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sgrd0q 04-11-2019 08:34 AM

Extreme Out Of Trim Flight
 
Looking at the Ethiopian preliminary accident report and the one from the Lion Air accident, I am starting to think there is generally lack of training and understanding of how to trim in an extremely out of trim condition. I should start by saying that I am not bashing the crew in either accident; I blame Boeing 100%. But I think everyone may be somewhat deficient in this area.

Generally, trimming in the usual scenario is an easy balancing act. There are three key points, the action is quick, it is done automatically/subconsciously and the feedback is instant. This is similar to driving a car and keeping it in your lane – you observe the car getting closer to one side, you make a quick small adjustment automatically/subconsciously and you get an instant feedback when you see the car move to the other side. This is repeated many times per minute. It is a balancing act. Another analogy is riding a bicycle, particularly at slow speed – you make small inputs, subconsciously (it is much harder to explain to your kid how to do it, vs just doing it) and the feedback is instant. It is the same with walking - also a balancing act. So the action of trimming is very straight forward and everyone does it reasonably well, just like driving, or riding a bike, or walking, whichever analogy you prefer.

The situation is different in an extremely out of trim state. Trimming is now not a small, instant, automatic adjustment, and even worse - the feedback is grossly distorted. What I mean by this is this – imagine you are pulling hard at the control column, say 100 pounds. Nobody, no matter how strong can sustain this for any significant period of time. You get tired. Your muscles want to give out. So you trim in the usual way, for a short burst, the back pressure is so much that you get very small relief comparatively, but you may not even perceive it. The feedback is distorted. In fact as you get tired, you may even feel like you are pulling harder, even though you got a small relief. So the feedback loop is broken. Your brain is wired to not keep on if there is no positive feedback, and you stop and move on to the next thing.

The failure to trim properly is astounding in both accidents.

With the Ethiopian accident, you have the captain (pilot flying) doing very little to trim after the MCAS kicks in and while they still have the electric trim. His feedback is distorted and he likely assumes his trim is not working so he asks the first officer to help trim. The first officer does a great job pulling up with him, but is also not nearly aggressive enough with the trim. All the while they both recognize the out of trim condition. Then, of course, per the procedure they cut off the electric trim which is great because that kills MCAS, but not so great because they are now grossly out of trim, not controlling the speed (unfortunately), and ultimately finding that the manual trim wheel is not working in that configuration. At some point after that one of them (presumably the CA) turns on the electric trim. I don’t think this was a bad idea as others have speculated. At this point they are exhausted holding the back pressure, the manual trim wheel is not working presumably due to the speed and they have no other options. Throwing the procedure out of the window is the right call as there is no more procedure to follow. You have to do what you have to do to recover. So I would assume you turn the electric trim on and you absolutely lay on the thumb switch. It has been shown that not only you can interrupt MCAS but you can actually override it – as the Lion Air CA did repeatedly on that flight. The most disappointing thing with the Ethiopian accident is that they turned on the electric trim and did very little trimming. There is one blip on the graph where they tried, it changed little and they let go, then another blip, then nothing. They assumed it was not working. They gave up. Then MCAS kicks in and finishes the job. This is the most disappointing aspect.

With the Lion Air accident, the captain actually does a great job trimming nose up repeatedly, for many cycles of MCAS activation and for many minutes. Then he presumably gives control to the first officer, who is not nearly as aggressive and crashes.

This is astounding, 3 out of 4 pilots, 75%, failed to use the trim aggressively enough in a severely out of trim state. As for the Lion Air captain (again pilot flying) – to his credit he catches the first MCAS activation early enough, so he never gets in truly severe out of trim state – so the feedback loop is not as distorted and he is successful in trimming up. This then repeats many times and he gets into a groove with this, into rhythm, going back and forth and staying on top of it. We don’t know how he would have fared if he started with an extreme out of trim condition to begin with.

One may think this is all training, and a student pilot should be able to trim, but it goes beyond that. Everybody trims and does a good job under normal circumstances when the feedback loop is there. Once you go into an extreme out of trim situation and the feed back loop is distorted then this is an entirely different skill – you will need to trim, your only feedback will be the trim wheel spinning, and you will have to be persistent and not give up.

Not many were put in that situation in real flying before MCAS, save for a few test pilots who do that sort of thing on purpose.

I believe there is a training opportunity here – not how to trim under normal conditions, and not on any specific procedure either, but rather training to be persistent and aggressive with the trim even when it feels like it is not working. Hold the damn button for five, ten, fifteen seconds - whatever it takes.

JohnBurke 04-11-2019 09:43 AM

Quote:

Originally Posted by sgrd0q (Post 2801032)
I should start by saying that I am not bashing the crew in either accident;

You really should.

Quote:

Originally Posted by sgrd0q (Post 2801032)
I blame Boeing 100%.

Boeing didn't fly the airplane into the ground.

Do you blame Smith and Wesson for a liquor store robbery?

Fdxlag2 04-11-2019 10:04 AM

Quote:

Originally Posted by JohnBurke (Post 2801062)
You really should.



Boeing didn't fly the airplane into the ground.

