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MAX’s Return Delayed by FAA Reevaluation of 737 Safety Procedures

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MAX’s Return Delayed by FAA Reevaluation of 737 Safety Procedures

Old 7th Jul 2019, 21:08
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Originally Posted by OldnGrounded
Boeing and the FAA shouldn't need to be told, at this point, that being seen to protect "trade secrets" that might be related to the investigation can only have an extremely negative impact on the world's opinions about B-produced aircraft and the corporate culture that produces them. Perhaps it's not clear to some high-level decision-makers how serious this situation has become.
Agreed.
I suppose they are intending to say "we fixed it, but we won't tell what was wrong nor what we did".
Talk about restoring confidence...
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Old 7th Jul 2019, 21:33
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Originally Posted by Yeehaw22
Maxxer you contradict yourself. You lambast the maintenance staff for replacing the sensor or cleaning the connector on a 'brand new' aircraft, yet then ask why did they not suspect the 'brand new' wiring in the same paragraph?

The main issue in that case was the maintenance staff were hung out to dry by the diabolical pirep written up by the previous crew. Granted theres nothing been said about what was handed over verbally but with an issue so serious it should have been documented in much more detail, taking several pages of the techlog if required.

And talking of cleaning connectors. You'd be surprised just how often connectors can be contaminated by stray fluids and the like or have a pin that's bent or disengaged so it's always worth a look. Especially with more and more fibre optics in connectors where clean connections are paramount.
Sorry but i am an engineer and i am qualified to splice fiber optics, there is no fiber optics in the angle of attack sensors
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Old 7th Jul 2019, 21:44
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Dear Alchad:

The two traces of interest in the chart are the red one labelled CCForce_PitchCWSLocalFDR() and the green one labelled CCForce_PitchCWSForeignFDR(). As I understand it, the "local" one is for the left-side column; the "foreign" one is for the right-side column. These traces record the forces the pilots are applying when they push or pull on the yoke. The two yokes are tied together through a break-out mechanism. If only one pilot pushes or pulls, the break-out mechanism will cause his side's FDR trace to be very slightly greater than the other pilot's. Of course, the traces will diverge if the two pilots are both at work, but pushing or pulling in different directions or to different degrees. However, the two traces will also diverge if the differential input from the two pilots is so great that the break-out mechanism fails, something like an electrical fuse. After break-out, each yoke has independent control over the elevator on its side of the airplane.

Perhaps I should clarify my use of the word "failure". The break-out mechanism may have done what it was supposed to do -- break.

My knowledge about this issue comes directly from the Leeham News report November 28, 2018, just a couple of days after the preliminary report on the Lion Air crash was published. The second and third-to-last pages of Leeham's report describe this issue in some detail.

What wonkazoo and yoko1 are debating is whether the SIC, who took control at about this time, was somehow at greater fault than the PIC, who arguably had the airplane under control up until that point. A lot seems to have happened in the ten or fifteen seconds immediately before the airplane began its fatal plunge.

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Old 7th Jul 2019, 22:00
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Originally Posted by YYZjim
Dear Alchad:

The two traces of interest in the chart are the red one labelled CCForce_PitchCWSLocalFDR() and the green one labelled CCForce_PitchCWSForeignFDR(). As I understand it, the "local" one is for the left-side column; the "foreign" one is for the right-side column. These traces record the forces the pilots are applying when they push or pull on the yoke. The two yokes are tied together through a break-out mechanism. If only one pilot pushes or pulls, the break-out mechanism will cause his side's FDR trace to be very slightly greater than the other pilot's. Of course, the traces will diverge if the two pilots are both at work, but pushing or pulling in different directions or to different degrees. However, the two traces will also diverge if the differential input from the two pilots is so great that the break-out mechanism fails, something like an electrical fuse. After break-out, each yoke has independent control over the elevator on its side of the airplane.

Perhaps I should clarify my use of the word "failure". The break-out mechanism may have done what it was supposed to do -- break.

My knowledge about this issue comes directly from the Leeham News report November 28, 2018, just a couple of days after the preliminary report on the Lion Air crash was published. The second and third-to-last pages of Leeham's report describe this issue in some detail.

What wonkazoo and yoko1 are debating is whether the SIC, who took control at about this time, was somehow at greater fault than the PIC, who arguably had the airplane under control up until that point. A lot seems to have happened in the ten or fifteen seconds immediately before the airplane began its fatal plunge.

