Go Back  PPRuNe Forums > Flight Deck Forums > Rumours & News
Reload this Page >

Ethiopian airliner down in Africa

Rumours & News Reporting Points that may affect our jobs or lives as professional pilots. Also, items that may be of interest to professional pilots.

Ethiopian airliner down in Africa

Old 3rd Apr 2019, 15:14
  #2961 (permalink)  
 
Join Date: Jun 2001
Location: Rockytop, Tennessee, USA
Posts: 5,899
From the Reuters wire a report that the MCAS may have reactivated with the stab trim switches off:

Ethiopian Airlines crash: anti-stall system 'engaged repeatedly'

Software may have redeployed without human input before plane went down, say sources
Reuters Wed 3 Apr 2019 07.02 EDT

Boeing’s anti-stall software on a doomed Ethiopian Airlines jet re-engaged up to four times after the crew initially turned it off due to suspect data from an airflow sensor, two people familiar with the matter have said.

It was not immediately clear whether the crew had chosen to redeploy the system, which pushes the nose of the
Boeing 737 Max downwards, but one person with knowledge of the situation said investigators were studying the possibility that the software had kicked in again without human intervention.

A Boeing spokeswoman declined to comment. Ethiopian investigators were not immediately available for comment.

Investigators 'believe Ethiopian 737 Max's anti-stall system activated'
Boeing’s anti-stall software, known as MCAS, is at the centre of investigations into both the Ethiopian Airlines crash last month and a Lion Air
crash in Indonesia in October, which together killed nearly 350 people.

People familiar with the investigation said the anti-stall software – which automatically pushes the aircraft’s nose down to guard against a loss of lift – was activated by erroneous “angle of attack” data from a single sensor.

The investigation has now turned towards how MCAS was initially disabled by pilots following an emergency checklist procedure, but then appeared to repeatedly start working again before the jet plunged to the ground, they said.

A directive issued after the Indonesian crash instructed pilots to use cutout switches to disengage the system in the event of problems, and leave it switched off.

Doing so does not shut down the MCAS system completely, but severs an electrical link between the software and aircraft systems, a person familiar with the technology said.

Investigators are studying whether there are any conditions under which MCAS could reactivate itself automatically, without the pilots reversing the cutout manoeuvre. Boeing is in the process of upgrading the software while adding extra training.

A preliminary report is expected within days.

The pilots manoeuvred the plane back upwards at least two times before pressing the stabiliser cutout switches to disable the system, the other person familiar with the matter said.

However, initial flight data indicates the aircraft was not in a “neutral” attitude when pilots used the stabiliser cutout switches to disable the MCAS system, the person added, making the situation harder to manage.

After the pilots turned off MCAS, the plane gained roughly 2,000ft over the next few minutes, but dived to the ground after the renewed succession of nose-down inputs from MCAS.

None of the parties involved in the investigation was available for comment.

Airbubba is offline  
Old 3rd Apr 2019, 15:17
  #2962 (permalink)  
 
Join Date: Dec 2004
Location: Southern England
Posts: 109
Originally Posted by GordonR_Cape View Post
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.
Albino is offline  
Old 3rd Apr 2019, 15:30
  #2963 (permalink)  
 
Join Date: Aug 2000
Posts: 1,487
Originally Posted by Airbubba View Post
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?

ManaAdaSystem is offline  
Old 3rd Apr 2019, 15:37
  #2964 (permalink)  
 
Join Date: Jun 2001
Location: Rockytop, Tennessee, USA
Posts: 5,899
Originally Posted by ManaAdaSystem View Post
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?
Airbubba is offline  
Old 3rd Apr 2019, 15:44
  #2965 (permalink)  
 
Join Date: May 2000
Location: London, UK
Posts: 369
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.



SLF3 is offline  
Old 3rd Apr 2019, 15:46
  #2966 (permalink)  
 
Join Date: Dec 2002
Location: UK
Posts: 2,248
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
safetypee is online now  
Old 3rd Apr 2019, 15:51
  #2967 (permalink)  
 
Join Date: Aug 2002
Location: Zone of Alienation
Age: 77
Posts: 9
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?

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.
FIRESYSOK is offline  
Old 3rd Apr 2019, 15:53
  #2968 (permalink)  
 
Join Date: Jun 2009
Location: florida
Age: 79
Posts: 1,491
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
gums is offline  
Old 3rd Apr 2019, 16:14
  #2969 (permalink)  
 
Join Date: Nov 2018
Location: Vancouver
Posts: 68
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.
patplan is offline  
Old 3rd Apr 2019, 16:22
  #2970 (permalink)  
 
Join Date: May 2008
Location: Europe
Age: 43
Posts: 612
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.
SMT Member is online now  
Old 3rd Apr 2019, 16:36
  #2971 (permalink)  
 
Join Date: Mar 2006
Location: England
Posts: 932
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.

PEI_3721 is offline  
Old 3rd Apr 2019, 16:42
  #2972 (permalink)  
 
Join Date: Dec 2015
Location: Cape Town, ZA
Age: 60
Posts: 424
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.
GordonR_Cape is offline  
Old 3rd Apr 2019, 16:48
  #2973 (permalink)  
 
Join Date: Jul 2013
Location: SoCal
Age: 63
Posts: 9
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".
TachyonID is offline  
Old 3rd Apr 2019, 16:54
  #2974 (permalink)  
 
Join Date: Jul 2013
Location: Norway
Age: 55
Posts: 140
Originally Posted by GordonR_Cape View Post
The Mentour Pilot video has been disabled.
It was deleted because MentourPilots employer objected I have learned.
SteinarN is offline  
Old 3rd Apr 2019, 16:57
  #2975 (permalink)  
 
Join Date: Feb 2008
Location: victoria bc
Age: 80
Posts: 41
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.
ferry pilot is offline  
Old 3rd Apr 2019, 16:59
  #2976 (permalink)  
 
Join Date: Nov 2007
Location: Hong Kong
Posts: 445
Originally Posted by SteinarN View Post
It was deleted because MentourPilots employer objected I have learned.
Surely this was expected.
CodyBlade is offline  
Old 3rd Apr 2019, 17:02
  #2977 (permalink)  
 
Join Date: Nov 2010
Age: 54
Posts: 687
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.
hans brinker is offline  
Old 3rd Apr 2019, 17:03
  #2978 (permalink)  
 
Join Date: Nov 2010
Age: 54
Posts: 687
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.
hans brinker is offline  
Old 3rd Apr 2019, 17:11
  #2979 (permalink)  
 
Join Date: Sep 2001
Location: Toronto
Posts: 2,369
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.

RatherBeFlying is online now  
Old 3rd Apr 2019, 17:55
  #2980 (permalink)  
 
Join Date: Jan 2008
Location: uk
Posts: 861
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.
infrequentflyer789 is offline  

Thread Tools
Search this Thread

Contact Us - Archive - Advertising - Cookie Policy - Privacy Statement - Terms of Service - Do Not Sell My Personal Information -

Copyright © 2021 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.