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Ethiopian airliner down in Africa

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Ethiopian airliner down in Africa

Old 3rd May 2019, 00:38
  #4761 (permalink)  
 
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Originally Posted by david340r View Post
I have read the whole thread and I'm still a bit puzzled about the relative ability to trim electrically or manually. It's been asserted several times that the electric trim is more powerful than manual trimming, but we also have the checklist item "grasp and hold" if isolating electric trim doesn't control a runaway. This has been touched on earlier, but I can't envision a simple way that the manual trim wheels could win against the electric motor (stall it) whilst then not being able to actually trim over a wider range of conditions than the electric trim. Can anyone confirm there is some form of mechanism to achieve this and provide any information as to how it works?
My understanding is that the 'grasp and hold' would be for the case of failed brakes on the stab mechanism, it is a recirculating ball drive so can be back driven by aero loads
Manual wheel inputs actuates a clutch that disconnects the motor so you would not be driving or trying to stall it. (motor may be unclutched when not active as well).
Not sure of mechanics of that but easy enough to conceive of a 'tension in cable' mechanism that would actuate the disengage.

Whether my details are exactly correct does not matter much since the point is that one is not directly fighting the motor, just trying to move the stab.
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Old 3rd May 2019, 04:28
  #4762 (permalink)  
 
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The cutout switch design change is important.

So, why do the two cutout switches in the MAX work differently than before? The NG had one for disabling AP trim plus (?) SpeedTrim and one to cut all electric trim, meaning the thumb switches’ input too.
Max has both switches cutting all.
Why:

(1) Was there a perceived danger that one needs to make double sure to cut MCAS out otherwise it would fly the ac in the ground? Which it did anyway but for other reasons. But that switch choice shows that someone saw the danger.

(2) Troubleshooting what goes wrong with the stabilizer trim takes too long. Better cut out everything right away but keep the appearance of two switches to ensure continuity. That choice must then have been based on somebodies analyses that nobody uses the sequential cutout approach. Meaning AP and SpeedTrim never failed. That must have been documented.

(3) Disabling MCAS input together with the AP could not have been allowed due to certification issues. Having a switch for AP & SpeedTrim and one for thumb switches & MCAS was considered as too complicated, so two switches cutting out all seemed the best choice while keeping the layout.

It seem to me that whoever made that design choice was aware that MCAS could be dangerous and he/she tried a last minute fix.
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Old 3rd May 2019, 04:35
  #4763 (permalink)  
 
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Originally Posted by Chronus View Post
It remains an inescapable fact, meaning as in the sense of a reality, that the introduction of a software based modification became a necessary in order to get this plane certified. That must have been considered as the most optimal solution to achieve the commercial aims of introducing a plane that could be competitive to others on the market, namely the Airbus offerings. The B737 had to be kept alive to do that. But how could it be possible to keep a plane designed half a century ago may still be fit for today`s world of aviation. The Douglas DC10 was also an all time winner, but can you imagine kitting it out with the latest high ratio by pass turbo fans of today, installing some fancy computers and software in it and saying here is the answer to short haul commuter, so long as you can get your pax to don their oxy masks if we hit some bad wx. Not really all that much different to saying the B737 MAX is more than safe as is, but just to make sure no airline has sat a pair of morons up front, we have with our clever MCAS thingy tell the computer how to handle them. Now if that does not make sense as to why they put in this MCAS thingy majig, then why did they do it in the first place. That of course takes us back to where we started, which then means we got nowhere and that is the whole purpose of the whole exercise.
With the exception of the hull, the MAX is an entirely different aircraft than the original B737-100 or even the NG’s. Different wing, engines, avionics, APU, landing gear, etc. If they called it a B797 would that makes things better?

The same can be said of the B747. Today's 800 series ain’t the B747-100 of 1969. Same thing, new engines, wing, avionics, APU, etc. Is anyone trashing Boeing for that? And, for all we know, the B747-800 might have the odd bandaid too for some obscure issue just like the MAX.
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Old 3rd May 2019, 05:02
  #4764 (permalink)  
 
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Originally Posted by SystemsNerd View Post
With respect, I think there may be a breakdown in communication here that may be in large part responsible for the ongoing disagreement. When people say "human factors", they don't mean "the human element", they mean Human Factors*, i.e., the study of how the human mind and body interacts with designed systems.

