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Ethiopian airliner down in Africa

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Ethiopian airliner down in Africa

Old 9th Apr 2019, 08:41
  #3701 (permalink)  
 
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Originally Posted by AlexGG View Post
I presume the motor has some overheat/overload protection.
Probably not. What would be the point? It is a vital pitch control surface. Why would you intentionally make it unavailable because it might fail at some later time? It is better to have it available, and damage it, rather than to make it unavailable and potentially lose the entire aircraft.

I don't think there will be more than an overcurrent circuit breaker, but that is mostly to protect the wiring.


Bernd
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Old 9th Apr 2019, 09:05
  #3702 (permalink)  
 
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Originally Posted by Rananim View Post
We can't see the wood for the trees.
This one was just a faulty sensor(not even UAS)..
If MCAS would activate alone,any crew would simply
counter-trim and cut off its electrical supply without much thought.
But combine it with a "confusing" UAS scenario and shakers and
warnings and bingo..you get a smoking hole in the ground...
Pilots have to be trained more on these UAS scenarios before they kill again.
Aeroperu,birgenAF447 and the 2 MAXs,and others.....
Wise words. Seems to me that the entire concept of "artificial feel" and "artificial buffet" (AKA stickshaker) was envisioned many decades ago assuming pilots had stick and rudder skills ingrained and whose muscle instincts would guide them to do the right thing if their hands were provided with the correct aerodynamic, albeit artificial clues.
Today, the artificial manual feedback stuff is degrading the primary flight control ergonomics, and distracting and stressing the crew. Instead of providing clues, it may even make pilots loose the trim switch with their thumb as a result of a hydraulically shaken column with massive artificial pull on top.
MCAS could then be seen as the ultimate perversion of that concept. Abuse a secondary flight control to create artificial stick force, give it a delay of 5 s so the pilot will not intuitively get the message, and give it so much authority, that it effectively overrides the primary control.
2 ct

Last edited by spornrad; 9th Apr 2019 at 13:52.
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Old 9th Apr 2019, 09:09
  #3703 (permalink)  
 
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Originally Posted by TryingToLearn View Post
Oh, just one question:
People claim that the manual trim may not be operable in certain flight conditions while the electric trim motor is more powerful.
On the other hand the manual states that in case CUTOUT does not work, one should grasp and hold the wheel (?against the motor?). Did I miss something?
I don't think there is any dispute about the fact that grasping the trim wheel stops the stab moving. Reportedly, and depending on how positively you grab it, you may lose a bit of skin in the process.

Once the wheel is held, you are not fighting against the electric trim motor, which is disabled if resistance is detected at the cable drum.
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Old 9th Apr 2019, 09:12
  #3704 (permalink)  
 
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I never tried ( in the sim! ) grabbing and trying to hold the trim wheel during a runaway stab. Not sure it was possible without burning my hand or losing some fingers !

Was it possible?

Sorry, DR s post was being written as I was typing !

However, anyone actually have any first hand ( no pun intended ) experience of doing it ?
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Old 9th Apr 2019, 09:58
  #3705 (permalink)  
 
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Originally Posted by TryingToLearn View Post
People claim that the manual trim may not be operable in certain flight conditions while the electric trim motor is more powerful.
On the other hand the manual states that in case CUTOUT does not work, one should grasp and hold the wheel (?against the motor?). Did I miss something?
There is a clutch that ensures that manual trim has priority on electric trim. So Yes, grasping the wheel should stop trim runaway.
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Old 9th Apr 2019, 10:01
  #3706 (permalink)  
 
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Originally Posted by bsieker View Post
I don't think there will be more than an overcurrent circuit breaker, but that is mostly to protect the wiring.
Bernd
A motor which is forcibly stopped can pull a huge amount of current. Depends on motor type but for old fashioned non-electronic controls can be 20x full speed current. Of course we don't know the motor type or controlling electronics. Anyone?

Also DaveReid's post above about motors stopping if they meet resistance.

I can't see any reason for the 'blips' in nose up trim other than pilot trying it and it not working/ not appearing to work. Why else would you release the switch when it's the one thing you're focussing on, the one thing you know you need?
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Old 9th Apr 2019, 10:07
  #3707 (permalink)  
 
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The 737 manuals says that incase of extreme nose-down out-of-trim, one should INCREASE speed to relieve elevator load and permit manual trimming.

That's insane !

(see https://www.satcom.guru/2019/04/what...-on-et302.html)
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Old 9th Apr 2019, 10:13
  #3708 (permalink)  
 
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so why not have a separate cutout switch just for MCAS, keep the other two to cutout electric trim. But the new MCAS cutout switch would leave electric trim available.

