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Ethiopian airliner down in Africa

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Ethiopian airliner down in Africa

Old 18th Mar 2019, 18:11
  #1941 (permalink)  
 
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The Seattle Times runs an article with some bold claims, including that factual errors have crept in the certification process, and where raised to the attention of Boeing and FAA days before the ET302 crash. It is not paywalled where I stand.
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Old 18th Mar 2019, 18:16
  #1942 (permalink)  
 
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Originally Posted by flyingchanges
It is runaway stab trim...
Maybe not all at once, but if it is not doing what you want, then it is out of control.
Clearly MCAS is not a runnaway trim condition, otherwise we would be reaching for the cut-out switches every time the speed-trim operated. I think some people here do not realise that the trimmer doing its own thing is operations normal.

And the auro-trim systems are always mis-trimming the aircraft (the trim inputs by the speed-trim system are always wrong, and you always have to re-trim manually). So at what point does ‘operations normal’ become ‘operations abnormal’? At what point do you assume that the trimmer has gone awry..??

Silver
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Old 18th Mar 2019, 18:33
  #1943 (permalink)  
 
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Originally Posted by DaveReidUK
Interesting graphic.

The altitude spike where the aircraft dips below the runway surface(!) accompanied by a single, instantaneous 2000+ fpm ROC value is clearly an artifact (unless Newton got it all wrong), probably coinciding with rotation.

There is a similar, spurious altitude spike towards the RH edge of the plot, which you have wisely ignored - that one is easier to account for because a distance-vs-time plot shows the aircraft flying backwards at that point (i.e. it's a timestamp anomaly rather than bad ADS-B data).
In addition to often mentioned lack of fidelity in the ads-b info available on the internet. It is normal to see a VSI indication dip slightly at rotation. well, it used to be, not familiar with the most recent 15 years of aircraft development.
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Old 18th Mar 2019, 18:37
  #1944 (permalink)  
 
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Any reason there is not a warning light on the 737 MAX to indicate MCAS has activated?
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Old 18th Mar 2019, 18:38
  #1945 (permalink)  
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Originally Posted by flyingchanges
How many times does it have to do the same thing before you consider it to be continuously doing something you do not want. My number would be 2.
Ever flown a 737?
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Old 18th Mar 2019, 18:41
  #1946 (permalink)  
 
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Originally Posted by dufc
Any reason there is not a warning light on the 737 MAX to indicate MCAS has activated?
I can think of one reason: It was meant to be a secret!
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Old 18th Mar 2019, 18:41
  #1947 (permalink)  
 
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Originally Posted by silverstrata


Clearly MCAS is not a runnaway trim condition, otherwise we would be reaching for the cut-out switches every time the speed-trim operated. I think some people here do not realise that the trimmer doing its own thing is operations normal.

And the auro-trim systems are always mis-trimming the aircraft (the trim inputs by the speed-trim system are always wrong, and you always have to re-trim manually). So at what point does ‘operations normal’ become ‘operations abnormal’? At what point do you assume that the trimmer has gone awry..??

Silver
Thx Silver for clearification
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Old 18th Mar 2019, 18:46
  #1948 (permalink)  
 
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The single most powerful control surface on a transport jet is the THS.
Why Boeing would give control of it to a subsystem, like the MCAS is hard to understand.

No amount of hauling (or pushing) on the elevator is going to save you if the THS isn't where it should be.
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Old 18th Mar 2019, 18:48
  #1949 (permalink)  
 
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Does anyone know? If you have a 737 Max , airborne, flaps up, really high speed, full nose down trim, electric stabilizer trimming motors shut off, how much back pressure does it take to raise the nose with the elevator? While applying this large force to the elevator, how much force is required to turn the stabilizer trim hand wheel? How many turns of the hand wheel per degree of stabilizer trim. In other words, is it possible to get into a position in which it is impossible to recover, not enough elevator authority due to force required and or inability to retrim the stabilizer manually due to it binding from a combination of speed and forces being applied through the elevator.
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Old 18th Mar 2019, 18:56
  #1950 (permalink)  
 
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You have to put the THS back where it should be.
Until then, you remain in upset territory, or 'in the ****' as most pilots call it.
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Old 18th Mar 2019, 18:57
  #1951 (permalink)  
 
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Originally Posted by abdunbar
Does anyone know? If you have a 737 Max , airborne, flaps up, really high speed, full nose down trim, electric stabilizer trimming motors shut off, how much back pressure does it take to raise the nose with the elevator? While applying this large force to the elevator, how much force is required to turn the stabilizer trim hand wheel? How many turns of the hand wheel per degree of stabilizer trim. In other words, is it possible to get into a position in which it is impossible to recover, not enough elevator authority due to force required and or inability to retrim the stabilizer manually due to it binding from a combination of speed and forces being applied through the elevator.
As FCEng says in post #1946 you cannot overcome the StabTrim with elevator at high speed.
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Old 18th Mar 2019, 19:05
  #1952 (permalink)  
 
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Originally Posted by silverstrata


Clearly MCAS is not a runnaway trim condition, otherwise we would be reaching for the cut-out switches every time the speed-trim operated. I think some people here do not realise that the trimmer doing its own thing is operations normal.