The human mind does not, ironically, work in the ways most people think it does - it has well-documented limitations and sources of error plumbed into its design. A human factors expert can I believe pretty trivially design a scenario where most (if not all) humans will consistently fail to correctly solve even relatively trivial problems, regardless of their competence under normal conditions.

Thus, when asking "why didn't they just fly the plane?", one possible answer is undoubtedly some variant on "they were incompetent". But another possible answer is "they were put into a scenario in which any human being would consistently fail to solve the problem, regardless of competence". Probably the truth is somewhere between those two points.

*See Wikipedia article "Human factors and ergonomics"
That’s a fair point. My response and likely that of my “cohorts” is this: what was presented to the three crews upon lift-off was a classic Unreliable Airspeed (UAS) scenario which is a an emergency that any B737 type rated pilot ought to have seen in a simulator complete with all the bells, whistles and other distractions. The fidelity of simulators is really quite amazing.

So how is it that 1/3 crews did the drill and saved the aircraft (by controlling and flying the aircraft including a managing its speed thanks to doing the UAS drill) while the other 2 crews did not do the drill which ultimately lead to an uncontrollable aircraft as speed was so high that no human could manually trim the aircraft?

Once we have addressed that issue then the next one is how is it that the successful Lion Air crew needed a jumpseat pilot to point out that they had a runaway stab trim and the fatal Lion Air crew was thumbing through the checklist looking for a memory item when they lost control of the aircraft.

To me, this points to a serious training issue at both of these airlines.


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Old 3rd May 2019, 05:18
  #4765 (permalink)  
 
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Originally Posted by L39 Guy View Post

With the exception of the hull, the MAX is an entirely different aircraft than the original B737-100 or even the NG’s. Different wing, engines, avionics, APU, landing gear, etc. If they called it a B797 would that makes things better?

The same can be said of the B747. Today's 800 series ain’t the B747-100 of 1969. Same thing, new engines, wing, avionics, APU, etc. Is anyone trashing Boeing for that? And, for all we know, the B747-800 might have the odd bandaid too for some obscure issue just like the MAX.
Sorry, but your wrong. I’ve been flying 737’s for the last 28+ years. That covers the 200, 300, 500, 700, 800 and I have about a dozen flights in the Max8. You could take about 70-80% of just the -200 cockpit and use it for spare parts on a Max8. Same switches, gauges, lights, etc. The list goes on.
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Old 3rd May 2019, 06:02
  #4766 (permalink)  
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Originally Posted by L39 Guy View Post

With the exception of the hull, the MAX is an entirely different aircraft than the original B737-100 or even the NG’s. Different wing, engines, avionics, APU, landing gear, etc. If they called it a B797 would that makes things better?

The same can be said of the B747. Today's 800 series ain’t the B747-100 of 1969. Same thing, new engines, wing, avionics, APU, etc. Is anyone trashing Boeing for that? And, for all we know, the B747-800 might have the odd bandaid too for some obscure issue just like the MAX.
Not the same as the 747-400 that's for sure. Boeing will have to address this, perhaps! (Flown both BTW).
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Old 3rd May 2019, 06:20
  #4767 (permalink)  
 
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Originally Posted by L39 Guy View Post
To me, this points to a serious training issue at both of these airlines.
If we talk about human factors we should start at the Boeing management decision making. They had years to think about that safety case, and figured, that the two chaps in row zero would always solve this problem in seconds.
May be we need for the MAX a third mandatory jumpseat pilot which only looks for weirded trim movement to get the MAX into the air again...
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Old 3rd May 2019, 06:33
  #4768 (permalink)  
 
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Originally Posted by yanrair View Post

ie is the Boeing Ops Manual Bulletin TBC-19 entirely accurate... namely:

In the event of erroneous AOA data, the pitch trim system can trim the stabilizer
nose down in increments lasting up to 10 seconds. The nose down stabilizer trim
movement can be stopped and reversed with the use of the electric stabilizer trim
switches
but may restart 5 seconds after the electric stabilizer trim switches are
released.


