MAX’s Return Delayed by FAA Reevaluation of 737 Safety Procedures
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Only a bit off subject
RE cluster ...
Seems to me testing - analysis of MCAS meets the above definition re sampling.
But implementation and description ( lack of ) meets the alternate use of Cluster F . . .
RE cluster ...
Cluster Sampling. Cluster sampling refers to a type of sampling method . With cluster sampling, the researcher divides the population into separate groups, called clusters. Then, a simple random sample of clusters is selected from the population.
But implementation and description ( lack of ) meets the alternate use of Cluster F . . .
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On December 12, LowObservable gave a link to an article from “The Air Current”.
The article describes “week-long trials inside Boeing’s 737 Max engineering simulator focused on the human response to a variety of angle of attack indication failures and disagreements in real-world scenarios, in takeoff, landing and at cruise ...”
The article continues, “During the recent pilot trials, which tested how crews react to various scenarios involving the revised 737 Max flight control software and new checklists, all the pilots managed to get themselves out of trouble, but Boeing and regulators found that “more than half of pilots responded with the wrong procedures,” according to one of the three people briefed on the results ... “Troubleshooting the failure presented wasn’t intuitive based on the checklist,” said another person familiar with the trials...”
It looks to me like the trials were realistic, with the cacophany of sounds and lights that accompanies a real emergency. I am happy that none of the pilots crashed. But I am troubled that half of them fouled up the checklist.
These pilots had (presumably) been briefed on the new MCAS setup and went into the simulator knowing that MCAS problems were going to be served up. Yet half of them ended up with the wrong answer. What would happen to the average pilot on a bad day when his MCAS training is a year old?
I am going to speculate that the new MCAS checklists involve a pretty complicated decision tree, which takes some real mental gymnastics to work through. All of which is to decide whether or not to turn MCAS off. One could be forgiven for asking one more time, what exactly is it that MCAS does which would justify such a diversion of time and mental energy?
The onset of an emergency is the wrong time to play with an MCAS decision tree. The pilots, both of them, should focus first on airspeed, pitch, engine power, and nothing else, until they are ahead of the plane.
In my opinion, MCAS should be left on the ground. If it can’t be left on the ground because of some fundamental mis-aerodynamics of the airframe (other than yoke force monotonicity), then the airframe should be fixed first. Once that’s done, MCAS might not be needed at all.
The article describes “week-long trials inside Boeing’s 737 Max engineering simulator focused on the human response to a variety of angle of attack indication failures and disagreements in real-world scenarios, in takeoff, landing and at cruise ...”
The article continues, “During the recent pilot trials, which tested how crews react to various scenarios involving the revised 737 Max flight control software and new checklists, all the pilots managed to get themselves out of trouble, but Boeing and regulators found that “more than half of pilots responded with the wrong procedures,” according to one of the three people briefed on the results ... “Troubleshooting the failure presented wasn’t intuitive based on the checklist,” said another person familiar with the trials...”
It looks to me like the trials were realistic, with the cacophany of sounds and lights that accompanies a real emergency. I am happy that none of the pilots crashed. But I am troubled that half of them fouled up the checklist.
These pilots had (presumably) been briefed on the new MCAS setup and went into the simulator knowing that MCAS problems were going to be served up. Yet half of them ended up with the wrong answer. What would happen to the average pilot on a bad day when his MCAS training is a year old?
I am going to speculate that the new MCAS checklists involve a pretty complicated decision tree, which takes some real mental gymnastics to work through. All of which is to decide whether or not to turn MCAS off. One could be forgiven for asking one more time, what exactly is it that MCAS does which would justify such a diversion of time and mental energy?
The onset of an emergency is the wrong time to play with an MCAS decision tree. The pilots, both of them, should focus first on airspeed, pitch, engine power, and nothing else, until they are ahead of the plane.
In my opinion, MCAS should be left on the ground. If it can’t be left on the ground because of some fundamental mis-aerodynamics of the airframe (other than yoke force monotonicity), then the airframe should be fixed first. Once that’s done, MCAS might not be needed at all.
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. . . Boeing and regulators found that “more than half of pilots responded with the wrong procedures,” according to one of the three people briefed on the results ... “Troubleshooting the failure presented wasn’t intuitive based on the checklist,” said another person familiar with the trials...”
