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Ethiopian airliner down in Africa

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Ethiopian airliner down in Africa

Old 3rd Apr 2019, 16:14
  #2981 (permalink)  
 
Join Date: Nov 2018
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Originally Posted by ManaAdaSystem View Post
How is this possible? MCAS is still operational with the trim system disabled????
If this is true Boeing not only designed the MCAS system and installed it without telling the pilots, but they also failed to tell pilots it can’t be switched off, even after Lion Air crashed?
They made a procedure to deal with a runaway MCAS that is completely worthless and will not take care of the problem?
Hence, this might be the reason for the delay in releasing the preliminary report.

Apparently, according to WSJ, there were disagreements between investigators about how to interpret the FDR [& CVR] data.

...Safety experts have also tussled over the interpretation of certain data and their presentation in the report, according to people from both countries...
The major news is that MCAS was turning back on after being shutoff as per NNC for Runaway Trim. The question becomes why was it back on? There are two conflicting news coming out. The first version suggested that the crew had turned the stab trim motor back on because they'd had some difficulty to trim the AC manually, essentially going against the NNC procedure. And, the other version of the news reported that the MCAS system was turning back on by itself, suggesting there was yet another unknown/undocumented power mechanism in the Max-8 coming into play.

We can safely guess now that the disagreement between investigators mainly must have been about what/who turned the MCAS back on.

Personally, I think it is doubtful that MCAS really have another route to power up its trim. Unless, it had metamorphosed itself into a franken-system, unbeknownst to us all.
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Old 3rd Apr 2019, 16:22
  #2982 (permalink)  
 
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Originally Posted by Airbubba View Post
Or, were the column forces in pitch so great with the stab trim switches off that the crew turned them back on momentarily to retrim, not realizing that they could trim manually with the trim wheels?
Airbubba, see the video posted on Leeham news. They're simulating a high-speed runaway stabiliser after an unreliable airspeed event. The cut-off switches are thrown at roughly 3 degree ANU and 310 knots, and it is almost impossible to get the aircraft back in trim using manual trimming whilst the PF is holding almost full-aft stick. And this was at 3 degrees ANU, the ET crew was facing a stabiliser trimmed much further nose down. In short, it's physically impossible to get the aircraft back in trim manually without unloading the stabiliser, which require a lot of airspace between you and terra firma.
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Old 3rd Apr 2019, 16:36
  #2983 (permalink)  
 
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Yo gums,
Boeing certainly have their hands full with the Max, but if the high stick-force trim loads are a dominant factor, then any solution, MCAS or not, might also have to consider other variants of 737.

I surmise that an inability to trim the Max with excessive trim loads (MCAS induced), will be compared to previous variant certifications which had to consider high trim loads because of Trim Runaway (also still applicable in the Max), which necessitated the previous roller coaster manoeuvre. If it is concluded that the practicality of this procedure is unreasonable for pilots fly in order to recover from ‘any’ extreme trim failure then the trim system may have to be rethought - e.g stop-down the range of trim movement, if able in comparison with the required certification range of trim.

Fixing MACS / AoA should address the deficient stability margin, but this most probably will not overcome the high stick-forces with offset trim - basic aircraft issue.

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Old 3rd Apr 2019, 16:42
  #2984 (permalink)  
 
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The Mentour Pilot video has been disabled. This often happens for technical or copyright legal reasons, and may be re-posted. His recent videos cover MCAS in outline, and runaway stabiliser trim in an actual simulator, showing how hard manual control is, but not commenting in detail.

Edit: Mentour pilot's previous videos have been actual training on a simulator. Doing freelance accident investigation (during company paid for simulator time) was probably pushing the limits too far.

The article by Bjorm Fehrm describes the situation clearly: https://leehamnews.com/2019/04/03/et...as/#more-29790

My point (not mentioned in the article) was that the checklists and emergency AD fail to mention disengage auto-throttle. IMO this step leads to excessive airspeed after takeoff, turning a hazardous situation into an unrecoverable one.