If this is true then it would be possible (not desirable) to use electric trim to override MCAS without using the cutout switches. MCAS could be interrupted and corrected every time it kicked in. I suspect it is not entirely accurate... I wonder if anyone has an authoritative answer?
MCAS can be interrupted with the electric trim switches on the yoke each time it activates, and trim can be returned to a low/zero column force state each time if the pilot puts in adequate opposite trim inputs. That is what the Lion Air crew did for approximately 2 dozen cycles of MCAS before the final few cycles, where the pilot flying at that point failed to put in an adequate amount of opposite trim in those final cycles, allowing the out of trim condition to increase to the point where they couldn't recover in the altitude available.
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Old 3rd May 2019, 07:21
  #4769 (permalink)  
 
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Air
Originally Posted by EDLB View Post


If we talk about human factors we should start at the Boeing management decision making. They had years to think about that safety case, and figured, that the two chaps in row zero would always solve this problem in seconds.
May be we need for the MAX a third mandatory jumpseat pilot which only looks for weirded trim movement to get the MAX into the air again...
This “problem” didn’t have to be solved in seconds. It’s not as if the aircraft is on fire. As pointed out earlier, the ET aircraft flew for almost two minutes with UAS before the flaps were selected up and MCAS kicked in. That was two minutes to do the UAS drill. Same thing for the fatal Lion Air aircraft. You could have given them all day and I don’t think it would have got ‘er done.

As I and others of my “cohort” have stated, Boeing’s mistake was to assume that B737 type rated pilots were trained to handle a basic emergencies like UAS and Stab Trim Runaway. If either of the fatal flights had done at least UAS the aircraft would have been controllable and bought them time to figure out the stab trim issue and, once they determined that, be able to manually trim the aircraft. This is what happened in the successful Lion Air case. In fact, they completed the flight (1 1/2 hours) with UAS and MCAS disabled.

Instead, neither of the accident aircraft crews did that drill, they failed to control the aircraft as it was going way too fast for manual trim. I don’t think it’s too much to ask of professional pilots to know and do memory drills and also to fly the damn aircraft at a speed where one can manually trim and not at the barber pole.

And, to be clear fault for this lies squarely on the airlines that employ and train them, the national CAA’s that regulate them and, to a lesser extent, the aircraft manufacturers that sell them aircraft with their brand on the side of the aircraft. And, yes, MCAS needs to be toned down too.
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Old 3rd May 2019, 07:24
  #4770 (permalink)  
 
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Originally Posted by Dave Therhino View Post
MCAS can be interrupted with the electric trim switches on the yoke each time it activates, and trim can be returned to a low/zero column force state each time if the pilot puts in adequate opposite trim inputs. That is what the Lion Air crew did for approximately 2 dozen cycles of MCAS before the final few cycles, where the pilot flying at that point failed to put in an adequate amount of opposite trim in those final cycles, allowing the out of trim condition to increase to the point where they couldn't recover in the altitude available.
An undocumented system of which the pilots have no clue it even exists can interrupt airplane trim. If the pilot doesn't want to end in a coffin corner, they need to figure out on the spot that:
- this is not STS
- because it's not STS it must be either a bug or an undocumented system
- to save their lives they need to return the trim manually to a low/zero column force each time the undocumented command is triggered.

Despite facing those conditions, the Lion Air crew managed to react appropriately about 2 dozen cycles. Fighting the unknown system raised pilot's adrenaline and fear and induced panic. Thus, incapacitated by stress put on them, they no longer managed to manually correct the erroneous system input that was trying to - and succeeded to - kill them.
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Old 3rd May 2019, 07:51
  #4771 (permalink)  
 
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Originally Posted by derjodel View Post
An undocumented system of which the pilots have no clue it even exists can interrupt airplane trim. If the pilot doesn't want to end in a coffin corner, they need to figure out on the spot that:
- this is not STS
- because it's not STS it must be either a bug or an undocumented system
- to save their lives they need to return the trim manually to a low/zero column force each time the undocumented command is triggered.

