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Ethiopian airliner down in Africa

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Ethiopian airliner down in Africa

Old 17th Mar 2019, 21:36
  #1801 (permalink)  
 
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Originally Posted by hikoushi View Post


In the Airbus, a faulty AOA or ADR causes the airplane to either:
1. Do nothing, or
2. Turn off Normal Law.
maybe
For example

https://news.aviation-safety.net/201...-check-flight/



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Old 17th Mar 2019, 21:36
  #1802 (permalink)  
 
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Hi, another question from SLF and PPL, hope you dont mind.
I have followed this thread from the beginning and only seen this question asked once with no definitive replies.
How many other 'patches' are there on aircraft such as the MAX or that matter any aircraft from any manufacturer (particularly old designs dragged into the modern age to avoid complex certification) waiting in the background to cause future problems?
Does the situation with Boeing and the MAX possibly require a detailed review of all other aircraft system updates and work arounds to see if another similar issue is waiting in the background for exceptional circumstances?
One would like to think not but this thread indicates this is possible.
I propose this scenario (from insufficient technical knowledge to know the answer - but just as an example so please don't jump on me too hard). The Weight on Wheels sensor. Does it have multiple redundancy? Does it have one sensor each UC feeding one pilots computer and if so does it have a cross check system? What happens in the event of a sensor failure? I am only using this as an example as it springs to mind. No doubt hundreds of other possibilities exist.
If you lock all the toilet doors simultaneously, does the pilots coffee machine stop working?

Finally another small question, how strong is the drive motor on the auto trim on the MAX or similar? Could you stall it out by grabbing the spinning trim wheel or will it try and take your fingers off?
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Old 17th Mar 2019, 21:55
  #1803 (permalink)  
 
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Originally Posted by CONSO View Post
basic lever - the shorter the body length and the shorter the length from CG, the more ' force' is needed to tilt ( aoa ) or stop yaw ( if one engine out ). The longer the body- distance from CG, the less the force needed for normal AOA correction or yaw correction. Since the force needed is generally a function of size or AREA acted on by air pressure/lift - a longder body can allow a smaller area for control surfaces ( overly simplified ) then come the cost of designing a new smaller area or simply staying the same as current production, etc

And I think you ment the horizontal stabilizer- not the elevator ??

And if yoiu not the hight of the smallet airbus VERTical stabilizer it is longer than the longer airbus - for generally the same reasons
Yes, I am aware of the moment arm and how that affects the size requirement, especially for the rudder.

I had in mind the size of the elevator compared with the full horizontal stabilizer.

I tried to measure the relative size on the drawings, as far as they are accurate, which I ofc dont know for sure.
I get the A320 elevator is marginally larger than 1/3 of the full horizontal stabilizer including the elevator.
The B737 on the other hand seems to have an elevator only marginally smaller than 1/4 of the full horizontal stabilizer including the elevator.
This must be a significant difference.

It seems like the A320, if we make that aircraft the comparison, because of its larger percentage elevater/stabilizer ratio to a much larger extent can rely on only the elevator in maintaining pitch control in demanding areas of the flight envelope, whereas the B737 much quicker runs out of elevater authority, and therefore Boeing has no option other than to use the very slow acting stabilizer trim function when controlling pitch in the most demanding areas of the flight envelope. And couple this with the likely worse naturable stability of the aircraft due to the very forward placement of the engines. This might be a reason why they couldnt make use of a redesign of the EFS acting on the yoke/elevator which would have been in my mind a much more quickly acting system. But ofc, such a system would also need a good software, and not the cludge MCAS seems to have been.

Last edited by SteinarN; 17th Mar 2019 at 22:13.
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Old 17th Mar 2019, 22:03
  #1804 (permalink)  
 
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Originally Posted by SteinarN View Post
But, I must say, if anyone trying his best to count the passes couldnt see the gorilla, then I think the expectatations on what a cockpit crew are able to do in a high stress situation with a lot of stuff going on in the cockpit has to be signifcantly decreased.
Scary indeed.
Try it on random people who havent seen it before. Just share it in the way they don't suspect something. You'll be surprised.

