Ethiopian airliner down in Africa
It seems clear from the posts of various experienced 737 pilots that both sets of pilots messed up, didn't follow clear NNCs and are therefore solely and exclusively responsible for tarring Boeing's reputation and causing such unnecessary alarm that the 737 MAX was grounded. Obviously this would never have happened with US, European or Australian pilots who would have done the right thing. Since it's clear that there is nothing that Boeing can do to bring pilots from Asia and Africa up to the afore mentioned standards the solution is obvious. Just don't sell Boeings to Asia and Africa with perhaps the odd exception for Japan and Singapore. Job done!
What's that you say? Boeing says they have a problem with that because they won't make a big enough profit and that would leave the field open to Airbus? Surely that would just mean Airbus aircraft crashing with the consequent deep smelly stuff and no skin off Boeing nose? Still not good enough? Well I suppose Boeing will just have to change their assumptions about what pilots will and won't do and then design their aircraft and associated documentation so pilots from all continents will follow the correct action(s) and not crash their Boeing aircraft. After Boeing's a business and a key purpose of business is to make money.
N.B. In case you haven't twigged it yet I very much do not repeat not hold the views expressed in the first two sentences.
What's that you say? Boeing says they have a problem with that because they won't make a big enough profit and that would leave the field open to Airbus? Surely that would just mean Airbus aircraft crashing with the consequent deep smelly stuff and no skin off Boeing nose? Still not good enough? Well I suppose Boeing will just have to change their assumptions about what pilots will and won't do and then design their aircraft and associated documentation so pilots from all continents will follow the correct action(s) and not crash their Boeing aircraft. After Boeing's a business and a key purpose of business is to make money.
N.B. In case you haven't twigged it yet I very much do not repeat not hold the views expressed in the first two sentences.
Last edited by SamYeager; 7th Apr 2019 at 13:01. Reason: Typos
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Very much in agreement.
The Human Factors are, IMO, the most important/interesting part of these accidents.
To recap: There are many situations which require some sort of action from pilots, be it promptly or after consideration. The more time-critical an event is, the less time/capacity there is to figure out what to do, so responses to predictable events are based more on rules than extended cognition, hence “memory” or “recall” items are used. They need to have a simple, unambiguous trigger, e.g. an engine fails below V1, perform an RTO or GPWS says “PULL UP!”, perform the GPWS pull up manoeuvre.
When the situation is more complex and there is normally time for diagnosis, we have reference checklists which may contain decision trees, often leading to different actions and outcomes, dependent on further data. If no checklist really fits the bill completely, maybe due to multiple failures or unusual circumstances, then you need to use your general aviation understanding, backed up by specific type knowledge and all the resources you have access to in order to formulate and execute a plan of action. This is something you would generally do *after* you had determined there were no published normal or non-normal produces that were applicable, or you had applied the procedures and they had not helped or made the situation worse. Boeing specifically caution against “troubleshooting” unless all other possibilities have been exhausted but they also provide a useful “Situations Beyond the Scope of Non-Normal Checklists” guide in their training manuals.
Now, it is good aviation practice to have some kind of action associated with a single, predictable failure which affects the safe operation of the airframe, be it recall items or a reference checklist, or even just a note for crew awareness. In the case we are discussing, an AoA probe failure (which is singular, predictable and measurable) has caused a cascade of issues and warnings that are difficult to assimilate and don’t immediately point to any particular checklist, except maybe the Airspeed Unreliable one, which doesn’t include deactivating the trim. Remember we are looking at these accidents with hindsight and the warnings that occurred can be triggered by many different events that require different responses - we only know which was the correct path to take because we have most of the data in front of us to peruse at leisure.
There have been quite a few posts highlighting the startle effect plus the saturation of input channels by excess information of questionable usefulness, e.g. stick shaker, GPWS, fault messages, high control loadings, etc. It is quite easy to see how some things were missed, in fact most of the above is taught in basic HF modules but this seems have passed some manufacturers by.
It’s easy to say that you’d have disconnected the trim as soon as you got a stick shake in the climb out because the flaps are correct and power is set. Well done. But supposing that was a *real* stall warning because you put the wrong weights in the FMC so have rotated 20kts early? Not so well done now, eh? This has happened before and will happen again and is just one example of why it is so important NOT to rush to conclusions if you can absolutely help it.
The Human Factors are, IMO, the most important/interesting part of these accidents.
