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Ethiopian airliner down in Africa

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Ethiopian airliner down in Africa

Old 3rd Apr 2019, 22:45
  #3001 (permalink)  
 
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Originally Posted by Albino View Post
No it isn't. AFAIK

MCAS will operate regardless of the control column cutout switches.
It will not operate against the control column TRIM switches, or if the stab trim switches are cutout.
This is my understanding also, based on the schematic posted before:

737MAX Stab Trim architecture


When MCAS is engaged, control column "extreme deflection" towards pull will NOT disable MCAS trim down, but it will NOT disable your thumb switch trim up either, so you still win.

In other words, this battle will not be affected by too much pull.
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Old 3rd Apr 2019, 23:24
  #3002 (permalink)  
 
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Mentour Pilot latest video

Since this video may not be coming back I'll post a sort of transcript from memory since I was lucky enough to get to watch it. I'll try and just describe what I saw and keep my commentary/speculation to a minimum - in <italic>. Bear in mind this is a non-pilot observer's take on it from flaky memory:


There is a fair bit of intro talk then the sim.

They are in NG sim, not MAX, no surprise there. Mentour in left seat.

They start at low altitude, I think it was commented on, not at takeoff, I can't remember if they showed putting flaps up or started with flaps up and said it was just after flaps up.

No stick shaker, that I saw.
<presume means no elevator feel shift either, and that actual AOA error is not being simulated>

IAS disagree then simulated - or they just did the memory items, I didn't notice warning light (not that I would) and he didn't note it, there was an aural alarm but I think that was for AP disconnect
<I don't think this is exactly what the accident flights faced, they had shaker and IAS disagree from takeoff>

IAS disagree memory items, AP/AT OFF, FDs OFF, 75% N1, 4degrees

Throttles are pushed forward to get 75%, he comments that at low alt with denser air this is a lot of thrust and hence speed will increase

Trim runs, obviously sim doesn't have MCAS so not sure if they are simulating runaway or if he is doing it with the column switches

Comment is made that he was _expecting_ trim to run, because speed is changing, he says it will take a couple of cycles of fighting it with the switches before being definite that it is wrong

They discuss (he raises) that he is having flight control issue, they conclude it is trim that is the problem, they now run the stab trim runaway memory items finishing by hitting the switches. At this point he is clearly holding quite a bit of pressure on the column, but not obviously losing control of pitch

Now he points out that trim has only got down to (I think) 3 degrees on the indicator (zero being full nose down, I think) and that they are now going to "try something" - video captions say "don't try this at home", like we've all got a FFS in our shed or a 737 on the drive :-)

At this point the guy in the right seat uses the handle to wind the trim further _forward_. He stops when he clearly cannot wind it further - but they point out that it's still not at full nose down

Mentour is obviously struggling to keep the nose up at this point. I noticed he didn't seem to have the shoulder straps on (right seat did), possibly because he was frequently turning round to talk to the camera. That probably didn't help, but on the other hand he didn't have stick shaker or feel shift to cope with either.

Now, with Mentour pulling back, the right seat guy tries to wind the trim back with the handle - and he struggles to move it at all

They stop the sim, I think it was after stopping that he noted that at that point they were at 310 (maybe he said 340) knots.

I think there was then some further commentary, at one point I think he mentioned the rollercoaster to unload the stab and allow trimming, but commented that close to the ground the instinct is to pull back - I may be imagining that or remembering it from another video though.

<
And that was about it. I can try to answer questions on the video if anyone has any. The eye-opener for me wasn't the force on the control column (which was held anyway), it was that the trim couldn't be moved, in either direction. From somewhere I had got the impression that those wheels had a lot of leverage, due to the gearing, which was why a lot of turns would be required, but it seems that a lot of turns would be required and a gorilla to make them...
>
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Old 3rd Apr 2019, 23:29
  #3003 (permalink)  
 
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Salute!

Good thots, FDR and Murphy is correct, I like the generic FBW laws and 'bus implementaion for the most part.

Without control surface feedback, you can satisfy the FAR requirements for column force versus AoA because the control stick/wheel can use a simple spring as does the 'bus. There is no relationship to compare. The FBW pitch law commands a modified gee, and not AoA. I can tell you that trim technique for the Viper was just like any other plane I flew. You trimmed to have a neutral stick pressure/force. If you were trimming for an attitude, no problem. But you could not trim for an AoA. So we were speed neutral, kinda like the 737 seems to be or they would not need STS, huh?