For the record, I failed it.
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Old 17th Mar 2019, 22:05
  #1805 (permalink)  
 
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...The B737 on the other hand seems to have an elevator only marginally smaller than 1/4 of the full horizontal stabilizer including the elevator.
This must be a significant difference.
That MAY- repeat MAY be due to basic design for FBW versus ' cable ' control backup design for 737 and prior.

I note that seattle times article today mentions that initial stab movement was supposedly limited to .6 degrees for flight envelope and even for extreme csse. Flight test apparently showed/proved it needed to be 2.5 degrees for extreme conditions- due to extra lift from engine cowlings at high AOA- but somehow the documentation approved never got that number changed And/OR even thenit was not considered critical, etc
NO matter how one slices it- the ' fix' was FUBAR - and forgot that AOA sensors can easily be bent orhit by birds etc
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Old 17th Mar 2019, 22:13
  #1806 (permalink)  
 
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Seattle Times on 737Max Crashes

Link to Seattle Times Article. Excellent journalism with much new information regarding the process that game us MCAS:

https://www.seattletimes.com/busines...ion-air-crash/
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Old 17th Mar 2019, 22:25
  #1807 (permalink)  
 
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Originally Posted by bullfox View Post
Link to Seattle Times Article. Excellent journalism with much new information regarding the process that game us MCAS:

https://www.seattletimes.com/busines...ion-air-crash/
Like all 737s, the MAX actually has two of the sensors, one on each side of the fuselage near the cockpit. But the MCAS was designed to take a reading from only one of them.
A single point of failure

But several FAA technical experts said in interviews that as certification proceeded, managers prodded them to speed the process. Development of the MAX was lagging nine months behind the rival Airbus A320neo. Time was of the essence for Boeing.A former FAA safety engineer who was directly involved in certifying the MAX said that halfway through the certification process, “we were asked by management to re-evaluate what would be delegated. Management thought we had retained too much at the FAA.”
Regulatory Capture.


A normailsation of deviance.
The incremental degradation of robust system design, implementation and testing continued unabated.

Delegated to Boeing

The FAA, citing lack of funding and resources, has over the years delegated increasing authority to Boeing to take on more of the work of certifying the safety of its own airplanes.
Always in the ear of management is the cost reduction mantra.

Some posters suggest case studies. Humanity never learns,
As it was before it will be again, usually as sufficient time elapses for the human ego to proudly boast, "this time is different"
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Old 17th Mar 2019, 22:26
  #1808 (permalink)  
 
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Originally Posted by CONSO View Post
That MAY- repeat MAY be due to basic design for FBW versus ' cable ' control backup design for 737 and prior.

I note that seattle times article today mentions that initial stab movement was supposedly limited to .6 degrees for flight envelope and even for extreme csse. Flight test apparently showed/proved it needed to be 2.5 degrees for extreme conditions- due to extra lift from engine cowlings at high AOA- but somehow the documentation approved never got that number changed And/OR even thenit was not considered critical, etc
NO matter how one slices it- the ' fix' was FUBAR - and forgot that AOA sensors can easily be bent orhit by birds etc
That they found it was necessary with 2,5 degrees might indicate that the aircraft might be way off the required natural stability without the help of any system.
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Old 17th Mar 2019, 22:31
  #1809 (permalink)  
 
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I'm not a pilot (well, only ex-PPL), but I am an engineer, working in safety-critical infrastructure. These two accidents are going to shake this industry. I know they have not yet been linked, but the gun is smoking.

Three massive issues stand out for me.

1. What has gone wrong at Boeing, that could allow a system to intervene, unknown to the flightdeck, but which had no redundancy on a vital input? Any systems analysis of this solution should have picked up this critical flaw...if it didn't, then the analysis (or analysors) was patently in error.
2. What has gone wrong at Boeing, that allowed a system to be designed, which used trim as a primary flight control? Correct me here if I'm wrong, but is trim not there to alleviate control forces once a flightpath has been established? Any system where trim is used in a primary manner is completely counterintuitive to flight crew. (maybe my understanding is wrong here, so happy to be corrected)
3. What has gone wrong at the FAA, that no-one caught this system? It seems they tried to devolve responsibility back to Boeing, but the FAA cannot do that...they are on the hook for this regulatory failure.