To recap: There are many situations which require some sort of action from pilots, be it promptly or after consideration. The more time-critical an event is, the less time/capacity there is to figure out what to do, so responses to predictable events are based more on rules than extended cognition, hence “memory” or “recall” items are used. They need to have a simple, unambiguous trigger, e.g. an engine fails below V1, perform an RTO or GPWS says “PULL UP!”, perform the GPWS pull up manoeuvre.
When the situation is more complex and there is normally time for diagnosis, we have reference checklists which may contain decision trees, often leading to different actions and outcomes, dependent on further data. If no checklist really fits the bill completely, maybe due to multiple failures or unusual circumstances, then you need to use your general aviation understanding, backed up by specific type knowledge and all the resources you have access to in order to formulate and execute a plan of action. This is something you would generally do *after* you had determined there were no published normal or non-normal produces that were applicable, or you had applied the procedures and they had not helped or made the situation worse. Boeing specifically caution against “troubleshooting” unless all other possibilities have been exhausted but they also provide a useful “Situations Beyond the Scope of Non-Normal Checklists” guide in their training manuals.
Now, it is good aviation practice to have some kind of action associated with a single, predictable failure which affects the safe operation of the airframe, be it recall items or a reference checklist, or even just a note for crew awareness. In the case we are discussing, an AoA probe failure (which is singular, predictable and measurable) has caused a cascade of issues and warnings that are difficult to assimilate and don’t immediately point to any particular checklist, except maybe the Airspeed Unreliable one, which doesn’t include deactivating the trim. Remember we are looking at these accidents with hindsight and the warnings that occurred can be triggered by many different events that require different responses - we only know which was the correct path to take because we have most of the data in front of us to peruse at leisure.
There have been quite a few posts highlighting the startle effect plus the saturation of input channels by excess information of questionable usefulness, e.g. stick shaker, GPWS, fault messages, high control loadings, etc. It is quite easy to see how some things were missed, in fact most of the above is taught in basic HF modules but this seems have passed some manufacturers by.
It’s easy to say that you’d have disconnected the trim as soon as you got a stick shake in the climb out because the flaps are correct and power is set. Well done. But supposing that was a *real* stall warning because you put the wrong weights in the FMC so have rotated 20kts early? Not so well done now, eh? This has happened before and will happen again and is just one example of why it is so important NOT to rush to conclusions if you can absolutely help it.
Your explanation on how things are resolved in a modern day cockpit makes for a very interesting read and should be part of the curriculum for any up and coming MCC/JOC student. It should also be interesting for the laypeople frequenting these pages. For a professional airline pilot it should be obvious.
I agree with you that Human Factors is a subject of much interest and it is also where I feel I still have the most to learn about the Ethiopean accident. As much as I hate this MAX software addition and its capabilities, I do think I have picked up on the significant features of the MCAS and further detail on it would most likely not have had any influence on how I would deal with an "MCAS Runaway Stabilizer" or whatever we end up calling this scenario.
Although some contributors on this forum have a less than diplomatic way of stating certain facts and assumptions about the crew's actions and inactions I don't think this should be interpreted as putting the whole blame on the crew. Not even close. But there certainly is a lot to be explored following the statement by Ethiopean officials that the crew "followed expected procedures" implying there are no issues whatsover concerning the crew's way of dealing with the problems of this flight. And it is in this space I believe some posters in here get a little bit agitated, trying to get that point across.
There certainly were a number of crossroads at which catastrophy could have been avoided on ET302, especially up to the point of flap retraction and a bit, and from a Human Factors perspective it is extremely interesting to learn why certain choices were made. We all know that the company culture of an airline and also the culture of countries/regions greatly influence how we behave, both as people and as pilots. This has nothing to do with the "supremancy of the Western pilot" or however some may want to phrase it in these times of identity politics.
But when countries ban unions, when people are fired for having opposing views to those of their superiors, when airlines ban handflying within the autopilot envelope and mandate autolands, when airlines have the captain always be the Pilot Flying, when one thousand airline flying hours may entail only a dozen or two actual take-offs and landings.... If you become financially penalized or limited in your career advancement due to non-compliance with said policies, you know there are issues that need to be addressed. I don't think it should be perceived as offensive to ask if any of these or other factors were important when it comes to understanding why a seemingly experienced captain would try to engage the autopilot at 400'AGL while the stickshaker is going off? And why choose the onside autopilot? Why clean up? Regardless of any NNC memory/recall items or checklists, why not establish a known and safe pitch/thrust setting and fly the aircraft? Does everything boil down to "the startle effect" when at first the stick shaker goes off and then later the AP trips off at the same time they clean up? These are not unreasonable questions to ask.
