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osiris30
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Fri Mar 29, 2019 5:27 pm

hivue wrote:
osiris30 wrote:
It may not be able to simulate the aero, but you still run the drills AFAIK.


I believe you're thinking of approach to stall and not stall.


You are right. Been a day, sorry for that. BUT.. if you do one right you never deal with the other :)
I don't care what you think of my opinion. It's my opinion, so have a nice day :)
 
Amexair
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Fri Mar 29, 2019 5:52 pm

morrisond wrote:
speedbored wrote:
morrisond wrote:
It's irrelevant that it doesn't mentions MCAS - how would the pilots know it was MCAS when it wasn't indicated anywhere - they should have been reacting to the symptoms and applying the appropriate response - hit the trim cut-offs.

Given the available information on the ET crash, it seems that the sequence of events was something like:
    Pilots presented with stick shaker on one side and unreliable airspeed alerts
    Pilots carry out checklists and tasks related to unreliable airspeed
    This allows MCAS to kick in
    They then have just 40 seconds, during which they are trying to work out why they are getting an unreliable airspeed indication, and which, if any, airspeed indication is correct, while fighting the MCAS trim adjustments to keep the aircraft under control.

And while all this is going on, you are expecting them to work out that the unreliable airspeed indication and stick shaker is a red herring, work out that the trim adjustments are not the normal automatic trim changes they see every day, but due to the issue they got an AD about 3-4 months ago, then work through the runaway trim checklist, AND manually remove the excess nose-down trim? All in 40 seconds?

Seems a hell of a big ask to me.


Not to me - they were responsible for the lives of over 150 souls. They should have known the contents of that AD backwards and Forwards. It should have been top of mind and they could have easily counteracted the nose down trim with the electric trim before turning it off.

That being said - I wouldn't be surprised if it turns out the Airline never informed the Pilots of the AD in the first place - but that's another matter.



1 - I am confident if they put you in a simulator (or any experience airman for that matter), and replicated the same events, knowing what you know now, bet it will result in a crash.

2 - FAA issued that AD, without the full conclusion of the Lion Air crash - which means that they didn't have all the facts in place, in terms of everything that transpired in the cockpit and how crews would react especially at critical times of flight (ie. takeoff) with several conflicting warning signs. If that was never assessed, it was very irresponsible to issue such a directive in the first place.
 
morrisond
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Fri Mar 29, 2019 6:03 pm

Amexair wrote:
morrisond wrote:
speedbored wrote:
Given the available information on the ET crash, it seems that the sequence of events was something like:
    Pilots presented with stick shaker on one side and unreliable airspeed alerts
    Pilots carry out checklists and tasks related to unreliable airspeed
    This allows MCAS to kick in
    They then have just 40 seconds, during which they are trying to work out why they are getting an unreliable airspeed indication, and which, if any, airspeed indication is correct, while fighting the MCAS trim adjustments to keep the aircraft under control.

And while all this is going on, you are expecting them to work out that the unreliable airspeed indication and stick shaker is a red herring, work out that the trim adjustments are not the normal automatic trim changes they see every day, but due to the issue they got an AD about 3-4 months ago, then work through the runaway trim checklist, AND manually remove the excess nose-down trim? All in 40 seconds?

Seems a hell of a big ask to me.


Not to me - they were responsible for the lives of over 150 souls. They should have known the contents of that AD backwards and Forwards. It should have been top of mind and they could have easily counteracted the nose down trim with the electric trim before turning it off.

That being said - I wouldn't be surprised if it turns out the Airline never informed the Pilots of the AD in the first place - but that's another matter.



1 - I am confident if they put you in a simulator (or any experience airman for that matter), and replicated the same events, knowing what you know now, bet it will result in a crash.

2 - FAA issued that AD, without the full conclusion of the Lion Air crash - which means that they didn't have all the facts in place, in terms of everything that transpired in the cockpit and how crews would react especially at critical times of flight (ie. takeoff) with several conflicting warning signs. If that was never assessed, it was very irresponsible to issue such a directive in the first place.


I would take that bet anytime. Plane/electric trim starts doing weird things - Trim it nose up Electric to zero out the MCAS down (Lionair seems to have done this fine 22 times) then hit the trim cutoff switches within 5 seconds before MCAS activates again.

I doubt there is a crew that couldn't do that.

The Lionair flight previous to the crash was able to do this and they were fine. There are also other reports of flights in the United States experiencing similar issues and they were able to circumvent it (hitting the trim cut-off switches).

And it wasn't an AD - it was a Bulletin issued by Boeing to all it's customers https://theaircurrent.com/aviation-safe ... air-crash/
 
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SheikhDjibouti
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Fri Mar 29, 2019 6:20 pm

hivue wrote:
osiris30 wrote:
It may not be able to simulate the aero, but you still run the drills AFAIK.

I believe you're thinking of approach to stall and not stall.

My understanding is that no simulator can accurately simulate the aerodynamics of a stall in progress. And no one in their right mind is going to purposely stall a modern airliner just for a check ride (or likely for any other reason except flight testing by the manufacturer).

Thank you; that has been my understanding all along.

1) Practice is in a simulator, not in an actual aircraft in flight.
2) Practice is concerned with approach to stall, and avoiding the stall condition

This all comes about from one or several posters insisting that the 737 ( &/or 737 MAX) has benign stall characteristics that any basic pilot should be able to handle.

My argument is that I do not know, and more importantly, everything I have read tells me that the average airline pilot has never experienced a stall except in a Cessna.

In 2013 the FAA made a case for introducing full stall training in sims, and gave sim manufacturers five years to come up with solutions.
Elsewhere I read that stall training in live transport category aircraft has not been undertaken for some years (decades?), as the risks exceed the possible benefits.

Maybe here today in 2019, full stalls are now practised again (only in sims), but that has not been the case until recently.
Nothing to see here; move along please.
 
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PixelFlight
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Fri Mar 29, 2019 6:24 pm

osiris30 wrote:
speedbored wrote:
osiris30 wrote:
^ 2 stuck sensors: It has actually happened on an Airbus design, with triple redundant sensors and they DID overrule the good sensor. So it isn't even a theoretical problem, we have evidence of it happening in actual operation on a current design.