Late breaking news - - maybe the CVR mentioned a birdstrike, huh? Still comes down to a single point failure nd confusing procedures for stall and whacko trim.

Gums sends...
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Old 4th Apr 2019, 00:17
  #3004 (permalink)  
 
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Gums,

Yeah, simple FBW gives you that. But each philosofy has pros and cons, as you know.

You cited a big pro of simple (closed loop control of pitch rate, for instance) FBW. It will follow whichever control force feedback law you want. That's true, regardless of aerodinamic characteristic of the plane.

I'll give you some cons. In such FBW, a lot of feedback is lost. For instance, it's much harder to tell how authority you have left. 50% deflection at the stick will give you whatever deg/s roll regardless of the plane needing 5% aileron or 95% aileron. Controls do not get more sensible or harder at higher airspeed, so your subconscious mind do not have that clue to compute the actual airspeed. And you cannot feel trouble: sticky control surfaces, vibrations, hard spots or friction, all gets lost. Plane is trying to keep wings level if you don't touch the controls, which is nice, but it is also nice to know how hard it's trying. Otherwise it may surprise you when/if authority is depleted.

Of course you can make FBW with force feedback proportional to hydraulic pressure and stick deflection proportional to surface position. Only use FBW to "cheat" a little bit when you want to place protections (eg: if you are going fast and go for 90% stick deflection, force feedback will artificially ramp up a lot to keep you from easily ripping your wings out) or with dutch roll or overall damping (opposing a bit of control surface to a given pitch or roll rate). That would be my ideal system. I think it is not given sufficient thought most of the time because at first it seems a lot less fancy to directly correlate stick to control surfaces position instead of something with a much better sound like "target AOA that progressively changes to a target g when you accelerate". But it will have many advantages, you would be able to see and feel what autopilot does, feel the most subtle abnormality in the plane (cofg, drag, you name it)...
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Old 4th Apr 2019, 00:55
  #3005 (permalink)  
 
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Ethiopian pilots followed Boeing procedure

(Not allowed to post links, hence the weird format)
Just read this:
flightglobal.com/news/articles/report-that-crashed-737-crew-shut-off-mcas-raises-ne-457224/

Source:
wsj.com/articles/ethiopian-airlines-pilots-initially-followed-boeings-required-emergency-steps-to-disable-737-max-system-11554263276

It looks like the pilots did turn MCAS off following Boeing's procedure, which was Boeing's trump card in defending the system's propriety. It didn't do them any good, though, it seems. But then again, this thread is not called "Rumours" for nothing. "Unnamed sources" is also not very encouraging in terms of credibility. However, if true, it casts an even darker shadow on the whole MCAS calamity.

MCAS saga continues...
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Old 4th Apr 2019, 01:11
  #3006 (permalink)  
 
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Controls do not get more sensible or harder at higher airspeed, so your subconscious mind do not have that clue to compute the actual airspeed.
You must mean the Airbus FBW system. The Boeing and Embraer FBW has artificial feel. Works very well.
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Old 4th Apr 2019, 01:12
  #3007 (permalink)  
 
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Reuters - APRIL 3, 2019 / 7:07 PM ET / UPDATED 29 MINUTES AGO

FAA launches new review of Boeing 737 MAX to ensure safety

https://www.reuters.com/article/us-e...KCN1RF2VY?il=0

QUOTES:

WASHINGTON (Reuters) - The Federal Aviation Administration said late on Wednesday it is launching a new review of the safety of the now-grounded Boeing 737 MAX that will be headed by a formal top U.S. safety official.

The FAA said it is establishing a Joint Authorities Technical Review “to ensure the safety of the Boeing 737 MAX” and scrutinize an anti-stall software that’s been questioned in two fatal crashes since October.

The review will be chaired by former National Transportation Safety Board chairman Christopher Hart “and comprised of a team of experts from the FAA, NASA, and international aviation authorities.”

The FAA did not immediately disclose who was taking part but a Canadian government spokeswoman said Canada would join."
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Old 4th Apr 2019, 01:26
  #3008 (permalink)  
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When we gave the Americans the flying tailplane, was it hinged at the front?

Pivoted at the rear, or nearer to, it is inherently unstable. The nut failure, or some such would mean it thwacking over full deflection, but it hasn't happened, has it? Okay, so we've not had a wing detaching g force that I can remember, but now we've got a new reason to pivot at the front. The loads would be smooth and progressive, and even if it had been cranked all the way, hand-winding it back would now be aided rather than opposed.