I'm also unclear since the certification requirement was for force feedback on the stick during certain stall regimes why Boeing didn't just use some kind of motor/pneumatic on the stick to give this force, rather than connecting MCAS to control surfaces! Seems overkill, no pun intended. I mean the stick shaker no doubt uses a motor to shake the stick, it doesn't shake the ailerons in order to make the stick shake!

G
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Old 9th Apr 2019, 10:18
  #3709 (permalink)  
 
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Originally Posted by PerPurumTonantes View Post
I can't see any reason for the 'blips' in nose up trim other than pilot trying it and it not working/ not appearing to work. Why else would you release the switch when it's the one thing you're focussing on, the one thing you know you need?
I see on good reason : at very high speeds a long trim command would induce huge vertical acceleration, therefore you have to use it with caution, using actions of one second or so.

What I can't see is why they did not continue as many times as needed to trim back
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Old 9th Apr 2019, 10:24
  #3710 (permalink)  
 
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Originally Posted by groundbum View Post
so why not have a separate cutout switch just for MCAS, keep the other two to cutout electric trim. But the new MCAS cutout switch would leave electric trim available.

I'm also unclear since the certification requirement was for force feedback on the stick during certain stall regimes why Boeing didn't just use some kind of motor/pneumatic on the stick to give this force, rather than connecting MCAS to control surfaces! Seems overkill, no pun intended. I mean the stick shaker no doubt uses a motor to shake the stick, it doesn't shake the ailerons in order to make the stick shake!

G
There would be no force on the stick without the feel and centering system. It has been said that, for some reason, this system is not able to provide the extra force needed near stall. Of course it could have been modified to do so, but that mean a lot of money, whereas MCAS is just a software modification
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Old 9th Apr 2019, 10:29
  #3711 (permalink)  
 
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Originally Posted by DaveReidUK View Post
I don't think there is any dispute about the fact that grasping the trim wheel stops the stab moving. Reportedly, and depending on how positively you grab it, you may lose a bit of skin in the process.

Once the wheel is held, you are not fighting against the electric trim motor, which is disabled if resistance is detected at the cable drum.
Wasn't it the (unofficial) procedure to grab the copliot's leg and jam it as hard as you could against the wheel, then quickly unfolding your own
handle, shedding no skin at all !!
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Old 9th Apr 2019, 10:34
  #3712 (permalink)  
 
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Originally Posted by Deepinsider View Post
Wasn't it the (unofficial) procedure to grab the copliot's leg and jam it as hard as you could against the wheel, then quickly unfolding your own
handle, shedding no skin at all !!
Would this not require 3 hands?
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Old 9th Apr 2019, 10:41
  #3713 (permalink)  
 
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Originally Posted by Maninthebar View Post
Would this not require 3 hands?
Yes....that's how amazing captains are !

Sorry folks, just trying to lighten it up a bit,
but don't intend to imply any disrespect to
the victims of these crashes.

(It just happens that in my now ancient 737 times,
this was the joke about the runaway stab drill)

Last edited by Deepinsider; 9th Apr 2019 at 11:01.
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Old 9th Apr 2019, 10:59
  #3714 (permalink)  
 
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Originally Posted by ams6110 View Post
And yet Tesla, an automotive company which presumably follows this process, still has an "auto pilot" software function that on more than one occasion drove a car into a stationary object at 70mph.
Tesla used the same chip as Audi, BMW etc. from a company called Mobileye.
But Tesla called it AutoPILOT instead of Lane/TrafficASSISTANT and used the System far beyond it's clearly stated limitations (no cross-traffic detection, 0,4s driver reaction). All other OEMs limited the system to 30 sec. without driver interaction.
After the accident, the company stopped delivering their system to Tesla because they then knew that it was used beyond it's limits (like MCAS?)
Mobileye claimed Tesla was 'pushing the envelope in terms of safety'. I'm not allowed to post the link (Reuters).
In addition, Tesla was forced to prevent the forseeable misuse by stopping the car after a certain time without driver interaction (touching the steering wheel...)
All other OEMs ripped Teslas apart to learn all the modern new solutions and mostly considered the solutions not state of the art in terms of safety.

It's the same story, management wanted something impossible. In one case a new aircraft without additional training, in the other case being in the news as first autonomous car manufacturer with affordable electric cars...
In one case it may have been forseeable that pilots go into the stall memory item (more speed), in the other one that people may take a nap while driving.
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Old 9th Apr 2019, 11:02
  #3715 (permalink)  
 
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Originally Posted by YRP View Post
Jus' sec here. AF447 had plenty of stall warning. It only stopped after the crew held it into the deep stall. The crew didn't register the warning or believed it spurious.