AoA sensors? Care to give us a link to the incident report?


It was linked early in the thread. I want to say it was an LH flight. Lost 4000ft of altitude IIRC.

Ahh here it is:

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


This is exactly why I call the actual sensors redundancy method an industry width issue. Even the 4 sensors of the A350 will travel trought the same environment. If that environment is so harsh to froze one sensor in perfect condition then the others are certainly close to froze very soon. Adding more sensors is effective to disable erratic sensor that fail because there where damaged. Adding sensors is not effective if there will fail due to a common environmental cause. This risky game at the corner of the probability must be addresses more properly. Fortunately the solution exists: sensors filter with flight dynamic predictor. The individual sensor contribution to the flight dynamic predictor is filtered by the accuracy of the result of the previous prediction against all the others observable variables. The flight computers will gets a probability of the value instead of a discrete value with a unknown precision. This allow to compute the safest action given the reduced flight domain due to lost of precision.
:stirthepot: 737-8 MAX: "For all speeds higher than 220 Kts and trim set at a value of 2.5 units, the difficulity level of turning the manual trim wheel was level A (trim wheel not movable)." :stirthepot:
 
Amexair
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Fri Mar 29, 2019 6:30 pm

osiris30 wrote:
Planetalk wrote:
PixelPilot wrote:

ET boss himself said those pilots were trained on MCAS. Stop banging your head against the wall. IT will make you even less objective.
From what we know, something happened that in the end activated MCAS but at that point if they were trained like ET is stating they should have had no problem disconnecting it and flying manually. I bet on this. ET stated they will continue working with boeing and they have faith in them. You don't drop the tone in event like this (especially when entire world went to war against B) unless you realized that fault is somewhere in the middle.
There's a lot more here apparently. MCAS was just the final straw if we are to believe that this article is 100% true.


How on earth do you come to this conclusion? Considering this happened to two different crews on a new type recently introduced (when did that last happen in aviation history?) this is a staggering simplification, and with respect, not based on any revealed facts. Unless you have personally flown a 737 Max in the situation these pilots encountered you have no reason, or right, to make such assertions.

Given that reports that Boeing didn't even flight test it themselves, and the apparent surprise of the pilots in the simulator tests at the forces needed to counter MCAS - WHEN THEY WERE FULLY BRIEFED AND EXPECTING IT - I personally would hold off on these kinds of statements.

Then of course there is the EASA statement that training was necessary that was never provided. This raises another question of whether this puts EASA in the dock as well for not checking this happened.


See my last comment, the comments by ET's CEO regarding training have subsequently turned out to be potentially inaccurate (I don't have time to search for the articles/this thread). That alone moves things closer to the middle. He knew enough to say they had it, so the airline was aware of it, but potentially all their pilots hadn't received it yet.



Wrong, you are conflating two different issues. The article you are speaking of is with regards to whether or not the pilots of the crashed jet received further training on the MAX simulator which ET recently got. The pilots were briefed on the AD, and the contents of it were incorporated into all training manuals, procedures, and working manuals.
 
XRAYretired
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Fri Mar 29, 2019 6:34 pm

osiris30 wrote:
XRAYretired wrote:
osiris30 wrote:

See my last comment, the comments by ET's CEO regarding training have subsequently turned out to be potentially inaccurate (I don't have time to search for the articles/this thread). That alone moves things closer to the middle. He knew enough to say they had it, so the airline was aware of it, but potentially all their pilots hadn't received it yet.

Cant find any retraction only affirmation on 24th that the pilots on ET302 had been trained per FAA/Boeing requirements for conversion and post JT610.

Ray


a quick search turns up:

https://www.reuters.com/article/us-ethi ... SKCN1R20WD

The Max simulator is the only place they could have trained. He may have been briefed, but he wasn't trained (officially). Again, all from "sources" which is why I said potentially inaccurate.


Splitting hairs does you no justice.

Ray
 
mila
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Fri Mar 29, 2019 6:42 pm

speedbored wrote:
rideforever wrote:
so you are telling me the only option is to buy off the shelf AoAs that all freeze together.

But why would they all freeze together? They have heaters to prevent freezing so, if conditions are so bad that they will freeze despite the heaters, conditions will probably be bad enough to freeze every type of sensor.

Or do you think that all three would suffer a heater failure at the same time?

Maybe you can cite some instances where an aircraft has suffered multiple AoA sensor failures at the same time? You'll find it is extremely rare.

The problem is most likely that if they are of the same design and placed close to each other they will freeze at the same time.

AF447 is a great example.
 
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speedbored
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Fri Mar 29, 2019 6:48 pm

hivue wrote:
speedbored wrote:
AoA sensors? Care to give us a link to the incident report?


AoA sensors.
https://aviation-safety.net/wikibase/wiki.php?id=171411

Interesting. But nothing to suggest that the freezing was due to any specific property of the type of sensor being used so no reason to believe that having 3 different sensor types on the aircraft would have made any difference.
 
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speedbored
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Fri Mar 29, 2019 6:51 pm

mila wrote:
The problem is most likely that if they are of the same design and placed close to each other they will freeze at the same time.
AF447 is a great example.

But they are not placed close to each other.
 
morrisond
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Fri Mar 29, 2019 6:51 pm

SheikhDjibouti wrote:
hivue wrote:
osiris30 wrote:

This all comes about from one or several posters insisting that the 737 ( &/or 737 MAX) has benign stall characteristics that any basic pilot should be able to handle.


The same basic aerodynamic principles apply to a Cessna or a 737.

Watch this - looks just like it does in a Cessna and is about as benign - and how could you miss all those warnings?

https://www.youtube.com/watch?v=zCJco59tqoQ
 
Backseater
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Fri Mar 29, 2019 7:28 pm

UTC/Rosemount AoA sensors that are apparently installed on 737MAX are claimed by their manufacturer to be very reliable:
“Model 0861 AOA Transmitter. This swept tapered vane angle of attack transmitter:
- is aerodynamically aligned, has high reliability, low maintenance requirements and superior performance…
- is electrically de-iced by a solid state heater … These self-regulating heaters do not require thermostats, thereby lowering system complexity and increasing reliability

Now, does anybody believe that the Lion Air AoA sensor (and probably the Ethiopian AoA as well) failed while accelerating down the runway?