It is a sad fact that whoever is left holding the matches when the house burns down will be looked at with much scrutiny - even by his friends.
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I think it would be somewhat unlikely for liability to be attributed to Ethiopian Airlines for failing to doubt the safety of a brand new aircraft from a major manufacturer that had been certified as safe by the regulator. To my mind, operators buying aircraft are entited to rely on the assurances of a competent authority that design and manufacture complies fully with the standards that have been laid down. This is the fundamental principle behind the certification process - the standards are there to ensure safety, and purchasers should therefore be confident that the equipment satisfies their duty of care to pax and crew in this regard.
QUOTE] If, on the other hand, by “operator” you mean the particular pilots involved, well, in my opinion, pilots have a personal obligation to maintain a standard on top of that required by their employer and their regulator.
QUOTE] If, on the other hand, by “operator” you mean the particular pilots involved, well, in my opinion, pilots have a personal obligation to maintain a standard on top of that required by their employer and their regulator.
The good news for aviation safety is that these two accidents have shown a bright lite on aircraft design and certification. The liability question can be answered at this point. Regardless of how poor the skills ,training or supervision of the crews might be proven to be, the aircraft design led directly to the accidents. The fact that a well trained crew on Monday morning, could possibly have recovered the aircraft successfully, will not be relevant in shifting the major liability.
As far as the future of the 737 Max, hopefully Boeing will be required to do enough recertification to prove that no automated system can put the aircraft in an unrecoverable configuration, in other words, that the manual stab trim wheel can reasonably be used even at high speed, high g load and high elevator forces. Also they will need to find a simple way of allowing the crew to quickly analyse compounding failures.
in reviewing the performance of the crew, it cannot be over emphasized how disorienting multiple failure manifestations can be. If a crew does not fight an aggressive mental battle, fixation occurs quickly. For example, real stick shaker is rarely encountered. When it is, you are usually aware that you are approaching a limit anyway, perhaps slowing and near a flap extension speed and you hit some turbulence that gives you a momentary stick shaker. This is not alarming. But if you do not have a clue why you have a stick shaker, it is very distracting. In olden times the only way to get rid of it was to find the CB. Then you add other stall warning lights and sounds, if there is no way to rapidly get rid of erroneous warnings they take a toll on your mental state. A Navy flight instructor once told me that the first step in any emergency procedure was, "wind the clock." I don't think he was serious but the point is to maintain initiative. First due no harm. Do common sense things. Silence unneeded sound and get rid of warnings. Then confirm situational awareness. Altitude, terrain, speed, attitude, power setting, configuration, standby instruments. Make appropriate corrections, if not stable, get stable. This process, for an experienced pilot takes seconds.
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It's interesting that the Lion Air crew on the flight before the accident also raised the flaps while having unreliable airspeed and the stick shaker. So 3 out of 3 of the crews experiencing the failed AOA sensor did this.
Looking at the FDR traces for the previous Lion Air flight, one difference is that they also enabled the A/P, on the F/O side, when they retracted the flaps. The Ethiopian crew enabled A/P on the captain's side, and started retracting the flaps about 20 seconds later.
In both cases, MCAS activated after the A/P deactivated. For the previous Lion Air flight the fight with MCAS lasted over 4 minutes before they used the cutout switches. For the Ethiopian flight it lasted only 30 seconds.
Another difference for the Lion Air crew that saved the aircraft is that they did the unreliable air speed checklist, according to the preliminary report. And while we can't determine from the FDR trace of the previous Lion Air flight what their exact speeds were, it probably resulted in a more manageable speed.
Both crews later re-enabled electric trim (the Lion Air crew temporarily). And there is nothing in the runaway stabilizer memory items explicitly saying you should not re-enable electric trim. It does however explicitly say that for the autopilot and autothrottle: "Do not re-engage the autopilot." "Do not re-engage the autothrottle".
And, from the FDR traces, the Lion Air crew that saved the aircraft also didn't bring the aircraft to neutral trim before using the cutout switches. And later they did just what the Ethiopian crew did seconds before the crash: they re-enabled electric trim, they started trimming ANU, and MCAS started trimming AND again. Then they used the cutout switches again to stop the runway, again without bringing the aircraft to neutral trim with the thumb switches first. Then they trimmed with the trim wheels for the remainder of the flight.