On the 60 kt criteria, I find it hard to criticize that design decision. It would get increasingly difficult to get reliable meaningful data from the sensors at that point (i.e. IAS vs CAS spread). And who would have thought an airliner would actually manage to be flown to that point.

Something I have never understood wrt this - is it possible for the a330 to be in the air with an airspeed of 60 knots or even 70 knots and NOT be stalled? If not then why inhibit the warning? Worrying about sensor accuracy seems to be missing the bigger picture wrt the purpose of the warning!
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Old 9th Apr 2019, 11:03
  #3716 (permalink)  
 
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Originally Posted by PerPurumTonantes View Post
A motor which is forcibly stopped can pull a huge amount of current. Depends on motor type but for old fashioned non-electronic controls can be 20x full speed current. Of course we don't know the motor type or controlling electronics. Anyone?
Yes, so it will heat up, and eventually the wiring will burn up / melt /otherwise fail. But that will take a while. Being essential, that motor will be dimensioned rather larger to avoid such problems. And we know that on the Lion Air flight, the trim motor worked much more than in Ethiopia, and there was no question about it overheating or being disabled.

Also DaveReid's post above about motors stopping if they meet resistance.
No, that's not what he said. He said that the motor will be "disabled if resistance is detected at the cable drum.", which is different from just meeting any resistance to its motion, e. g. resistance from the jackscrew nut.

I can't see any reason for the 'blips' in nose up trim other than pilot trying it and it not working/ not appearing to work. Why else would you release the switch when it's the one thing you're focussing on, the one thing you know you need?
We don't know what they were focusing on at that time. Possibly not trim, but just pulling together. Just before the blips the "Captain asked the First Officer to pitch up together and said that pitch is not enough." And pitch trim did work, it moved from 2.1 to 2.3 units. I cannot comment on how much that would be felt in the control column.

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Old 9th Apr 2019, 11:18
  #3717 (permalink)  
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Quote:
Originally Posted by yanrair
The Tristar taught flying GPS G SPEED approaches in serious headwind landings - none of this is new, but it is being forgotten. So here we have big jets using this technique when it is the very opposite of still air!
Surely the Tristar predated GPS by some years.
I looked that up just to see how many were still flying. One thing I found is that you can apply a GPS package to almost any Flight Sim aircraft.
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Old 9th Apr 2019, 11:29
  #3718 (permalink)  
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LR, Yanrair, we used IRS GS for monitoring headwind correction. Did that on the DC8 too using the INS, from the early 70's on, as a formal, (book) procedure. The Lockheed, (100 & 500), didn't have GPS when I flew it in the late '80's..
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Old 9th Apr 2019, 11:41
  #3719 (permalink)  
 
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Originally Posted by DaveReidUK View Post
I don't think there is any dispute about the fact that grasping the trim wheel stops the stab moving.
Once the wheel is held, you are not fighting against the electric trim motor, which is disabled if resistance is detected at the cable drum.
But this proves that electronic trim is less powerful than manual trim, right? Or can the motor distinguish where the force is coming from?

To me as an engineer everything lines up if one adds this clutch/force limit:
Pilots try manual trim: Too much force, no chance (and free hands)
Pilots reactivate electric trim: Short movement and the clutch/force limit stops it. (FDR Trace...)
Pilots try a few times: Small blips... (FDR Trace...)
Pilots give up: MCAS kicks in again...

If you find people at Boeing with lot's of bandaid, you know they had the same idea recently...
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Old 9th Apr 2019, 12:05
  #3720 (permalink)  
 
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The cutout switch function was changed with the 737MAX from all prior 737 models. The legacy switch combination was one switch to cutout electric trim altogether, the other to cutout the autopilot trim commands. MCAS and Speed Trim System are both commands from the “autopilot”. With the legacy switch configuration, the flight crew can disable the autopilot commands and retain electric trim. With the 737MAX, the flight crew lose both electric trim and autopilot trim with the cutout switch.

The Flight Standardization Board (FSB) took notice of the nomenclature change of the cutout switches but did not make any mention of the difference in responding to autopilot stab trim runaway. On the 737NG, the flight crew retain electric trim; on the 737MAX the flight crew must use manual trim. It turns out, this is a significant difference in pilot workload and pilot capacity to fly the airplane.
Was this taught in the difference powerpoint "training"?
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