Whatever the details, it's hard to imagine any explanation for half of the line pilots responding "with the wrong procedures" that isn't seriously disturbing. What in the world is going on?
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Boeing is basically stuck, all the delivered grounded planes put them in a bind. They might as well all be on the moon; they are stuck designing the fix to existing hardware, leaving software fixes only.
This might be the best they can do. I'm 85% convinced it won't fly again.
This might be the best they can do. I'm 85% convinced it won't fly again.
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It is a known phenomenon that some people react to negative G with a large and sustained PUSH on the stick to a crazy attitude (+forward trim if applicable), even if there are massive visual cues that it is excessive. For example, it has resulted in fatal glider accidents after a winch cable break (first action, adopt a normal gliding attitude = brief period of negative G), where the pilot has pushed, and continued to push extreme nose down, right into the runway clearly visible outside the canopy.
So:
1) Pull cable release
2) Joystick forward "fill canopy with green" until airspeed sufficient for flight. This is the point at which you discover why heavy things need to be secured, as all the detritus in the cockpit rises up.
3) Adopt normal attitude and scan for and review options - land ahead/ find other suitable landing area/ do a circuit.
It my be that training has changed.
With enough AND trim, the plane will be forced to a negative G maneuver, regardless of how much ANU elevator is used. Both planes experienced negative G and likely high control pull forces at the end.
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Boeing is basically stuck, all the delivered grounded planes put them in a bind. They might as well all be on the moon; they are stuck designing the fix to existing hardware, leaving software fixes only.
This might be the best they can do. I'm 85% convinced it won't fly again.
It’s also alarming that pilots are once again (here in this forum) getting the fingers pointed at them. The sim results alone bear witness there’s something wrong with the machine, not the operator. You can debate all day about the should of, could of or what if’s but Boeing is playing 3-card-monte and trying to trick their mark. Guess we’re all the marks. Ugh!
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It seems to me that YYZjim's speculates thoughtfully and intelligently on the information in the cited article. When LO posted the link, I read it, shook my head in despair (if not in surprise) and suggested that it is important reading. I really think it is.
Whatever the details, it's hard to imagine any explanation for half of the line pilots responding "with the wrong procedures" that isn't seriously disturbing. What in the world is going on?
Whatever the details, it's hard to imagine any explanation for half of the line pilots responding "with the wrong procedures" that isn't seriously disturbing. What in the world is going on?
And in the sim- knowing that some sort of 'emergency ' will happen, its a good bet that the adrenaline rush is much less than at night, turbulent weather, or after 3 hours of boredom for real .
Last edited by Grebe; 14th Dec 2019 at 22:29. Reason: fat fingers andspelling
There are two; what MCAS does when the AoA system fails and what it does when the AoA system is working correctly.
Example - there was no neutral-gear detect switch in my former manual transmission car, so one time I tried engaging the cruise control while on a slight down-grade so the speed was constant and the car out of gear. The cruise control engaged. But when I came to a rise and the car slowed slightly, car still in neutral, the cruise control went WOT. Independent of the cruise control the engine had a rev limiter which prevented over-RPM. I would not describe cruise control as a system intended to provide WOT, but when some other system has failed it acts like that.
Based on other comments, I wonder if it would have been better for MCAS to run continuously to the AND limit instead of the safety interrupt timer cutting it short and having the 5 second delay.
Example - there was no neutral-gear detect switch in my former manual transmission car, so one time I tried engaging the cruise control while on a slight down-grade so the speed was constant and the car out of gear. The cruise control engaged. But when I came to a rise and the car slowed slightly, car still in neutral, the cruise control went WOT. Independent of the cruise control the engine had a rev limiter which prevented over-RPM. I would not describe cruise control as a system intended to provide WOT, but when some other system has failed it acts like that.
Based on other comments, I wonder if it would have been better for MCAS to run continuously to the AND limit instead of the safety interrupt timer cutting it short and having the 5 second delay.
Psychophysiological entity
In an idle moment.