I can't help but wonder if their knowledge about MCAS is what contributed significantly to the Ethiopian accident, by making them prioritize the stabilizer runaway memory items over everything else, making them tunnel vision and focus on the trim problems primarily, and ignoring other issues, like the increasing speed, and the need to perform other checklists.
Looking at the FDR traces for the previous Lion Air flight, one difference is that they also enabled the A/P, on the F/O side, when they retracted the flaps. The Ethiopian crew enabled A/P on the captain's side, and started retracting the flaps about 20 seconds later.
In both cases, MCAS activated after the A/P deactivated. For the previous Lion Air flight the fight with MCAS lasted over 4 minutes before they used the cutout switches. For the Ethiopian flight it lasted only 30 seconds.
Another difference for the Lion Air crew that saved the aircraft is that they did the unreliable air speed checklist, according to the preliminary report. And while we can't determine from the FDR trace of the previous Lion Air flight what their exact speeds were, it probably resulted in a more manageable speed.
Both crews later re-enabled electric trim (the Lion Air crew temporarily). And there is nothing in the runaway stabilizer memory items explicitly saying you should not re-enable electric trim. It does however explicitly say that for the autopilot and autothrottle: "Do not re-engage the autopilot." "Do not re-engage the autothrottle".
And, from the FDR traces, the Lion Air crew that saved the aircraft also didn't bring the aircraft to neutral trim before using the cutout switches. And later they did just what the Ethiopian crew did seconds before the crash: they re-enabled electric trim, they started trimming ANU, and MCAS started trimming AND again. Then they used the cutout switches again to stop the runway, again without bringing the aircraft to neutral trim with the thumb switches first. Then they trimmed with the trim wheels for the remainder of the flight.
I can't help but wonder if their knowledge about MCAS is what contributed significantly to the Ethiopian accident, by making them prioritize the stabilizer runaway memory items over everything else, making them tunnel vision and focus on the trim problems primarily, and ignoring other issues, like the increasing speed, and the need to perform other checklists.
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It seems clear from the posts of various experienced 737 pilots that both sets of pilots messed up, didn't follow clear NNCs and are therefore solely and exclusively responsible for tarring Boeing's reputation and causing such unnecessary alarm that the 737 MAX was grounded.
Boeing ARE responsible for a poorly designed system, I've yet to meet anyone who doesn't feel the MCAS should not have been certified, allowed to work from a single sensor or able to make the level of input that it does.
Where the difference of opinion lies is that Boeing are solely responsible, particularly for the Ethiopian crash. Their press release stated that all procedures were followed and press around the world are stating as fact that this was completely the fault of the aircraft.
Looking at the information released it is hard to agree. Procedures were not followed. Control of the aircraft was not maintained. The crew had direct control over the stabilizer (apart from when the cutouts were used) at all times. Flying the aircraft is the most basic aspect of our job and the most important.
My final post on this topic.
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Following this thread and others on other forums I've seen the reason for MCAS explained and occasionally debated and I'm left with a question about the decision making that determined that software that controlled the trim was the best way to manipulate stick feel.
My understanding is that MCAS applies AND in order to comply with the regulation requirement that says that the stick pressure must feel a certain way as the aircraft's nose pitches upwards. If it's only the "feel" of flying the aircraft that needs to be changed why not write software that applies forces to the controls themselves instead of applying sporadic input to one of the main pieces that keeps the plane balanced in flight?
My understanding is that MCAS applies AND in order to comply with the regulation requirement that says that the stick pressure must feel a certain way as the aircraft's nose pitches upwards. If it's only the "feel" of flying the aircraft that needs to be changed why not write software that applies forces to the controls themselves instead of applying sporadic input to one of the main pieces that keeps the plane balanced in flight?
I disagree....
Boeing ARE responsible for a poorly designed system, I've yet to meet anyone who doesn't feel the MCAS should not have been certified, allowed to work from a single sensor or able to make the level of input that it does.
Where the difference of opinion lies is that Boeing are solely responsible, particularly for the Ethiopian crash. Their press release stated that all procedures were followed and press around the world are stating as fact that this was completely the fault of the aircraft.
Looking at the information released it is hard to agree. Procedures were not followed. Control of the aircraft was not maintained. The crew had direct control over the stabilizer (apart from when the cutouts were used) at all times. Flying the aircraft is the most basic aspect of our job and the most important.
My final post on this topic.
Boeing ARE responsible for a poorly designed system, I've yet to meet anyone who doesn't feel the MCAS should not have been certified, allowed to work from a single sensor or able to make the level of input that it does.
