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Ethiopian airliner down in Africa

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Ethiopian airliner down in Africa

Old 30th Mar 2019, 19:29
  #2801 (permalink)  
 
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Originally Posted by GlobalNav View Post
Band-aid on a band-aid - that's the Boeing design philosophy of the Max. The AoA display makes little, if any, safety contribution to the flight deck (procedure wise) and the AOA disagree light even less. What is a pilot supposed to do when the AoA disagree light illuminates? Hit the trim switches? I wonder how often that light will illuminate, anyway. Probably often enough to get ignored.
I think "MCAS Disabled" would be more useful than either of those two. After all, that's what "AOA disagree" will mean.
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Old 30th Mar 2019, 19:46
  #2802 (permalink)  
 
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Originally Posted by GlobalNav View Post
Band-aid on a band-aid - that's the Boeing design philosophy of the Max. The AoA display makes little, if any, safety contribution to the flight deck (procedure wise) and the AOA disagree light even less. What is a pilot supposed to do when the AoA disagree light illuminates? Hit the trim switches? I wonder how often that light will illuminate, anyway. Probably often enough to get ignored.
It would have been better to give everyone the AoA indicator (misplaced though it is) and for AOA Disagree replace the graphic of the indicator with AOA DISAGREE - after all with two AoA's you cannot present guaranteed correct information, and to use the old aphorism - "no information is better than bad information"
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Old 30th Mar 2019, 19:50
  #2803 (permalink)  
 
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Originally Posted by OldnGrounded View Post
From reading the comments on the mainstream media stories covering this issue, my sense is that a large percentage of pax don't have that faith. I'll be surprised if there isn't widespread reluctance to fly the MAX as SLF, when it returns to commercial service.
Notably, the Max had already got a poor passenger reception for reduced passenger ambience standards, with carriers such as American, with (compared to the NG) reduced seat pitch, particularly cheaper-feeling and less padded seats, and a very minimalist toilet module that some felt difficult to even turn round in. When assigned to long runs such as Miami down to South America these were all apparently noticeable. Yet the carrier did not seem to find them an issue, and continued to market the services and take delivery of additional aircraft without issue.
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Old 30th Mar 2019, 19:56
  #2804 (permalink)  
 
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BBC News: Ethiopian Airlines crash: 'Pitch up, pitch up!'

Leaks this week from the crash investigation in Ethiopia and in the US suggest an automatic anti-stall system was activated at the time of the disaster
https://www.bbc.co.uk/news/business-47759966
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Old 30th Mar 2019, 21:17
  #2805 (permalink)  
 
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Originally Posted by GlobalNav View Post
Band-aid on a band-aid - that's the Boeing design philosophy of the Max. The AoA display makes little, if any, safety contribution to the flight deck (procedure wise) and the AOA disagree light even less. What is a pilot supposed to do when the AoA disagree light illuminates? Hit the trim switches? I wonder how often that light will illuminate, anyway. Probably often enough to get ignored.
The NGs I fly have this AOA disagree caution. Not sure if it is an option or standard, but this is not new for the MAX.
I have never had it come on. Never had a problem related to the AOA sensors either.
Are the MAX sensors a new design?
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Old 30th Mar 2019, 21:20
  #2806 (permalink)  
 
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Originally Posted by ManaAdaSystem View Post


The NGs I fly have this AOA disagree caution. Not sure if it is an option or standard, but this is not new for the MAX.
I have never had it come on. Never had a problem related to the AOA sensors either.
Are the MAX sensors a new design?
To my limited knowledge it's an option for the MAX.
But neither Ethiopian nor Lion had it installed.
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Old 30th Mar 2019, 23:02
  #2807 (permalink)  
 
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Originally Posted by DaveReidUK View Post
There's no reference to any maintenance action involving the AoA sensor at Jakarta in the report.
The more I think about these AoA sensors, the less likely I think they are physically defective, especially given the same nose down scenario was previously reported anonymously by at least 4 US pilots, although they recovered from the incidents and did not crash.
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Old 30th Mar 2019, 23:04
  #2808 (permalink)  
 
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Originally Posted by weemonkey View Post
In what form is the output from the AOA sensor transmitted to the avionics? Apologies if this is going over old stuff...
There is a schematic in this thread for NG: 3 way link, labeled sin, cos and com. That to me points to a resolver, which is really like a synchro but with two poles at 90 deg instead of 3 at 120.

Basically analog, AC, fixed freq, varying amplitude, going from maxAOA (vmax, 0) to minAOA (0, vmax) and being centered in (0.707vmax, 0.707vmax).

I'm not sure, though.