And the auro-trim systems are always mis-trimming the aircraft (the trim inputs by the speed-trim system are always wrong, and you always have to re-trim manually). So at what point does ‘operations normal’ become ‘operations abnormal’? At what point do you assume that the trimmer has gone awry..??

Silver
I haven’t flown a 73 but on the 72 (if I recall correctly) during a runaway, the first instinctual response was to apose the runaway with opposite elevator. This ingaged the trim brake. The noise of the brake verses the runaway trim was a giveaway to use the cutout switches.

I don’t think this would happen as the MCAS does not activate the brake. All that sim training on runaway stab wouldn’t help because it’s not a runaway.

The stall horn and stick shaker would make pulling back and trimming nose up counter to all training that a pilot receives from initial stall recovery in a Cessna with a stall horn through to transport aircraft.

Two responses to two different stimulus. One Stall Recovery and one Unreliable Airspeed mask the third undocumented MCAS.

To learn anything from any accident you need to have empathy for those involved. Not just the pilots but the line mechanics, Boeing and FAA engineers. The true villains, senior management, board members and yes, even politicians will never be held accountable

The USA government shutdown that both political parties participated in was also a factor.

... and hence, the voters like you
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Old 18th Mar 2019, 19:12
  #1953 (permalink)  
 
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Originally Posted by dozing4dollars


I haven’t flown a 73 but on the 72 (if I recall correctly) during a runaway, the first instinctual response was to apose the runaway with opposite elevator. This ingaged the trim brake. The noise of the brake verses the runaway trim was a giveaway to use the cutout switches.

I don’t think this would happen as the MCAS does not activate the brake. All that sim training on runaway stab wouldn’t help because it’s not a runaway.

The stall horn and stick shaker would make pulling back and trimming nose up counter to all training that a pilot receives from initial stall recovery in a Cessna with a stall horn through to transport aircraft.

Two responses to two different stimulus. One Stall Recovery and one Unreliable Airspeed mask the third undocumented MCAS.

To learn anything from any accident you need to have empathy for those involved. Not just the pilots but the line mechanics, Boeing and FAA engineers. The true villains, senior management, board members and yes, even politicians will never be held accountable

The USA government shutdown that both political parties participated in was also a factor.

... and hence, the voters like you

I understand all that, and yes, I vaguely remember the trim brake. but the question is still this. Is there a conceiveable way to load the stabilizer to the point that it cannot manually be trimmed back to a point were elevators will work again?
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Old 18th Mar 2019, 19:17
  #1954 (permalink)  
 
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I know it may look a bit stupid but I need to clarify that. I would like if someone who flies 737 could reply.
Why Boeing put MCAS to MAX? As I understood there was problem with pitch moment created by engines at some occasions. But is it possible to fly without it and it will be just difficult or it is impossible to handle the aircraft without MCAS? I though it is there just to be safer and easier for pilots but I have read many strange things about that. But I think that is just mess made up by media.
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Old 18th Mar 2019, 19:18
  #1955 (permalink)  
 
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Originally Posted by abdunbar
I understand all that, and yes, I vaguely remember the trim brake. but the question is still this. Is there a conceiveable way to load the stabilizer to the point that it cannot manually be trimmed back to a point were elevators will work again?
I also wonder if the forward position of the engines, which gives a pitch up moment at high angles of attack, and led to the addiction of MCAS, could possibly give a pitch down moment at low angles of attack?
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Old 18th Mar 2019, 19:19
  #1956 (permalink)  
 
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Originally Posted by abdunbar
Does anyone know? If you have a 737 Max , airborne, flaps up, really high speed, full nose down trim, electric stabilizer trimming motors shut off, how much back pressure does it take to raise the nose with the elevator? While applying this large force to the elevator, how much force is required to turn the stabilizer trim hand wheel? How many turns of the hand wheel per degree of stabilizer trim. In other words, is it possible to get into a position in which it is impossible to recover, not enough elevator authority due to force required and or inability to retrim the stabilizer manually due to it binding from a combination of speed and forces being applied through the elevator.
I cannot speak to the potential for binding of the horizontal stabilizer control (either via electric motor or via manual turn of mechanical trim wheel) but I can shed some light on the first question. Where the stabilizer needs to be for trim is a function of all of the contributors to pitching moments that must be balanced. CG is the biggest factor and will have the most influence on where the stabilizer sits for trim(i.e., no column push or pull required for steady flight). How "out of trim" the airplane is with the stabilizer moved all the way to its airplane nose down limit depends on where you start (i.e., what position represents "in trim"). If the CG is at its forward limit, trim will involve a fair amount of airplane nose up stabilizer so there will be a larger increment of stabilizer travel from there to the nose down limit. If the CG is at is aft limit, trim will place the stabilizer much closer to the airplane nose down limit so the increment from there to full nose down will be smaller.