I have a strong suspicion that an “unserviceable” AoA sensor was installed and somehow passed the post-installation ground tests.

To me, that is a more serious MRO issue because, if it is indeed the case, the MCAS improvement may still leave pilots debugging a “non serviceable” AC while in flight!
 
jollo
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Fri Mar 29, 2019 7:48 pm

osiris30 wrote:
jollo wrote:
speedbored wrote:
Or a maintenance nightmare and an increased likelihood of minor sensor disagreements. Increased complexity such as having to maintain 3 different types of sensor, or to make adjustments to exactly match different sensor technologies, in my experience, almost always leads to increased risk of errors.


Agreed, no redundant sensor set is ever implemented with different sensor models: calibration would be much less robust, failure modes would multiply (the order of failures would affect the outcome), basically you end up with a system which, right out of the factory, is much less robust than with 3 identical sensors. Then you have maintenance, which as noted would be a nightmare.

If you really want a safe architecture, you plan for a primary controller with (at least) 3 identical sensors, and a backup control stack with different everything: different sensor, different data bus, different controller hardware, different software developed by a different vendor (on the same requirements). Both controllers are always on, but normally only the primary actually drives actuators; when the primary quits because 2 sensors failed*, you switch the actuators to the backup, which will likely be unaffected by the current failure mode.

* There are ways to detect a failed/stuck sensor, but not with absolute confidence; on the other hand you can very reliably detect 2 failed sensors. This is important because 2 sensors stuck on the same position (very rare occurrence, but it can happen) could outvote the single remaining good sensor; in this scenario, the controller must detect the double sensor failure and quit, handing control to the backup (or to the human pilot).


^ 2 stuck sensors: It has actually happened on an Airbus design, with triple redundant sensors and they DID overrule the good sensor. So it isn't even a theoretical problem, we have evidence of it happening in actual operation on a current design.


You are correct, this isn't a theoretical problem: double sensor failures do occur, and as an automation designer you must plan for the contingency.

I believe the Airbus accident you refer to is GXL888T: that was 10 years ago, on a flight control system designed in the '80s (the very first FBW system on a civilian airliner). You may call that a "current" design because the model is still in active service, but automation has come a long way since. Today's designs do include logic to detect double sensor failures very reliably. If you want to read up, try https://arc.aiaa.org/doi/10.2514/6.2016-1135: the gist of it is that every sensor data channel is diagnosed separately, and by correlating the diagnostics you get a very low probability of mistaking 2 stuck sensors in agreement for 2 good sensors in agreement.

To put things in perspective: in the whole service history of the A3XX family there is exactly one recorded occurrence of a double sensor failure preventing a triple-redundant envelope protection system to work as expected (and that plane only crashed because pilots were improvising test protocols at low altitude). Frequency = 1 / number of flights since 1988.
 
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speedbored
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Fri Mar 29, 2019 8:15 pm

Backseater wrote:
Now, does anybody believe that the Lion Air AoA sensor (and probably the Ethiopian AoA as well) failed while accelerating down the runway?

I have a strong suspicion that an “unserviceable” AoA sensor was installed and somehow passed the post-installation ground tests.

To me, that is a more serious MRO issue because, if it is indeed the case, the MCAS improvement may still leave pilots debugging a “non serviceable” AC while in flight!

Do we even know that it was actually the sensor itself that failed? It could just have easily been a fault in an intermediate data module, a flight computer, or even a faulty connector.

I see no evidence whatsoever so far to support the idea that an unserviceable sensor was installed on either aircraft.
 
Backseater
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Fri Mar 29, 2019 8:48 pm

speedbored wrote:
Backseater wrote:
Now, does anybody believe that the Lion Air AoA sensor (and probably the Ethiopian AoA as well) failed while accelerating down the runway?

I have a strong suspicion that an “unserviceable” AoA sensor was installed and somehow passed the post-installation ground tests.

To me, that is a more serious MRO issue because, if it is indeed the case, the MCAS improvement may still leave pilots debugging a “non serviceable” AC while in flight!

Do we even know that it was actually the sensor itself that failed? It could just have easily been a fault in an intermediate data module, a flight computer, or even a faulty connector.

I see no evidence whatsoever so far to support the idea that an unserviceable sensor was installed on either aircraft.

Of course, I have no hard evidence to support my suspicion.
But If you read my post #3676, an AoA sensor of a different manufacturer had been installed and flown in a 747-400 in 2012, although it turned out that it should never have been installed and successfully tested:
“Inspection of the AOA sensors showed that the set screw connected to the synchro transmitter was not correctly attached to the AOA sensor shaft”.
That is why I think that wrongly (re)assembled parts may find their way onto "serviceable" AC and of course cause problems in flight.
 
smartplane
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Fri Mar 29, 2019 9:11 pm

osiris30 wrote:
Stall recovery is routinely practiced in sims and is part of the check ride (sim) for ?many/most/all? airlines.

Pointless on NG simulators (because MAX is the same argument)? And on MAX simulators that didn't replicate 'real' MCAS behaviour?
 
Planetalk
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Fri Mar 29, 2019 9:17 pm

osiris30 wrote:
gatibosgru wrote:
osiris30 wrote:

Actually, ET CEO's comments on MCAS training was subsequently announced (somewhere in this thread/press) to be untrue. The CEO knew enough to know his pilots SHOULD have had the training, but apparently that was not an accurate statement on his part.


Do you have a source for this? Not saying you're wrong, just couldn't find one myself.


https://www.reuters.com/article/us-ethi ... SKCN1R20WD

The pilot may have been briefed but wasn't 'trained' as far as I can tell. There were a few clearer articles that I can't find immediately, but the search terms are a bit tricky. I will try to find the others later.


This was extensively discussed earlier. Despite the article's attempt to sensationalise the issue, it actually shows Ethiopian Airlines to have been ahead of the game as they were amongst the first in the world to be getting hold of the simulators, which practically noone currently has. So yes the CEO was absolutely correct saying they had received the new training.