YYZjim
Interesting article, but in months of following these events, this is the only time I have seen the suggestion there was a control problem other than AND trim by MCAS. I think more news would have followed if this story was correct.
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Old 7th Jul 2019, 22:09
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Hopefully, the final report into the accident will include the FDR traces for the elevator position, which were not in the preliminary report. That would clear up some of the uncertainty. Of course, the MAX will likely be flying before then.

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Old 7th Jul 2019, 23:21
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Originally Posted by OldnGrounded
Boeing and the FAA shouldn't need to be told, at this point, that being seen to protect "trade secrets" that might be related to the investigation can only have an extremely negative impact on the world's opinions about B-produced aircraft and the corporate culture that produces them. Perhaps it's not clear to some high-level decision-makers how serious this situation has become.
What you have stated has merit (IMHO).Even at this stage of the MAX grounding, I truly believe that the "high level" decision makers are still drinking the cool aid.You only have to read or listen to the choreographed Muppet words from the PR (or lack thereof) department in the windy City to learn that they cannot fathom the gravity of the situation.
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Old 7th Jul 2019, 23:53
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Originally Posted by YYZjim
However, the two traces will also diverge if the differential input from the two pilots is so great that the break-out mechanism fails, something like an electrical fuse. After break-out, each yoke has independent control over the elevator on its side of the airplane.

Perhaps I should clarify my use of the word "failure". The break-out mechanism may have done what it was supposed to do -- break.
My understanding is that there is no mechaninal "failure", the breakout mechanism comprizes cams, springs and rollers, to allow disengaging each yoke from the other.
It is rather a matter of pull/push overcoming a springed detent.

Cf picture from Peter Lemme's Satcom Guru website :





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Old 8th Jul 2019, 01:27
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Wonkazoo posts:

At the moment that the PF handed off control of LT610, MCAS was in the MIDDLE of an 11-second run....
First of all, MCAS doesn’t run for 11 seconds - ever.

Next, you have misidentified where the change in control took place. As I understand it, you’ve never been part of a two-person airline crew, so I can understand if you are not familiar with the protocol. I suspect that you are instead focusing on that blue vertical line that was added by the author of the Leeham article you have cited, but the author was actually marking another event.

Whenever aircraft control is transferred in a multi-crew aircraft when the autopilot is not engaged, the proper technique is to first place the aircraft in a neutral trim state (i.e. no control pressures, represented by the spot of relative calm on the CCCForce FDR trace before the blue line) and then make the hand-off (procedurally accompanied by some verbalization such as “You have the aircraft” “I have the aircraft” though this part is sometimes omitted). Ideally the pilot on the receiving end would not have to make any immediate control input. A pilot does not, I repeat does not, transfer control when there is an ongoing control input or out of trim state. That would be a significant error.

We know that MCAS will pause for 5 seconds after a Main Electric Trim input. We can see by the FDR traces that the Captain was making aggressive Main Electric Trim inputs to keep the the stab in a properly trimmed position. Thus the proper sequence of events would be that the Captain trimmed up the aircraft, and during the subsequent pause he would have transferred control to the First Officer. The FDR does not break out the separate Capt and FO trim inputs, but as the Leeham author points out, the “CCCForce” red and green lines give a good indication where the primary control forces were originating. The vertical blue line indicates the first significant control input the FO made in response to MCAS after the change of control. It was not the moment of the change in control.

When MCAS activated there was a slight delay in the FO’s response, as one might expect. After this point he responded with aggressive elevator inputs (height of the green CCCForce line) and only minimal stab trim input. This was the opposite of the Captain who used much less aggressive elevator inputs (height of the red CCCForce line), and much more aggressive trim inputs.

From that point on, the FDR traces tell the rest of the story. The First Officer fought MCAS primarily with elevator inputs and only ineffectually with Main Electric Trim inputs. As a result, the stabilizer worked its way to an untenable position resulting in loss of control. Why the Captain did not pick up on this struggle is a bit of a mystery. It is possible he went immediately went “heads down” into the QRH (Quick Reference Handbook) and didn’t realize the FO was losing control until it was too late.

An alternative explanation that might also explain the divergence in the two CCCForce lines (the so-called “malfunction”) is that the Captain may have been bending over to pick up something off the floor (like his QRH manual) or was contorting his body around to get this manual out of his kit bag (stored behind and to the left) or perhaps reaching for the stick shaker circuit breaker behind him and, as a result, part of the Captain’s body was in between the control column and the seat. If the FO yanked back on the control column with great force at this moment, he could have pinned the Captain in place, possibly causing injury. This effective push/pull on the control columns would have registered as a force divergence. It would have happened quickly and may have added an additional distraction with a possibly injured Captain and an FO mishandling the aircraft. Of course, this is all speculation at this point, but hopefully the CVR would add some clarity.

