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Ethiopian airliner down in Africa

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Ethiopian airliner down in Africa

Old 12th Mar 2019, 23:16
  #841 (permalink)  
 
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Originally Posted by Rudder Sir
Some detail lacking here. The master FCC is set by crew, normally to the side of the PF, initially by selecting the onside FD on first. Selecting the opposite autopilot flips the master to that side (I.e. if left seat is flying, but engages AP B, right side FCC becomes master). The nominated master FCC is annunciated on the MCP and is obvious to crew.
One detail that must not be overlooked is that the crew has control over which FCC is engaged to perform autopilot / flight director functions, but does not have control over which FCC provides STS and MCAS when flying manually. As stated in other posts, first power-on yields STS and MCAS from the left FCC. Each subsequent air-to-ground cycle without FCC electric power down and back up causes the FCC to be used for STS and MCAS to toggle between the two.
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Old 12th Mar 2019, 23:20
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What's the risk assessment?

Sorry to intrude here, just a passenger, but I'm baffled what risk assessment in a safety critical industry means that an aircraft that is already airborne needs to find a destination other than the one it was planning to go to in the UK?

I appreciate the fact that the type is effectively prohibited from UK/European airspace but surely asking the crew to go hawking around the world looking for a diversion is introducing additional risk to the baseline risk now associated with this aircraft rather than reducing it. It's got to land somewhere right? And even if it's going to go wrong it's better it goes wrong with every potential advantage in the crew's favour even if that's only ATC in English and familiar with the terrain at a familiar airport. As opposed to an unfamiliar airport with altitude / temperature that might even predispose to the failure condition being encountered after wandering round introducing additional constraints such as fuel.

I apologise if that risk assessment was done today on the basis of the weather in the UK being a risk - but I can't see it.

I work in a safety critical business; medical devices. If I know there's a safety advisory on a piece of kit then I'll risk assess the likelihood/impact of keeping it in service vs the benefit to the patient. That's a very different conversation when the operation's not started (on the ground) vs patient "on the table" (aircraft airborne). And sometimes we might be "brave" when the patient really needs it.

Just askin'


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Old 12th Mar 2019, 23:23
  #843 (permalink)  
 
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Why did it take so long and 300+ pax and crew deaths for the industry to acknowledge that a 50 years old original design cannot be modified/updated/re-engineered endlessly?
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Old 12th Mar 2019, 23:26
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Originally Posted by hans brinker
You would be making things worse by adding power. To get out of a high AOA, you lower the nose before adding power.....
Hans - your patience is amazing. You are correct about the relationship between 737MAX engines and need for MCAS. It has nothing to do with the thrust pitching moment!!!

There is a cert requirement that as AOA increases, the nose up pilot command required must not decrease. This is demonstrated at fixed thrust levels so there is no change in thrust pitching moment. The 737MAX issue here that gives rise to the need for MCAS is that as AOA increases the lift provided by the engine cowling that is so large and mounted so far forward of the wing causes a nose up pitching moment that results is a decrease in the column pull needed to maintain a steady positive AOA rate. That characteristic is not compliant with the requirements. MCAS comes active during this maneuver putting in nose down stabilizer that must be countered by the column. The net effect of engine cowling lift and MCAS nose down stabilizer as AOA increases is that the column needed to complete the maneuver does not decrease part way through the range of AOA for which characteristics must be demonstrated. 737MAX without MCAS fails the cert demo. 737MAX with MCAS passes the cert demo.
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Old 12th Mar 2019, 23:27
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Sen. Ted Cruz (R-Texas), who leads a Senate subcommittee overseeing aviation, said in a statement Tuesday that U.S. authorities should ground the planes.

"Further investigation may reveal that mechanical issues were not the cause, but until that time, our first priority must be the safety of the flying public," Cruz said.


https://www.dallasnews.com/business/...ed-safety-flaw
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Old 12th Mar 2019, 23:33
  #846 (permalink)  
 
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Does anyone know if the EASA notice is based on some new input (presumably from early readout of Ethiopian FDR) ?
If not I think this is draconian and frankly unwarranted - they could at the very least allow en-route flights to operate normally as the issue - if there is actually one - is in the takeoff phase.

On a different topic can anyone explain how an automation system (regardless of brand/purpose), let alone on a modern airliner, can be certified with only one control source ?
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Old 12th Mar 2019, 23:34
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Originally Posted by KRUSTY 34
One big read [sic] button on the yoke that disables ALL automatic functions, including MCAS!
I don't believe this is true on the MAX from what I've read here.
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Old 12th Mar 2019, 23:38
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Originally Posted by Luc Lion
pudknocker,
I can't find back where it was, but I read somewhere that the control column actuated trim cutout switches were ineffective for stopping MCAS trim inputs.
Are there control column actuated trim cutout switches on this plane? Aren't the trim cutout switches on the center console above the number 2 fire handle?
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Old 12th Mar 2019, 23:42
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Just thinking ... not judging, just wondering... so nice to be naive sometimes...