So hopefully we will all acknowledge and give credit where it is true for Ethiopian apparently being leaders on this , rather than bringing up already debunked media nonsense to throw more dirt at the pilots and the airline.
 
mxaxai
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Fri Mar 29, 2019 9:21 pm

jollo wrote:
To put things in perspective: in the whole service history of the A3XX family there is exactly one recorded occurrence of a double sensor failure preventing a triple-redundant envelope protection system to work as expected (and that plane only crashed because pilots were improvising test protocols at low altitude). Frequency = 1 / number of flights since 1988.

eh ...
http://avherald.com/h?article=40de5374/0006&opt=0
Automatic nose down command after a single faulty AoA sensor confused the ADIRU.

http://avherald.com/h?article=47d74074/0000&opt=0
Alpha prot / Automatic nose down command due to 2 frozen AoA vanes (of 3).

And that's without frozen or damaged pitot tubes, which can also trigger stall warnings and all the nice things that come along.

On the other hand, this 787 handled iced pitot tubes quite well, but they had a skilled crew too.
http://avherald.com/h?article=49126557&opt=0
 
ikramerica
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Fri Mar 29, 2019 9:53 pm

rheinwaldner wrote:
ikramerica wrote:
rheinwaldner wrote:
Simple: None!

You continue to overlook the evidence of decade long trouble free operations, which is overwhelming in case of 767 and 757. Not so with the MAX.

Yeah. Who says they have been trouble free?

Statistics. And with trouble I mean comparable trouble. As even the hysterical social media crowd seems to be getting the difference, I wonder why you cant see it.

Have you studied statistics and econometrics at a college level? Show me the statistical significance of 2 clustered crashes out of 200,000 when we don't know the cause of the second and we have a good idea about the first (pilot error/CRM failure that was the aftermath of a fault). And again, can you point me to why we only suspect this is a MAX issue and not a loarger NG one or CFM, considering we don't know what crashed ET but we do know that things went south on the runway before the fancy MAX acronyms could even interfere?

And show me the data for the “trouble free” history of the 756/767. Multiple 757 crashes, recent 767 crash involving reportedly due to pilot error that followed what may be a design flaw just recently discovered despite 40 years (call it the TOGA time-bomb). Years and years of engine shut downs, uncontained failures. We had a write off of an AA 767 at LAX after engine failure on a test run. If AA weren't as diligent as they should be, maybe that 767 gets dispatched.

The 747 certainly hasn't been trouble free. Many crashes and incidents due to design flaws. We have an unexplained crash of a 777 that people blame on sabotage yet we don't actually have lots of proof. Heck, the MD11 is inherently unstable on landing and yet we still seem to fly those deathtraps about.
Of all the things to worry about... the Wookie has no pants.
 
osiris30
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Fri Mar 29, 2019 10:04 pm

smartplane wrote:
osiris30 wrote:
Stall recovery is routinely practiced in sims and is part of the check ride (sim) for ?many/most/all? airlines.

Pointless on NG simulators (because MAX is the same argument)? And on MAX simulators that didn't replicate 'real' MCAS behaviour?

We were discussing stalls not MCAS ... But hey... Why be relevant...
I don't care what you think of my opinion. It's my opinion, so have a nice day :)
 
osiris30
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Fri Mar 29, 2019 10:05 pm

Planetalk wrote:
osiris30 wrote:
gatibosgru wrote:

Do you have a source for this? Not saying you're wrong, just couldn't find one myself.


https://www.reuters.com/article/us-ethi ... SKCN1R20WD

The pilot may have been briefed but wasn't 'trained' as far as I can tell. There were a few clearer articles that I can't find immediately, but the search terms are a bit tricky. I will try to find the others later.


This was extensively discussed earlier. Despite the article's attempt to sensationalise the issue, it actually shows Ethiopian Airlines to have been ahead of the game as they were amongst the first in the world to be getting hold of the simulators, which practically noone currently has. So yes the CEO was absolutely correct saying they had received the new training.

So hopefully we will all acknowledge and give credit where it is true for Ethiopian apparently being leaders on this , rather than bringing up already debunked media nonsense to throw more dirt at the pilots and the airline.


I am not throwing any dirt in anyone. I am saying there are conflicting reports. Then provided evidence of conflicting reports. Your turn: provide evidence ET are leaders in this area.
I don't care what you think of my opinion. It's my opinion, so have a nice day :)
 
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zeke
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Fri Mar 29, 2019 10:11 pm

mxaxai wrote:
And that's without frozen or damaged pitot tubes, which can also trigger stall warnings and all the nice things that come along.


Incorrect, stall warning is based off angle of attack, nothing to do with speed. That is why the ADR fault procedure says to respect stall warnings even with faulty air data.

The backup speed scale on the Airbus replaces the speed information on the PFD with a fast/slow angle of attack indicator.
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osiris30
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Fri Mar 29, 2019 10:16 pm

jollo wrote:
osiris30 wrote:
jollo wrote:

Agreed, no redundant sensor set is ever implemented with different sensor models: calibration would be much less robust, failure modes would multiply (the order of failures would affect the outcome), basically you end up with a system which, right out of the factory, is much less robust than with 3 identical sensors. Then you have maintenance, which as noted would be a nightmare.

If you really want a safe architecture, you plan for a primary controller with (at least) 3 identical sensors, and a backup control stack with different everything: different sensor, different data bus, different controller hardware, different software developed by a different vendor (on the same requirements). Both controllers are always on, but normally only the primary actually drives actuators; when the primary quits because 2 sensors failed*, you switch the actuators to the backup, which will likely be unaffected by the current failure mode.

* There are ways to detect a failed/stuck sensor, but not with absolute confidence; on the other hand you can very reliably detect 2 failed sensors. This is important because 2 sensors stuck on the same position (very rare occurrence, but it can happen) could outvote the single remaining good sensor; in this scenario, the controller must detect the double sensor failure and quit, handing control to the backup (or to the human pilot).


^ 2 stuck sensors: It has actually happened on an Airbus design, with triple redundant sensors and they DID overrule the good sensor. So it isn't even a theoretical problem, we have evidence of it happening in actual operation on a current design.


