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Ethiopian airliner down in Africa

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Ethiopian airliner down in Africa

Old 17th Mar 2019, 18:21
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Wonder no more

Originally Posted by WHBM
On many of the accidents discussed here on PPRuNe, commentators are regularly criticised for "not waiting until the accident report is released".

I wonder why, in contrast, it seems accepted that Boeing can have a software fix done in weeks, way before any reports are produced, to get the aircraft back in the air.
Wonder no more --> $
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Old 17th Mar 2019, 18:22
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So how often does MCAS operate?

Naive question from slf. I seem to recall that T tail aircraft had stick pushers that operated if you got very close to the stall, but that you normally would not get that close.

At what angle of attack does MCAS operate and how far from the normal post take off angle of attack is this?
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Old 17th Mar 2019, 18:25
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Originally Posted by gearlever
Two crews went into that trap. Doesn't this make you think more critical about the design of MCAS?
this forum is full of people who severely overestimate the capacity of human brain, also (or speciall) their own.

At the same time, most would fail a simple attention test

not that it’s their fault. It’s due to the design of human brain. Yet we design machines pretending this is not the case. Just another human fault i suppose.
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Old 17th Mar 2019, 18:46
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Originally Posted by OldnGrounded
Just a reminder: Ultimately, a third of the Electras ever built were either lost in crashes or written off as too damaged to repair. Perhaps it will be a good thing if "that" does not happen now.
otoh, the Electra continued as the Navies P-3. For a very long time. One of the last Electra crashes I recall was attitude indicator failure.
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Old 17th Mar 2019, 19:15
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Is an Easy fix proof of sloppy work the first time around?

Here is a thought.

Rumors will have it that Boeing has an MCAS software fix by the end of March, a mere five months after the Lion Air crash, and if this fix is indeed a real fix, and not just a small tweak of some parameters, doesn't this show that Boeing has the knowledge, skills and capacity to crate safe MCAS software.

So this leads me to ask, if this is really true, why the hell did they not do it correctly from the beginning. I am certain that if it comes out that this is an easy fix, and that Boeing did not prioritize it the first time around, that Boeing will be open to severe liability claims.

Clearly this shows that the priority was to get the MAX out fast, and grab as many costumers from the NEO as possible.

I really think that a fast fix shows that Boeing could have done it correctly from the beginning, but chose not to spend the required resources on it.
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Old 17th Mar 2019, 19:16
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It seems as if the bottom line is that the safety margin of the legacy 737 was simply eroded to an unacceptable degree with the new engines and became “cigarette paper” thin with the MAX in the search for ever better fuel economy. Boeing recognized this during the development phase and tried to code their way out of it with MCAS thereby creating a solution which may well be more dangerous than the original risk.

Is that reasonable summary ?

I wonder what parameters have been changed with the new software patch, and I’m still curious about the purpose of the 5 second delay which could easily trick pilots into believing there was no problem with the system.

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Old 17th Mar 2019, 19:18
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Originally Posted by HarryMann
No, i dont believe most are saying that exactly . . But aren't you equally saying engineers no longer need to be engineers (that live and breathe aeronautic and human interfaces, and are proactive designers, whilst this sounds a somewhat reactive solution ).
Amazed spinning that trimwheel about like that ever passed muster at Boeing let alone nodded through by AW @ FAA - a dozen things could be predicted to go wrong day one of concept by a brainstorming group of experienced systems and aeronautic engineers.
assuming that trim wheel is just like in the 727 and the stab does not move without that big wheel spinning and that it is as loud as it ever was? It is a powerful visual and aural que of what is going on. If it is turning then it should be because speed and or configuration is changing and if I have commanded neither and that stab is moving, I want to know about it.
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Old 17th Mar 2019, 19:21
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A software patch to fix and inherently unstable aircraft. brilliant. Cant wait for it
The aircraft is not inherently unstable. Where on earth did you get that idea? MCAS is about reducing AoA at extremes due engine nacelle effects. The fact that a faulty AoA sensor can activate it is the issue. Then that SOME crews have been unable to process what is occurring and turn off the stab trim, or hold manual wheel, or use electric trim against MCAS input.
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Old 17th Mar 2019, 19:41
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Originally Posted by derjodel
Lion air's FDR show that the trim was moved to full of the available 7 notches (it's not clear how those translate to degrees). They would certainly still be alive if there as a limit. They kept it in air at ~ 3 notches. If max needs more to get out of stall, perhaps it does need a larger hstab/eleveator instead of a hacked together software?