The first scenario we can discount because of history. The second issue a major change in design philosophy, but not a huge change in pilot handling and seemingly needed. I'd never dreamed of having to unload it in a series of switchback rides. It would be so easy to crank it with a front fulcrum and I'd guess a lot cheaper than gum's "rehanging the engines".

Where to put the Jack? I'd have cut a slot out of the rudder before I'd have put the fulcrum at the rear. But seriously, a horizontal jack would only need a redesigned lever and the loads would be less and far less consistent.
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Old 4th Apr 2019, 01:39
  #3009 (permalink)  
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Thumbs up

Originally Posted by gums View Post
Salute!

Good thots, FDR and Murphy is correct, I like the generic FBW laws and 'bus implementaion for the most part.

Without control surface feedback, you can satisfy the FAR requirements for column force versus AoA because the control stick/wheel can use a simple spring as does the 'bus. There is no relationship to compare. The FBW pitch law commands a modified gee, and not AoA. I can tell you that trim technique for the Viper was just like any other plane I flew. You trimmed to have a neutral stick pressure/force. If you were trimming for an attitude, no problem. But you could not trim for an AoA. So we were speed neutral, kinda like the 737 seems to be or they would not need STS, huh?

Late breaking news - - maybe the CVR mentioned a birdstrike, huh? Still comes down to a single point failure nd confusing procedures for stall and whacko trim.

Gums sends...
Very good explanation
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Old 4th Apr 2019, 01:52
  #3010 (permalink)  
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In total agreement.
As far as I am aware no simulator training for the 737 type mentions this even at FAA/ICAO training establishments.
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Old 4th Apr 2019, 02:06
  #3011 (permalink)  
 
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1. Sorry if this was answered before, but assuming the flaps to be still extended during the Ethiopian 302 MCAS event, how would any other failure or failed sensor allow allow MCAS to operate? ( MCAS is electrically engineered NOT to function with flaps extended)
2. If at 400 feet descending fast and PM manual operation of the trim wheel too slow, would reengaging the trim cutout switches to use electrical column trim switches to override MCAS and provide a faster rate of corrective trim be a “ Hailmary” consideration?
THANKS.
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Old 4th Apr 2019, 02:19
  #3012 (permalink)  
 
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Originally Posted by infrequentflyer789 View Post
Since this video may not be coming back I'll post a sort of transcript from memory since I was lucky enough to get to watch it. I'll try and just describe what I saw and keep my commentary/speculation to a minimum - in <italic>. Bear in mind this is a non-pilot observer's take on it from flaky memory:


There is a fair bit of intro talk then the sim.

They are in NG sim, not MAX, no surprise there. Mentour in left seat.

They start at low altitude, I think it was commented on, not at takeoff, I can't remember if they showed putting flaps up or started with flaps up and said it was just after flaps up.

No stick shaker, that I saw.
<presume means no elevator feel shift either, and that actual AOA error is not being simulated>

IAS disagree then simulated - or they just did the memory items, I didn't notice warning light (not that I would) and he didn't note it, there was an aural alarm but I think that was for AP disconnect
<I don't think this is exactly what the accident flights faced, they had shaker and IAS disagree from takeoff>

IAS disagree memory items, AP/AT OFF, FDs OFF, 75% N1, 4degrees

Throttles are pushed forward to get 75%, he comments that at low alt with denser air this is a lot of thrust and hence speed will increase

Trim runs, obviously sim doesn't have MCAS so not sure if they are simulating runaway or if he is doing it with the column switches

Comment is made that he was _expecting_ trim to run, because speed is changing, he says it will take a couple of cycles of fighting it with the switches before being definite that it is wrong

They discuss (he raises) that he is having flight control issue, they conclude it is trim that is the problem, they now run the stab trim runaway memory items finishing by hitting the switches. At this point he is clearly holding quite a bit of pressure on the column, but not obviously losing control of pitch

Now he points out that trim has only got down to (I think) 3 degrees on the indicator (zero being full nose down, I think) and that they are now going to "try something" - video captions say "don't try this at home", like we've all got a FFS in our shed or a 737 on the drive :-)

At this point the guy in the right seat uses the handle to wind the trim further _forward_. He stops when he clearly cannot wind it further - but they point out that it's still not at full nose down

Mentour is obviously struggling to keep the nose up at this point. I noticed he didn't seem to have the shoulder straps on (right seat did), possibly because he was frequently turning round to talk to the camera. That probably didn't help, but on the other hand he didn't have stick shaker or feel shift to cope with either.