Despite facing those conditions, the Lion Air crew managed to react appropriately about 2 dozen cycles. Fighting the unknown system raised pilot's adrenaline and fear and induced panic. Thus, incapacitated by stress put on them, they no longer managed to manually correct the erroneous system input that was trying to - and succeeded to - kill them.
A stab trim runaway affecting the fly ability of the aircraft is no time to “figure out “ anything. The figuring out happens back on terra firma. Whether the source of the runaway is a short circuit in a switch or motor, MCAS or anything other source, when the aircraft experiences uncommanded flight control movements in pitch it’s a stab trim runaway for which there is a clear and simple memory drill. The instinctive thing would to pull or push to restore the desired path then trim for it with the electric trim switches, even if it means long burst of trim. Whatever it takes. If the trim continues to be uncontrollable, turn it off and manually trim with the wheel, however one has to be flying at something less than Vmo to do that which means controlling the thrust or, in other words, flying the airplane.
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Old 3rd May 2019, 08:06
  #4772 (permalink)  
 
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Originally Posted by L39 Guy View Post
A stab trim runaway affecting the fly ability of the aircraft is no time to “figure out “ anything.
Stabilizer Trim Runaway. a malfunction which occurs when the Trimmable Horizontal Stabiliser (THS), or tailplane, on the aircraft tail fails to stop at the selected position and continues to deflect up or down.
Was it? By this definition, isn't any STS operation a trim runaway?
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Old 3rd May 2019, 08:26
  #4773 (permalink)  
 
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Originally Posted by L39 Guy View Post


A stab trim runaway affecting the fly ability of the aircraft is no time to “figure out “ anything. The figuring out happens back on terra firma. Whether the source of the runaway is a short circuit in a switch or motor, MCAS or anything other source, when the aircraft experiences uncommanded flight control movements in pitch it’s a stab trim runaway for which there is a clear and simple memory drill. The instinctive thing would to pull or push to restore the desired path then trim for it with the electric trim switches, even if it means long burst of trim. Whatever it takes. If the trim continues to be uncontrollable, turn it off and manually trim with the wheel, however one has to be flying at something less than Vmo to do that which means controlling the thrust or, in other words, flying the airplane.
In the isolation of a simulator session where the sim instructor selects a runaway trim malfunction, fully agree with you.

Press play below before reading on...


This was not a classic runaway trim. No trim issues were encountered until the flaps were retracted. Retract flaps, now some forward trim starts, trim back with the electric trim and everything is good for 5 seconds, just enough time to start thinking about else, there goes the trim again, fix it with electric trim, all good for 5 seconds, repeat until end of sequence. You are also dealing with an airspeed unreliable. Not easy with that racket going on the background.

To the pilots in all three event flights, this was a trim fight, not a continuous runaway in the QRH condition statement for a Runaway Stabilizer. Judge for yourself from a current in-service document:

Condition: Uncommanded stabilizer trim occurs continuously
The trim worked as they expected, sort of. If English was not your first language, it would be even more difficult.

The Lion Air crews were in the worst position, they had no prior knowledge of the subtle system changes and faults that had led them to trim fight, not a runaway.
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Old 3rd May 2019, 09:23
  #4774 (permalink)  
 
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I am not disagreeing with you but if it was a trim fight, then why could they not keep the aircraft flying (albeit very untidily), and keep on feeding opposing trim inputs to return to land?

Why were the pilots in fear and panicked? Why did they not run their memory drills?

I would like to think that faced with this problem, I would think right bugger this : “pitch - power - speed”, now what the hell is going on? But would I ?

I think SIM training needs to be seriously looked at. UAS (and trim runaway) drills are pre-briefed, and the actions explained. Then into the SIM and a UAS event occurs. Unsurprisingly, the pilots do the drill and recover the aircraft. Tick. Next item.

But UAS is not done every SIM visit every 6 months. It might only be done once every 2 or 3 years, as the training cycle rotates. Even then, it will be one of several training elements the pilots will do in that SIM session, and each pilot will typically fly just one of each exercise each, then move on to the next training item.

Just as we always have to do an engine failure at take-off, a single engine ILS to a go-around, then a single engine NPA, I think that we should always practice situations where we have to revert to basic pitch - power - speed. No autopilots, no flight directors, no auto-thrust, no speed reading/UAS. And it should be sprung on us with no prior warning. Recovery from UAS or unusual aircraft behaviour needs to be an instinctive reflex.

(For Single engine, read OEI.)
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Old 3rd May 2019, 09:43
  #4775 (permalink)  
 
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Originally Posted by Uplinker View Post
I am not disagreeing with you but if it was a trim fight, then why could they not keep the aircraft flying (albeit very untidily), and keep on feeding opposing trim inputs to return to land?

Why were the pilots in fear and panicked? Why did they not run their memory drills?

I would like to think that faced with this problem, I would think right bugger this : “pitch - power - speed”, now what the hell is going on? But would I ?