P.S. I have been away from my desk for a few hours, so responding to earlier posts won't add anything to the thread clarity.

Last edited by GordonR_Cape; 3rd Apr 2019 at 18:35.
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Old 3rd Apr 2019, 16:48
  #2985 (permalink)  
 
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Youtube videos now being pulled?

Originally Posted by safetypee View Post

Also see the video (via SteinerN)...
Whilst it appears easier to set nose down trim, it is less so to recover back to a trimmed condition. The nose down direction might be aided by the aerodynamic forces, whilst nose up the trim wheel has to overcome them.
Also, MCAS could run the trim nose down after flap retraction - lower stab trim loads, but if speed increases due to descending flight, then back trim at a higher speed is less achievable, having to overcome much higher stab trim loads.

This is a dynamic, escalating situation. And for those following the ‘40secs time to react’ theme, consider that recognition might take two MCAS cycles 10sec trim, 5 sec pause / back trim, 15 x 2 = 30 sec, only leaves 10secs for action - select trim inhibit, then apply back trim wheel. See the video, move seat back, pull the handle out, then wind - how much, how long, if able.


'
Now, it's worrisome to note that Mentour Pilot's very-illuminating videos on Youtube are being suppressed. Without being too paranoid, it would appear Boeing's PR department is now working overtime to "damage control" the revelation that the ET pilots HAD followed procedure.

It's inconceivable that, having followed the Procedure to disable TRIM, that the pilots would have re-enabled TRIM unless they found the trim wheels insufficient to overcome the nose-down attitude MCAS-HAL gave them. It's a large number of revolutions to make much impact, especially with the all the back pressure PF and PNF were likely applying via the column, and with only limited time to recover the pilots may have wished to re-enable electric trims in order to expedite matters. Perhaps the first thing MCAS-HAL does, since he'd be out of the loop on the physical disconnection of the electrical circuit, might actually be to "catch up" with a full Down Cycle when the motors are turned back on? No matter how you view it, this appears like Boeing didn't "think the realities of the situation through thoroughly".
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Old 3rd Apr 2019, 16:54
  #2986 (permalink)  
 
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Originally Posted by GordonR_Cape View Post
The Mentour Pilot video has been disabled.
It was deleted because MentourPilots employer objected I have learned.
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Old 3rd Apr 2019, 16:57
  #2987 (permalink)  
 
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Originally Posted by aeronaut321 View Post
737qanda that's a great idea.

Ferry pilot, I think producing pilots capable of hand flying with confidence is an essential skill - it can be achieved without much cost but just requires a change of culture. Some airlines already do this just by encouraging turning off the automation (when appropriate, ie good weather, low traffic levels).

I remember a skipper I flew with when I almost overcooked a hand flown approach say: what would the passengers rather have, a perfectly flown approach by the autopilot everytime or a pilot who can confidently fly if the situation requires it, even if we'd had to throw that approach away?
​​​​
There are a great many out there who think exactly as you do, and I am one of them in spite of my argument. Hand flying is an essential skill. But it is a dying one. The tide, my fellow artful flyers, has turned against us. Were it any other way, we would not be having this discussion. Like your car that spends ninety five percent of its useful life parked on the ground, airliners may as well be spending theirs parked in the sky when it comes to improving your driving skills. The truth is, you get those skills the hard way, before you arrive in the big leagues. The only way in not all that long ago.
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Old 3rd Apr 2019, 16:59
  #2988 (permalink)  
 
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Originally Posted by SteinarN View Post
It was deleted because MentourPilots employer objected I have learned.
Surely this was expected.
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Old 3rd Apr 2019, 17:02
  #2989 (permalink)  
 
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Originally Posted by gums View Post
Salute!

Looking more and more like Big B needs to bite the bullet and do something with the engine mounting design and possibly the stabilizer/elevator configuration. Screw MCAS. Fix the aero problem for certification and general good handling characteristics.

It can be done, and was long ago by Lockheed, but......

