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Ethiopian airliner down in Africa

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Ethiopian airliner down in Africa

Old 12th Mar 2019, 22:42
  #861 (permalink)  
 
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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, 22:42
  #862 (permalink)  
 
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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, 22:45
  #863 (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, 22:46
  #864 (permalink)  
 
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Updated FAA statement:

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Old 12th Mar 2019, 22:48
  #865 (permalink)  
 
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Originally Posted by Luc Lion View Post
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, 22:50
  #866 (permalink)  
 
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Originally Posted by atakacs View Post
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, 22:54
  #867 (permalink)  
 
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Originally Posted by DaveReidUK View Post
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, 22:55
  #868 (permalink)  
 
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Originally Posted by KRUSTY 34 View Post
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, 22:56
  #869 (permalink)  
 
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Originally Posted by DaveReidUK View Post
Updated FAA statement:

The FAA is doubling down.
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Old 12th Mar 2019, 22:56
  #870 (permalink)  
 
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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 12th Mar 2019, 23:01
  #871 (permalink)  
 
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Originally Posted by AlexGG View Post
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 12th Mar 2019, 23:08
  #872 (permalink)  
 
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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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Old 12th Mar 2019, 23:12
  #873 (permalink)  
 
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EASA became crazy

Originally Posted by LookingForAJob View Post
I openly admit that I am no fan of the way in which EASA works - being overly reliant on rules and law with sometimes peculiar interpretations of that law - but it's strange to see, following rather than leading, its member States' CAAs, that it chooses to issue an AD which appears to fail to meet the legal requirements set out in Commission Regulation No 748/2012 for such documents.

Of course, if evidence shows that the safety level of this aircraft may be compromised I would hope that this would be declared, even if the details of that evidence are not provided. Overall, as others have suggested, this is a situation which is being driven by public opinion (which may include a good many pilots). Those who claim that it's driven by safety I fear may be deluding themselves. I'm not suggesting that it is wrong that these aircraft are being grounded, but actions are hardly being led by the agencies that are established to protect the travelling and innocent ground-dwelling public.
I agree. A grounding is certainly justified but using an AD for this is ridicolous. Moreover a number of B38M returning flights, that were airborne and at cruising levels, had to divert because of a stupid AD deadline at 19 UTC, leaving hundreds of European citizens somewhere abroad. EASA is a political nonsense tool as much as FAA became a commercial tool.
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Old 12th Mar 2019, 23:13
  #874 (permalink)  
 
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Originally Posted by Charley View Post
The FZ8xxx callsigns are empty (non-revenue) positioning flights. Both FlightStats and each airports websites confirmed the flights they should have been making were cancelled.

The flight out of Kiev though does have pax aboard. Wonder if it will be held short of the Bucharest or Sofia FIR/UIRs in the same was as the earlier QS flight was.
Bucuresti FIR to FZ730: Thou shall not pass.
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Old 12th Mar 2019, 23:15
  #875 (permalink)  
 
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Originally Posted by FCeng84 View Post
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.
That is a very clear explanation - the most clear of anything I've read. Well done FCeng84.

What is interesting, then, is that MCAS activates without column input. If the purpose of MCAS is to essentially negate the lift of the engine cowling - which causes lift when AOA increases - then one would think the system would only activate as a result of column pull. In other words - the system is to create a consistent feel on the column - so why have it activate absent deliberate pull on the column? Why doesn't the system require both an increase in AOA and a pull on the column before it trims AND?
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Old 12th Mar 2019, 23:21
  #876 (permalink)  
 
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The new Boeing is NOT the same as “old” Boeing. Old Boeing was an engineering company that built solid, reliable aircraft. Everything was done in house by American. New Boeing are bean counters and exporters of the cheapest widget to put between parts A and B. Think of old Boeing as Toyota. Engineering tells accounting what they need. Accounting figures how to make it work. New Boeing is accounting telling engineering what they need. They’re really not even the same company. The only similarities are that they both make airplanes. A perfect example. Boeing has representatives that accompany new aircraft orders. This people used to be liaisons that would smooth things over between mx, finance, safety, training and even sales. They had a company credit card and a lot of freedom and leeway. These same individuals now have their dinner receipts audited by an accountant to make sure that they didn’t order steak or lobster. Boeing has become a good barometer of Merika. No leadership, petty micromanaging and mediocrity.
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Old 12th Mar 2019, 23:24
  #877 (permalink)  
 