Now, with Mentour pulling back, the right seat guy tries to wind the trim back with the handle - and he struggles to move it at all

They stop the sim, I think it was after stopping that he noted that at that point they were at 310 (maybe he said 340) knots.

I think there was then some further commentary, at one point I think he mentioned the rollercoaster to unload the stab and allow trimming, but commented that close to the ground the instinct is to pull back - I may be imagining that or remembering it from another video though.

<
And that was about it. I can try to answer questions on the video if anyone has any. The eye-opener for me wasn't the force on the control column (which was held anyway), it was that the trim couldn't be moved, in either direction. From somewhere I had got the impression that those wheels had a lot of leverage, due to the gearing, which was why a lot of turns would be required, but it seems that a lot of turns would be required and a gorilla to make them...
>
From another forum.

I agree it's a flawed design. And I used to work there. I'm glad I don't now.

Regarding the trim wheels: When the NG was being introduced, I happened to be the Lead Engineer in charge of them and a whole lot of other stuff. There were some issues. The new display system created a pinch point between the dash and the wheel. We had to make the wheel smaller. And the new trim motor resulted in the wheel, which is directly connected to the stabilizer by a long cable, springing back when electric trim was used. It was an undamped mass on the end of a spring. We had to add a damper.
Result: Depending on the flight conditions, the force to manually trim can be extremely high. We set up a test rig and a very fit female pilot could barely move it.
As I said, I'm glad I'm no longer there.
From an ex Boeing employee.
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Old 4th Apr 2019, 02:35
  #3013 (permalink)  
 
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Electric trim defeats MCAS...

Ok, I have to confess Iím confused.

All this talk of manual trim forces, etc.

MCAS applies trim in increments of 2.5 degrees over 10 seconds. Any pilot pickle switch trim ceases MCAS action for 5 seconds.

If MCAS runs again, again any pilot trim action defeats MCAS.

There is is no need to manually trim against any large nose down MCAS trim surely? Electrically trim the aircraft neutral AND THEN DISABLE ELECTRIC TRIM. From then on you are tweaking trim manually and no heroic fight against aero forces is required.

Am I wrong?

- GY
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Old 4th Apr 2019, 02:58
  #3014 (permalink)  
 
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Garage years I agree. However if you initially allow some trim rotation assuming the STS system is operating. Then when you feel the aircraft coming out of trim you identify the problem as a runaway stab. The memory items that exist do not state as you recommend. They state Disconnect AP/AT if engaged and if it continues then stab switches off, if not engaged switches OFF. Seeing that no MCAS memory items exist then they use the most relevant which is runaway stab, where no attempt to electrically trim aircraft first exist.
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Old 4th Apr 2019, 03:34
  #3015 (permalink)  
 
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Originally Posted by GarageYears View Post
Ok, I have to confess Iím confused.

All this talk of manual trim forces, etc.

MCAS applies trim in increments of 2.5 degrees over 10 seconds. Any pilot pickle switch trim ceases MCAS action for 5 seconds.

If MCAS runs again, again any pilot trim action defeats MCAS.

There is is no need to manually trim against any large nose down MCAS trim surely? Electrically trim the aircraft neutral AND THEN DISABLE ELECTRIC TRIM. From then on you are tweaking trim manually and no heroic fight against aero forces is required.

Am I wrong?

- GY
I agree. When did we stop becoming pilots?
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Old 4th Apr 2019, 03:42
  #3016 (permalink)  
 
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Originally Posted by GarageYears View Post
Ok, I have to confess Iím confused.

All this talk of manual trim forces, etc.

MCAS applies trim in increments of 2.5 degrees over 10 seconds. Any pilot pickle switch trim ceases MCAS action for 5 seconds.

If MCAS runs again, again any pilot trim action defeats MCAS.

There is is no need to manually trim against any large nose down MCAS trim surely? Electrically trim the aircraft neutral AND THEN DISABLE ELECTRIC TRIM. From then on you are tweaking trim manually and no heroic fight against aero forces is required.

Am I wrong?

- GY
If the runaway MCAS is countered early enough, then nose up trim, and disabing the cutoff switches is sufficient. That was the official version from Boeing and the FAA, until shortly after the second MAX crash. If left too long, the situation enters uncharted territory, and nobody has come out alive (except those in the simulator).