Where the difference of opinion lies is that Boeing are solely responsible, particularly for the Ethiopian crash. Their press release stated that all procedures were followed and press around the world are stating as fact that this was completely the fault of the aircraft.
Looking at the information released it is hard to agree. Procedures were not followed. Control of the aircraft was not maintained. The crew had direct control over the stabilizer (apart from when the cutouts were used) at all times. Flying the aircraft is the most basic aspect of our job and the most important.
My final post on this topic.
It’s fine when things are normal, deadly when they are not. It was not designed for fault tolerance. If AOA inputs are invalid, perhaps with IAS disagree, the initial procedures (pitch & power), coupled with unwanted nose down trim will naturally lead pilots to maintain proper pitch, speed increases, MCAS trim down more and on and on. Pilots hit Trim Cutout and are left with manual (slow) trim which becomes increasingly difficult to use as speed increases, until it becomes impossible. Can’t unload (nose down) at 1000 feet, and there’s too much nose down trim to control the airplane.
Hi FullWings.
Your explanation on how things are resolved in a modern day cockpit makes for a very interesting read and should be part of the curriculum for any up and coming MCC/JOC student. It should also be interesting for the laypeople frequenting these pages. For a professional airline pilot it should be obvious.
I agree with you that Human Factors is a subject of much interest and it is also where I feel I still have the most to learn about the Ethiopean accident. As much as I hate this MAX software addition and its capabilities, I do think I have picked up on the significant features of the MCAS and further detail on it would most likely not have had any influence on how I would deal with an "MCAS Runaway Stabilizer" or whatever we end up calling this scenario.
Although some contributors on this forum have a less than diplomatic way of stating certain facts and assumptions about the crew's actions and inactions I don't think this should be interpreted as putting the whole blame on the crew. Not even close. But there certainly is a lot to be explored following the statement by Ethiopean officials that the crew "followed expected procedures" implying there are no issues whatsover concerning the crew's way of dealing with the problems of this flight. And it is in this space I believe some posters in here get a little bit agitated, trying to get that point across.
There certainly were a number of crossroads at which catastrophy could have been avoided on ET302, especially up to the point of flap retraction and a bit, and from a Human Factors perspective it is extremely interesting to learn why certain choices were made. We all know that the company culture of an airline and also the culture of countries/regions greatly influence how we behave, both as people and as pilots. This has nothing to do with the "supremancy of the Western pilot" or however some may want to phrase it in these times of identity politics.
But when countries ban unions, when people are fired for having opposing views to those of their superiors, when airlines ban handflying within the autopilot envelope and mandate autolands, when airlines have the captain always be the Pilot Flying, when one thousand airline flying hours may entail only a dozen or two actual take-offs and landings.... If you become financially penalized or limited in your career advancement due to non-compliance with said policies, you know there are issues that need to be addressed. I don't think it should be perceived as offensive to ask if any of these or other factors were important when it comes to understanding why a seemingly experienced captain would try to engage the autopilot at 400'AGL while the stickshaker is going off? And why choose the onside autopilot? Why clean up? Regardless of any NNC memory/recall items or checklists, why not establish a known and safe pitch/thrust setting and fly the aircraft? Does everything boil down to "the startle effect" when at first the stick shaker goes off and then later the AP trips off at the same time they clean up? These are not unreasonable questions to ask.
It is a sad fact that whoever is left holding the matches when the house burns down will be looked at with much scrutiny - even by his friends.
Your explanation on how things are resolved in a modern day cockpit makes for a very interesting read and should be part of the curriculum for any up and coming MCC/JOC student. It should also be interesting for the laypeople frequenting these pages. For a professional airline pilot it should be obvious.
I agree with you that Human Factors is a subject of much interest and it is also where I feel I still have the most to learn about the Ethiopean accident. As much as I hate this MAX software addition and its capabilities, I do think I have picked up on the significant features of the MCAS and further detail on it would most likely not have had any influence on how I would deal with an "MCAS Runaway Stabilizer" or whatever we end up calling this scenario.
Although some contributors on this forum have a less than diplomatic way of stating certain facts and assumptions about the crew's actions and inactions I don't think this should be interpreted as putting the whole blame on the crew. Not even close. But there certainly is a lot to be explored following the statement by Ethiopean officials that the crew "followed expected procedures" implying there are no issues whatsover concerning the crew's way of dealing with the problems of this flight. And it is in this space I believe some posters in here get a little bit agitated, trying to get that point across.