You are correct, this isn't a theoretical problem: double sensor failures do occur, and as an automation designer you must plan for the contingency.

I believe the Airbus accident you refer to is GXL888T: that was 10 years ago, on a flight control system designed in the '80s (the very first FBW system on a civilian airliner). You may call that a "current" design because the model is still in active service, but automation has come a long way since. Today's designs do include logic to detect double sensor failures very reliably. If you want to read up, try https://arc.aiaa.org/doi/10.2514/6.2016-1135: the gist of it is that every sensor data channel is diagnosed separately, and by correlating the diagnostics you get a very low probability of mistaking 2 stuck sensors in agreement for 2 good sensors in agreement.

To put things in perspective: in the whole service history of the A3XX family there is exactly one recorded occurrence of a double sensor failure preventing a triple-redundant envelope protection system to work as expected (and that plane only crashed because pilots were improvising test protocols at low altitude). Frequency = 1 / number of flights since 1988.


Couple of things:. There have been other issues. Someone highlighted a few below. Also there may be other instances of dual sensor failures that went undetected and/or unreported. For example vanes frozen outside of stall AoA would be undetectable by pilots.

Besides my point here wasn't a comparison it was merely to support that dual sensor failure is not just a hypothetical failure and provide evidence of such.
I don't care what you think of my opinion. It's my opinion, so have a nice day :)
 
osiris30
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Fri Mar 29, 2019 10:19 pm

XRAYretired wrote:
osiris30 wrote:
XRAYretired wrote:
Cant find any retraction only affirmation on 24th that the pilots on ET302 had been trained per FAA/Boeing requirements for conversion and post JT610.

Ray


a quick search turns up:

https://www.reuters.com/article/us-ethi ... SKCN1R20WD

The Max simulator is the only place they could have trained. He may have been briefed, but he wasn't trained (officially). Again, all from "sources" which is why I said potentially inaccurate.


Splitting hairs does you no justice.

Ray


Sorry you consider conflicting media reports splitting hairs. We will see when the preliminary comes out. It should answer it for sure.
I don't care what you think of my opinion. It's my opinion, so have a nice day :)
 
WIederling
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Fri Mar 29, 2019 10:30 pm

osiris30 wrote:
Sorry you consider conflicting media reports splitting hairs. We will see when the preliminary comes out. It should answer it for sure.


Splitting hairs? You are quartering them!

Your argument is moot as no real existing commercial flight simulator dedicated MAX or not in airline hands knows about MCAS.
Murphy is an optimist
 
XRAYretired
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Fri Mar 29, 2019 10:46 pm

osiris30 wrote:
XRAYretired wrote:
osiris30 wrote:

a quick search turns up:

https://www.reuters.com/article/us-ethi ... SKCN1R20WD

The Max simulator is the only place they could have trained. He may have been briefed, but he wasn't trained (officially). Again, all from "sources" which is why I said potentially inaccurate.


Splitting hairs does you no justice.

Ray


Sorry you consider conflicting media reports splitting hairs. We will see when the preliminary comes out. It should answer it for sure.



Lateral disection of rabbits then.
 
osiris30
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Fri Mar 29, 2019 10:47 pm

WIederling wrote:
osiris30 wrote:
Sorry you consider conflicting media reports splitting hairs. We will see when the preliminary comes out. It should answer it for sure.


Splitting hairs? You are quartering them!

Your argument is moot as no real existing commercial flight simulator dedicated MAX or not in airline hands knows about MCAS.


Read the article. It is stated the refresher training hadn't been done with that pilot. To me that is irrelevant unless said refresher training is where they did the mcas training. Of course I am not surprised you won't read it that way. Hell it could be black and white right there saying it (as other articles did) and you'd still downplay it. But again the preliminary shall be out in a few days and we will see. You have your assumptions you cling to, I have mine, hopefully in a few days we get answers.
I don't care what you think of my opinion. It's my opinion, so have a nice day :)
 
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PW100
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Fri Mar 29, 2019 11:13 pm

ExDubai wrote:
The EASA document Reuter’s referring to:
https://www.easa.europa.eu/sites/defaul ... S%2010.pdf

Issue 10, Page 15.

Interesting reading:
Furthermore, the additional crew procedures and training material will clearly explain to pilots the situations where use of the trim wheel may be needed due to lack of trim authority with the wheel mounted switches.


Can someone explain this to me? How can the manual trim wheel have more trim authority than the wheel-(column?) mounted switches? Both drive the stabilizer jack screw.
Is it being suggested that the electric trimming (control column trim switches) is overruled by MCAS?
Immigration officer: "What's the purpose of your visit to the USA?" Spotter: "Shooting airliners with my Canon!"
 
asdf
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Fri Mar 29, 2019 11:36 pm

PW100 wrote:
ExDubai wrote:
The EASA document Reuter’s referring to:
https://www.easa.europa.eu/sites/defaul ... S%2010.pdf

Issue 10, Page 15.

Interesting reading:
Furthermore, the additional crew procedures and training material will clearly explain to pilots the situations where use of the trim wheel may be needed due to lack of trim authority with the wheel mounted switches.


Can someone explain this to me? How can the manual trim wheel have more trim authority than the wheel-(column?) mounted switches? Both drive the stabilizer jack screw.
Is it being suggested that the electric trimming (control column trim switches) is overruled by MCAS?


you can not trim UP as long as MCAS trimms DOWN
in the time frame MCAS is at work the crew has no authority over the trim

to cut the electric trim out only helps if the nose is not to far down becaus with the manual trim wheels you are pretty slow in trim the nose up again
 
mxaxai
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Fri Mar 29, 2019 11:39 pm

zeke wrote:
mxaxai wrote:
And that's without frozen or damaged pitot tubes, which can also trigger stall warnings and all the nice things that come along.


Incorrect, stall warning is based off angle of attack, nothing to do with speed. That is why the ADR fault procedure says to respect stall warnings even with faulty air data.

The backup speed scale on the Airbus replaces the speed information on the PFD with a fast/slow angle of attack indicator.