Corporate and regulatory culture is the problem here, and it stinks. I've always assumed Boeing were good guys, with a track record second to none. But something has gone wrong. And the FAA? I just find the whole thing staggering.

Pity the poor flightcrew...left with an airplane that had systems they didn't know about, without the necessary redundancy, and which was doing things they couldn't hope to assimilate at a crtical juncture in the flight.

The safest form of transport is facing a lot of questions just now.

Last edited by NWSRG; 17th Mar 2019 at 22:43.
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Old 17th Mar 2019, 22:39
  #1810 (permalink)  
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Originally Posted by dakarman View Post

Finally another small question, how strong is the drive motor on the auto trim on the MAX or similar? Could you stall it out by grabbing the spinning trim wheel or will it try and take your fingers off?
Well, that actually forms part of the runaway stab trim checklist. If the cutout switches dont stop the trim then grab the wheel which is supposed to stop it.

Never tried it, don't want to.
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Old 17th Mar 2019, 22:45
  #1811 (permalink)  
 
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Originally Posted by NWSRG View Post
I'm not a pilot (well, only ex-PPL), but I am an engineer, working in safety-critical infrastructure. These two accidents are going to shake this industry. I know the yhave not yet been linked, but the gun is smoking.

Three massive issues stand out for me.

1. What has gone wrong at Boeing, that could allow a system to intervene, unkown to the flightdeck, but which had no redundancy on a vital input? Any systems analysis of this solution should have picked up this critical flaw...if it didn't, then the analysis (or analysors) was patently in error.
2. What has gone wrong at Boeing, that allowed a system to be designed, which used trim as a primary flight control? Correct me here if I'm wrong, but is trim not there to alleviate control forces once a flightpath has been established? Any system where trim is used in a primary manner is completely counterintuitive to flight crew.
3. What has gone wrong at the FAA, that no-one caught this system? It seems they tried to devolve responsibility back to Boeing, but the FAA cannot do that...they are on the hook for this regulatory failure.

Corporate and regulatory culture is the problem here, and it stinks. I've always assumed Boeing were good guys, with a track record second to none. But something has gone wrong. And the FAA? I just find the whole thing staggering.

Pity the poor flightcrew...left with an airplane that had systems they didn't know about, without the necessary redundancy, and which was doing things they couldn't hope to assimilate at a crtical juncture in the flight.

The safest form of transport is facing a lot of questions just now.
One easy explanation to your question #1 is that Boeing discovered this only in flight testing (at least how serious it was) and there simply was no time to make it much better, nevermind redesigning parts of the aircraft, like the size of the elevator surfaces which probably would have cost one or two years additional delay.
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Old 17th Mar 2019, 22:48
  #1812 (permalink)  
 
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Originally Posted by SteinarN View Post
One easy explanation to your question #1 is that Boeing discovered this only in flight testing (at least how serious it was) and there simply was no time to make it much better, nevermind redesigning parts of the aircraft, like the size of the elevator surfaces which probably would have cost one or two years additional delay.
But that doesn't explain why the system wasn't (a) briefed to the end users, and (b) built with the necessary redundancy...
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Old 17th Mar 2019, 22:58
  #1813 (permalink)  
 
