Ethiopian airliner down in Africa

[ecto1]

Originally Posted by GordonR_Cape

ecto



Your analysis is fundamentally flawed because AOA is not valid before takeoff, and any data points prior to that must be ignored. The AOA sensor relies on significant forward speed to align the vane with the airflow, and this is not possible while taxiing.

IMHO,

Any data points before takeoff (or after landing) do not correlate with real AOA values, without significant forward speed the vane will not reflect anything resembling AOA: Obviously correct.

These data points should be ignored? I don't agree. Lots and lots of hints there.

For instance, a constant offset theory (like bad indexing) doesn't hold water:

If the offset were there from the power on, as in a software error, it is an amazing coincidence that the right side vane, supposedly ok, has no noise and very minimal changes on the ground while the left one (suspect) has significant noise and/or large changes in both flights. (true I'm only basing this on 3 taxi events, but each is some minutes long). As opposed as in the air, where you could not tell one from the other if it wasn't for the offset. Wind on the ground will move the vanes randomly, of course, but it is an amazing coincidence that only left side dances in all three taxiing events.

Another example. If the offset were a consequence of a wrong correction table based on airspeed being used in the left side computer, it would be an impossible coincidence that the offset remained after landing with airspeed back to zero, as we can see in the data trace of the previous flight.

I would regard any proposed theory better if it is consistent with that behaviour in the air and on the ground seen in both data traces.

In fact, due to Occam's razor, any theory should also be consistent with the rest of the alarms. Specially the FEEL PRESS DIFF. There must be a root cause for all this.

Don't you agree?

[rcsa]

Originally Posted by OldnGrounded

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.

Many of us said the same about the early 78, during its 'Firebird' days. Five years later, the 78 gets consistently high ratings by that minority of the passenger community who have any clue what aircraft type they are flying on. Of course, there were no revenue hull losses during the 78's problem period, and one can assume the two crashes will count more against the 73-Max in perception terms. But I suspect in 5 years time most pax will be flying the 73-Max-10/11/12 without a second thought.

Boeing are going to make damn sure branding of the next variant of the Max will be an ocean of clear blue water away from the Max-8/9. They might even drop the 'Max' name, and come up with something touchy-feely that taps into the 'Dreamliner' imagery - The '737-Sunliner', perhaps.

[OldnGrounded]

Originally Posted by rcsa

But I suspect in 5 years time most pax will be flying the 73-Max-10/11/12 without a second thought.

Agreed. But I don't think that's likely to be true for the year or two after the MAX gets back into the air.

Boeing are going to make damn sure branding of the next variant of the Max will be an ocean of clear blue water away from the Max-8/9. They might even drop the 'Max' name, and come up with something touchy-feely that taps into the 'Dreamliner' imagery - The '737-Sunliner', perhaps.

Indeed. There's probably a branding and imagery team working on it as we type.

[vbp.net]

“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”

I’m former ATC and I can tell you that even before the MAX was grounded I had checked that my next flight was NOT a MAX, otherwise I would have cancelled it right away. This beeing said, I think that with time, assuming the MAX is allowed to fly again, fewer and fewer people will keep in mind that this version of the venerable 737 has gone a step too far and is probably the last “improved” version of this cable and pulleys dinausaur.
Yet, our last chance of pushing certification agencies to take their mission seriously is for the travellers to refuse to board a plane when they have good reasons to believe their safety was sacrified to better profit for the shareholders which is clearly the case here.

Vincent

[formulaben]

Originally Posted by weemonkey

Interesting choice of aoa information presentation.

Wouldn't a vertical strip type lead to superior intuitive comprehension?

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

[GlobalNav]

Originally Posted by formulaben

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

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.

[ktcanuck]

Originally Posted by GlobalNav

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.

[Ian W]

Originally Posted by GlobalNav

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"

[WHBM]

Originally Posted by OldnGrounded

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.

[slfool]

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

[ManaAdaSystem]

Originally Posted by GlobalNav

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?

[gearlever]

Originally Posted by ManaAdaSystem

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.

[Dee Vee]

Originally Posted by DaveReidUK

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.

[ecto1]

Originally Posted by weemonkey

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.

[DaveReidUK]

Originally Posted by ManaAdaSystem

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.

[patplan]

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

[dozing4dollars]

Originally Posted by dozing4dollars

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.

[compressor stall]

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.

[LandIT]

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).

[joe falchetto 64]

Originally Posted by Unhooked

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