Surely big G is 6.674 28 (+/- 0.000 67) x 10-11 m3 kg-1 s -2. ? If we had negative G, the problems of Boeing would seem trivial since the world would fly apart and the sun would go out. Big G, by a still unknown mechanism, causes little g, that ~9.8 m/s squared we enjoy at the Earth's surface.
Detritus coming off a glider's floor or cows getting bigger to the point our shoulder harnesses are tugging, is serious stuff. I find it hard to imagine being near the surface, especially flat out, and even letting the controls go forward a micro-tad. I think it would be one heck of a mental battle to Yo-yo, even if you knew it was the procedure.
Surely big G is 6.674 28 (+/- 0.000 67) x 10-11 m3 kg-1 s -2. ? If we had negative G, the problems of Boeing would seem trivial since the world would fly apart and the sun would go out. Big G, by a still unknown mechanism, causes little g, that ~9.8 m/s squared we enjoy at the Earth's surface.
Detritus coming off a glider's floor or cows getting bigger to the point our shoulder harnesses are tugging, is serious stuff. I find it hard to imagine being near the surface, especially flat out, and even letting the controls go forward a micro-tad. I think it would be one heck of a mental battle to Yo-yo, even if you knew it was the procedure.
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The recent comments about MCAS reinforce the point that it is very difficult to design a complex system that is safe, effective and reliable, and operates within the limitations of the human-machine interface.
From an entirely different perspective, this
reminds me of the (apocryphal) story of the monkey trap. Once the hand has gripped the food reward, the size of the fist is too large to withdraw from the trap.
MCAS software seems like a clever fix, but may actually be a trap. All kinds of contortions and wriggling, do not solve the underlying physical problem,.
Letting go of the 'easy' software fix may seem painful, but it might be worse to be trapped in a never-ending tug-of-war between physics, regulations and safety.
From an entirely different perspective, this
reminds me of the (apocryphal) story of the monkey trap. Once the hand has gripped the food reward, the size of the fist is too large to withdraw from the trap.
MCAS software seems like a clever fix, but may actually be a trap. All kinds of contortions and wriggling, do not solve the underlying physical problem,.
Letting go of the 'easy' software fix may seem painful, but it might be worse to be trapped in a never-ending tug-of-war between physics, regulations and safety.
Re the Ethiopian accident - It has been inferred (both officially and unofficially?) that a bird strike immediately after take off likely tore off the AoA vane which in turn then started the chain of events where MCAS extreme ND inputs lead to the crash a few minutes later.
In these days of fantastic Forensics that we now have, I am puzzled that any evidence of the vane and/or the bird were not found along the aircraft track...
Surely as these tragic and deadly events have now caused such a huge impact on civil aviation that no Forensic sweep(s) seem to have been undertaken at no expense...
Just my tuppence, but if a bird strike was suspected soon after the crash why was this not an imperative, nor a return to the scene to sweep again?
In these days of fantastic Forensics that we now have, I am puzzled that any evidence of the vane and/or the bird were not found along the aircraft track...
Surely as these tragic and deadly events have now caused such a huge impact on civil aviation that no Forensic sweep(s) seem to have been undertaken at no expense...
Just my tuppence, but if a bird strike was suspected soon after the crash why was this not an imperative, nor a return to the scene to sweep again?
Last edited by rog747; 15th Dec 2019 at 11:05.
Re the Ethiopian accident - It has been inferred (both officially and unofficially?) that a bird strike immediately after take off likely tore off the AoA vane which in turn then started the chain of events where MCAS extreme ND inputs lead to the crash a few minutes later.
In these days of fantastic Forensics that we now have, I am puzzled that any evidence of the vane and/or the bird where not found along the aircraft track...
Surely as these tragic and deadly events have now caused such a huge impact on civil aviation that no Forensic sweep(s) seem to have been undertaken at no expense...
Just my tuppence, but if a bird strike was suspected soon after the crash why was this not an imperative, nor a return to the scene to sweep again?
In these days of fantastic Forensics that we now have, I am puzzled that any evidence of the vane and/or the bird where not found along the aircraft track...
Surely as these tragic and deadly events have now caused such a huge impact on civil aviation that no Forensic sweep(s) seem to have been undertaken at no expense...
Just my tuppence, but if a bird strike was suspected soon after the crash why was this not an imperative, nor a return to the scene to sweep again?