Thanks for the correction. I guess I got confused by reports like this one:
http://avherald.com/h?article=40b278ab&opt=0
where unreliable airspeed and faulty AoA sensors were present.
 
jollo
Posts: 395
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Fri Mar 29, 2019 11:40 pm

mxaxai wrote:
eh ...
http://avherald.com/h?article=40de5374/0006&opt=0
Automatic nose down command after a single faulty AoA sensor confused the ADIRU.


This is (in)famous Quantas Flight 72: nothing to do with double sensor failure.

mxaxai wrote:
http://avherald.com/h?article=47d74074/0000&opt=0
Alpha prot / Automatic nose down command due to 2 frozen AoA vanes (of 3).


This is exactly what we're talking about: 2 sensors stuck at the same angle outvoting the single good sensor remaining. Thanks for pointing it out to me, I didn't know about this accident. So I stand corrected, there are multiple occurrences reported (and there may well have been more going unreported/undetected). The perspective, however, doesn't change much: twin sensor failures fooling a triple-redundant architecture into outvoting the single good data source are very rare. Not impossible, though, so you have to design for it.
 
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zeke
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Sat Mar 30, 2019 12:02 am

mxaxai wrote:
Thanks for the correction. I guess I got confused by reports like this one:
http://avherald.com/h?article=40b278ab&opt=0
where unreliable airspeed and faulty AoA sensors were present.


Completely different architecture between the 747 and a FBW Airbus, the 747 architecture is closer to a 737.
Human rights lawyers are "ambulance chasers of the very worst kind.'" - Sky News
 
osiris30
Posts: 2681
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Sat Mar 30, 2019 12:45 am

XRAYretired wrote:
osiris30 wrote:
XRAYretired wrote:

Splitting hairs does you no justice.

Ray


Sorry you consider conflicting media reports splitting hairs. We will see when the preliminary comes out. It should answer it for sure.



Lateral disection of rabbits then.


:rotfl: :rotfl: Well played (we need a hat tip emoji)
I don't care what you think of my opinion. It's my opinion, so have a nice day :)
 
osiris30
Posts: 2681
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Sat Mar 30, 2019 12:46 am

asdf wrote:
PW100 wrote:
ExDubai wrote:
The EASA document Reuter’s referring to:
https://www.easa.europa.eu/sites/defaul ... S%2010.pdf

Issue 10, Page 15.

Interesting reading:
Furthermore, the additional crew procedures and training material will clearly explain to pilots the situations where use of the trim wheel may be needed due to lack of trim authority with the wheel mounted switches.


Can someone explain this to me? How can the manual trim wheel have more trim authority than the wheel-(column?) mounted switches? Both drive the stabilizer jack screw.
Is it being suggested that the electric trimming (control column trim switches) is overruled by MCAS?


you can not trim UP as long as MCAS trimms DOWN
in the time frame MCAS is at work the crew has no authority over the trim

to cut the electric trim out only helps if the nose is not to far down becaus with the manual trim wheels you are pretty slow in trim the nose up again


False. This has been discussed many many many many many times. This is one of those a.net myths.
I don't care what you think of my opinion. It's my opinion, so have a nice day :)
 
osiris30
Posts: 2681
Joined: Sat Sep 30, 2006 10:16 am

Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Sat Mar 30, 2019 12:47 am

PW100 wrote:
ExDubai wrote:
The EASA document Reuter’s referring to:
https://www.easa.europa.eu/sites/defaul ... S%2010.pdf

Issue 10, Page 15.

Interesting reading:
Furthermore, the additional crew procedures and training material will clearly explain to pilots the situations where use of the trim wheel may be needed due to lack of trim authority with the wheel mounted switches.


Can someone explain this to me? How can the manual trim wheel have more trim authority than the wheel-(column?) mounted switches? Both drive the stabilizer jack screw.
Is it being suggested that the electric trimming (control column trim switches) is overruled by MCAS?


No. There are trim limits on the electronic trim IIRC. Manual use of the wheel has greater authority and might potentially be able to be driven more rapidly than electric (last part I am far less sure of).
I don't care what you think of my opinion. It's my opinion, so have a nice day :)
 
Lrockeagle
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Sat Mar 30, 2019 1:17 am

speedbored wrote:
morrisond wrote:
It's irrelevant that it doesn't mentions MCAS - how would the pilots know it was MCAS when it wasn't indicated anywhere - they should have been reacting to the symptoms and applying the appropriate response - hit the trim cut-offs.

Given the available information on the ET crash, it seems that the sequence of events was something like:
    Pilots presented with stick shaker on one side and unreliable airspeed alerts
    Pilots carry out checklists and tasks related to unreliable airspeed
    This allows MCAS to kick in
    They then have just 40 seconds, during which they are trying to work out why they are getting an unreliable airspeed indication, and which, if any, airspeed indication is correct, while fighting the MCAS trim adjustments to keep the aircraft under control.

And while all this is going on, you are expecting them to work out that the unreliable airspeed indication and stick shaker is a red herring, work out that the trim adjustments are not the normal automatic trim changes they see every day, but due to the issue they got an AD about 3-4 months ago, then work through the runaway trim checklist, AND manually remove the excess nose-down trim? All in 40 seconds?

Seems a hell of a big ask to me.

Nobody stood there with a watch and said “you have 40 seconds, go”. Ever think maybe it’s possible they only made it 40 seconds because they forgot to AVIATE?
CA:”you fly the plane, I’m gonna figure this out”
FO: “aight I’m flying the plane”
Lrockeagle
14 years ago

I got $20 says AA takes their 787's with GE powerplants. Just a hunch. Any takers?
 
Planetalk
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Sat Mar 30, 2019 1:56 am

ikramerica wrote:
rheinwaldner wrote:
ikramerica wrote:
Yeah. Who says they have been trouble free?

Statistics. And with trouble I mean comparable trouble. As even the hysterical social media crowd seems to be getting the difference, I wonder why you cant see it.

Have you studied statistics and econometrics at a college level? Show me the statistical significance of 2 clustered crashes out of 200,000 when we don't know the cause of the second and we have a good idea about the first (pilot error/CRM failure that was the aftermath of a fault). And again, can you point me to why we only suspect this is a MAX issue and not a loarger NG one or CFM, considering we don't know what crashed ET but we do know that things went south on the runway before the fancy MAX acronyms could even interfere?