Or perhaps the key really is the reset. Does mcas reset with each trim input and takes the current position as the new neutral? If AoA vane is sending wrong data it's easy to see how this would result in a runaway trim.

This image shows the difference between a 737-800 (yellow) and MAX (magenta). Notice the bigger nacelles and same hstab size.

I thought 0.6 was a hard limit... e.g, we move this much and then it's up to the pilot. If it was 0.6 every 5 seconds it's still bad, but at least easier to manage.
It would appear that MCAS has no memory of previous activations after each reset its world starts again it is totally context free. So when it wakes up it looks at the AoA and if it is above limits (and perhaps other conditions pertain ) it activates and puts in 0.6 nose down on whatever the trim currently is pilot blips the trim pickle switch and MCAS goes to sleep and 5 seconds later MCAS wakes up and repeats the exercise as it is context free it has no knowledge of the previous activation. That would appear to be the fault in the system that means an incorrect AoA will result in repeated nose down trim increments for which there is no need. A nose down trim sensor that would inhibit MCAS trimming more nose down than a parameter value that would be calculated based on nose down trim and speed would prevent the over application of nose down trim.
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Old 17th Mar 2019, 19:48
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Originally Posted by Icarus2001
The aircraft is not inherently unstable. Where on earth did you get that idea?
Perhaps from the circumstance that the engines are now mounted so far forward that application of power within the normal envelope sends the aircraft into stall territory?
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Old 17th Mar 2019, 19:53
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Originally Posted by VFR Only Please
Perhaps from the circumstance that the engines are now mounted so far forward that application of power within the normal envelope sends the aircraft into stall territory?
from many previous discussions in this thread - no it has to do with at high AOA, the engine cowling provides extra lift which drives the nose up- as compared to previous locations which may partly negate lift at high AOA

At least thats how this SLF understands ..
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Old 17th Mar 2019, 20:03
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Yes, it's to prevent reducing stick force at increasing alpha which is a certification failure. It's not for stall prevention.
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Old 17th Mar 2019, 20:06
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I counted 14 and missed the gorilla.But thats not important.Whats important is that
Mullenberg doesnt miss the elephant in the room the next time round.
Boeing screwed the pooch on 3 counts:
-------->clandestine installation of MCAS
-------->MCAS activation based on single sensor
-------->failure to provide MAX simulators in good time for an aircraft whose differences cannot be trained on an ipad

Mullenberg is an MA in aeronautics and by all accounts a well-rounded guy.He has a good engineering background.
Hopefully hes the type who knows exactly whats going on on that assembly line and involved in the "nuts and bolts"
from the ground up.
The MAX can be safe,they just have to come clean and fix it.....and then win the flying public back again.I wish them
luck because in general they build great airplanes.
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Old 17th Mar 2019, 20:09
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Originally Posted by groundbum
I give full respect to the Ethiopian safety board investigating this crash.

but given that the two 737max crashes raise such massive questions about aircraft manufacturing,government and trans national oversight and trillion dollar industries as well national interests for the US aircraft msnufacturing industry vis a vis China snd Europe ,are the Ethiopians a tiny bit out of their depth?
Boeing don't seem to have thought the Ethiopians were "out of their depth" when they sold them, in recent years, significant quantities of 767s, 777s, 787s, 737NG's, 737 Max's ...

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Old 17th Mar 2019, 20:12
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Interesting Twitter thread
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Old 17th Mar 2019, 20:16
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Originally Posted by Discorde
A preview of a possible future QRH excerpt:


Applying nose up trim with the trim switches on the control column should help ease loads before operating the stab trim cutout switches.

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Old 17th Mar 2019, 20:21
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Originally Posted by Royale
I really think that a fast fix shows that Boeing could have done it correctly from the beginning, but chose not to spend the required resources on it.
Good thought. But I'd rather think they just weren't aware of any risks with their first software. And this is because they didn't spend the required ressources on safety analysis.
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Old 17th Mar 2019, 20:22
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MCAS and autopilot together?
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Old 17th Mar 2019, 20:29
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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 !!
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Old 17th Mar 2019, 20:51
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Originally Posted by abdunbar
assuming that trim wheel is just like in the 727 and the stab does not move without that big wheel spinning and that it is as loud as it ever was? It is a powerful visual and aural que of what is going on. If it is turning then it should be because speed and or configuration is changing and if I have commanded neither and that stab is moving, I want to know about it.
Wonder if stick shaker noise will mask trim wheel clicking
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