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Ethiopian airliner down in Africa

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Ethiopian airliner down in Africa

Old 17th Mar 2019, 23:25
  #1821 (permalink)  
 
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Discovered late in flight testing????
As a total outsider (apart from some jet engine design many moons ago), I would have thought that the design process would have gone something like:-
What a pity we cant fit these larger engines to the 737.
But we could if you moved them forward and up.
That's a crazy suggestion, it would totally destabilise the aeroplane.
Yes, I know that, but you can fly an unstable aeroplane if you have computer assist, the military do it all the time, and we already have plenty of computing power in the system.
True, that would work, and we can't see any other quick solution. We'll have to go that way.
Just speculation!!
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Old 17th Mar 2019, 23:36
  #1822 (permalink)  
 
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@edmund 3500 perhaps? Doesn't alter argument though.
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Old 17th Mar 2019, 23:43
  #1823 (permalink)  
 
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Since I'm working on car functional safety, I'm sometimes around here just to learn from accidents in aviation.

This story here is, if true, really a deviation from good practice and established safety standards on all levels.
The only persons I don't blame are the pilots. If a possible safety hazard is evaluated, there is always the parameter of controlability by the driver / pilot... But this is not 0% or 100%, it's statistics (high, medium, low...). Put one pilot/driver 10 times in the same unexpected situation and he will miss the solution once...
So the residual hazard is always the product of an already safe system and a good estimate of the controlability and training. One cannot design a crappy system and then rely on or blame the human problem solving skill for everything that may happen. Especially of something is repeatedly doing something complete unexpected and useless without warning and gives the pilot a free bodybuilding exercise.
Since many pilots here claim this situation is quite controlable, I just ask myself: How many undocumented or disclosed events of this kind were there?

So despite the failures made in many, if not all aspects of functional safety:
-> Crappy design to avoid recertification (and therefore a flying museum on steroids instead of a state-of-the-art design in all aspects)
-> Basic aerodynamic design flaws
-> Impact analysis of all the changes done within the MAX development
-> Risk accessment for MCAS based on wrong values (0.6)
-> Single sensor/single point fault
-> Sensor comparison sold for $$$ (wtf, imagine this in automotive: Yes for only 500$ extra a blocking rear axle on the highway would be detected by the gearbox and stopped...). Lawyers will love that one
-> Dependent failure analysis incomplete (reset, 5 seconds and there it goes again)
-> Configuration management (application boundaries, 0,6 vs. 2.5)
-> Integration testing (was this error introduces in a test flight/sim and was the reaction controllable)? If, in automotive (ISO26262) one relies on the controlability of a situation, one has to prove it on a test track with every model / release.
-> Safety case consistency (these 2.5 never found their way back in the risk accessment / accessment)
-> Training (MCAS what?)
-> Documentation
-> Accessor independence
-> Financial and time pressure

But still there is one open point to me:
500 Airplanes shipped, maybe 250 days flying on average, 16h a day -> 2,000,000 hours in the air
And already (at least) 2 defective sensors? -> 1,000 FIT???
That's the point where a car manufacturer would consider a recall for a non-safety related part like seat heating. But such a critical part should have:
-> high coverage measure such as 1oo2 / 2oo3 selection or at least comparison and safe state (ne action/warning)
-> low coverage measures like short/open/stuck detection
-> redundancy within the sensor (two potentiometers or other rotary sensors which are compared, again resulting in a high coverage detection method and error signaling)
-> sufficient testing to do statistics that show <10 FIT, FMEDA...
-> FMEA, environmental tests, shaker... the whole program

In this case only one AoA vane was used and this one went into a critical fault without self-diagnosis. And furthermore something like 'frozen to stuck-at' can almost be excluded, or does the airplane see such high angles at startup and the sensors typically freeze just after acceleration?

Someone wrote that the sensors were a carry-over part from the old model. Are ground crews always running around with a bunch of them in their pockets because they fail all over the place or freeze every second rainy day?
Maybe someone can give me a hint on what I'm missing here. Why are we talking about a highly critical part in aviation and it shows 1000 undetected critical failures per billion hour? Even the squeeze protection of a car's power window lifter is far better!

The lives lost in these probably avoidable accidents are a shame and I feel with the relatives.
Since I consult OEM and TIER1/2 automotive companies on critical safety functions, I do my best to get as much lessons learned out of this and transfer this into automotive.
I already sent out the great seattle times article to a lot of people, helps me a lot in justifying the high effort and development costs of safety related functions. I will keep this article on my computer and any time someone is claiming cost or development time or asks for some one-eye blindness, I just need this one link, It really covers everything one should NOT do.

Thanks a lot for all the research which get's collected here, this is really the best and most up-to-date place. The effort is not wasted but read by people who may be able to do it better next time in this or even different industries.
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Old 17th Mar 2019, 23:44
  #1824 (permalink)  
 
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Originally Posted by DaveReidUK View Post
Particularly when you consider that "AOA DISAGREE" warning functionality is fitted to many 737 Max aircraft.
Apparently this is an additionally chargeable option. All three major US customers (Southwest, American, United) have bought it. Lion and Ethiopian did not. I wonder about others.