And show me the data for the “trouble free” history of the 756/767. Multiple 757 crashes, recent 767 crash involving reportedly due to pilot error that followed what may be a design flaw just recently discovered despite 40 years (call it the TOGA time-bomb). Years and years of engine shut downs, uncontained failures. We had a write off of an AA 767 at LAX after engine failure on a test run. If AA weren't as diligent as they should be, maybe that 767 gets dispatched.

The 747 certainly hasn't been trouble free. Many crashes and incidents due to design flaws. We have an unexplained crash of a 777 that people blame on sabotage yet we don't actually have lots of proof. Heck, the MD11 is inherently unstable on landing and yet we still seem to fly those deathtraps about.


I assure you the people who made the decision to ground these planes know about statistics and econometrics, at a level far beyond 'college level' which, with due respect, provides absolutely no qualification here. They also know considerably more than anyone posting here about what caused these crashes. Some posters really do seem to have a deluded idea of their own knowledge, which is apparently greater than all the regulators and investigators of the world combined. Not sure why such smart people are left posting their opinions on internet forums.
 
GalebG4
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Sat Mar 30, 2019 2:34 am

Boeing you made a huge mistake. Accept it and get on with it, I don’t care about your airliners.net forum protectionists who will protect you no matter what. You made mistake, pay the families of the victims. Anybody could be in that plane(even you Boeing airliners.net forum protectionist- keyboard employee warrior) with uniformed pilots about system. This is your fault Boeing so stop being sneaky and trying to say we haven’t done anything wrong. You have, people died second time for the same reason.

Please don’t answer any Boeing airlines.net forum protectionists-keyboard warriors, because that’s spiting on people that have innocently died.
 
sgrow787
Posts: 450
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Sat Mar 30, 2019 4:53 am

flybucky wrote:
Even 3 AOA sensors only reduces the risk and does not eliminate it. Airbus had at least 2 incidents where 2 of the AOA sensors froze and gave the same invalid input, outvoting the 3rd AOA sensor (which was the valid one!). The computer forced the plane to pitch down, which could not be compensated even with full stick back.

2008 A320 acceptance flight - crashed into the sea with no survivors.
2014 A321 Lufthansa 1829 - dropped 4000 ft before the pilots disconnected the ADR and recovered the flight.


But AOA sensors don't freeze until 32000 ft. Plenty of height to deal with nose down issues.
Just one sensor,
Oh just one se-en-sor,
Just one sensor,
Ooh ooh oo-ooh
Oo-oo-ooh.
 
PlanesNTrains
Posts: 9524
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Sat Mar 30, 2019 6:03 am

GalebG4 wrote:
Boeing you made a huge mistake. Accept it and get on with it, I don’t care about your airliners.net forum protectionists who will protect you no matter what. You made mistake, pay the families of the victims. Anybody could be in that plane(even you Boeing airliners.net forum protectionist- keyboard employee warrior) with uniformed pilots about system. This is your fault Boeing so stop being sneaky and trying to say we haven’t done anything wrong. You have, people died second time for the same reason.

Please don’t answer any Boeing airlines.net forum protectionists-keyboard warriors, because that’s spiting on people that have innocently died.


You’re great at casting stones. How about we wait for the investigation?
-Dave


MAX’d out on MAX threads. If you are starting a thread, and it’s about the MAX - stop. There’s already a thread that covers it.
 
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Finn350
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Sat Mar 30, 2019 6:04 am

mxaxai wrote:
http://avherald.com/h?article=40de5374/0006&opt=0
Automatic nose down command after a single faulty AoA sensor confused the ADIRU.


Out of curiosity, I checked the failure mode description. It was very specific, now corrected, and at the time of the event, it was 1 out of 28,000,000 flight hours occurrence.

FCPC design limitation

AOA is a critically important flight parameter, and full-authority flight control systems such as those equipping A330/A340 aircraft require accurate AOA data to function properly. The aircraft was fitted with three ADIRUs to provide redundancy and enable fault tolerance, and the FCPCs used the three independent AOA values to check their consistency. In the usual case, when all three AOA values were valid and consistent, the average value of AOA 1 and AOA 2 was used by the FCPCs for their computations. If either AOA 1 or AOA 2 significantly deviated from the other two values, the FCPCs used a memorised value for 1.2 seconds. The FCPC algorithm was very effective, but it could not correctly manage a scenario where there were multiple spikes in either AOA 1 or AOA 2 that were 1.2 seconds apart.

Although there were many injuries on the 7 October 2008 flight, it is very unlikely that the FCPC design limitation could have been associated with a more adverse outcome. Accordingly, the occurrence fitted the classification of a ‘hazardous’ effect rather than a ‘catastrophic’ effect as described by the relevant certification requirements. As the occurrence was the only known case of the design limitation affecting an aircraft’s flightpath in over 28 million flight hours on A330/A340 aircraft, the limitation was within the acceptable probability range defined in the certification requirements for a hazardous effect.

As with other safety-critical systems, the development of the A330/A340 flight control system during 1991 and 1992 had many elements to minimise the risk of a design error. These included peer reviews, a system safety assessment (SSA), and testing and simulations to verify and validate the system requirements. None of these activities identified the design limitation in the FCPC’s AOA algorithm.

The ADIRU failure mode had not been previously encountered, or identified by the ADIRU manufacturer in its safety analysis activities. Overall, the design, verification and validation processes used by the aircraft manufacturer did not fully consider the potential effects of frequent spikes in data from an ADIRU.


https://www.atsb.gov.au/publications/in ... -2008-070/
 
rheinwaldner
Posts: 1857
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Sat Mar 30, 2019 6:54 am

ikramerica wrote:
rheinwaldner wrote:
Statistics. And with trouble I mean comparable trouble. As even the hysterical social media crowd seems to be getting the difference, I wonder why you cant see it.

Have you studied statistics and econometrics at a college level? Show me the statistical significance of 2 clustered crashes out of 200,000...

Stop. We talked about the statistics of the 757 and 767. You argued that one case among dozens of millions would be significant and comparable. So you should doubt the guy in the mirror before doubting my statistics skills.