Also with regard to your reference to "very high speed" specifics make a difference as Mach effects come into play along with dynamic pressure. At cruise speeds and faster elevator travel is limited by actuator force capability. The faster you go the less the elevator can be deflected and thus the more critical it is to have the horizontal stabilizer near its trim position.
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Old 18th Mar 2019, 19:20
  #1957 (permalink)  
 
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Clearly MCAS is not a runnaway trim condition, otherwise we would be reaching for the cut-out switches every time the speed-trim operated. I think some people here do not realise that the trimmer doing its own thing is operations normal.

And the auro-trim systems are always mis-trimming the aircraft (the trim inputs by the speed-trim system are always wrong, and you always have to re-trim manually). So at what point does ‘operations normal’ become ‘operations abnormal’? At what point do you assume that the trimmer has gone awry..??

Silver
DING DING DING We have a winner!

That’s one of the biggest elephants (gorillas?) in the room. By the time you’ve thought “hmm, that’s not quite right” at low-level the situation has gone from nuisance to critical. The 737 trim is on the move all the time, be it from pilot inputs or STS/MCAS/Autopilot. Clickety-clack is the most heard noise on a 737 flight deck as the trim wheel spins it’s merry way backwards and forwards. Add an unreliable airspeed scenario to the above and no wonder things go from bad to worse. I really feel sorry for the crews who were dumped in this situation.
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Old 18th Mar 2019, 19:23
  #1958 (permalink)  
 
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Originally Posted by silverstrata


Clearly MCAS is not a runnaway trim condition, otherwise we would be reaching for the cut-out switches every time the speed-trim operated. I think some people here do not realise that the trimmer doing its own thing is operations normal.

Silver
Correctly functioning MCAS is not a runaway trim condition. If you really approach high AoA, MCAS kicks in, AoA drops and (assuming it was just some kind of upset and you have sufficient hight) you should be fine.

However, when an AoA is faulty, it will continously indicate high AoA to MCAS. MCAS kicks in, but still get high AoA input so it kicks again.. and again.. and again....
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Old 18th Mar 2019, 19:25
  #1959 (permalink)  
 
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Originally Posted by dozing4dollars


I haven’t flown a 73 but on the 72 (if I recall correctly) during a runaway, the first instinctual response was to apose the runaway with opposite elevator. This ingaged the trim brake. The noise of the brake verses the runaway trim was a giveaway to use the cutout switches.

I don’t think this would happen as the MCAS does not activate the brake. All that sim training on runaway stab wouldn’t help because it’s not a runaway.

The stall horn and stick shaker would make pulling back and trimming nose up counter to all training that a pilot receives from initial stall recovery in a Cessna with a stall horn through to transport aircraft.

Two responses to two different stimulus. One Stall Recovery and one Unreliable Airspeed mask the third undocumented MCAS.

To learn anything from any accident you need to have empathy for those involved. Not just the pilots but the line mechanics, Boeing and FAA engineers. The true villains, senior management, board members and yes, even politicians will never be held accountable

The USA government shutdown that both political parties participated in was also a factor.

... and hence, the voters like you
Yes, clearly different than a runway and yes, the column cutout doesn't work with MCAS. Yes the trim wheel moving, even in manual flight, even when not trimming with the yoke switch is normal in a 737. That said you would think in 7-12 minutes of watching the nose get heavier and heavier and the trim moving downward on occasion on its own you would kill the trim with the stab cutout switches. I totally get the anger at Boeing but experienced 737 pilots should be able to figure this out, in particular with a bit of time, and after the Lion Air accident and the required reading of the MCAS system and its failure mode you would think any 737 MAX pilot would be able to figure this out very, very quickly let alone with time. Lots of blame to go around here in these accidents, starts with Boeing but as usual it ends in the point end of the jet.
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Old 18th Mar 2019, 19:32
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Originally Posted by megapete
I also wonder if the forward position of the engines, which gives a pitch up moment at high angles of attack, and led to the addiction of MCAS, could possibly give a pitch down moment at low angles of attack?
How the engines do that? What is supposed to be a problem? I expected that power and placement of engines creates this pitch up moment. Is it something aerodynamics related?
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