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Ethiopian airliner down in Africa

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Ethiopian airliner down in Africa

Old 15th Apr 2019, 21:21
  #4061 (permalink)  
 
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Originally Posted by GordonR_Cape View Post
Interesting, but inconclusive. My first reaction is that like many words in English "both" is ambiguous, it can mean "together" (noun) or "either" (adverb), which have very different connotations. The placard does not state that the function of the switches has changed, it is only implied if you already understand the consequences of the MCAS trim changes. I may be being obtuse, but a competent lawyer will see right though that...
Given the grammar ambiguity the title of the bullet/callout "nomenclature has changed" adds to the possibility to interpret it either way, much clearer would be "function has changed".
Another try to minimize difference ?

Accurate description is "EITHER switch will deactivate both"

Last edited by MurphyWasRight; 15th Apr 2019 at 21:21. Reason: typo
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Old 15th Apr 2019, 21:37
  #4062 (permalink)  
 
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Originally Posted by YYZjim View Post

But, history shows that Boeing will survive this. Remember 737 rudder hardovers?

1. March 1991, United585 in Colorado Springs. It rolled to the right on approach and crashed. What shocked everybody was that the NTSB could not figure out the cause. Their final report (December 1992) guessed that it might be: (i) loss of directional control, or (ii) turbulence.
2. September 1994, USAir427 in Pittsburg. It rolled to the left on approach and crashed. While the second investigation was still underway, there was a third incident. In June 1996, Eastwind517 experienced two episodes of rudder reversal while on approach to Trenton, New Jersey. With the help of a live pilot and a malfunctioning aircraft still in one piece, the NTSB had some clues. Their final
report (March 1999) implicated the PCU servo.
.
I do remember this, we used to practice recoveries in the SIM, not at all easy. You had to maintain extra speed on the approach so the ailerons would have enough authority over the full rudder. As far as I remember the 737 wasn't grounded then but it was a long time ago.
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Old 15th Apr 2019, 21:42
  #4063 (permalink)  
 
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Originally Posted by GordonR_Cape View Post
Interesting, but inconclusive. My first reaction is that like many words in English "both" is ambiguous, it can mean "together" (noun) or "either" (adverb), which have very different connotations. The placard does not state that the function of the switches has changed, it is only implied if you already understand the consequences of the MCAS trim changes. I may be being obtuse, but a competent lawyer will see right though that...
Just curious, how many would read that slide, take perfunctory note of the change, and move on, and how many would stop short, and start asking "What? What does this change mean? Is this just a labeling change? Can I still cut out the auto trim separately from the manual electric trim? What has changed about the trim operation? Where can I find out more?" and what would be the result of such inquiries made to the company training department/chief pilot?

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Old 15th Apr 2019, 22:14
  #4064 (permalink)  
 
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Originally Posted by ams6110 View Post
Just curious, how many would read that slide, take perfunctory note of the change, and move on, and how many would stop short, and start asking "What? What does this change mean? Is this just a labeling change? Can I still cut out the auto trim separately from the manual electric trim? What has changed about the trim operation? Where can I find out more?" and what would be the result of such inquiries made to the company training department/chief pilot?
Given the "nomenclature changed" label and awkward text I would guess that at least some who might have gone "huh" would decide it had to a be label change only since it would be hard to believe that critical core functionality had changed, at least without a strong warning.
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Old 15th Apr 2019, 23:02
  #4065 (permalink)  
 
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Originally Posted by Sucram View Post
I do remember this, we used to practice recoveries in the SIM, not at all easy. You had to maintain extra speed on the approach so the ailerons would have enough authority over the full rudder. As far as I remember the 737 wasn't grounded then but it was a long time ago.
That is spot on Sucram. 220 kts permitted safe flight with aileron countering full rudder. If below 220 a quick acceleration to 220 did the trick.
Y
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Old 15th Apr 2019, 23:42
  #4066 (permalink)  
 
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I say again....

Originally Posted by ams6110 View Post
Just curious, how many would read that slide, take perfunctory note of the change, and move on, and how many would stop short, and start asking "What? What does this change mean? Is this just a labeling change? Can I still cut out the auto trim separately from the manual electric trim? What has changed about the trim operation? Where can I find out more?" and what would be the result of such inquiries made to the company training department/chief pilot?
I posted this yesterday morning, but I think it got buried awaiting moderator approval (hopefully I'll be off probation soon )

Procedurally, it does not matter what the switches do or how they are labeled. You could call the switches "Hank" and "Frank", and it does not matter. From Boeing's perspective, you don't have to know what these switches are connected to. Whether the NG or the MAX, you always cutoff BOTH switches when called for in the NNC.