Do you blame Smith and Wesson for a liquor store robbery?

If Smith and Wesson designed a revolver that randomly fired when a trigger spring failed I might be inclined to blame them for shooting the TV.

TiredSoul 04-11-2019 10:28 AM

You’re making a lot of assumptions and accusations.
Have you flown the 73? Do you fly professionally?

ItnStln 04-11-2019 11:54 AM

Quote:

Originally Posted by JohnBurke (Post 2801062)
Boeing didn't fly the airplane into the ground.

Do you blame Smith and Wesson for a liquor store robbery?

That’s actually a good analogy.

Fdxlag2 04-11-2019 01:17 PM

Quote:

Originally Posted by ItnStln (Post 2801131)
That’s actually a good analogy.

Boeing designed an airplane where a single unannounced malfunctioning probe failed multiple systems and caused another system to eventually make the aircraft uncontrollable. It has nothing to do with the intentions of the operators. I do not blame Boeing for Islamic Terrorists flying 767s into the World Trade Center. I do not blame Smith and Wesson for robbing liquor stores. The analogy sucks.

Adlerdriver 04-11-2019 02:39 PM

Quote:

Originally Posted by Fdxlag2 (Post 2801178)
.. a single unannounced malfunctioning probe

:confused: If it was "unannounced" why did both pilots verbalize "left alpha vane" at the same time during the event?

Fdxlag2 04-11-2019 02:56 PM

Quote:

Originally Posted by Adlerdriver (Post 2801225)
:confused: If it was "unannounced" why did both pilots verbalize "left alpha vane" at the same time during the event?

Lion air too? Doesn’t change the flocked up analogy.

JohnBurke 04-11-2019 02:59 PM

The nature of being a pilot means accepting ultimate responsibility. Mechanical equipment fails; given enough time and cycles, it all fails. Part of our job, our reason for drawing breath on this earth (and a pay check) while in the cockpit, is having accepted ultimate responsibility, to ensure a safe outcome to the flight. Much of the time, mechanical failures amount to little, and we flow a checklist and move on. On occasion, they are momentous, heart-wrenching tests of professional faith, preparation, and a willingness to fly the aircraft to a full stop. Sometimes in between.

A poor carpenter blames his tools.

Both cases of the 737 Max loss involved third world countries and poor choices in which the pilots were NOT flying the airplane, but let it fly them. The subsequent prohibitions on the 737 Max internationally were all political knee-jerk reactions, and with one exception ALL in contravention and violation of the 1944 Chicago convention. This is to say, without basis or foundation

The procedure for stopping unwanted trim has been known, taught and a required memory item for decades in the 737. This is not new.

The principle of following the procedure and not freelancing, also not new.

There is no point in the procedure by Boeing, or in any training program anywhere in the world, which directs the crew to fly past Vmo and impact the ground in excess of 600 knots, or to maintain a high power setting and accelerate away from a trimmed speed.

There is no procedure, once having shut off stab trim, to re-engage it.

There is such a thing as painting one's self into a corner; making a recoverable situation unrecoverable. This happened in both cases.

Presently the FAA has assembled a JATR involving the civil aviation authority of each nation, as well as manufacturer representatives, pilot groups, and investigative interests. Every operator, every nation is included, who wishes to be included, such that the discovery and process is together, to streamline the return to service and eliminate a series of political drama as each nation makes a pretense at recertification.

In the meantime, if pilots cannot accept responsibility for the safe outcome and quit blaming the aircraft, they reveal themselves as incompetent and unworthy, and should remove themselves from the cockpit. It's no place for the spineless who cannot take responsibility for their own action, and who are not prepared to handle not only the normal, but abnormal and emergency conditions which may arise.

Adlerdriver 04-11-2019 05:01 PM

This entire premise is flawed.

Quote:

Originally Posted by sgrd0q (Post 2801032)
Looking at the Ethiopian preliminary accident report and the one from the Lion Air accident, I am starting to think there is generally lack of training and understanding of how to trim in an extremely out of trim condition.
A "general lack of training and understanding" where? Here in the US? :confused: I and my peers at the 3 airlines I've worked at along with those in the USAF seemed to have a pretty good handle on trimming. :rolleyes:

I should start by saying that I am not bashing the crew in either accident; I blame Boeing 100%. But I think everyone may be somewhat deficient in this area. Quite the broad brush you paint with - Everyone is deficient in what?.... Trimming again?


Generally, trimming in the usual scenario is an easy balancing act. There are three key points, the action is quick, it is done automatically/subconsciously and the feedback is instant. This is similar to driving a car and keeping it in your lane – you observe the car getting closer to one side, you make a quick small adjustment automatically/subconsciously and you get an instant feedback when you see the car move to the other side. This is repeated many times per minute. It is a balancing act. Another analogy is riding a bicycle, particularly at slow speed – you make small inputs, subconsciously (it is much harder to explain to your kid how to do it, vs just doing it) and the feedback is instant. It is the same with walking - also a balancing act. So the action of trimming is very straight forward and everyone does it reasonably well, just like driving, or riding a bike, or walking, whichever analogy you prefer.

