157 aboard Ethiopian Airlines flight to Nairobi involved in fatal crash

Ockie

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So just been reading around and something is weird - it looks like the media has picked up on the MCAS system, and the anti-stall feature whereby if the plane is in auto-pilot and it detects a stall that it puts the nose of the plane down to try recover the plane before it it's a critical stall.

Surely the same system has been installed on all new Boeings, so this problem would be more of a global boeing problem? Just a question that's bugging me
As I understand, no. Only on the 737 Max. Reason being the new CFM engines installed on it creates their own lift, and this can cause the nose to lift higher than intended and so, to counter this, Boeing came up with MCAS to neutralize that effect from the engines. This is a issue only on the 737 Max.

Other airliners including Airbus and Embraer and Bombardier have stall warning systems where they shake the stick pretty violently when a potential stall situation is detected by avionics.
 

Daruk

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As I understand, no. Only on the 737 Max. Reason being the new CFM engines installed on it creates their own lift, and this can cause the nose to lift higher than intended and so, to counter this, Boeing came up with MCAS to neutralize that effect from the engines. This is a issue only on the 737 Max.

Other airliners including Airbus and Embraer and Bombardier have stall warning systems where they shake the stick pretty violently when a potential stall situation is detected by avionics.
The issue with the 737 Max is the size of the engine and the fact that the rest of the plane is effectively a bog standard 737. They had to mount the engine further forward on the wing and slightly higher to get the right ground clearance which creates the different center of gravity and aerodynamics. The anti-stall software is to counter the extra lift when banking at slow speed which creates the stall I believe.

I think Boeing are partly right when they say that standard emergency recovery procedures would have prevented both crashes. Given that the Lion air plane had behaved in the same way just the flight before the ill-fated one and the pilots managed to do a recovery procedure of flipping the auto off and trimming the tail wing manually using the cranks / buttons on the yoke, it makes one wonder why the other pilots didn't follow the same procedure. That doesn't excuse Boeing for the oversight that people should have been told of the changes.
 

Gordon_R

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The issue with the 737 Max is the size of the engine and the fact that the rest of the plane is effectively a bog standard 737. They had to mount the engine further forward on the wing and slightly higher to get the right ground clearance which creates the different center of gravity and aerodynamics. The anti-stall software is to counter the extra lift when banking at slow speed which creates the stall I believe.

I think Boeing are partly right when they say that standard emergency recovery procedures would have prevented both crashes. Given that the Lion air plane had behaved in the same way just the flight before the ill-fated one and the pilots managed to do a recovery procedure of flipping the auto off and trimming the tail wing manually using the cranks / buttons on the yoke, it makes one wonder why the other pilots didn't follow the same procedure. That doesn't excuse Boeing for the oversight that people should have been told of the changes.
The exact description of the MCAS systems is quite complex, and worth reading in full detail: https://leehamnews.com/2018/11/14/b...-the-737-max-was-not-disclosed-to-the-pilots/

A few minor differences from your description. AFAIK its not an anti-stall system (that's done by the stick-shaker), but a stability requirement to smoothly limit the rate of pitch up in response to pilot stick forces at high AOA:
The drawback of a larger nacelle, placed further forward, is it destabilizes the aircraft in pitch. All objects on an aircraft placed ahead of the Center of Gravity (the line in Figure 2, around which the aircraft moves in pitch) will contribute to destabilize the aircraft in pitch.
But if the pilot for whatever reason manoeuvres the aircraft hard, generating an angle of attack close to the stall angle of around 14°, the previously neutral engine nacelle generates lift. A lift which is felt by the aircraft as a pitch up moment (as its ahead of the CG line), now stronger than on the 737NG. This destabilizes the MAX in pitch at higher Angles Of Attack (AOA). The most difficult situation is when the manoeuvre has a high pitch ratio. The aircraft’s inertia can then provoke an over-swing into stall AOA.

To counter the MAX’s lower stability margins at high AOA, Boeing introduced MCAS. Dependent on AOA value and rate, altitude (air density) and Mach (changed flow conditions) the MCAS, which is a software loop in the Flight Control computer, initiates a nose down trim above a threshold AOA.
 

Daruk

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The exact description of the MCAS systems is quite complex, and worth reading in full detail: https://leehamnews.com/2018/11/14/b...-the-737-max-was-not-disclosed-to-the-pilots/

A few minor differences from your description. AFAIK its not an anti-stall system (that's done by the stick-shaker), but a stability requirement to smoothly limit the rate of pitch up in response to pilot stick forces at high AOA:
I totally own the very simplistic write up I did there lol. I'm definitely not an aviation expert - not even on sim haha. I'm picking up bits that I've read and possibly misinterpreting some. Thanks for the more detailed explanation.

IMO the real worry from Boeing's end is that despite having redundant computers and AOA sensors, only one side is used at any time and thus a single faulty sensor will not be detected. If they factored in both in the decision making, with small margin for discrepancy, the system would have immediately been able to alert the pilots to an issue and MCAS could have been disabled.
 

Gordon_R

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I totally own the very simplistic write up I did there lol. I'm definitely not an aviation expert - not even on sim haha. I'm picking up bits that I've read and possibly misinterpreting some. Thanks for the more detailed explanation.