It wasn't always so on the NG. A while back, the 737NG stab runaway procedure was changed so that BOTH cutout switches are always selected together, and we no longer try to isolate the offending circuit. I was kind of curious why the change, but I was simply told that Boeing thought this was a better to handle runaway trim. The conspiracy theorist in me now says that Boeing did this because they were looking down the road at the MAX certification and were looking for any opportunity to harmonize procedures.
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Old 16th Apr 2019, 04:08
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I for one, don't want to fly in a plane flown by HAL.
Are you a pilot?

Have you ever flown in a modern Airbus?

You do realise that if HAL had been flying (AP in) then the MCAS would not have activated?
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Old 16th Apr 2019, 04:23
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Boeing’s 767-based tankers use a version of the pitch augmentation system that grounded the 737 Max 8 fleet, the manufacturer and U.S. Air Force officials say.
The disclosure provides a new data point in the unfolding story of how Boeing installed the Maneuvering Characteristics Augmentation System (MCAS) on narrowbody airliner fleet.
Both the KC-767 and KC-46 fleets delivered to air forces in Italy, Japan and the U.S. rely on the MCAS to adjust for pitch trim changes during refueling operations.
In the 1980s, Boeing’s engineers considered using a pitch augmentation system for the commercial version of the 767, but dropped the idea after finding that vortex generators provided adequate control.
Boeing designed the integration on the KC-767 and KC-46 slightly differently than on the 737 Max family.
The single-aisle airliner uses one angle of attack vane — either the captain’s or first officer’s — to generate the data used by the flight computer to activate the MCAS.
By comparison, the KC-767 and KC-46 are designed to use two sensor inputs to feed angle of attack data, Boeing says.
Boeing spokesmen declined to elaborate on which sensor inputs are used to provide the data in the tanker design. The options include using data from the angle of attack vanes on both sides of the cockpit, or an angle of attack vane an inertial gyroscope.


I find the last sentence interesting, although mis-spelled... angle of attack vane AND inertial gyroscope? The unmanned drones use the inertial system for AoA...


https://www.mro-network.com/airframe...d-pitch-system

Last edited by Smythe; 16th Apr 2019 at 04:36.
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Old 16th Apr 2019, 06:39
  #4069 (permalink)  
 
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Originally Posted by MurphyWasRight View Post
Given the "nomenclature changed" label and awkward text I would guess that at least some who might have gone "huh" would decide it had to a be label change only since it would be hard to believe that critical core functionality had changed, at least without a strong warning.
Not a pilot
still I wonder why the MAX needs a PRI and B/U cut off! Forget the label changing, what surprises me, is that on a new design the two switches are in connected basically in series, and either one is doing a cut off! Means the previous design was faulty? And in the new design was considered safermto have a back up cut off switch, just in case the primary fails? What kind of engineer will design a system with a single sensors, single computer, single motor to drive a flight control, and feels the need to add a back up cut off?
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Old 16th Apr 2019, 06:47
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Originally Posted by Smythe View Post
I find the last sentence interesting, although mis-spelled... angle of attack vane AND inertial gyroscope? The unmanned drones use the inertial system for AoA...
This is not new. It has been covered e.g. by Mentour Pilot in his 737 MAX Q&A video (sorry, can't post links yet, look it up on Youtube under Mentour Pilot - Five questions about the Boeing 737 MAX).
Key thing is that the MCAS built into the KC-46 was meant to counter a slightly different phenomenon than in case of the 737 MAX. It was designed specifically to counter CoG shifts from the moving fuel as opposed to countering the aircraft's nose-up tendency in high AoA conditions in case of the 737 MAX MCAS variant. That being said, the KC-46 potentially could have used a different selection of sensors.

However, the fact that the KC-46 did make use of sensor redundancy as well as introduced a simple manual override by the pilot's column movement, points pretty clearly to the fact, that these good engineering practices were once present at Boeing and their absence in case of the 737 MAX MCAS design constitutes a gross negligence. It should now be the role of authorities to determine, why this has been the case.