There certainly were a number of crossroads at which catastrophy could have been avoided on ET302, especially up to the point of flap retraction and a bit, and from a Human Factors perspective it is extremely interesting to learn why certain choices were made. We all know that the company culture of an airline and also the culture of countries/regions greatly influence how we behave, both as people and as pilots. This has nothing to do with the "supremancy of the Western pilot" or however some may want to phrase it in these times of identity politics.
But when countries ban unions, when people are fired for having opposing views to those of their superiors, when airlines ban handflying within the autopilot envelope and mandate autolands, when airlines have the captain always be the Pilot Flying, when one thousand airline flying hours may entail only a dozen or two actual take-offs and landings.... If you become financially penalized or limited in your career advancement due to non-compliance with said policies, you know there are issues that need to be addressed. I don't think it should be perceived as offensive to ask if any of these or other factors were important when it comes to understanding why a seemingly experienced captain would try to engage the autopilot at 400'AGL while the stickshaker is going off? And why choose the onside autopilot? Why clean up? Regardless of any NNC memory/recall items or checklists, why not establish a known and safe pitch/thrust setting and fly the aircraft? Does everything boil down to "the startle effect" when at first the stick shaker goes off and then later the AP trips off at the same time they clean up? These are not unreasonable questions to ask.
It is a sad fact that whoever is left holding the matches when the house burns down will be looked at with much scrutiny - even by his friends.
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The primary problem is the design. PERIOD
It’s fine when things are normal, deadly when they are not. It was not designed for fault tolerance. If AOA inputs are invalid, perhaps with IAS disagree, the initial procedures (pitch & power), coupled with unwanted nose down trim will naturally lead pilots to maintain proper pitch, speed increases, MCAS trim down more and on and on. Pilots hit Trim Cutout and are left with manual (slow) trim which becomes increasingly difficult to use as speed increases, until it becomes impossible. Can’t unload (nose down) at 1000 feet, and there’s too much nose down trim to control the airplane.
It’s fine when things are normal, deadly when they are not. It was not designed for fault tolerance. If AOA inputs are invalid, perhaps with IAS disagree, the initial procedures (pitch & power), coupled with unwanted nose down trim will naturally lead pilots to maintain proper pitch, speed increases, MCAS trim down more and on and on. Pilots hit Trim Cutout and are left with manual (slow) trim which becomes increasingly difficult to use as speed increases, until it becomes impossible. Can’t unload (nose down) at 1000 feet, and there’s too much nose down trim to control the airplane.
This certification statement about the authority of the trim wheel over the entire flight envelope is certainly not correct, if the trim wheel cannot be cranked ANU at 10000 ft, 320 KIAS.
The holes line up in the cheese: Boeing, crew, FAA, EASA, ...
Litigation - where Boeing will claim that QRHs, NNCs are more a recommendation for great independant airmen, while Lion/ET and victims lawyers will claim that a manual/NNC is to be followed exactly, including what's not in there shall not be done.
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[Not a pilot] From one of the documents on the Ethiopian Preliminary Report: "If relaxing the column causes the trim to move, set stabilizer trim switches to CUTOUT."
So, if relaxing the column does not allow trim to be moved, what then? Slow down? Immelmann? Something else?
Or does this sentence not apply to the possibility of manual trim? The word "causes" rather than "allows." Is this sentence merely a method of determining whether you have a classic trim runaway? That is, if the runaway stops because the jackscrew is binding, you can confirm this by letting off column back pressure. If trim continues, yep, you have a classic runaway. If no more trim, the runaway has stopped for now.
In either reading, is Boeing not saying that the jackscrew might bind around the time a pilot might be contemplating hand cranking?
So, if relaxing the column does not allow trim to be moved, what then? Slow down? Immelmann? Something else?
Or does this sentence not apply to the possibility of manual trim? The word "causes" rather than "allows." Is this sentence merely a method of determining whether you have a classic trim runaway? That is, if the runaway stops because the jackscrew is binding, you can confirm this by letting off column back pressure. If trim continues, yep, you have a classic runaway. If no more trim, the runaway has stopped for now.
In either reading, is Boeing not saying that the jackscrew might bind around the time a pilot might be contemplating hand cranking?
Last edited by fotoguzzi; 7th Apr 2019 at 17:56. Reason: add interpretation
As I stated earlier, nobody is sure of the actual envelope where electric trim and manual trim are assured, including on the 737NGs that are operating today. If I was representing an AOC holder I would be seeking urgent clarification of the trimmable flight envelope for the current 737 family.