IMO the real worry from Boeing's end is that despite having redundant computers and AOA sensors, only one side is used at any time and thus a single faulty sensor will not be detected. If they factored in both in the decision making, with small margin for discrepancy, the system would have immediately been able to alert the pilots and MCAS could have been disabled.
I get the feeling that MCAS might never be acceptable in any form, due to technical and legacy limitations, and another sort of other solution is needed. IMO this matter is a relatively obscure certification issue, only affecting a few scenarios, and not often encountered in commercial aviation. It may be better to have no MCAS and accept some remote risk, rather than have a high risk of death and/or complexity and uncertainty through a badly designed system.

Boeing and the FAA will have to do some hard thinking.
 

Daruk

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I get the feeling that MCAS might never be acceptable in any form, due to technical and legacy limitations, and another sort of other solution is needed. IMO this matter is a relatively obscure certification issue, only affecting a few scenarios, and not often encountered in commercial aviation. It may be better to have no MCAS and accept some remote risk, rather than have a high risk of death and/or complexity and uncertainty through a badly designed system.

Boeing and the FAA will have to do some hard thinking.
Agree... imagine the impact on Boeing if it meant 100% hardware recall and back to the drawing board...
Surely not tho...
 

Gordon_R

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Agree... imagine the impact on Boeing if it meant 100% hardware recall and back to the drawing board...
Surely not tho...
If they could somehow fix it with $1 million of hardware per aircraft, that would be cheap compared to the cost of keeping 350 aircraft on the ground for months. The real problem is that design, testing and certification take months.

The other big factor is there are firm orders placed for 2000 new MAX aircraft worth $600 billion. That's a lot of potential lost revenue if the airlines all started cancelling and switching to A320s...

Going back to production of the old 737 NGs is not a viable option, due to fuel economy differences, and the cost of retooling the production lines. Its a deep hole they have dug themselves into...
 

Daruk

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If they could somehow fix it with $1 million of hardware per aircraft, that would be cheap compared to the cost of keeping 350 aircraft on the ground for months. The real problem is that design, testing and certification take months.

The other big factor is there are firm orders placed for 2000 new MAX aircraft worth $600 billion. That's a lot of potential lost revenue if the airlines all started cancelling and switching to A320s...

Going back to production of the old 737 NGs is not a viable option, due to fuel economy differences, and the cost of retooling the production lines. Its a deep hole they have dug themselves into...
Cutthroat private sector competition is not always good. They really rushed into this one by the looks.
 

Gordon_R

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Aharon

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As I understand, no. Only on the 737 Max. Reason being the new CFM engines installed on it creates their own lift, and this can cause the nose to lift higher than intended and so, to counter this, Boeing came up with MCAS to neutralize that effect from the engines. This is a issue only on the 737 Max.

Other airliners including Airbus and Embraer and Bombardier have stall warning systems where they shake the stick pretty violently when a potential stall situation is detected by avionics.
Dumb question - is that the vibration felt often during takeoff?
 

bromster

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Dumb question - is that the vibration felt often during takeoff?
No. That's just because of the weird configuration the plane is in when they take off. Lots of the weight is still on the wheels, but the wings are already generating lift and the plane is pitching quite sharply upwards. It just takes a few seconds after takeoff for all of the aerodynamic forces to balance and settle down. If the conditions are just right, this can cause vibration through the fuselage. Nothing to worry about.

The stick shaker is computer generated. It vibrates the control column to let the pilots know that they are flying too slowly and that the wings might stop working properly. The usual reaction is to lower the aircraft nose in order to build speed and keep the aerodynamic forces over the wing working correctly.

Only the pilots feel the stick shaker. As a passenger, you would only realise as you started to float out of your seat.
 

Ockie

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Dumb question - is that the vibration felt often during takeoff?
No not at all. The stick shaking is only felt by the pilot on the controls.

Vibrations felt during take off would be due merely to the engines spinning up and a multi ton tube of metal picking up speed and rushing down a runway.:)
 

Gordon_R

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Cross-post, Jamie decided to create another thread: https://mybroadband.co.za/news/tren...737-evidence-shows-plane-was-set-to-dive.html

The piece of evidence was a so-called jackscrew, used to set the trim that raises and lowers the plane’s nose, according to the person, who requested anonymity to discuss the inquiry.

A preliminary review of the device and how it was configured at the time of the crash indicated that it was set to push down the nose, according to the person, who wasn’t authorized to speak publicly about the investigation.
Not just a hole in the ground, quite a lot of high-strength hardware survives impact...
 
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TheJman

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Just makes you wonder though, if the airlines just thrust a new aircraft onto pilots without the necessary training - as you can see from the one ASRS report, the pilots literally didn't even know what the one warning was that was being displayed pre-flight, but then still proceeded with the flight. The pilot even acknowledges that a more cautious pilot in their situation probably wouldn't have taken off until he figured out what the warning was....

Shows a lack of skill on all parties sides in my opinion....

And then you couple this with the pressure the pilots are put under to ensure flights aren't delayed etc... perfect storm
 

buka001

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Interesting from the NYT

https://www.nytimes.com/2019/03/14/world/boeing-737-max-ethiopian-airlines.html

Big concerns regarding the speed of the aircraft.

“The thing that is most abnormal is the speed,” said John Cox, an aviation safety consultant and former 737 pilot.
“The speed is very high,” said Mr. Cox, a former executive air safety chairman of the Air Line Pilots Association in the United States. “The question is why. The plane accelerates far faster than it should.”
Can anyone shed some light? I don't think the MCARS changes the engine speeds? Or could the pilots have been increasing thrust to compensate for a perceived stall?
 

Cr419

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