And a shift of blame to a bird - with zero evidence.
but known AoA unit failures & illegal repairers.
Thanks Bendalot --- I too was puzzled by this bird strike story...
Nose down input in negative G.
Detritus coming off a glider's floor or cows getting bigger to the point our shoulder harnesses are tugging, is serious stuff. I find it hard to imagine being near the surface, especially flat out, and even letting the controls go forward a micro-tad. I think it would be one heck of a mental battle to Yo-yo, even if you knew it was the procedure.
The bird strike theory may be all my fault?
I proposed a failure mechanism in post
Ethiopian airliner down in Africa
#3238
" It therefore seems quite likely that the vane was lost or perhaps damaged soon after take off, perhaps by a bird strike or otherwise."
The AoA sensor is I assume balanced so that with no airflow it will hold whatever position it is left at. The Preliminary report has FDR data that includes the Left AoA and the Vertical Acceleration (g). The sign of the AoA (+/-) and the sign of the vertical acceleration track each other exactly.
This suggests to me that the sensor rotor assembly has become unbalanced. The direction of the imbalance if the vane (which is to the rear of the axis) is lost would allow the shaft to rotate such that the vane, if it was still there, would move UP if +g (straight and level).
Up vane relative to the fuselage is +ve AoA.
I am sure that the investigators will also have noticed this correlation, so hopefully it is nothing to do with me.
There seems strong evidence that the vane was lost soon after take off. The mechanism of the loss is unknown and since the sensor was at the business end of a very fast crash it may well never be known. Finding the vane would be a good start though.
I proposed a failure mechanism in post
Ethiopian airliner down in Africa
#3238
" It therefore seems quite likely that the vane was lost or perhaps damaged soon after take off, perhaps by a bird strike or otherwise."
The AoA sensor is I assume balanced so that with no airflow it will hold whatever position it is left at. The Preliminary report has FDR data that includes the Left AoA and the Vertical Acceleration (g). The sign of the AoA (+/-) and the sign of the vertical acceleration track each other exactly.
This suggests to me that the sensor rotor assembly has become unbalanced. The direction of the imbalance if the vane (which is to the rear of the axis) is lost would allow the shaft to rotate such that the vane, if it was still there, would move UP if +g (straight and level).
Up vane relative to the fuselage is +ve AoA.
I am sure that the investigators will also have noticed this correlation, so hopefully it is nothing to do with me.
There seems strong evidence that the vane was lost soon after take off. The mechanism of the loss is unknown and since the sensor was at the business end of a very fast crash it may well never be known. Finding the vane would be a good start though.
Left side AoA sensor vs vertical acceleration (g)I offer an explanation for the behaviour of the Left hand AoA indication throughout the flight.
If the vane had been lost the AoA sensor would become unbalanced about its usual axis of rotation. The internal balance weight** would then cause the axle to be subject to movement when the aircraft transitioned from +g to -g. +g would cause the indication of +AoA. (If I have got this the right way round
Looking at the FDR traces it can be seen that this appears to be the case. I have drawn four green vertical lines to indicate the transitions from +g to -g and vice versa. In each case they appear to align with a change in the direction of movement of the sensor in the correct sense. Remember that the data consists of discrete samples and we do not know the sample rate and I am assuming that any small discrepancies are due to errors introduced by the sampling.
I have (rather crudely) chopped out a period in the middle of the chart so that it is a bit narrower so that the scale markings can be easily seen. The horizontal blue line in the "g" section of the chart is coincidentally exactly on 0g.
It therefore seems quite likely that the vane was lost or perhaps damaged soon after take off, perhaps by a bird strike or otherwise. Note however that if the vane had been bent back its balance would be moved in the other direction and its aerodynamic influences would still have been felt so I think that the best conclusion consistent with the data is that the vane was lost.
** A post on PPRuNe regarding this incident showed an exploded view of the AoA sensor and it featured an internal balance weight. Unfortunately I cannot recall where it was now.