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Originally Posted by NWSRG View Post
But that doesn't explain why the system wasn't (a) briefed to the end users, and (b) built with the necessary redundancy...
Totally agree. There's no problem with the necessity of an MCAS type system with the MAX, but the seemingly absense of sufficient input monitoring, let alone training and information regarding the system seems diabolically wrong and completely alien to any system philosophy I've ever encountered.
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Old 17th Mar 2019, 22:59
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Originally Posted by NWSRG View Post
But that doesn't explain why the system wasn't (a) briefed to the end users, and (b) built with the necessary redundancy...
Well, discovered (late) in flight testing might be part of the reason why it wasnt built with redundacy. Better reliable and redundant programming obviousIy take more time than simple basic programming, and even more so when one includes the increased testing necessary on a more complicated piece of software. Dont know, but maybe it is requiring quite a bit of programming just to get the other AoA vane into the loop?
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Old 17th Mar 2019, 23:04
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Originally Posted by SteinarN View Post
Well, discovered (late) in flight testing might be part of the reason why it wasnt built with redundacy. Better reliable and redundant programming obviousIy take more time than simple basic programming, and even more so when one includes the increased testing necessary on a more complicated piece of software. Dont know, but maybe it is requiring quite a bit of programming just to get the other AoA vane into the loop?
Yep, that's probably all true. But do you then go ahead and release a system into service that isn't actually fit for purpose? It just seems to me here that something is fundamantally wrong in the philosophy of the system design...it should never have gone into service with these shortcomings.
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Old 17th Mar 2019, 23:05
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Originally Posted by SteinarN View Post
Well, discovered (late) in flight testing might be part of the reason why it wasnt built with redundacy. Better reliable and redundant programming obviousIy take more time than simple basic programming, and even more so when one includes the increased testing necessary on a more complicated piece of software. Dont know, but maybe it is requiring quite a bit of programming just to get the other AoA vane into the loop?
Don't really agree that Boeing can use that as an excuse, a simple 'Alpha Disagree' discreet would be sufficient monitoring to inhibit MCAS and in my mind there is zero excuse for such a dangerous state of affairs to be allowed to exist on any commercial aeroplane.
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Old 17th Mar 2019, 23:09
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Originally Posted by M2dude View Post
Don't really agree that Boeing can use that as an excuse, a simple 'Alpha Disagree' discreet would be sufficient monitoring to inhibit MCAS and in my mind there is zero excuse for such a dangerous state of affairs to be allowed to exist on any commercial aeroplane.
Particularly when you consider that "AOA DISAGREE" warning functionality is fitted to many 737 Max aircraft.
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Old 17th Mar 2019, 23:13
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Seattle Roulette.

Seattle Times indicates that the AoAsystem is designed for a 1/100 000 failure rate, which I expect means 1 per 1 e10**5 hours.
There are 350 of the Max flying as of now maybe 10 hours a day, ie 35 000 hours a day.
So one MCAS incident due to a bad sensor can be expected every few days. Exactly what we've been seeing so far.
Seatlle Roulette?

Even if the AoA design study had been made for 1 in 10 Million hours, as it should have been for certification, with the full fleet of 5000 of these flying cows, you would have 50 000 hours a day, and several incidents a year, a hull loss could be expected every few years..

Edmund
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Old 17th Mar 2019, 23:16
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Yes...those figures seemed concerning.
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Old 17th Mar 2019, 23:17
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Originally Posted by SteinarN View Post
I saw the video. I stopped counting the passes after a couple seconds as it was way to difficult. So I looked at the other things going on, saw the gorilla immediately. But then I knew it was a trick video.

But, I must say, if anyone trying his best to count the passes couldnt see the gorilla, then I think the expectatations on what a cockpit crew are able to do in a high stress situation with a lot of stuff going on in the cockpit has to be signifcantly decreased.
Scary indeed.
The funny thing is I knew there was a gorilla in the video, because I saw that video in the past, but I followed the instruction to watch very carefully the ball exchanges, and I did that to the best of my ability, so I missed the gorilla I knew was there.

I didn't even believe I missed it after the video replayed the sequence. I thought that replay may have been faked, and I had to manually replay the video to convince me that there indeed was one, and I actually missed it.

So it's perhaps not surprising that the Ethiopian crew, even if they knew about the MCAS gorilla and how it can be disabled, still missed it, if they were focused on following other procedures and checklists to the letter.

Humans are not good at multitasking, especially when dealing with stuff that is not ingrained as muscle memory.

And if it takes only two MCAS cycles to bring the stabilizer to full nose down trim, it means this aircraft is capable to configure itself to kill you in less than a minute when the AoA sensor fails. I wouldn't want to fly such a plane, even if procedures that can prevent that from happening exist.

The FAA certification process needs to be overhauled so that this can't happen again in the future. In my opinion the FAA and Boeing bear together 90% of the responsibility for killing those people.

I found especially disgusting the way Boeing kept implying the pilots were at fault after the Lion Air accident and that the aircraft is perfectly safe, and how after the second accident the FAA kept saying the aircraft was safe and doesn't need to be grounded, when everyone else all over the world started grounding them.

I mean, everyone can make mistakes, Boeing, the FAA, the pilots, the airlines. Not admitting to those mistakes when they become obvious disgusts me.
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