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It is not the stall charectoristics. The B737 MAX has pitch up tendencies which don’t meet FAA Static Longitudinal Stability certification standards. To meet the standard, MCAS was needed to reduce the pitch up tendency at high angles of attack.
Addtional sim training won’t exempt you from meeting the certification standard.
Sec. 25.173 Static longitudinal stability.
Under the conditions specified in Sec. 25.175, the characteristics of the elevator control forces (including friction) and the elevator control surface displacement must be as follows:
(a) A pull must be required to obtain and maintain speeds below the specified trim speed, and a push must be required to obtain and maintain speeds above the specified trim speed. In addition, if the elevator control forces are not dependent upon the hinge moments of the elevator control surface, it must also be shown that upward displacement of the elevator trailing edge is required to obtain and maintain speeds below the specified trim speed, and a downward displacement of the elevator trailing edge is required to obtain and maintain speeds above the specified trim speed. This must be shown at any speed that can be obtained except speeds higher than the landing gear or wing flap operating limit speeds or VFC / MFC , whichever is appropriate, or lower than the minimum speed for steady, unstalled flight.
(b) The airspeed must return to within 10 percent of the original trim speed when the control force is slowly released from any speed within the range specified in paragraph (a) of this section.
(c) The stable slope of the stick force versus speed curve may not be less than 0.5 pound for each three knots or exceed a value beyond which control of the airplane is difficult.
Sec. 25.173 Static longitudinal stability.
Under the conditions specified in Sec. 25.175, the characteristics of the elevator control forces (including friction) and the elevator control surface displacement must be as follows:
(a) A pull must be required to obtain and maintain speeds below the specified trim speed, and a push must be required to obtain and maintain speeds above the specified trim speed. In addition, if the elevator control forces are not dependent upon the hinge moments of the elevator control surface, it must also be shown that upward displacement of the elevator trailing edge is required to obtain and maintain speeds below the specified trim speed, and a downward displacement of the elevator trailing edge is required to obtain and maintain speeds above the specified trim speed. This must be shown at any speed that can be obtained except speeds higher than the landing gear or wing flap operating limit speeds or VFC / MFC , whichever is appropriate, or lower than the minimum speed for steady, unstalled flight.
(b) The airspeed must return to within 10 percent of the original trim speed when the control force is slowly released from any speed within the range specified in paragraph (a) of this section.
(c) The stable slope of the stick force versus speed curve may not be less than 0.5 pound for each three knots or exceed a value beyond which control of the airplane is difficult.
"
"The B737 MAX has pitch up tendencies which don’t meet FAA Static Longitudinal Stability certification standards. To meet the standard, MCAS was needed to reduce the pitch up tendency at high angles of attack."Presumably this is because they have gone and under slung the engines way ahead of the LE of the wings which would make the whole thing go tits up in no time at all, if you get a bit excitable and give a generous helping with stick and power. So to guard against the ham- fisted, they have come up with a little thing clever bit of electronic wizardry and named it MCAS. The end result seems so far to be the Correction bit of it is worse than that which could have been achieved by the ham -fisted.
It's worth pointing out US commercial aviation did not suddenly burst into being as is now the case but it evolved. Let's face it surely any "halfwit" would know better than to get near to the plane in front to try to melt the snow on the wings right?
20/20 hindsight is not something pilots find particularly useful on the day
Yes, it doesn’t say “must”. It also doesn’t say “must not”. Given that there is a reminder there that it CAN be used prior to cutout, what would be the reason for NOT using it to fully counter the MCAS? Aside from the design failures themselves, a key to this accident is why weren’t they trimming up as far as they needed to? I know it’s been asked numerous times already in this thread, but it is perplexing.
BTW, it does say at the very start of the trim runaway (in the AD not the abbreviated memory item procedure) to disconnect the autopilot and control pitch with column and electric trim. That’s not a “may” or “can”.
In the MCAS context, you're now asked to decide that you can't trust it, but then maybe keep trusting it until you've got back in trim, then cut it off. If you can't trust the electric trim, and you need to cut it off, it's very strange to have to trust it a while more. If you can trust it, why are you even turning it off?
The 737NG procedure, as someone pointed out, identifies whether the automation or the electric drive is the problem. This detail seems more and more important.
It's interesting that the Lion Air crew on the flight before the accident also raised the flaps while having unreliable airspeed and the stick shaker. So 3 out of 3 of the crews experiencing the failed AOA sensor did this.