The inflection point in the aircraft state that occurred at the point of aircraft control provides a critical lesson about why the first three pilots succeeded, and the next two pilots failed, to manage the erroneous MCAS inputs. The Captain clearly demonstrated that aggressive use of the Main Electric Trim could effective counter MCAS. The First Officer, on the other hand, demonstrated what happens when the pilot opts to use primarily elevator, and only limited trim inputs - MCAS will overcome the elevator if the stab is not kept in trim. We will see this behavior repeated by the Captain of Ethiopian302.

Since trimming the elevator and/or stab is such a basic and fundamental skill that any pilot - much more so one with a commercial certificate - should have wired deep into muscle memory, then it is very germane to ask what was different about the training, experience, and/or environment of the JT610 First Officer and the ET302 Captain that resulted in them not trimming when it should have been the most natural response to the control forces that MCAS generated.











Last edited by yoko1; 8th Jul 2019 at 01:46.
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Old 8th Jul 2019, 01:36
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Originally Posted by Fly Aiprt
The committee, led by former National Transportation Safety Board Chairman Chris Hart and including Brazil, Canada, China and the European Union, met recently while those restrictions were pending. The group is conducting a comprehensive review of flight-control features on the MAX fleet, which the FAA hopes will enhance the global credibility of eventual fixes.
Nothing inspires confidence like secret investigations protected by NDAs, a complete reversal of the philosophy of openness practiced (with varying degrees of success) for the past half century of aircraft accident investigations. The Trump FAA is really outdoing itself in its implosion. Even the CAAC now has greater credibility.
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Old 8th Jul 2019, 02:07
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Originally Posted by yoko1

First of all, MCAS doesn’t run for 11 seconds - ever.


With respect, no one can possibly know that. We know that the maximum per-activation runtime per design is 9.26 seconds, but we don't have nearly enough data to state with certainty that it "never" runs for longer than that. When I say "we," I mean to include all of humanity, because no one, in all of humanity, has enough data or enough experience with MCAS to credibly assert what it "never" or "always" does.

We do, of course, have significant evidence that MCAS has behaved in unexpected and very undesirable fashion in at least a couple of instances. I suspect that, before those flights, many of the relatively-few people who knew that MCAS existed and what it was intended to do would have said it would never "do that."
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Old 8th Jul 2019, 02:35
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Originally Posted by yoko1
-snip-
s I understand it, you’ve never been part of a two-person airline crew, so I can understand if you are not familiar with the protocol. I suspect that you are instead focusing on that blue vertical line that was added by the author of the Leeham article you have cited, but the author was actually marking another event.

Whenever aircraft control is transferred in a multi-crew aircraft when the autopilot is not engaged, the proper technique is to first place the aircraft in a neutral trim state (i.e. no control pressures, represented by the spot of relative calm on the CCCForce FDR trace before the blue line) and then make the hand-off (procedurally accompanied by some verbalization such as “You have the aircraft” “I have the aircraft” though this part is sometimes omitted). Ideally the pilot on the receiving end would not have to make any immediate control input. A pilot does not, I repeat does not, transfer control when there is an ongoing control input or out of trim state. That would be a significant error.
yoko1, I have been an aircraft commander in a multi-crew aircraft who has taken controls when the other pilot was having difficulty controlling the aircraft - no, they were not trimmed when the controls were passed.
The inverse of that happened once to me - as a "not the aircraft commander" pilot - on a dark and moonless night where I hardly had it trimmed when the aircraft commander took controls.

I'd be careful of making such a sweeping statement about what a pilot would or would not do on a forum with a lot of pilots (and of course other interested folks).

Yes, the normal passing of control is as you describe.

We are, I think you'll agree, discussing a not-quite-normal situation.
*return to lurk*

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Old 8th Jul 2019, 02:50
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Yoko,With respect,
"Since trimming the elevator and/or stab is such a basic and fundamental skill that any pilot - much more so one with a commercial certificate - should have wired deep into muscle memory, then it is very germane to ask what was different about the training, experience, and/or environment of the JT610 First Officer and the ET302 Captain that resulted in them not trimming when it should have been the most natural response to the control forces that MCAS generated".