I think SIM training needs to be seriously looked at. UAS (and trim runaway) drills are pre-briefed, and the actions explained. Then into the SIM and a UAS event occurs. Unsurprisingly, the pilots do the drill and recover the aircraft. Tick. Next item.

But UAS is not done every SIM visit every 6 months. It might only be done once every 2 or 3 years, as the training cycle rotates. Even then, it will be one of several training elements the pilots will do in that SIM session, and each pilot will typically fly just one of each exercise each, then move on to the next training item.

Just as we always have to do an engine failure at take-off, a single engine ILS to a go-around, then a single engine NPA, I think that we should always practice situations where we have to revert to basic pitch - power - speed. No autopilots, no flight directors, no auto-thrust, no speed reading/UAS. And it should be sprung on us with no prior warning. Recovery from UAS needs to be an instinctive reflex.

(For Single engine, read OEI.)
The enormous elephant in the room is training. Luckily I was from the old school where we had to hand fly a lot, it was trained and encouraged, I still practice. Our organisation recently decided to do away with circling approaches because the GNSS will always be available... until it isn't because of traffic, ATC requiring a visual approach or circuit etc. Circuits are now back on the menu in sims, after an absence of 5 or 6 years as line crews are actually having to do them instead of having a runway aligned VNAV path to 500' or less. We had been deskilled, and it was recognised we needed to bring these skills back.

Unfortunately executive level management across the industry have seen automation as their nirvana, it reduces training costs if you get a pilot to stick in an autopilot at 500' and disconnect at the minima. It can be a measured skill, and therefore converted into a KPI for automated compliance monitoring, which equates to a the safest possible operation in the executives mind. The issue is the industry has deskilled it's pilots in the quest for the minimum training footprint. It works until those rusty or non-existent skills are required on a dark and stormy night. Loss of control is the major source of fatalities in the industry. Until there is a genuine commitment to keeping up the basic flying skills, these type of accidents will occur. Boeing didn't help with the MAX.
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Old 3rd May 2019, 10:12
  #4776 (permalink)  
 
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Originally Posted by L39 Guy View Post

That’s a fair point. My response and likely that of my “cohorts” is this: what was presented to the three crews upon lift-off was a classic Unreliable Airspeed (UAS) scenario which is a an emergency that any B737 type rated pilot ought to have seen in a simulator complete with all the bells, whistles and other distractions. The fidelity of simulators is really quite amazing.

So how is it that 1/3 crews did the drill and saved the aircraft (by controlling and flying the aircraft including a managing its speed thanks to doing the UAS drill) while the other 2 crews did not do the drill which ultimately lead to an uncontrollable aircraft as speed was so high that no human could manually trim the aircraft?

Once we have addressed that issue then the next one is how is it that the successful Lion Air crew needed a jumpseat pilot to point out that they had a runaway stab trim and the fatal Lion Air crew was thumbing through the checklist looking for a memory item when they lost control of the aircraft.

To me, this points to a serious training issue at both of these airlines.


"How is it that...?" is exactly the right question IMO, but the answer may be "they were physiologically incapable under the circumstances" rather than "they didn't know how".

Like, the first step in response is probably to ensure that pilots' rational minds do indeed know how to recover the aircraft in a classroom setting. If that's missing then yeah, incompetence, basic training issue, needs fixing immediately. It's possible that this was missing in all three of these cases. It's also possible, based on available evidence, that it wasn't; in this scenario, we proceed to the next step.

If the pilots' rational minds have the solution but they're not applying it, then my understanding of human factors suggests that the likely problem is that their reacting minds - Mark Levy's "chimpanzee brain" from the video linked earlier - is siezing control, in keeping with a few billion years of evolutionary training, and letting the aircraft fly itself into the ground, because chimpanzees can't fly jet aircraft.

There's a couple of obvious approaches to deal with this scenario. The first is to figure out what stimuli are causing the chimpanzee to take over, and removing those stimuli. This is classic human factors work. For example, the stick shaker is AIUI a nice bit of human factors design that is intended to reliably break the pilot's concentration and draw attention to the fact that the aircraft is approaching a stall. Probably there is an amount of time it needs to run before 99.9% of humans have consciously noted it, and that's probably single-digit seconds. Having it drop down to an insistent throb after that point might maintain the information while allowing the pilot to concentrate again. (Maybe this is the wrong fix; the point is that this is the *class* of solution you'd be looking for.)