Plus, 2 crashes out of 200k is a horrible accident rate in civil aviation, reminds us of times long gone. It is so bad, that just the suspicion of related causes warrants the grounding.

Plus, from a statistical viewpoint, the crucial difference is the short time after EIS when these crashes happened. If today a 767 would crash and 6 months later another one (with strong similarities), we would still know that the crashes are unrelated. Why? Because a common fault would have brought down many 767s since 1981. NGs hampered by the same flaw would have crashed by the hundreds since EIS. That's how far off you are with your comparison.

I mean, in the same post, you declare the MAX crashes as not significant while fabricating some weird theory, that the 757, 767, 777 would be affected by significant safety flaws? I recommend you to quickly recap the very first hour in statistics that you ever attended.
Many things are difficult, all things are possible!
 
marcelh
Posts: 1012
Joined: Wed Jun 19, 2013 12:43 pm

Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Sat Mar 30, 2019 7:07 am

PlanesNTrains wrote:
GalebG4 wrote:
Boeing you made a huge mistake. Accept it and get on with it, I don’t care about your airliners.net forum protectionists who will protect you no matter what. You made mistake, pay the families of the victims. Anybody could be in that plane(even you Boeing airliners.net forum protectionist- keyboard employee warrior) with uniformed pilots about system. This is your fault Boeing so stop being sneaky and trying to say we haven’t done anything wrong. You have, people died second time for the same reason.

Please don’t answer any Boeing airlines.net forum protectionists-keyboard warriors, because that’s spiting on people that have innocently died.


You’re great at casting stones. How about we wait for the investigation?

Pot...kettle...black :ziplip:
 
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SomebodyInTLS
Posts: 1840
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Sat Mar 30, 2019 9:01 am

osiris30 wrote:
Stall recovery is routinely practiced in sims and is part of the check ride (sim) for ?many/most/all? airlines.


Nope...

Recovery from APPROACH to stall is practiced regularly. Because that's what simulators can actually simulate and what systems are actually designed around and what training is actually based on.

You are never supposed to actually get to be in a stall since then all bets are off.
"As with most things related to aircraft design, it's all about the trade-offs and much more nuanced than A.net likes to make out."
 
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speedbored
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Sat Mar 30, 2019 9:10 am

SomebodyInTLS wrote:
osiris30 wrote:
Stall recovery is routinely practiced in sims and is part of the check ride (sim) for ?many/most/all? airlines.


Nope...

Recovery from APPROACH to stall is practiced regularly. Because that's what simulators can actually simulate and what systems are actually designed around and what training is actually based on.

You are never supposed to actually get to be in a stall since then all bets are off.

:checkmark:

Just collecting enough data about the behaviour of an aircraft in a stall, in order to be able to realisticlly simulate it, would be very dangerous and expensive, possiibly resulting in a number of hull losses and deaths. Even if it did not result in any crashes, there would be the huge cost of new underpants for the test pilots involved in collecting this data.
 
mila
Posts: 52
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Sat Mar 30, 2019 9:19 am

speedbored wrote:
mila wrote:
The problem is most likely that if they are of the same design and placed close to each other they will freeze at the same time.
AF447 is a great example.

But they are not placed close to each other.

Two different "things" never behave the same, so if you like to design to be as good as possible use different products.

Ask any designer and they will agree 100%
 
mila
Posts: 52
Joined: Mon May 16, 2011 10:47 am

Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Sat Mar 30, 2019 9:20 am

speedbored wrote:
mila wrote:
The problem is most likely that if they are of the same design and placed close to each other they will freeze at the same time.
AF447 is a great example.

But they are not placed close to each other.

They are on the same airplane right?
 
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speedbored
Posts: 2230
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Sat Mar 30, 2019 9:36 am

mila wrote:
speedbored wrote:
mila wrote:
The problem is most likely that if they are of the same design and placed close to each other they will freeze at the same time.
AF447 is a great example.

But they are not placed close to each other.

Two different "things" never behave the same, so if you like to design to be as good as possible use different products.

Ask any designer and they will agree 100%

Perhaps. But, given the extremely small multiple failure rate, the maintenance and system complexity risks of using multiple different types of sensor would almost certainly outweigh the risk of a multiple failure.
 
asdf
Posts: 695
Joined: Tue Mar 18, 2014 12:03 am

Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Sat Mar 30, 2019 9:45 am

osiris30 wrote:
asdf wrote:
PW100 wrote:

Can someone explain this to me? How can the manual trim wheel have more trim authority than the wheel-(column?) mounted switches? Both drive the stabilizer jack screw.
Is it being suggested that the electric trimming (control column trim switches) is overruled by MCAS?


you can not trim UP as long as MCAS trimms DOWN
in the time frame MCAS is at work the crew has no authority over the trim

to cut the electric trim out only helps if the nose is not to far down becaus with the manual trim wheels you are pretty slow in trim the nose up again


False. This has been discussed many many many many many times. This is one of those a.net myths.


look at the FDR diagram of the lion air crash
electric up trim movement commanded by the console only in those timeframes when there is no trim down command from MCAS

will you suggest that it is simple coincidence that the crew only tried to trim the nose up when MCAS was not trimming down?
they only could apply 5 seconds then MCAS comes into play

the FDR data sheet with the 0/1 imputs is some douzend pages behind here in the thread
 
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PixelFlight
Posts: 1018
Joined: Thu Nov 08, 2018 11:09 pm

Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Sat Mar 30, 2019 10:46 am

Finn350 wrote:
As with other safety-critical systems, the development of the A330/A340 flight control system during 1991 and 1992 had many elements to minimise the risk of a design error. These included peer reviews, a system safety assessment (SSA), and testing and simulations to verify and validate the system requirements. None of these activities identified the design limitation in the FCPC’s AOA algorithm.


Thanks for the precision: this was a limitation not identified despite many efforts to prevent it. This not comparable to the MCAS that was deliberately hidden to minimize certification risk and pilot training.
:stirthepot: 737-8 MAX: "For all speeds higher than 220 Kts and trim set at a value of 2.5 units, the difficulity level of turning the manual trim wheel was level A (trim wheel not movable)." :stirthepot:

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