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Ethiopian airliner down in Africa

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Ethiopian airliner down in Africa

Old 22nd Mar 2019, 23:24
  #2361 (permalink)  
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Having read every post since the first crash I'm at a loss as to how we're not, for the most part, progressing logical thought.

To see this 'Why didn't they fly the plane'. chanted out again and again is beyond offensive. The congressman has "been in contact with . . ." etc., etc. I'm sure he would have handled the MAX like a Warbird, and saved the day.

For the first time in many, many years on PPRuNe, I'm allowing myself to really bristle at some of the posts.

There are so many factors coming out of the woodwork. The Seattle Times was the first to spell out some of the home truths. The technical article today left me astonished. The rear switch (in the column) removed, and the function of the left and right Stabilizer cut out switches changed in the MAX. ??? Have I missed these points? Are they not correct? They're major factors.

'gums' has a lot of experience and his considered thoughts today about being in the hot seat for those first moments says a lot. Mostly, the problem was NOT bloody obvious, it was, insidious - proceeding in a gradual, subtle way, but with very harmful effects. A word I chose carefully in one of my earlier posts.
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Old 22nd Mar 2019, 23:28
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Originally Posted by RatherBeFlying
I'm thinking that the JT610 P1 retrimmed completely from each MCAS excursion, but P2 did not allowing the nose down trim excursions from MCAS to accumulate while P1 was head down in the manual - which had no information on MCAS.

​​​​​​Will the CVR, once released, show whether P1 communicated to P2 what P1 was doing with trim before handing over control?

Remember also that stick shaker was adding workload.

We now know that a faulty AoA will both trigger shaker and MCAS once at a safe height where flaps are normally retracted and more thorough diagnosis of the situation can begin, but then they were handed a new problem.

​​​​​
The LEFT/CAPT shaker was triggered immediately, IAS/ALT disagreed as well. Meanwhile, MCAS trim was activated after the AC was flap up.
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Old 23rd Mar 2019, 00:07
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Salute!

Apparently the Chuck Yeager cadre here lives on....
So today we see other examples:
That one is esay [sic], you cross check the 3 airspeed indicators, thrust, performance and attitude to determine if the stickshaker is real or false.
errrr, sir? What's with the airspeed and altitude warning lights ? "No problem, pilgrim, I can tell our speed is O.K. by how fast the trees are going by and the ground ain't getting a lot bigger"

stick shaker is on one side only, it is an AOA failure & not a valid stall warning.
errrr, sir, my stick ain't shakling, therefore, it must not be a valid stall warning, right.? I guess the airspeed and altitude and feel difference lights must also be false, ya think? "trust me, dweeb, I know a stall when I feel one"
Beam me up.

Gums sends...
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Old 23rd Mar 2019, 00:14
  #2364 (permalink)  

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Originally Posted by Loose rivets
Having read every post since the first crash I'm at a loss as to how we're not, for the most part, progressing logical thought.

To see this 'Why didn't they fly the plane'. chanted out again and again is beyond offensive. The congressman has "been in contact with . . ." etc., etc. I'm sure he would have handled the MAX like a Warbird, and saved the day.

For the first time in many, many years on PPRuNe, I'm allowing myself to really bristle at some of the posts.

There are so many factors coming out of the woodwork. The Seattle Times was the first to spell out some of the home truths. The technical article today left me astonished. The rear switch (in the column) removed, and the function of the left and right Stabilizer cut out switches changed in the MAX. ??? Have I missed these points? Are they not correct? They're major factors.

'gums' has a lot of experience and his considered thoughts today about being in the hot seat for those first moments says a lot. Mostly, the problem was NOT bloody obvious, it was, insidious - proceeding in a gradual, subtle way, but with very harmful effects. A word I chose carefully in one of my earlier posts.
Scratching my head now: If the cause of these two accidents was an MCAS event due to a faulty sensor, then the solution would be to click off those two Stab Trim Cutoff switches, then fly the airplane, make a landing, then go to the hotel and have a beer.
I have been practicing the Stab Trim-Run away on Boeing’s in various simulators for over 30 years and I would Hopefully remember these 2 switches if it happened in real life.
If this is beyond what is to expected of airline pilots these days, then I will take the train.
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Old 23rd Mar 2019, 00:14
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Originally Posted by safetypee
[LEFT]Alchad, #2365,
there is merit in your linked reference. https://www.satcom.guru/2019/03/ethi...lion.html#more
It's said that angle of attack disagree was 22°5 (at least on Lion Air). But the AoA vane does not directly measure angle of attack, but angle of airflow around the fuselage, which is higher - about twice the angle of attack - due to aerodynamics around a long body

That means the error at the Angle of Airflow vane was not 22°5 but about 45°, which correspond to the angle between AoA screws.
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Old 23rd Mar 2019, 00:19
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"Much like tapping the brake pedal in a car to disengage cruise control, a sharp tug on the controls of older models of Boeing Co’s 737 used to shut off an automatic trim system that keeps the plane flying level, giving the pilot control.