Back when the earth was still cooling, Lockheed had to modify all of the Electra airliners due to harmonic vibrations and such. Hell, the wings were being ripped off! The public relations war was lost, however, and even though the fix cured the problem, had great results and the legendary P-3 Orion resulted. the damage had been done and folks wouldnt fly the thing.

I can't unnerstan why slots or slats on the nacelles wouldn't help with the pitch moments. Maybe small cannards. Reshape the nacelles?. And so forth. With many features of the old design already certified, doesn't seem to me that re-certifying without the MCAS kludge would not be as expensive as a complete new design, although the billions about to be paid for the lawsuits could influence that proposal.
_____________________________________
I tried to imagine the roller coaster procedure posted here to regain useable trim and had to laugh. Imagine the pax barfing and screaming, plus flight attendants bouncing off the overhead bins and more. And just when it seems to the SLF in seat 23A that things are under control, whooo hooo one more time!!

Gums sends...
I would have thought a wing-tip extension, not to increase span, but to extend the chord further aft, between the aileron and the tip could help (just a line pilot, not a designer), as it is a lot further aft than the MAC.
Obviously need to make sure that that part of the wing stalls last as well.
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Old 3rd Apr 2019, 17:03
  #2990 (permalink)  
 
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Originally Posted by PEI_3721 View Post
Yo gums,
Boeing certainly have their hands full with the Max, but if the high stick-force trim loads are a dominant factor, then any solution, MCAS or not, might also have to consider other variants of 737.

I surmise that an inability to trim the Max with excessive trim loads (MCAS induced), will be compared to previous variant certifications which had to consider high trim loads because of Trim Runaway (also still applicable in the Max), which necessitated the previous roller coaster manoeuvre. If it is concluded that the practicality of this procedure is unreasonable for pilots fly in order to recover from ‘any’ extreme trim failure then the trim system may have to be rethought - e.g stop-down the range of trim movement, if able in comparison with the required certification range of trim.

Fixing MACS / AoA should address the deficient stability margin, but this most probably will not overcome the high stick-forces with offset trim - basic aircraft issue.

Very good point IMHO.
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Old 3rd Apr 2019, 17:11
  #2991 (permalink)  
 
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Pilots vs Gorilla

It appears that MCAS can in ten seconds move the stab whenever it's in the mood, but the pilots need considerably longer to bring back the stab with dozens of cranks of manual trim - provided that airload allows them to move the trim.

Very much an unequal contest.

​​​​​​MCAS really shouldn't be putting in more trim than can be corrected by the crew in the interval before it reactivates.

But then, limiting MCAS authority might fail to achieve required stick force increase approaching stall. The software will have to get even fancier to satisfy 10E-9 reliability.

I'm with gums. Dump MCAS and fix the nacelle aerodynamics.

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Old 3rd Apr 2019, 17:55
  #2992 (permalink)  
 
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Originally Posted by GordonR_Cape View Post
The Mentour Pilot video has been disabled. This often happens for technical or copyright legal reasons, and may be re-posted.
Disappeared while I was watching it I think - soon as I finished it I was going to comment and say something like "wow that cleared a lot up", but when it ended, it was just "unavailable".

Edit: Mentour pilot's previous videos have been actual training on a simulator. Doing freelance accident investigation was probably pushing the limits too far.
He has a bunch of other videos on LionAir, MCAS, etc. which don't seem to have been a problem. I've saved copies of the Leeham page and Peter Leeme's latest, for my own records in case the takedown is not originating directly at the employer and spreads wider. The investigation seems to have been leaking eight ways to Sunday, but everyone who had the info (possibly including tdracer on here) has been too scared to go public (there was just one post hinting on here, I recall) until WSJ blew it open. Then everyone felt safe, but maybe that was misplaced...

The video was eye-opening, raised a few more questions as well, still digesting it - made more difficult by only being able to rewind in my memory now.

Whatever, it is clear this is getting worse, Boeing are definitely not going to be able to fix this with a small patch over the hole, buffing it out with PR and a final coat of blame-johnny-foreigner.
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Old 3rd Apr 2019, 18:15
  #2993 (permalink)  
 
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Salute!

