout'

Why wouldn't you?
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