But Boeing disabled the “yoke jerk” function when it brought out the 737 MAX, the latest version of its top-selling jet - and many pilots were unaware of the change, aviation experts told Reuters....

...pilots would have needed to know that MCAS existed, that it had unusual power to force the plane down and that “a hard pull on the yoke” would no longer turn off the automatic trim that uses MCAS, John Hansman, an aeronautics professor at MIT, said in an interview.

“That wasn’t clear to the pilots flying the airplane,” Hansman said. “The training material was not clear on that.”"


https://www.reuters.com/article/us-e...-idUSKCN1R322M

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Old 23rd Mar 2019, 00:36
  #2367 (permalink)  
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Towhee:

So it seems that rear switch in the pole has been removed on the MAX.

That is a major difference. I wonder if it was mentioned in the few minutes of conversion notes.

TowerDog:

......If the cause of these two accidents was an MCAS event due to a faulty sensor, then the solution would be to click off those two Stab Trim Cutoff switches, then fly the airplane, make a landing, then go to the hotel and have a beer.
Well, that's the point. If. As in, If you know it's happening.

First and foremost: it's not a stab trim runaway in the usual sense. The inputs, resets and then re-datumizing is quite, quite different. Plus you're in a chaotic condition before 1000' and flaps up.

Remember, you observe the STS running on a daily basis, and the MCAS actions are so intermittent and subtle that you don't know there's something inputting into the Horizontal Stabilizer from that source. You're not going to be able to diagnose what's happening while under stress - especially if you've never been told there's a software system that's taking this mysterious action.
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Last edited by Loose rivets; 23rd Mar 2019 at 01:03.
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Old 23rd Mar 2019, 01:11
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Originally Posted by deltafox44
It's said that angle of attack disagree was 22°5 (at least on Lion Air). But the AoA vane does not directly measure angle of attack, but angle of airflow around the fuselage, which is higher - about twice the angle of attack - due to aerodynamics around a long body

That means the error at the Angle of Airflow vane was not 22°5 but about 45°, which correspond to the angle between AoA screws.
I don't believe I really get this point. It sounds OK if indeed the airflow was not parallel with the fuselage at some locations. But why wouldn't the streamline effects be well known beforehand from wind tunnel testing and the AOA vanes located at a point where the lines are truly parallel?
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Old 23rd Mar 2019, 01:24
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Originally Posted by deltafox44
That means the error at the Angle of Airflow vane was not 22°5 but about 45°, which correspond to the angle between AoA screws.
Are you suggesting the AOA sensor was installed 45° from the proper angle? Is that even possible? (No keyway or other locating method?)
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Old 23rd Mar 2019, 01:25
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So what's being said is, the AoA vane hub is rotated in error by one screw-hole place?

For it to be able to be so misaligned seems impossible - for the main casting to not be designed D shaped, or have a flat edge would be deeply worrying. But it is a compelling scenario since the output error is so consistent.

I'd personally discounted damage to the vane after the second crash, and would be mystified if it were to be a mechanical problem since the vanes are so strong. They look frail, but they're anything but.
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Last edited by Loose rivets; 23rd Mar 2019 at 01:47.
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Old 23rd Mar 2019, 01:30
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Originally Posted by Loose rivets
So what's being said is, the AoA vane hub is rotated in error by one screw-hole place?

For it to be able to be so misaligned seems impossible - for the main casting to not be designed D shaped, or have a flat edge would be deeply worrying.
I think that it's been established elsewhere on the thread/s that there are lugs or something that means that they can only be installed in the correct orientation - but tdracer has said that he has seen them carefully machined off so that they can in fact be incorrectly fitted...
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Old 23rd Mar 2019, 02:32
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The only reason I can think of for doing that would be for one unit to be able to fit a new aircraft. Hmmm . . . now let me think.

'We could make those NG vanes fit the MAX if we shaved the lug a little.'
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Old 23rd Mar 2019, 03:23
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Since it has not been disclosed the conditions and settings where the engine nacelles provide extra lift and nose up the ac (if/when MCAS kicks in)...an AoA sensor is meaningless.

The UT AoA sensors have an offset bolt pattern to insure correct installation.