Another solution that keeps the basic construction jigs and such in place for building more dinosaurs was proposed earlier here, but will still require certification, just not as much. Expensive, yes. But not as expensive as all the $$$ that will be paid out to the families and possibly airlines with useless airframes on the ramp.

Ditch all the STS, feel system, MCAS and such crapola. Go FBW and retain a few of those ropes, levers, pulleys, tubes and such that some here still prefer for a modern airliner. You wouldn't have to worry about control force versus AoA or "Q" or mach gradients, just ask the Airbus folks how they got by the FAR 25 requirements. And you knoiw what? I don't think the FBW version of the MAX would pass. The design is not as inherently as "nice" and gentle and forgiving as it should be.

The 'bus showed its inherent stability and pretty good aerodynamic characteristics on at least two crashes - the "showboat" public relations pass and AF447. Without all the "protections" and such, most pilots could fly the thing in the "direct mode" and get it back on the ground in one piece. After all, FBW primarily means replacing all those mechanical connections with a hydraulic source and an actuator commanded by an electrical signal. You do not even need a computer to have what the 'bus calls "direct law".

So I have a feeling this "fix" is gonna take a lot more time and $$$ before many carriers and countries are gonna buy in. I wish Boeing well, but I also wish Boeing would get back to the basics that made them one of the premier aircraft production empires in aviation history.
And just so you know, I never flew a single model of anything Boeing ever built. I flew McDonnell, Cessna, Lockheed, Convair/General Dynamics and Vought.military planes , and on the civilian side Luscombe, Piper, Aeronica and Taylorcraft.

Gums sends...
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Old 3rd Apr 2019, 18:45
  #2994 (permalink)  
 
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Not a very good lesson learned from lion.

I think the procedure should be:

If Trim is bad and you didn't put it there (memory item, but quite intuitive).

1. Bring it back to something reasonable with column switches.
2. Then cut it.

Maybe also including a suggestion to check that you actually are restoring trim in the direction you desire with a quick look at the trim wheel at step one, and go straight to 2 if you are not (different failure than what we are discussing).

If for some reason you need minute adjust afterwards, use the wheel.

Column switch vs mcas, column wins, it's faster and overrides mcas.

But,

Hand crank vs mcas, mcas wins. Hand crank too slow and perhaps underpowered. You may run out of usable sky or energy before you get it back.

I'm also in the group of those who would like to see an aero solution, although for some reason I would expect some lift added in the rear lateral fuselage at high aoa only, rather than modify the nacelles (I can't see in which way) or add a trailing lift device at the tip of the wings (big mess, and heavier due to shorter leverage)

Main advantage over software patch: it will actually help in real life.
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Old 3rd Apr 2019, 18:59
  #2995 (permalink)  
 
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One sensor, 10E-9 reliability, LoL!
(Referring to Post #3024 from RatherBeFlying).

Last edited by jpfle; 3rd Apr 2019 at 19:08. Reason: Added context.
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Old 3rd Apr 2019, 19:17
  #2996 (permalink)  
 
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MCAS authory vs column switch?

Originally Posted by ecto1 View Post
Column switch vs mcas, column wins.
I that dead sure? Have an authoritative source?
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Old 3rd Apr 2019, 19:28
  #2997 (permalink)  
 
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The problem is the instant you get airborne, you have the stick shaker AND IAS disagree. If you have the mental capacity to realise at this point that you aren't actually stalling (first instinct would be "oh sh!t, are my takeoff performance or flaps figures correct"), AoA probe failure wouldn't be my first thought.

Once you have had time and brainspace to process, "good, I'm actually still flying, no buffet, not stalling my speed & config are probably good", the next thought would be to notice IAS disagree, disconnect the autopilot (not engaged at this point) autothrottle blip blip off, lets climb at my initial performance tool target (if available ~15 +/- degrees). Now we are climbing away with a know thrust, known good pitch attitude, not stalling and that is going to get me toward a safe place (away from the hard stuff).