Looking at the FDR traces for the previous Lion Air flight, one difference is that they also enabled the A/P, on the F/O side, when they retracted the flaps. The Ethiopian crew enabled A/P on the captain's side, and started retracting the flaps about 20 seconds later.
In both cases, MCAS activated after the A/P deactivated. For the previous Lion Air flight the fight with MCAS lasted over 4 minutes before they used the cutout switches. For the Ethiopian flight it lasted only 30 seconds.
Another difference for the Lion Air crew that saved the aircraft is that they did the unreliable air speed checklist, according to the preliminary report. And while we can't determine from the FDR trace of the previous Lion Air flight what their exact speeds were, it probably resulted in a more manageable speed.
Both crews later re-enabled electric trim (the Lion Air crew temporarily). And there is nothing in the runaway stabilizer memory items explicitly saying you should not re-enable electric trim. It does however explicitly say that for the autopilot and autothrottle: "Do not re-engage the autopilot." "Do not re-engage the autothrottle".
And, from the FDR traces, the Lion Air crew that saved the aircraft also didn't bring the aircraft to neutral trim before using the cutout switches. And later they did just what the Ethiopian crew did seconds before the crash: they re-enabled electric trim, they started trimming ANU, and MCAS started trimming AND again. Then they used the cutout switches again to stop the runway, again without bringing the aircraft to neutral trim with the thumb switches first. Then they trimmed with the trim wheels for the remainder of the flight.
I can't help but wonder if their knowledge about MCAS is what contributed significantly to the Ethiopian accident, by making them prioritize the stabilizer runaway memory items over everything else, making them tunnel vision and focus on the trim problems primarily, and ignoring other issues, like the increasing speed, and the need to perform other checklists.
Looking at the FDR traces for the previous Lion Air flight, one difference is that they also enabled the A/P, on the F/O side, when they retracted the flaps. The Ethiopian crew enabled A/P on the captain's side, and started retracting the flaps about 20 seconds later.
In both cases, MCAS activated after the A/P deactivated. For the previous Lion Air flight the fight with MCAS lasted over 4 minutes before they used the cutout switches. For the Ethiopian flight it lasted only 30 seconds.
Another difference for the Lion Air crew that saved the aircraft is that they did the unreliable air speed checklist, according to the preliminary report. And while we can't determine from the FDR trace of the previous Lion Air flight what their exact speeds were, it probably resulted in a more manageable speed.
Both crews later re-enabled electric trim (the Lion Air crew temporarily). And there is nothing in the runaway stabilizer memory items explicitly saying you should not re-enable electric trim. It does however explicitly say that for the autopilot and autothrottle: "Do not re-engage the autopilot." "Do not re-engage the autothrottle".
And, from the FDR traces, the Lion Air crew that saved the aircraft also didn't bring the aircraft to neutral trim before using the cutout switches. And later they did just what the Ethiopian crew did seconds before the crash: they re-enabled electric trim, they started trimming ANU, and MCAS started trimming AND again. Then they used the cutout switches again to stop the runway, again without bringing the aircraft to neutral trim with the thumb switches first. Then they trimmed with the trim wheels for the remainder of the flight.
I can't help but wonder if their knowledge about MCAS is what contributed significantly to the Ethiopian accident, by making them prioritize the stabilizer runaway memory items over everything else, making them tunnel vision and focus on the trim problems primarily, and ignoring other issues, like the increasing speed, and the need to perform other checklists.
Psychophysiological entity
It is, and I still beg the question as to whether the five seconds pause applies upon resetting the Stab supply switches.
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MCAS activated even after cutout, it is visible in the FDR traces, but was unable to move the stab because of the cutout. It was a single full 10 sec. intervention and did not repeat again because was not reset by the thumb switches operation. Looking at the schematics and the description of the system, i would speculate that it will not activate upon resetting the stab supply switches, unless there is a thumb operation, in such case it will pause for 5 seconds.
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Design for WORST airmen
Designing civil air transport aircraft for great airmen is completely out of the question. Don't even think about it!
The primary problem is the design. PERIOD
It’s fine when things are normal, deadly when they are not. It was not designed for fault tolerance. If AOA inputs are invalid, perhaps with IAS disagree, the initial procedures (pitch & power), coupled with unwanted nose down trim will naturally lead pilots to maintain proper pitch, speed increases, MCAS trim down more and on and on. Pilots hit Trim Cutout and are left with manual (slow) trim which becomes increasingly difficult to use as speed increases, until it becomes impossible. Can’t unload (nose down) at 1000 feet, and there’s too much nose down trim to control the airplane.