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Old 30th Mar 2019, 23:11
  #2809 (permalink)  
 
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Originally Posted by ManaAdaSystem View Post
The NGs I fly have this AOA disagree caution. Not sure if it is an option or standard, but this is not new for the MAX.
I have never had it come on. Never had a problem related to the AOA sensors either.
Are the MAX sensors a new design?
No, sensors are interchangeable with those on the NG.
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Old 31st Mar 2019, 00:13
  #2810 (permalink)  
 
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From the NY Times...
In Ethiopia Crash, Faulty Sensor on Boeing 737 Max Is Suspected

March 29 2019

Black box data from a doomed Ethiopian Airlines flight suggests the crash was caused by a faulty sensor that erroneously activated an automated system on the Boeing 737 Max, a series of events suspected in an Indonesian disaster involving the same jet last year.
Data from a vane-like device, called the angle-of-attack sensor, incorrectly activated the computer-controlled system, according to several people who have been briefed on the contents of the black box in Ethiopia. The system, known as MCAS, is believed to have pushed the front of the plane down, leading to an irrecoverable nose-dive that killed all 157 people aboard.

The black box, also called the flight data recorder, contains information on dozens of systems aboard the plane. The black boxes on the jets, Boeing’s latest generation of the 737, survived the crashes, allowing investigators to begin piecing together what caused the disasters. Both investigations are continuing, and no final determinations have been made.

The new connections between the two crashes point to a potential systemic problem with the aircraft, adding to the pressure on Boeing. The company already faces scrutiny for its role in the design and certification of the plane. The Federal Aviation Administration delegated significant responsibility and oversight to Boeing...



- https://www.nytimes.com/2019/03/29/b...max-crash.html
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Old 31st Mar 2019, 05:21
  #2811 (permalink)  
 
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Originally Posted by dozing4dollars View Post
I would like to know how many similar snags ( Stick Shaker, Unreliable AS, use of Stab Trim cutout switches ) have been logged on the MAX?
I mean world wide.
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Old 31st Mar 2019, 05:39
  #2812 (permalink)  
 
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Originally Posted by Fortissimo View Post
Please can we stop conflating Boeing's MCAS and Airbus' ALPHA PROT? The latter is part of an envelope protection system, whereas MCAS addresses handling characteristics (stick forces) at or near the stall.
Are you being serious? A faulty AOA vane instructs the flight control computers/stabilizer to pitch the nose down in both the Airbus and the Boeing events, overriding the pilots inputs and you fail to see the similarities. Do you work for Airbus by any chance or are you just being ignorant. In both causes software is attempting to prevent the stall.
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Old 31st Mar 2019, 05:46
  #2813 (permalink)  
 
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In both causes software is attempting to prevent the stall.
not quite true. The MCAS was developed not to prevent the stall but to ensure that the stick forces approaching the stall continually are heavier iaw FAR design criteria. It does not prevent the stall.
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Old 31st Mar 2019, 05:57
  #2814 (permalink)  
 
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Why only 2 AOA sensors

The new connections between the two crashes point to a potential systemic problem with the aircraft, adding to the pressure on Boeing. The company already faces scrutiny for its role in the design and certification of the plane. The Federal Aviation Administration delegated significant responsibility and oversight to Boeing...
If MCAS is so necessary because of the engine cowling moment in certain attitudes, wouldn't it be better to have a third AOA sensor to enable voting in the system. The bigger Boeing's and AB's have more than 2. The 737 is and is going to continue to be among the most numerous planes in the sky. Why not ensure it is as safe as them. I don't accept that saving a relatively small amount of money on a smaller airplane or quoting failures in the per billion hours is really valid when the larger planes have it, obviously for a good reason. There are far more 737's flying, far more takeoffs and landings making for just as much overall risk as the 777's and 787's (assuming more AOA's were provided for greater passenger capacity).
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Old 31st Mar 2019, 06:07
  #2815 (permalink)  
 
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Originally Posted by Unhooked View Post

Are you being serious? A faulty AOA vane instructs the flight control computers/stabilizer to pitch the nose down in both the Airbus and the Boeing events, overriding the pilots inputs and you fail to see the similarities. Do you work for Airbus by any chance or are you just being ignorant. In both causes software is attempting to prevent the stall.
Not only Fortissimo but myself being serious, it is like comparing apples and oranges. The Airbus AoA protection is indeed a component of a global envelope protection, in a FBW flight control system. I beg your pardon, my intention is not to give a lecture, but I think I should outline some of the AOA protection features on Airbus for better understanding. If the AoA reaches a value defined as "alphaprot" then the AOA protection activates, and will keep "alphaprot" value without pilot inputs. At this time any stabilizer nose up inputs are inhibited. The pilot's inputs on sidesticks are not anymore a g-load demand but become an AOA demand: the pilot can still increase backpressure on the sisdestick but cannot go beyond the so called "alphaMAX" no matter how much is the pulling: the system keeps the aircraft close at 1 g stall but doesn't exceed it . Let's not talk here about how the autothrust plays the game in "alphaprot". The most important difference that I see is that on Airbus the stabilizer is inhibited in any ANU demand, and gives AND autotrim following the pilot pushing his/her sidestick. That is obviously in a normal condition without mulfunztions.
So there is one big difference: Airbus AOA protection doesn't move the stabilizer at all: it acts on the elevators. It uses three AOA vanes with a voting system. While I am not saying at all that this implementation is the best can be built by the industry, I think it is way different from the path that Boeing has followed with MCAS
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Old 31st Mar 2019, 06:09
  #2816 (permalink)  

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Quote. "Totally agree, absolutely horrible placement of both AOA indicator and AOA disagree flag. Both should be adjacent to airspeed indicator."