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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 12th Mar 2019, 23:30
  #878 (permalink)  
 
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737 Pitch Trim Related Switches

There seems to be some confusion with regard to 737 switches associated with pitch trim. That is very understandable as there are quite a few and it is easy to get them mixed up. Let me take a run at an overview:

Wheel mounted pilot electric pitch trim switches - two pairs of side-by-side switches with one pair mounted on each of the two control wheels for thumb activation
- Spring centered with contacts in both the fwd/push and aft/pull directions.
- Fwd/push commands airplane nose down stabilizer motion via electric stab trim motor
- Aft/pull commands airplane nose up stabilizer motion via electric stab trim motor
- Stabilizer motion requires activation of both switches found on the same wheel in the same direction. This design avoids unintended stabilizer motion for a failure of one switch or a short in one of the two associated wiring circuits.

Column cutout switches - one each in push and pull directions
- Not visible to the crew, hidden within the column mechanism
- One is activated for column push beyond a certain threshold, the other for column pull beyond a certain threshold
- These prevent pilot electric pitch trim in the direction opposite the column (nose up trim inhibited when column is pushed for example)
- These also serve to stop STS stabilizer commands in the direction opposite the column
- These do not stop MCAS stabilizer commands in either direction

Column cutout override switch (not sure of the location(s) or how many there are)
- When in the override position, this causes the column cutout switches to be bypassed allowing electric stabilizer trim in either direction regardless of column position
- These do not have any role with respect to normal operation
- These have no function with respect to MCAS as MCAS stabilizer commands are not subject to the column cutout functionality that is overridden here

Stabilizer cutout switches - on pair of guarded switches located on the lower, aft end of the aislestand
- These are the switches that when activated remove electric power to the stabilizer trim motor and thus disable all electric trim (pilot wheel switches, STS, MCAS, autopilot offload)
- These are the switches that have been most discussed in this thread
- These are the switches that the runaway stabilizer procedure calls for toggling to stop errant stab motion

I hope this helps.

Last edited by FCeng84; 13th Mar 2019 at 03:49. Reason: formatting for easier reading
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Old 12th Mar 2019, 23:37
  #879 (permalink)  
 
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Originally Posted by 4runner View Post
The new Boeing is NOT the same as “old” Boeing. Old Boeing was an engineering company that built solid, reliable aircraft. Everything was done in house by American. New Boeing are bean counters and exporters of the cheapest widget to put between parts A and B. Think of old Boeing as Toyota. Engineering tells accounting what they need. Accounting figures how to make it work. New Boeing is accounting telling engineering what they need. They’re really not even the same company. The only similarities are that they both make airplanes. A perfect example. Boeing has representatives that accompany new aircraft orders. This people used to be liaisons that would smooth things over between mx, finance, safety, training and even sales. They had a company credit card and a lot of freedom and leeway. These same individuals now have their dinner receipts audited by an accountant to make sure that they didn’t order steak or lobster. Boeing has become a good barometer of Merika. No leadership, petty micromanaging and mediocrity.
Yes, and this happened when they acquired McDonnell-Douglas and brought-in most of MD's executives to run things.
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Old 12th Mar 2019, 23:38
  #880 (permalink)  
 
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Originally Posted by WillFlyForCheese View Post
That is a very clear explanation - the most clear of anything I've read. Well done FCeng84.

What is interesting, then, is that MCAS activates without column input. If the purpose of MCAS is to essentially negate the lift of the engine cowling - which causes lift when AOA increases - then one would think the system would only activate as a result of column pull. In other words - the system is to create a consistent feel on the column - so why have it activate absent deliberate pull on the column? Why doesn't the system require both an increase in AOA and a pull on the column before it trims AND?
I'm glad to be able to provide some clarity. MCAS operates as a function of AOA with no regard to column position. As you state, "MCAS is to essentially negate lift (more specifically pitching moment) of the engine cowling". By cancelling out the nose up pitching moment from the cowling with increased AOA, MCAS smooths out the overall Cm-alpha (pitching moment vs. AOA) characteristic of the airplane so that column required to command a maneuver to high AOA does not decrease along the way.
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