If the vane had been lost the AoA sensor would become unbalanced about its usual axis of rotation. The internal balance weight** would then cause the axle to be subject to movement when the aircraft transitioned from +g to -g. +g would cause the indication of +AoA. (If I have got this the right way round
Looking at the FDR traces it can be seen that this appears to be the case. I have drawn four green vertical lines to indicate the transitions from +g to -g and vice versa. In each case they appear to align with a change in the direction of movement of the sensor in the correct sense. Remember that the data consists of discrete samples and we do not know the sample rate and I am assuming that any small discrepancies are due to errors introduced by the sampling.
I have (rather crudely) chopped out a period in the middle of the chart so that it is a bit narrower so that the scale markings can be easily seen. The horizontal blue line in the "g" section of the chart is coincidentally exactly on 0g.
It therefore seems quite likely that the vane was lost or perhaps damaged soon after take off, perhaps by a bird strike or otherwise. Note however that if the vane had been bent back its balance would be moved in the other direction and its aerodynamic influences would still have been felt so I think that the best conclusion consistent with the data is that the vane was lost.
** A post on PPRuNe regarding this incident showed an exploded view of the AoA sensor and it featured an internal balance weight. Unfortunately I cannot recall where it was now.
Last edited by jimjim1; 15th Dec 2019 at 12:18.
Possible sensor internals. These images are from
https://www.satcom.guru/2019/03/aoa-...oeing-fix.html
and appear to be from a 747-400.
https://www.satcom.guru/2019/03/aoa-...oeing-fix.html
and appear to be from a 747-400.
Sick, Semreh, et al,
Thanks for the views on ‘negative’ ‘g’ and pushing the controls. The discussion continues in Flydubai crash at RVI final report out, see the report section 2.4. ‘On the possible impact of somatogravic illusions’, page 166; and also related aspects of ‘unusual’ pitch control and trim characteristics, ‘feel’ feedback, page159.
Thanks for the views on ‘negative’ ‘g’ and pushing the controls. The discussion continues in Flydubai crash at RVI final report out, see the report section 2.4. ‘On the possible impact of somatogravic illusions’, page 166; and also related aspects of ‘unusual’ pitch control and trim characteristics, ‘feel’ feedback, page159.
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Re the Ethiopian accident - It has been inferred (both officially and unofficially?) that a bird strike immediately after take off likely tore off the AoA vane which in turn then started the chain of events where MCAS extreme ND inputs lead to the crash a few minutes later.
In these days of fantastic Forensics that we now have, I am puzzled that any evidence of the vane and/or the bird were not found along the aircraft track...
Surely as these tragic and deadly events have now caused such a huge impact on civil aviation that no Forensic sweep(s) seem to have been undertaken at no expense...
Just my tuppence, but if a bird strike was suspected soon after the crash why was this not an imperative, nor a return to the scene to sweep again?
In these days of fantastic Forensics that we now have, I am puzzled that any evidence of the vane and/or the bird were not found along the aircraft track...
Surely as these tragic and deadly events have now caused such a huge impact on civil aviation that no Forensic sweep(s) seem to have been undertaken at no expense...
Just my tuppence, but if a bird strike was suspected soon after the crash why was this not an imperative, nor a return to the scene to sweep again?
It has been reported that the Ethiopian AIB had three full-time employees (at the time of the crash) and that they were relying on airline personnel to help with the investigation. Perhaps the airline didn't provide enough help to sweep the runway and the area off the end of the runway. Perhaps it wasn't in the airline's interest to find the part (if it wasn't a bird strike then another possible explanation is faulty maintenance).
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"But all of the pilots managed to recover the plane." When this sort of information leaks I suspect a bit more PR judo going on here, at what altitude did the simulated failure occur? Maybe I am a simplistic groundling, but when half of the tests fail you go back to the drawing board. I always assumed that in aerospace when one pilot stuffed it up you rethought the design or training, better to do that now rather than after collecting the smoking body parts into bags.
There are two tracks going on at the same time -- the legitimate engineering effort to ensure that hundreds more people are not killed by the product and the absolute desperation by management to salvage the stock price by getting product onto the right side of the balance sheet. The efforts should be independent but given the past behavior I'm doubtful that they are.
There are two tracks going on at the same time -- the legitimate engineering effort to ensure that hundreds more people are not killed by the product and the absolute desperation by management to salvage the stock price by getting product onto the right side of the balance sheet. The efforts should be independent but given the past behavior I'm doubtful that they are.