Historically Boeing has always been quite clear and open about serious issues.
And thereby one, certainly not the only, of the companies and organizations that has made aerospace as safe as it is.
That reputation certainly got dented recently during the 787 program. Some are happy with it now, others still have professional reservations.
The Lion Air case caused other dents. The suggestion is that Boeing has been withholding information. They certainly have not been open.
Boeing did not open up about the design philosophy of MCAS, the design itself, the way in which it was tested, and certified, and documented and trained, etcetera.
This Ethiopian case magnifies this unusual lack of openness.
Simply said modern certification (not only in aerospace) puts a lot of proof and testing on the desk of the manufacturer rather than on the desk of the certification authority.
You wonder what was written and agreed about what kind of 'publication obligation of the certification process and results' this shift has caused.
To this day informed people know little of MCAS. Certainly not enough for peace of mind.

So what could Boeing do to start limiting the damage that is being done and still increasing rapidly. So rapid that it may dent the industry.
What would personally appeal to me is the chief engineer of the program giving an explanation about MCAS in general. So a very competent technical person with 'signature responsibility', don't think anyone else would do anymore.
This does not disrupt the Ethiopian investigation because we don't know if MCAS is even involved. So there would be no excuse not doing it citing this one, or for that matter even the Lion investigation. It is just basic historic knowledge and intent you might say.

You get the feeling that if they don't volunteer this now that at some stage they will be ordered to do this and add a number of other people and disciplines.

Chicago has a problem.
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Old 12th Mar 2019, 23:42
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Thrust Pitching Moment Basics

Pitching moment caused by engine thrust is a function of how much thrust and where the engine is mounted vertically with respect to the center of gravity. Thrust pitching moment is not a function of how far forward or aft the engine is located. With this in mind, the nose up thrust induced pitching moment generated by the 737MAX engine is not greater than that for a 737NG. In fact, it is probably less as the center line of the larger MAX engine is higher than the center line of the smaller NG engine given their respective attachment geometries.

Hopefully it is now clear that the pitching moment of concern with the 737MAX engines that gives rise to the need for MCAS is related to the aerodynamic impact of the engine cowling location and geometry, not the magnitude nor location of the thrust vector generated by those engines.
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Old 12th Mar 2019, 23:45
  #851 (permalink)  
 
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Airbubba, the "control column actuated trim cutout switches" are switches located in the control column that stop an electric trim movement when the control column requests an elevator deflection contradicting the trim movement. This is the immediate response to a stuck electric trim button before using the STAB TRIM MAIN ELECT cutout switch on the control stand.
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Old 12th Mar 2019, 23:46
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Updated FAA statement:

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Old 12th Mar 2019, 23:48
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Originally Posted by Luc Lion
Airbubba, the "control column actuated trim cutout switches" are switches located in the control column that stop an electric trim movement when the control column requests an elevator deflection contradicting the trim movement. This is the immediate response to a stuck electric trim button before using the STAB TRIM MAIN ELECT cutout switch on the control stand.
But my understanding is that these switches do not stop MCAS activity. Is that correct?
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Old 12th Mar 2019, 23:50
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Originally Posted by atakacs
Does anyone know if the EASA notice is based on some new input (presumably from early readout of Ethiopian FDR) ?
If not I think this is draconian and frankly unwarranted - they could at the very least allow en-route flights to operate normally as the issue - if there is actually one - is in the takeoff phase.
We don't know what caused the crash of the Ethiopian plane. So how can you know for a fact that whatever issue possibly is at play, only exists in the take-off phase? Perhaps it is a failure mode that can pop-up in any phase and turn a 737 MAX into an impact crater for CEOs to rummage through. We simply don't know, so safety should be the main priority here.

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Old 12th Mar 2019, 23:54
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Originally Posted by DaveReidUK
Updated FAA statement:

FAA seems to be incredibly stubborn. Interesting to see how it pans out in the end.
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Old 12th Mar 2019, 23:55
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Originally Posted by KRUSTY 34
Perhaps, but one has to ponder that the inevitable class action arising from both crashes, along with the evaporation of sales, will certainly test the theory of “Too big to fail”.
At least this will probably hit hard. Will not be so easy (and take Years) to restore trust of the travelling public into the MAX. It had a hard time against the NEO before this. After this it will be even much harder to cope with the NEO.
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Old 12th Mar 2019, 23:56
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Originally Posted by DaveReidUK
Updated FAA statement:

The FAA is doubling down.
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Old 12th Mar 2019, 23:56
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It seems the issue is not so much with MCAS as with the engine location relative to the wing.

MCAS reads like a half baked solution to a problem that should not be there in the first place.

If so, this is not the kind of design philosophy I associate with Boeing.

Diverting aircraft in the cruise because they have a problem taking off doesn’t sound like a terribly rational response either.
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Old 13th Mar 2019, 00:01
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Originally Posted by AlexGG
But my understanding is that these switches do not stop MCAS activity. Is that correct?
That's also my understanding : "control column actuated trim cutout switches" have no effect on MCAS while the "stabilizer trim cutout switches" on the control stand do stop MCAS.
(I understand that it's the AUTOPILOT Cutout switch that does the job).
But I am not a B737 pilot, so I am happy to stand corrected.
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Old 13th Mar 2019, 00:08
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Yes - This ban is not being followed by carriers even if the country has grounded the aircraft over there airspace.
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