One would assume that the crew knew how to trim out control column forces, basic flying skills 101, but with all the other alerts/cautions they also had to contend with at that time, then no amount of training would have helped their situation. During simulator training for type, I can provided the crew with 2 basic malfunctions, one of which is loss of airspeed on the PM (PFD) side. Shortly after, another small malfunction appears which isn't a huge problem (PM FMC failure) but the task saturation becomes very interesting to watch. We don't seem to train crews how to deal with these situations and how best to "prioritize malfunctions" in simulator events anymore!Recently, there was a video floating around on the internet showing 2 pilots, one trying to trim the stab/elevator on a 737 simulator, but this pilot wasn't fully able to trim the stab/elevator using the manual trim wheels (has been discussed).I am eagerly awaiting the outcome of the investigation(s) before I comment fully (I have numerous hours training and flying on this type).

Last edited by 568; 8th Jul 2019 at 02:51. Reason: text
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Old 8th Jul 2019, 02:51
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Lonewolf,You beat me to it!
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Old 8th Jul 2019, 03:31
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Final minutes of Lion Air LT601 (accident flight).

It is true, if proper procedure was followed, then the PIC handed control over to the SIC at a peaceful moment when the airplane was reasonably good trim. Maybe things did happen like that, and the SIC made a mess of a perfectly flyable situation. However, there is not a lot of data in the FDR traces to confirm that the proper procedure was followed.

I agree that the altitude and airspeed of LT601 during the five minutes the PIC was flying do seem to be steadier than in the Ethiopean mishap. But a couple of trends can be detected in the FDR traces.

1. The airspeed gradually increases during the period the PIC was in control.

2. The swings in altitude get progessively greater during the period the PIC was in control.

3. The pitch trim position gradually worsens during the period the PIC was in control.

4. Two minutes before he handed over control, the PIC advanced the throttles. He did this in response to a fall in altitude. He returned the throttles to their previous position after about a minute of additional thrust. (See the fuel flow traces.) It was about a minute after that that he turned over control.

It is possible that the favourable changes in altitude which occurred as a result of the throttle push gave the PIC confidence that the airplane was controllable, and could be made to go up and down even if the trim was acting up. His decision to turn things over to the SIC would then have been a natural follow-up, to give himself the time to think or investigate. That is possible, but by no means a certainty.

I expect that the CVR will help sort this out.

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Old 8th Jul 2019, 03:35
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About the Non-Disclosure Agreements (NDAs).

NDAs typically arise when a company with proprietary technology intends to have a voluntary discussion about the technology, or stuff relating to it, with another company that has equal rights. The three ingredients are: (i) technology, (ii) technology that is proprietary and (iii) parties with equal standing.

1. In this instance, it is the FAA (not Boeing) who asked for the NDAs. Why? What technology, proprietary or not, does the FAA own?

2. The relationship between Boeing and the FAA is not that of two independent parties with equal standing. The FAA has a statutory right to inquire into the workings of Boeing's product. I assume that the FAA has the right to ask any question it wants about any system it chooses. What would happen, for example, if Boeing refused to let the FAA see some of the software code? The FAA is entitled to see everything; and it is not practical for Boeing to refuse. Even so, Boeing could ask the FAA to execute an NDA that would prevent its staff from disclosing anything to third parties without Boeing's approval. It would make sense if Boeing was asking for the NDAs, but that is not what is being reported.

3. On the other hand, these NDAs might not have anything to do with proprietary technology. Perhaps they are intended to keep what is said during negotiations under wraps. Public confidence could be shaken if it became known, for example, that agency XAA was very concerned about detail XYZ, and suggested that Being deal with it by doing thus and so, but, in the final "deal" among the regulators, detail XYZ was put aside and not fixed at all.

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Old 8th Jul 2019, 04:07
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Originally Posted by yoko1
As I understand it, you’ve never been part of a two-person airline crew, so I can understand if you are not familiar with the protocol. I suspect that you are instead focusing on that blue vertical line that was added by the author of the Leeham article you have cited, but the author was actually marking another event.


Wrong on the first statement and wrong on the second. (And yes, I know MCAS runs for 9.2 seconds. Shocking that you would focus on that detail.)

I've elected to not read the rest of what you wrote as it would serve no purpose. (It was the crew, the training, we should look at what they did, how the handoff happened, since it all went to **** after the handoff. Yes, Boeing is in part responsible, but so is the "foreign" crew and the "foreign" airline and the "foreign" training regimen, and the industry for allowing the degradation in training and certification requirements, but really, it was the crew..."

Other posters have nailed the crucial data point- there is not enough information in the public domain to begin questioning either the crew who were flying or mechanically what happened. We are far short of the necessary data points to begin critiquing what the crew did and when they did it, as well as what failed, when it failed and in general what happened overall.