Last edited by Smythe; 23rd Mar 2019 at 03:39.
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Old 23rd Mar 2019, 03:39
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Operational useof angle of attack - boeing

Does this help

OPERATIONAL USEOF ANGLE OF ATTACK
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Old 23rd Mar 2019, 03:39
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A nuance that I have not seen stated here previously, one well worth considering as people go back and forth arguing over whether or not the pilots should have saved the day:

MCAS introduced a single point of failure that without pilot intervention in a highly specific way results 100 percent of the time in the aircraft flying itself into the ground. Either the pilot nails the answer to the question while all hell is breaking loose and g-loads are all over the place (about a system which they had no awareness existed), and they do it within a very very short period of time, or the airplane will 100 percent fly itself into the ground. Straight into the ground BTW.

I cannot recall any other instance of a single point of failure system or sensor (or any system for that matter) on a commercial airplane which places the airplane in a state where the only chance for survival is a single action by the pilot, without which the airplane will crash. Once the AOA failed in Indonesia the airplane was essentially trying to fly itself into the ground. The Capt. kept that from happening for a bit, then it succeeded when he handed the airplane to the FO to grab the book and look for an answer that was not in fact there.

I can recall tons of technical issues that resulted in incidents and accidents, in fact I’ve survived a few on my own, but none where the failure of a single sensor meant that a perfectly good airplane was literally trying to kill everyone on board.

We can go round and round about whether or not the flight crew should have been able to aviate their way out of the circumstance they found themselves in, but if the penalty for failure to act quickly enough and perfectly enough on any given in-flight issue on a single sensor and a system about which you knew nothing was immediate death for you and your passengers would you still choose to fly?? Are you that certain of your perfection in the air??

If you knew that there might be a system on your airplane that you knew nothing about and that had the power to command the airplane to try to kill you, would you fly in that airplane, or god forbid take command of it with a couple hundred people in your care??

That is exactly what Boeing did to every MAX crew that flew the airplane. And whether with ill-intent or not they did it knowingly and deliberately. We don’t know them now, but Boeing is filled with smart people. Someone(s) knew exactly what Boeing was doing putting MCAS into service in the clandestine way they did, and I presume it was done that way for an (as yet unknown) reason. Those people will speak up at some point, or I hope they will anyway because it was no accident that MCAS anonymously arrived in the MAX without flight crews being made aware of its presence.

We can argue that the Lion Air crews who successfully survived an otherwise fatal experience should have alerted the airline, and we can argue a ton of other things too.

What we cannot argue, for one moment, is that the regulatory system that allowed Boeing to self-certify safety of the 737 MAX functioned as intended.

What we cannot argue is that Boeing and the regulatory system produced a safe airplane.

Quite to the contrary they produced an airplane that with the right type of single sensor failure would immediately try to kill everyone on board, with only the immediate and correct intervention of the pilots, who had no idea that the system trying to kill them even existed, to prevent that outcome.

The surprising thing isn’t that it happened, it’s that it took so long to happen.

Regards-
dce
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Old 23rd Mar 2019, 03:40
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Originally Posted by GH5
There is a Boeing document made around year 2000 regarding how Boeing defines AOA I cannot post the link but the cover sheet label is
" operational use of angle of attack on modern commercial airplanes "

Aero 10 Flight operations
John cashman director
brian d kelley technical fellow

can be downloaded as a pdf or viewed in html
Here is your link: OPERATIONAL USE OF ANGLE OF ATTACK (pdf)
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Old 23rd Mar 2019, 03:41
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Originally Posted by Smythe
Since it has not been disclosed the conditions and settings where the engine nacelles provide extra lift and nose up the ac (if/when MCAS kicks in)...an AoA sensor is meaningless.

The UT AoA sensors have an offset bolt pattern to insure correct installation.
What about positioning of the internal sensors? Are they indexed for location?
Can you take the units apart?


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Old 23rd Mar 2019, 03:51
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Yes, the sensor vane is integral to the internals.


It is indexed, according to the individual aircraft angle of attack of the wing to fuselage angle. I believe that if you consider the fuselage horizontal or at 0, the wing chord line is at an angle of 2.5 degrees on the 737?

What is unclear to me is why it is necessary for the AoA sensor to be a vane outside of the ac. It is assumed that airflow is horizontal, and the fuselage/wing combination is at an angle to horizontal. Why is the AoA sensor not internal like the IRU gyro?

Last edited by Smythe; 23rd Mar 2019 at 04:12.
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Old 23rd Mar 2019, 03:53
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Originally Posted by CurtainTwitcher
Here is your link: OPERATIONAL USE OF ANGLE OF ATTACK (pdf)
Metadata indicates that this document was created and last edited in Sept 2009.
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Old 23rd Mar 2019, 04:01
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Originally Posted by WingNut60
Metadata indicates that this document was created and last edited in Sept 2009.
OK, there is an archive.org version of the document from < 2004 Version OPERATIONAL USE OF ANGLE OF ATTACK
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