The second one is to actively train the chimpanzee to sit down and shut up, which probably requires replicating the systems' conditions more faithfully in training. Yes, a simulator captures the aircraft system's condition very accurately, I'm not disputing that, but it's not obvious that it's capturing the human system's condition. Specifically, I would imagine that the chimpanzee learns very quickly that the simulator is essentially safe and it has nothing to worry about, so it doesn't flip out if it suspects the simulator is about to crash. In a real in-flight emergency, that's not going to be the case, so pilots probably should be explicitly trained to manage their own minds and bodies in emergency situations to prevent the chimp from taking over.

One possible solution (on which there is probably a bunch of research that may show it to be a very poor idea) would be to hook crews up to an IV line in sim training, and give them a massive slug of adrenaline when they first realise something is wrong. Their body is then going to want to drop into a classic fight-or-flight response; given that a stall can neither be run away from nor punched to death, this is unproductive, so you'd want to train pilots to manage this physiological process so they can get back to applying their rational-mind training as quickly as possible, and fly the damn plane. If they don't have this training, it's not surprising that they're failing at this in real life, and if that's the case then all the sim time and process-knowledge in the world isn't going to save them.
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Old 3rd May 2019, 10:21
  #4777 (permalink)  
 
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I confess I have not read ALL the previous posts. I trust I am not treading on anyone's toes here. Pitch-power-speed is the go-to mantra for most of us who learned to fly with an AVGAS engine, a fixed pitch propeller in front of us and an instructor to our right. However, when the aircraft misbehaves in an unexpected fashion not mentioned in any QRH or training manual then the sense of disorientation, surprise, incredulity, inadequacy, anger, and frustration will swamp the brain and preclude all rational thought. Disengaging the auto-pilot, leveling the wings, looking for the horizon, and applying 75% of available power will still appear to the observer as a failed exercise and lead to further confusion etc, intensifying the cycle until utter hopelessness swamps the poor pilot. Imho, these two MAX 8 crashes were design faults and Boeing is squarely to blame for the failure to engage with owners regarding the subtle changes to the anti-stall system. I am glad I was not on board because even though we can all sit here and imagine that we would have done it differently, many of us might not.
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Old 3rd May 2019, 10:48
  #4778 (permalink)  
 
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Originally Posted by derjodel View Post
An undocumented system of which the pilots have no clue it even exists can interrupt airplane trim. If the pilot doesn't want to end in a coffin corner, they need to figure out on the spot that:
- this is not STS
- because it's not STS it must be either a bug or an undocumented system
- to save their lives they need to return the trim manually to a low/zero column force each time the undocumented command is triggered.

Despite facing those conditions, the Lion Air crew managed to react appropriately about 2 dozen cycles. Fighting the unknown system raised pilot's adrenaline and fear and induced panic. Thus, incapacitated by stress put on them, they no longer managed to manually correct the erroneous system input that was trying to - and succeeded to - kill them.
I want to be clear I was simply answering a previous poster's question about how MCAS worked, and not attempting to defend the system design.

Regarding your last paragraph, one theory is that for some reason the pilot who had been successfully countering MCAS for 24 cycles transferred control to the other pilot, who did not put in sufficiently large opposite trim inputs and lost it in three cycles.
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Old 3rd May 2019, 11:47
  #4779 (permalink)  
 
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Originally Posted by ottorot8 View Post


Sorry, but your wrong. I’ve been flying 737’s for the last 28+ years. That covers the 200, 300, 500, 700, 800 and I have about a dozen flights in the Max8. You could take about 70-80% of just the -200 cockpit and use it for spare parts on a Max8. Same switches, gauges, lights, etc. The list goes on.
Yes, the overhead panel is 1960’s but the cockpit displays, FMS, engines, wings, and other major components sure aren’t. The point is not a part by part count but the major components of the MAX are completely different than the -100 even to the extent that one could legitimately not call it a B737.
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Old 3rd May 2019, 11:55
  #4780 (permalink)  
 
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Originally Posted by derjodel View Post
Was it? By this definition, isn't any STS operation a trim runaway?
Runaway Stabilizer: Uncommanded stabilizer trim movement occurs continuously. (Source B737 NNC)
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