Last edited by Portallo; 17th Apr 2019 at 13:43.
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Old 16th Apr 2019, 07:03
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Originally Posted by FrequentSLF View Post
Not a pilot
still I wonder why the MAX needs a PRI and B/U cut off! Forget the label changing, what surprises me, is that on a new design the two switches are in connected basically in series, and either one is doing a cut off! Means the previous design was faulty? And in the new design was considered safermto have a back up cut off switch, just in case the primary fails? What kind of engineer will design a system with a single sensors, single computer, single motor to drive a flight control, and feels the need to add a back up cut off?
Well, that is precisely the point: It is so unreliable that you want to make double sure that it can be switched off. Being able to switch it on is not guarded by a backup switch.
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Old 16th Apr 2019, 08:03
  #4072 (permalink)  
 
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Stab Trim Simulation Inputs

OK, not a pilot or anything to do with aviation, but being basically housebound for the past few months have followed the LIon Air and Ethiopian accidents and the resulting Max saga on here and elsewhere (and have tried to DMOR before asking questions). They are fascinating from so many aspects which the ongoing debate on here and other forums have sought to draw out, it is just sad that it has to be on the back of such a tragic loss of life.

This post is promoted by watching the Mentour video, and in particular the struggle they had trying to use the manual wheel trim to restore stab trim. My understanding is that a flight simulator is programmed to simulate real aircraft behaviour by using test flight data from all of the flight envelope and no doubt from wind tunnel testing and other research?

So watching the struggle to manually trim under the flight conditions they were attempting to simulate gave me the obvious thought that manual trim reaction was being supplied by some algorithm, look up chart, whatever which said in my layman understanding “these are the simulated flight conditions, therefore apply a force of x to the manual trim wheel”.

If this is correct, if I were a regulator looking to recertify the MAX, or more so if I was a lawyer looking to build a case, I would be very keen to see this background data, and exactly how much of the flight envelope is actually covered while still allowing the manual trim wheel to retain authority, and not assuming the pilot was superhuman.

Alternatively, probably not sure how realistic, but if the data wasn't complete, wouldn't it be “relatively easy” for interested parties to commission wind tunnel testing to obtain the countering manual trim force required throughout a complete range of speed, altitude, stab trim angle and with say a maximum countering column elevator force being applied ?

Apologies if this is ignorant nonsense, if it is “move on nothing to see here!” If there is any logic in what I say I'd love feedback.

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Old 16th Apr 2019, 09:08
  #4073 (permalink)  
 
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Alchad, timely and relevant questions; as to be expected from ‘West of the M5’

“ …very keen to see this background data, and exactly how much of the flight envelope is actually covered …’

This is an important issue. One scenario is that Boeing FAA accepted previous data from the 737 NG, or even 737 classics for the MAX; based on the aerodynamic design, wind tunnel and flight tests - grandfather rights. This probably involved some extrapolation, thus the associated processes are of interest.
Did Boeing convince themselves - and then the FAA, that the MAX is sufficiently similar to the NG so that deep questioning was glossed over. Unfortunately the MAX is not the same as witnessed by MCAS - probably a late addition to meet certification (not to be the same as precious variants), etc, etc.

From a flight test viewpoint (hindsight), the tests required would be very hazardous; thus data as far as was flown for certification opposed to simulator information beyond the recognised flight envelope would depend on extrapolation. Without ‘real’ data, the aircraft and simulator certification could be based on previous variants and ‘linear’ interpretations (not mathematically linear) for simulation - it’s good enough for training, because the pilots won’t get into that situation, the system does not fail that way, etc, etc.

Thus the FAA and other regulators could (should) be reconsidering these aspects, and based on piloting experiences, the concerns about trim forces and practicality of recovery for trim runaway (not MCAS because that won’t malfunction in the same way post mod) could be well founded, and thus a much bigger problem for Boeing.

If the certification approvals for the aircraft and simulator meet current requirements there should not be need for more data; this should be (has been) collected for certification approval, proof that the failures can be managed by human alleviation, and that pilots ‘will not’ (certification probability) encounter such situation again.

No need to move on, dig-in for the long battle; certification ramifications and possibly Boeing rework / rethink.
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Old 16th Apr 2019, 12:08
  #4074 (permalink)  
 
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Originally Posted by oggers View Post
I think we can agree that it is easier to hold the trim switch with the stick shaker off. Nonetheless, the data shows clearly that the thumb switch can be held closed with the stick shaker on.
But the Lion Air data also shows "off-blips" during automatic trim every now and then,
Nope. There is a clear temporary loss of input in many of the manual, but none of the automatic commands. The latter show only "ragged" flanks.

Lionair Upper: manual trim middle: automatic trim

On the ET FDR PF asks PNF to help him with the manual electric trim. So he may have had difficulties actuating his thumb switch.