Several sources indicate that electric trim was intentionally limited in scope, to avoid unintentional runaway nose up trim (whether by the pilot or by a wiring fault). Runaway nose up trim may be just as deadly as nose down trim, so there was logical justification for this restriction.

It has been suggested that pitted against runaway MCAS, the electric trim never wins enough authority to recover from severe nose down trim, where there is aerodynamic loading of the horizontal stabiliser. Whether electric trim would be sufficient against the upgraded MCAS is not clear, and that risk needs to be scrutinised.

Several tests, leaks, and EASA documentation have knocked a huge hole in the initial assertions. I don't have detailed references handy for all of those points, but they have been interspersed throughout the last few days posts. I expect to see more media articles and blogs on these topics.

Edit: The link posted by ProPax gives the latest overview: https://www.flightglobal.com/news/ar...ses-ne-457224/

The FAA is presumably not happy with all of this contradictory information, and being made to look sheepish by ongoing media revelations. The certification review should require detailed evidence, rather than the bland reassurances we had last November after the first MAX crash.
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Old 4th Apr 2019, 04:39
  #3017 (permalink)  
 
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Originally Posted by GordonR_Cape View Post
Don't you just love the spin Boeing are putting out, right now its:

Boeing warns against drawing conclusions before investigators release more details
You can bet your bottom dollar after the findings are released it'll all be:

"We don't want to comment on the past, we want to look to the future, as we make a safer aircraft even safer, and we've ALREADY released software to do that, nothing to see here, move along"........
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Old 4th Apr 2019, 05:01
  #3018 (permalink)  
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Originally Posted by GordonR_Cape View Post

Edit: The link posted by ProPax gives the latest overview: https://www.flightglobal.com/news/ar...ses-ne-457224/

The FAA is presumably not happy with all of this contradictory information, and being made to look sheepish by ongoing media revelations. The certification review should require detailed evidence, rather than the bland reassurances we had last November after the first MAX crash.
The article doesn't seem to know what it's talking about. MCAS is (temporarily) disabled by pilot use of the electric trim. There's no two steps down, one step up scenario at play here, where MCAS has greater authority over the stabiliser than the pilot. The only way MCAS puts the aircraft in an unrecoverable dive is if the pilot fails to trim out MCAS nose down inputs and then activates the stab trim cutout switches, leaving the pilot with manual trim only.
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Old 4th Apr 2019, 05:09
  #3019 (permalink)  
 
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Originally Posted by ecto1 View Post
This is my understanding also, based on the schematic posted before:

737MAX Stab Trim architecture


When MCAS is engaged, control column "extreme deflection" towards pull will NOT disable MCAS trim down, but it will NOT disable your thumb switch trim up either, so you still win.

In other words, this battle will not be affected by too much pull.
So that is a selonoid on the column cutout override switch, right? What happens if it sticks ON, perhaps because someone installed the wrong one? (I have seen this.). Since MCAS is never engaged normally such a fault could lie in wait a long time. What woukd be the consequence, there is not much detail in that schematic.
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Old 4th Apr 2019, 05:33
  #3020 (permalink)  
 
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Originally Posted by gmx View Post
The article doesn't seem to know what it's talking about. MCAS is (temporarily) disabled by pilot use of the electric trim. There's no two steps down, one step up scenario at play here, where MCAS has greater authority over the stabiliser than the pilot. The only way MCAS puts the aircraft in an unrecoverable dive is if the pilot fails to trim out MCAS nose down inputs and then activates the stab trim cutout switches, leaving the pilot with manual trim only.
I agree the article is badly worded. The point is, do you believe anything that Boeing and the FAA tell you at this stage? More proof is needed to regain trust, rather than assertions and paper circuit diagrams. Since MCAS cannot be independently turned on or off, there is no way for a maintenance technician to test any of this, nor a pre-flight check on a specific aircraft.

Originally Posted by Water pilot View Post
So that is a selonoid on the column cutout override switch, right? What happens if it sticks ON, perhaps because someone installed the wrong one? (I have seen this.). Since MCAS is never engaged normally such a fault could lie in wait a long time. What woukd be the consequence, there is not much detail in that schematic.
More questions for each answer in this thread! Having a non-redundant column cutout switch solenoid would be another single point of failure. Presumably the fact that there are two control columns has something to do with it. Since MCAS is wired into both columns, then either one can be used to control the stabiliser trim in the event that the other fails.
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