Beyond that I'm going to remain disengaged as this (and your argument) became tiresome a long time ago.

This quote "I am in the middle of a very hectic multi-day trip (yes, I do have a day job), so I don’t really have the time to break it down for you. I’m going to suggest that you dial back the emotion" is as chauvinistic as it is pedantic and frankly insulting. As it is beneath contempt I'm not going to comment other than to offer that you nailed it- I'm an emotionally sensitive wreck prone to being aggravated by online posters, but curiously one who (unlike you) survived an actual near-death situation that required my immediate, correct and lucky inputs and actions and somehow survived despite my emotionally volatile tendencies. In fact it's a small miracle that I, an emotional vortex of uncertainty managed to survive probably the nearest close-call (resulting in the complete loss of the hull) of anyone who has posted here. (If my chute had opened like 1.3 seconds later you wouldn't be reading these words right now... It was that close...) In fact it boggles the mind. Emotionally unstable miscreant somehow survives a mechanical control failure that takes the lives of nearly all of the pilots similarly afflicted.

In going after the crew, and in cloaking it in polite terms you are doing a disservice to your profession and to your peers, especially the ones who died at the pointy end of LT610 and ET302. I can only hope that your peers treat you with such kindness if someday you find yourself in front of the firing squad of public scrutiny.

Regards,
dce
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Old 8th Jul 2019, 04:30
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I lied.

I read your post Yoko-

And I laughed out loud. (You know us emotional folks- we do stuff like that...)

You honestly think that in the mayhem of that cockpit there was some fancy schmancy hand-off more specific than "Your airplane." and that it was made at some time of "stable" flight??

The fact that you even think this was possible shows your complete ignorance of what a situation like that is really like. (Oops- got you there- I've been there... Experience speaking... Hard to argue with!!)

You live and fly in a special world dear Yoko1.

C'mon man, you cannot possibly be that obtuse!!

But apparently you can, since your next offering is that the reason for the immense control column force-divergence was not (as would make sense) an immense input on the co-pilot side, but was instead the captain placing his generous thighs (ass??) between the column and his seat?? Seriously?? That's what we're arguing about given the paucity of actual data- what body part the Captain put between the column and his seat??

Let it go. You think the crew failed. We get it. And perhaps they did, let's be honest- they could have done better. But when the grade for your pass or failure is drilling yourself into the ground at 600MPH perhaps a little slack can be given in the post-mortem, at least until all the facts are in??

When your words convey an antagonistic and jingoistic view of the majority of crews who are intended to fly the damn thing in the first place it is reasonable to ask what purpose they serve. And lord help you if you are ever placed in a similar crucible. Here's hoping your peers will be more respectful of you than you were of them.

Regards,
dce
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Old 8th Jul 2019, 04:37
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MCAS trims at a greater rate than electric (yoke switch) trim.

How many seconds of electric trim would be required to counterract 9.2 seconds of MCAS?

Are there any other circumstances under which you would expect to have to trim continuously for that length of time (or more if more than one MCAS activity had run undetected)?
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Old 8th Jul 2019, 05:24
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A full return to service date is pure speculation. I'm convinced the FAA (after due diligence) will return the Max to the skies and the US airlines will gladly launch them. But there are other elephants in the room. Arte other certification systems going to accept the FAA's recertification at face value? You can bet in the current climate that China won't. Ethiopia and Indonesia are going to be very sceptical as well. And what about the training? If pilots require practical training to convert to the Max, there aren't many Max simulators available right now. And you are going to have to convince the public the aircraft is safe. The IAG order was a big vote of confidence, but I'm sure we are going to see more order cancellations.
https://www.bbc.com/news/business-48899588
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Old 8th Jul 2019, 05:40
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Originally Posted by Maninthebar
MCAS trims at a greater rate than electric (yoke switch) trim.

How many seconds of electric trim would be required to counterract 9.2 seconds of MCAS?

Are there any other circumstances under which you would expect to have to trim continuously for that length of time (or more if more than one MCAS activity had run undetected)?
The short answer is there is no earthly reason to let the trim run that long without doing something about it - that is why it is called Runaway Stab Trim. Keep in mind that the expected pilot reaction time to Runaway Trim was 3 seconds. Now even I think that’s a bit tight, but 9 seconds is three times as long. If the pilot doesn’t like where the trim is, or where the trim is going, the solution is literally right under his/her thumb.

Last edited by yoko1; 8th Jul 2019 at 05:54.
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