The situation is different in an extremely out of trim state. Trimming is now not a small, instant, automatic adjustment, and even worse - the feedback is grossly distorted. What I mean by this is this – imagine you are pulling hard at the control column, say 100 pounds. Nobody, no matter how strong can sustain this for any significant period of time. You get tired. Your muscles want to give out. So you trim in the usual way, for a short burst, the back pressure is so much that you get very small relief comparatively, but you may not even perceive it. The feedback is distorted. In fact as you get tired, you may even feel like you are pulling harder, even though you got a small relief. So the feedback loop is broken. Your brain is wired to not keep on if there is no positive feedback, and you stop and move on to the next thing. This paragraph and the one above are based on the assumption that a pilot attempting to trim has no actual understanding of the physics involves, the relationship between airspeed and trim setting and what he is actually doing by moving the trim switch (or the manual trim wheel for that matter). If a pilot has to pull 100 lbs of force to move the yoke back in attempt to raise the nose, he knows his aircraft is grossly out of trim for the current speed. If he doesn't then he shouldn't be in the aircraft in the first place. 100 lbs of pull on the control column is going to tell any competent pilot that he's going to have to trim like crazy to get it back into a normal range. He's not going to give a couple of clicks of trim, have the control forces go to 99 lbs, shrug his shoulders and give up because the problem wasn't instantly corrected. This whole "feedback loop" discussion is nonsense.
If a pilot in a grossly out of trim aircraft tries one small attempt to trim, gets no immediate relief and then gives up, it's because he has no idea what he's doing - not because of some distorted "feedback loop".


The failure to trim properly is astounding in both accidents.

Really? What if both crews never bothered to hand fly the aircraft. What if the entirety of their actual hand flying experience in the jet is takeoff roll, rotation, climb to 500' in t/o configuration, followed by autopilot on - then on final, clicking it off at 300' fully configured, fully trimmed and landing.

With the Ethiopian accident, you have the captain (pilot flying) doing very little to trim after the MCAS kicks in and while they still have the electric trim. His feedback is distorted and he likely assumes his trim is not working so he asks the first officer to help trim. The first officer does a great job pulling up with him, but is also not nearly aggressive enough with the trim. All the while they both recognize the out of trim condition. Then, of course, per the procedure they cut off the electric trim which is great because that kills MCAS, but not so great because they are now grossly out of trim, not controlling the speed (unfortunately), and ultimately finding that the manual trim wheel is not working in that configuration. At some point after that one of them (presumably the CA) turns on the electric trim. I don’t think this was a bad idea as others have speculated. At this point they are exhausted holding the back pressure, the manual trim wheel is not working presumably due to the speed and they have no other options. Throwing the procedure out of the window is the right call as there is no more procedure to follow. You have to do what you have to do to recover.

But they didn't "do what they have to do". They turned a malfunctioning system back on and they did nothing with it. Justifying their actions with logic they weren't using doesn't validate their choices. It also makes no sense to approve of a decision matrix that starts at a point that no competent 737 crew should have allowed their aircraft to reach in the first place. So I would assume you turn the electric trim on and you absolutely lay on the thumb switch. It has been shown that not only you can interrupt MCAS but you can actually override it – as the Lion Air CA did repeatedly on that flight. The most disappointing thing with the Ethiopian accident is that they turned on the electric trim and did very little trimming. There is one blip on the graph where they tried, it changed little and they let go, then another blip, then nothing. They assumed it was not working. They gave up. Then MCAS kicks in and finishes the job. This is the most disappointing aspect.

With the Lion Air accident, the captain actually does a great job trimming nose up repeatedly, for many cycles of MCAS activation and for many minutes. Then he presumably gives control to the first officer, who is not nearly as aggressive and crashes.

This is astounding, 3 out of 4 pilots, 75%, failed to use the trim aggressively enough in a severely out of trim state. As for the Lion Air captain (again pilot flying) – to his credit he catches the first MCAS activation early enough, so he never gets in truly severe out of trim state – so the feedback loop is not as distorted and he is successful in trimming up. This then repeats many times and he gets into a groove with this, into rhythm, going back and forth and staying on top of it. We don’t know how he would have fared if he started with an extreme out of trim condition to begin with.

One may think this is all training, and a student pilot should be able to trim, but it goes beyond that. Everybody trims and does a good job under normal circumstances when the feedback loop is there. Once you go into an extreme out of trim situation and the feed back loop is distorted then this is an entirely different skill – you will need to trim, your only feedback will be the trim wheel spinning, and you will have to be persistent and not give up. :rolleyes: Back to the feedback loop and pilots who apparently have no idea what trim is actually doing and are unable to differentiate between needing more or less depending on airspeed and control forces.

Not many were put in that situation in real flying before MCAS, save for a few test pilots who do that sort of thing on purpose.

I believe there is a training opportunity here – not how to trim under normal conditions, and not on any specific procedure either, but rather training to be persistent and aggressive with the trim even when it feels like it is not working. Hold the damn button for five, ten, fifteen seconds - whatever it takes. Again, if this concept is new to any pilot, may I suggest that pilot find another line of work.



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