And I wonder how the Boeing sales team went about selling this add-on. Why did the US carriers spend the money and others not. Presumably the sales team offered it to everyone. What were their justifications, and why did the US carriers, no fools at tough negotiations, go for it but not others. And how did the FAA certification let it be optional rather than required. How often, for those that fitted it, did it operate ?
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Old 17th Mar 2019, 23:49
  #1825 (permalink)  
 
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Originally Posted by StrongEagle View Post
Isn't this rather similar to a Lufthansa A321 incident that occurred Nov 5th 2014, near Bilbao, (Spain), where the aircraft experienced a rate of descent of 4,000 FPM before the pilots got the aircraft back under control?

Incident recorded here: https://avherald.com/h?article=47d74074

And here: https://aviation-safety.net/wikibase/wiki.php?id=171411
Except that A321 has 3 AoA probes, 2 of which were faulty, and the stall protection could be countered by aft stick (on mini-stick required force may not exceed pilot strength, contrary to a control column)
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Old 17th Mar 2019, 23:52
  #1826 (permalink)  
 
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Originally Posted by WHBM View Post
How often, for those that fitted it, did it operate ?
I think the answer to that is in the telemetry databases, and will determine the way the way the compensations trials go, and also how many people from Boeing resign.
Unless the fleet telemetry data turns out to have gone the way of Mrs Clinton's emails, and a State of Washington judge looks the other way.

Edmund
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Old 17th Mar 2019, 23:53
  #1827 (permalink)  
 
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737 get smart...

https://en.wikipedia.org/wiki/Get_Smart

The french title for "Get Smart" TV series is "Max la menace"... here it gives :

737 MAX the mennace
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Old 17th Mar 2019, 23:54
  #1828 (permalink)  
 
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At some point it may be necessary to review also whether the Lion Air accident was given sufficient attention / emphasis; and if not, why not.

It seems to me that a lot of people, including Ppruners, may have been lulled into thinking that the Lion Air incident was, to a certain extent, really their own fault.
And maybe, to a certain extent, it was. But was the response to the incident, in hindsight, even half-way adequate?

An airline with dubious safety, training and procedural standards, prior history, lax management of fault correction immediately prior to final crash, questionable actions on part of the fatal flight crew.
We'll send out a bulletin, throw in a software patch when we get around to it; we just need to make it idiot proof.

Maybe just not affording the incident the degree of attention that it deserved.
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Old 18th Mar 2019, 00:01
  #1829 (permalink)  
 
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From BBC News website and also on News At Ten
Flight data from the Ethiopian Airlines disaster a week ago suggest "clear similarities" with a crash off Indonesia last October, Ethiopia's transport minister has said.Both planes were Boeing 737 Max 8 aircraft.

Last Sunday the Ethiopian Airlines jet crashed after take-off from Addis Ababa, killing all 157 people on board.

Transport Minister Dagmawit Moges told journalists that a preliminary report would be released within 30 days."Clear similarities were noted between Ethiopian Airlines Flight 302 and Indonesian Lion Air Flight 610, which would be the subject of further study during the investigation," Ms Dagmawit told journalists on Sunday.In both cases flight tracking data showed the aircraft's altitude had fluctuated sharply, as the planes seemed to experience erratic climbs and descents.
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Old 18th Mar 2019, 00:07
  #1830 (permalink)  
 
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Originally Posted by CONSO View Post
8 years ago, An Airbus crashed due to a blocked' AOA sensor- which fooled both the pilots AND HALBUS .
So a few years later during gestation-certification of MAX, Boeing played word games re critical definitions in how failures affect safety of flight- which allowed a single point ' failure' to take control from pilot ( for the first time ever ? ) and then decdided to not notify anyone via some oversight or creative pencil whipping

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


Report: blocked AOA sensors caused loss of control during A320 check flight

note this was with experienced pilots !!
In this Airbus crash 2 out of 3 AoA sensors were frozen. The stall was NOT caused by faulty flight computers but was the result of the pilots voluntarily trying to stall the aircraft to "check" the AoA protection (which could not save them since sensors were frozen). At 2000 ft this is kind of a roulette russe
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Old 18th Mar 2019, 00:10
  #1831 (permalink)  
 
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Originally Posted by sky9 View Post
A/P autoland needs three a/p channels, why isn't the same criteria used for the AOA indicators? What they really need is 4 AOA vanes so they can dispatch with one unserviceable.

