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Ethiopian airliner down in Africa

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Ethiopian airliner down in Africa

Old 3rd Apr 2019, 15:17
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Originally Posted by GordonR_Cape
Sources differ, and that was the advice from Boeing and the FAA (see my earlier post). There is a strong suggestion that the electric trim was intentionally restricted in power, specifically to prevent runaway nose up trim. This meant that overpowering MCAS this way was not possible, though it might have made a few degrees difference before they hit the cutoff switches.
If I've read your post correctly I think you are getting confused with the wording. The bulletin (the one I read anyway) specifically states that MCAS can be stopped and reversed with use of the electric trim switches on the control column. The note in the Operating Instructions implies that the electric trim should be used to neutralise the pitch force required to maintain controlled flight - then placing the stab trim switches to cutout. So position the stabilizer exactly where you want it and then cut power to the system.

If the information leaked is accurate and the system was behaving as Boeing expected it to in the bulletin, this was misunderstood by the pilots.
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Old 3rd Apr 2019, 15:30
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Originally Posted by Airbubba
From the Reuters wire a report that the MCAS may have reactivated with the stab trim switches off:
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?

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Old 3rd Apr 2019, 15:37
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Originally Posted by ManaAdaSystem
How is this possible? MCAS is still operational with the trim system disabled????
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?
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Old 3rd Apr 2019, 15:44
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If the 'fix' advised by Boeing post Lion Air turns out to be have been followed by the Ethiopian crew that will not reflect well on either Boeing or the FAA.

If they have got it wrong twice what else is out there? The questions will go way beyond MCAS implementation.



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Old 3rd Apr 2019, 15:46
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Albino, #3008, further to the post Ethiopian airliner down in Africa
and EASA text via Boeing advice on "aerodynamically relieving airloads" using manual stabilizer trim there could be questions about the validity of the AD procedure, at least if it was evaluated in the abnormal conditons or only in theory.

Also see the video (via SteinerN) https://www.youtube.com/watch?v=EzgBft-79U8&feature=youtu.be
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.



Last edited by safetypee; 3rd Apr 2019 at 15:58. Reason: dynamic, 40 secs
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Old 3rd Apr 2019, 15:51
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Originally Posted by ManaAdaSystem


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?

The poster you’re responding to didn’t read the article critically enough. It says ‘may have re-activated up to four times after INITIALLY being switched off.’

It was poorly written to begin with or written to elicit reaction from people who don’t read well.
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Old 3rd Apr 2019, 15:53
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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...

Last edited by gums; 3rd Apr 2019 at 16:38. Reason: added rationale
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Old 3rd Apr 2019, 16:14
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Originally Posted by ManaAdaSystem
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
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Originally Posted by Airbubba
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
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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
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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
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Youtube videos now being pulled?

Originally Posted by safetypee

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
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Originally Posted by GordonR_Cape
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
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Originally Posted by aeronaut321
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
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Originally Posted by SteinarN
It was deleted because MentourPilots employer objected I have learned.
Surely this was expected.
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Old 3rd Apr 2019, 17:02
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Originally Posted by gums
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
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Originally Posted by PEI_3721
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
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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
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Originally Posted by GordonR_Cape
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
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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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