And I can't say that having AOA DISAGREE displayed in dark-yellow (#C1994C) on khaki (#5E4300) is exactly attention-drawing...



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Old 31st Mar 2019, 06:29
  #2817 (permalink)  
 
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Originally Posted by LandIT View Post
If MCAS is so necessary because of the engine cowling moment in certain attitudes, wouldn't it be better to have a third AOA sensor to enable voting in the system. The bigger Boeing's and AB's have more than 2. The 737 is and is going to continue to be among the most numerous planes in the sky. Why not ensure it is as safe as them. I don't accept that saving a relatively small amount of money on a smaller airplane or quoting failures in the per billion hours is really valid when the larger planes have it, obviously for a good reason. There are far more 737's flying, far more takeoffs and landings making for just as much overall risk as the 777's and 787's (assuming more AOA's were provided for greater passenger capacity).
The B737 series is a mostly safe and reliable aircraft, with limited levels of automation. To my knowledge no B737 has crashed (other than the MAX MCAS incidents) solely because of a single isolated AOA failure. AOA is not even a primary flight indicator, as shown by the fact that many airlines declined to fit it.

Trying to fix a faulty MCAS system by adding a third AOA sensor would not be a simple exercise. The necessary design, testing, certification, maintenance and type training changes could take years.

MCAS is not so vital that it justifies rewiring large parts of the aircraft. It only adresses a regulatory issue of pilot yoke elevator feedback in the high AOA part of the manual flight regime.

It is deeply ironic that the issue MCAS was designed to cater for was never flight critical, and might never have occurred during the lifetime of the aircraft. Instead the fix ended up killing hundreds of people.
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Old 31st Mar 2019, 07:54
  #2818 (permalink)  
 
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Originally Posted by GordonR_Cape View Post
Trying to fix a faulty MCAS system by adding a third AOA sensor would not be a simple exercise. The necessary design, testing, certification, maintenance and type training changes could take years.

MCAS is not so vital that it justifies rewiring large parts of the aircraft. It only adresses a regulatory issue of pilot yoke elevator feedback in the high AOA part of the manual flight regime.

It is deeply ironic that the issue MCAS was designed to cater for was never flight critical, and might never have occurred during the lifetime of the aircraft. Instead the fix ended up killing hundreds of people.
Are you serious? We have the year 2019 and not 1950. Customers expect a thorough analysis and solution to regain confidence and not an additional kludge.

Thats what the 737 MAX looks on statistics:
https://qz.com/1571820/deaths-on-the...cial-aircraft/

It is a great case for the industry to learn. And it is more about the decision making processes on all levels, than on a technical only analysis of this latent fault condition of the MCAS system. There is a reason that the FAA AIM has about 800 pages written mostly with blood.

Currently Boeing could have made the complete skin of the B737 MAX only from AoA vanes and would still be better off.
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Old 31st Mar 2019, 09:22
  #2819 (permalink)  
 
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Originally Posted by EDLB View Post
Are you serious? We have the year 2019 and not 1950. Customers expect a thorough analysis and solution to regain confidence and not an additional kludge.

Thats what the 737 MAX looks on statistics:
https://qz.com/1571820/deaths-on-the...cial-aircraft/

It is a great case for the industry to learn. And it is more about the decision making processes on all levels, than on a technical only analysis of this latent fault condition of the MCAS system. There is a reason that the FAA AIM has about 800 pages written mostly with blood.

Currently Boeing could have made the complete skin of the B737 MAX only from AoA vanes and would still be better off.
My comment was in response to a specific question, and not a commentary about the MAX aircraft in general. Nor am I trying to discount the disastrous nature of MCAS, but pointing out that adding a 3rd AOA to an old airframe does not solve anything (unless the avionics are adapted to read and process the 3rd sensor).

I concur with your other comments, which are best directed at Boeing and the FAA. Being judgemental does not help solve this specific problem.

Last edited by GordonR_Cape; 31st Mar 2019 at 10:57. Reason: Clarify wording.
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Old 31st Mar 2019, 09:42
  #2820 (permalink)  
 
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Another issue often missed by software teams is the fact that with analogue sensors, any erratic indications are damped by the meters or are simply ignored by the crew. Converting the outputs of the sensors to digital format doesn’t ignore the noise in the signal and, with polling if the sensor, could lead to large discrepancies in signal used for the controls.

You simply must do thorough testing of flight safety critical systems including flight trials.

Inexcusable imho.
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