But then using software to correct an inherently unstable design at the extreme of its envelope shows how far the industry has gone away from safety first.
there are only 2 channels on a 73
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Old 18th Mar 2019, 00:11
  #1832 (permalink)  
 
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Originally Posted by WHBM View Post
Apparently this is an additionally chargeable option. All three major US customers (Southwest, American, United) have bought it. Lion and Ethiopian did not. I wonder about others.
Take-offs were included in the price, not landings
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Old 18th Mar 2019, 00:12
  #1833 (permalink)  
 
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Originally Posted by WHBM View Post
Apparently this is an additionally chargeable option. All three major US customers (Southwest, American, United) have bought it. Lion and Ethiopian did not. I wonder about others.

And I wonder how the Boeing sales team went about selling this add-on. Why did the US carriers spend the money and others not. Presumably the sales team offered it to everyone. What were their justifications, and why did the US carriers, no fools at tough negotiations, go for it but not others. And how did the FAA certification let it be optional rather than required. How often, for those that fitted it, did it operate ?
Southwest is retrofitting with AoA indicators as well. Believe American had them from the get-go. As I understand, the option is about $60K. Seems like noise level in terms of overall cost per airframe. Can't understand why that would even be an option and not included in the basic frame given the need for MCAS and total cost per airframe.

There was a report on Reuters awhile back after Lion indicating that WestJet, SilkAir, and flydubai also had AoA Diagree installed so at least some of the international carriers.
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Old 18th Mar 2019, 00:16
  #1834 (permalink)  
 
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Old 18th Mar 2019, 00:18
  #1835 (permalink)  
 
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the solution (sarcasm mode on)

If the MCAS isn't that important.... It can't be, because their was no mention of it in the extensive flight training that pilots received on it, according to
Boeing, it would just confuse them. So, why not just deactivate it, and have the planes fly merrily on their way? As all the 'other' 737's do. You don't think there might actually be a reason Boeing hasn't suggested this, do you?
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Old 18th Mar 2019, 00:28
  #1836 (permalink)  
 
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Interesting point in the Seattle Times article, I assume this refers to the Lion Air crash, AOA sensors

The black box data provided in the preliminary investigation report shows that readings from the two sensors differed by some 20 degrees not only throughout the flight but also while the airplane taxied on the ground before takeoff.
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Old 18th Mar 2019, 00:29
  #1837 (permalink)  
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https://www.bloomberg.com/news/artic...tle-times-says
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Old 18th Mar 2019, 00:34
  #1838 (permalink)  
 
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'
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.


nope- it is sufficiently stable without MCAS - which is why they only needed it for the extreme unlikely case which allowed them to use the non flight critical certification. The biggedst screw up was NOT limiting its use and allowing a single sensor to control over the normal pilot disconnect. for 737 and similar

read the seattle times article today
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Old 18th Mar 2019, 00:34
  #1839 (permalink)  
 
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Originally Posted by WHBM View Post
Apparently this is an additionally chargeable option. All three major US customers (Southwest, American, United) have bought it. Lion and Ethiopian did not. I wonder about others.

And I wonder how the Boeing sales team went about selling this add-on. Why did the US carriers spend the money and others not. Presumably the sales team offered it to everyone. What were their justifications, and why did the US carriers, no fools at tough negotiations, go for it but not others. And how did the FAA certification let it be optional rather than required. How often, for those that fitted it, did it operate ?
I wonder too about the sales process. It does seem a little odd that carriers in the domestic market opted for an extra element there was no obvious reason to buy (if they didn't know there was a software feature for which it was a single point of failure), while third-world airlines did not. Was it just cost-saving, or did Boeing push a little harder / offer discounts where failures were less likely to be written off as down to poor maintenance / airmanship?
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Old 18th Mar 2019, 00:47
  #1840 (permalink)  
 
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Thoughts on Seattle Times article published Sunday morning Seattle time

This article is generally well written and seems quite accurate. One point of clarification is that early on in the 737MAX development it was thought that MCAS would only be needed at particularly high Mach numbers. For those conditions the prediction was that the original 0.6 degrees of MCAS stabilizer authority would be sufficient. That proved to be pretty close to the case during flight testing and the final MCAS increment size for cruise and higher Mach numbers is very close to 0.6 deg. Later on it was determined that MCAS would also be needed at lower Mach numbers. With that extension of MCAS came the MCAS authority vs. Mach number schedule that is in the current design. The high Mach end of that schedule is approximately 0.6 degrees. Only with Mach Number less than 0.4 is the MCAS authority 2.5 degrees. The larger authority at lower Mach numbers is needed as the effectiveness of the horizontal stabilizer is less at lower speed. It is quite common that flight control functions are given higher authority at lower airspeed and less authority at airspeed increases.

A second point that did not come through particularly clearly in the Seattle Times article is that the pending MCAS software update has been in the works at Boeing since shortly after the Lion Air accident. As the data for the Ethiopian accident is not yet available (or maybe just came available) nothing that Boeing would be getting out the 737MAX fleet over the next couple of weeks could possibly be based on the most recent event. I'm sure that the team at Boeing will be evaluating the ET accident data as soon as they are able to see (1) if MCAS played any role in this accident, and (2) if MCAS did play a role, how would MCAS have behaved differently had the proposed updates been in place.
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