Last edited by spornrad; 16th Apr 2019 at 12:27.
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Old 16th Apr 2019, 12:47
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Originally Posted by spornrad View Post
Nope. There is a clear temporary loss of input in many of the manual, but none of the automatic commands. The latter show only "ragged" flanks.

Lionair Upper: manual trim middle: automatic trim

On the ET FDR PF asks PNF to help him with the manual electric trim. So he may have had difficulties actuating his thumb switch.
I do not agree with your analysis. We will know in the end if that is identified as a contributing factor. I predict it will not be.
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Old 16th Apr 2019, 13:25
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There is an excellent article in Flight International this week: "Questions persist after Ethiopian loss".

If there are questions about pilot training, I feel that they should be directed not so much at type-rating and airline training, but rather at the first 200 hours of a pilot's training. There have been too many crashes where the very, very basics of flying an aeroplane seems to have been forgotten.

Quote from the 'Effect of Controls' lesson at the very beginning of flying training: "At high airspeeds, typically with a low nose attitude, the controls are harder to move, very effective and require only small movements to bring about a change of flight path. They feel firm." The last paragraph of that Flight article is very very pertinent.
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Old 16th Apr 2019, 13:42
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Originally Posted by FrequentSLF View Post
Not a pilot
still I wonder why the MAX needs a PRI and B/U cut off! Forget the label changing, what surprises me, is that on a new design the two switches are in connected basically in series, and either one is doing a cut off! Means the previous design was faulty? And in the new design was considered safermto have a back up cut off switch, just in case the primary fails? What kind of engineer will design a system with a single sensors, single computer, single motor to drive a flight control, and feels the need to add a back up cut off?
Am a 737 pilot.

Reason I was given was to provide redundancy in case of a rare instance of switch (or actually relay) welding. That phenomenon occurs when a relay remains in a set position for so long that it basically welds the contacts closed. I'm not an electrical engineer, so I don't know how to evaluate this statement, but it is not unlike the rationale for the split thumb switches on the yoke.

I suspect another unspoken reason was to maintain the look and feel of the 737NG switches. As long as there were two switches that were always used together, then Boeing could take the position that no additional training was required.
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Old 16th Apr 2019, 13:50
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Originally Posted by NoelEvans View Post
There is an excellent article in Flight International this week: "Questions persist after Ethiopian loss".

If there are questions about pilot training, I feel that they should be directed not so much at type-rating and airline training, but rather at the first 200 hours of a pilot's training. There have been too many crashes where the very, very basics of flying an aeroplane seems to have been forgotten.

Quote from the 'Effect of Controls' lesson at the very beginning of flying training: "At high airspeeds, typically with a low nose attitude, the controls are harder to move, very effective and require only small movements to bring about a change of flight path. They feel firm." The last paragraph of that Flight article is very very pertinent.
That could be one explanation of the seemingly tentative trim inputs especially by Lion Air FO, although the (possible) ergonomic factors discussed above are intriguing.
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Old 16th Apr 2019, 14:24
  #4079 (permalink)  
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Originally Posted by oggers View Post
I do not agree with your analysis. We will know in the end if that is identified as a contributing factor. I predict it will not be.
As has been pointed out many times in the two main threads discussing the 737 MAX crashes, the LT610 PF counteracted uncommanded (MCAS) nose-down trim on 21 separate occasions, yet for whatever reason did not believe he was experiencing a stab trim runaway, and failed to activate the CUTOUT switches.

There are two big questions:
  • why did he fail to recognize the stab trim runaway and activate the CUTOUT ?
  • why did he hand control of the trim to the FO with such a critical malfunction occurring ?
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Old 16th Apr 2019, 14:41
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Originally Posted by gmx View Post
As has been pointed out many times in the two main threads discussing the 737 MAX crashes, the LT610 PF counteracted uncommanded (MCAS) nose-down trim on 21 separate occasions, yet for whatever reason did not believe he was experiencing a stab trim runaway, and failed to activate the CUTOUT switches.

There are two big questions:
  • why did he fail to recognize the stab trim runaway and activate the CUTOUT ?
  • why did he hand control of the trim to the FO with such a critical malfunction occurring ?
Good questions, but as I said much much earlier, I think we can turn this one on its head and ask "what enabled the supernumerary Captain on the prior flight to recognise, at least in part, that CUTOUT was the solution?". I believe that, even then, electric trim was re-engaged albeit briefly.

So, even with 3 heads in the cockpit, one of whom was free from immediate control issues, it did not appear to that crew the Trim Runaway NNC was the obvious choice.
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