In all the confusion my buddy would probably be prompting me to turn off the flight directors too. At this point we have done the first part of the IAS disagree memory items, pitch and thrust to come.

This might make this sound somewhat logical, possibly easy, but believe me, that would be a REALLY bad day already and I might be between 400 to 1000' AGL before I can even begin to comprehend what MAY be wrong with my aircraft.

Boeing only gives guidance of 10 degrees nose up pitch and 80% thrust for this scenario. Would you really wanting do that with the stick shaker going off just after takeoff? It's going to climb like a dog and there are hills around and I have the SS going off, so I think I'm going to try to climb away for a while with some known good datums.

So, the problem is in this scenario disconnecting the autothrottle with the blip blip is actually going to leave you with takeoff, not climb thrust, not 80% N1 set. You may not revisit the thrust for some time because I still have the stick shaker. That is possibly a trap in all this. There is so much other stuff going on, that having takeoff thrust set is going to get you into the >230 knot realm real quick once you lower the nose to 10 degrees and forget to set the 80% N1 . Oh did I mention, that, at this point I may have to consider moving the stab trim switches to cutout too before retracting the flaps. Now I have to use the manual pitch trim wheel too as we accelerate.

I am actually now running TWO memory checklist simultaneously, the IAS disagree and Runaway Stabiliser. All because of a single sensor failure. Surely the certification basis for the aircraft is fundamentally flawed on this count alone.

Gums, the reason Boeing don't want to certify a new type is probably not so much the actual cost of the certification, rather the cost of type rating pilots. It was the operators who put the pressure on Boeing. Boeing knew if it was a new type they it would hand operators an opportunity to play the Airbus card against them, if you are going to have to put your pilots through a rating, does it matter if it is Boeing or Airbus?
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Old 3rd Apr 2019, 20:01
  #2998 (permalink)  
 
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Originally Posted by fgrieu View Post
I that dead sure? Have an authoritative source?
Control column cutout switches do not inhibit MCAS trimming (which makes sense if you think why the system was designed in the first place, but also no sense to a 737 pilot that doesn't expect the trimwheel to move AND when pulling up, pre-MCAS discovery).
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Old 3rd Apr 2019, 20:02
  #2999 (permalink)  
 
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CT:
It is a shame that the Mentour Pilot video has been disabled, I managed to watch it and it showed what happens when the IAS disagree and runaway trim checklist are followed in the (presumed) ET MCAS case. Overall fairly similar to your scenario.

The pilots in the sim calmly and methodically followed the checklists in what I would call a demonstrating or teaching mode, certainly not stressed or surprised.
Don't believer they even had a stick shaker going.

Even so they ended up in a state where manual trim inputs were physically close to impossible after electrical trim cutout due to the air speed.
My takeaway was that unless the pilot trimmed close to neutral before electrical tim cutout there was no way to manually trim.
Note that this should be possible (as shown in both lion air flights) since pilot trim cancels (for 5 seconds) MCAS trim actions.

One other observation from the video is that from the jumpseat camera point of view the trim wheel action is very obvious. I suspect it might be much less so for stressed pilots trying to make sense of the situation. This may be why the jumpseat pilot was able to save the penultimate Lion air flight.

Gums: If you are referring my post re making a full FBW 737, that was meant as a thought experiment on automation more than a practical suggestion, if for no other reason that it 737 FBW would certainly require more than a slideware conversion course.
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Old 3rd Apr 2019, 20:24
  #3000 (permalink)  
 
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Given the known the MCAS problem, and Boeing air directive, I would use flaps 1 for as long as possible to prevent MCAS from engaging if pilot sees IAS disagree. Once atleast 2500 agl retract flaps to see if MCAS engages. If yes, extend flaps immediately and return to airport. WSJ reported MCAS engaged in this flight at 450 agl which suggests plane already in clean configuration. Interesting to see what fdr shows for flap settings and retraction.
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