Go Back  PPRuNe Forums > Flight Deck Forums > Tech Log
Reload this Page >

Ethiopian interim report on Max 737

Tech Log The very best in practical technical discussion on the web

Ethiopian interim report on Max 737

Old 9th Mar 2020, 16:30
  #1 (permalink)  
Thread Starter
 
Join Date: Nov 2000
Location: Canada
Posts: 550
Ethiopian interim report on Max 737

Different sensors recorded plane's angle of attack 59 degrees apart, one of which triggered MCAS system

https://www.cbc.ca/news/world/ethiop...490763?cmp=rss
Longtimer is offline  
Old 9th Mar 2020, 17:59
  #2 (permalink)  
 
Join Date: Jul 2019
Location: London
Posts: 1
Interim report, not final.




Thread title edited

Senior Pilot
wigbam is offline  
Old 9th Mar 2020, 18:04
  #3 (permalink)  
 
Join Date: Jun 2001
Location: Rockytop, Tennessee, USA
Posts: 5,864
This isn't the final report. But, thanks for posting the news item.

From your link above, emphasis mine:

A faulty sensor reading and the activation of an anti-stall system on a Boeing 737 Max preceded the crash of an Ethiopian Airlines flight in 2019 that killed 157 people, an interim report by the government in Addis Ababa found.
Airbubba is online now  
Old 9th Mar 2020, 18:14
  #4 (permalink)  
 
Join Date: Oct 2017
Location: Vienna
Posts: 139
Interesting to call it an “anti-stall” system. It wasn’t supposed to be, was it?
derjodel is offline  
Old 9th Mar 2020, 18:16
  #5 (permalink)  
 
Join Date: Dec 2002
Location: UK
Posts: 2,116
The embedded link from the cbc site is to the ' Interim Investigation Report ' which is dated 9 Mar 2020; the very latest information.
This does not appear to disclose any new aspects, but does provide insight to the thoroughness and professionalism of the investigation.

The system descriptions should be easier to understand than previous technical documents.

The investigations into the effect of AoA failure on most aircraft systems, provides details and context of malfunctions, from which the enormity of the situation that the crew faced can be imagined.
A lesson for all 'cherry pickers' who consider each in simplistic isolation.

http://s3.documentcloud.org/document...rch-9-2020.pdf
safetypee is offline  
Old 10th Mar 2020, 01:33
  #6 (permalink)  
 
Join Date: Nov 2007
Location: dublin
Posts: 2
From report yesterday——-
Boeing indicated that as part of the development process of MCAS, although not formally part of the FHA, engineering personnel and test pilots considered the scenario of multiple MCAS inputs due to pilot trim action following an erroneous AOA input. Their assessment was that each MCAS input could be controlled with column alone and subsequently re-trimmed to zero column force while maintaining the flight path. Five seconds after cessation of the pilot trim command, the subsequent MCAS command could be controlled in the same manner as the previous instance. Eventually, use of the stabilizer cutout switches would be an option to stop the uncommanded stabilizer motion per the runaway stabilizer procedure (which is a trained flight crew memory item).

Thats it in a nutshell. That’s what you do and the report doesn’t say why that didn’t happen as far as I can see.
the absence of CVR is damning. It should show exactly what was happening. Why hide it?
Cheers
Yan
yanrair is offline  
Old 10th Mar 2020, 06:53
  #7 (permalink)  
 
Join Date: Apr 2019
Location: Toronto
Posts: 15
Originally Posted by yanrair View Post
Thats it in a nutshell. That’s what you do
I remember reading the threads from before ET302, when JT610 was still the main topic and MCAS was just becoming known.

The advice given then was: "You see the trim is running away. All you do is flip the cutout switches. Then get back in trim using the wheel. Why didn't they just do that?"

But then ET302 happened, and people stated questioning whether the trim wheel could be turned at 300+ knots and 2.5 units out-of-trim.

The advice given then was: "You see the trim is running away. You get back in trim with the pickle switches, obviously. Then you flip the cutout switches. Then control the trim using the wheel. Why didn't they just do that?"

Notice the subtle change there? That's what one might call moving the goalposts.

The fact is, the "obvious" solution given by the blame-the-pilots crowd changed, and no one has acknowledged that. The fact is, the classic advice for trim runaway is to hit the cutouts as soon as possible, not futz around with the pickle switches first. If the runaway is not caused by MCAS but by some electrical fault, pilots may be wasting precious time, trim, and controllability trying to troubleshoot the switches. The "get back in trim using the electrics first, duh" advice only works if you see that the runaway is effected by MCAS. You know, by seeing the helpful little "MCAS active" light Boeing installed in all the 737 MAXes.

Oh, wait.
Tobin is offline  
Old 10th Mar 2020, 16:10
  #8 (permalink)  
 
Join Date: Mar 2018
Location: Central UK
Posts: 487
I think ranyair is quite right but the elsphant in the room that so many are ignoring is that the pilots 'forgot' they were at TOGA thrust and failed to hear/notice they were approaching warp speed.
No way on earth could/should Boeing designers have anticipated anything as far off-scale as that being involved when they made their - imho entirely appropriate and correct - asessment of the action to take, action that would without any doubt have saved the day.
Neither can Boeing really beheld accountable for designing a trim system that becomes too heavy to use beyond Vmo as no one expects it to be required to work massively out of trim at that end of the envelope.
You can't design an aeroplane to cope with every imaginable (let alone all but unimaginable) foul-up a pilot can possibly make.

As to the lack of CVR, one can only surmise why such vital info has been left out. If the pilots had reacted properly and professionally there would be no excuse whatsoever to withold this, indeed the presentation of a coherent and rational response to the event would amply demonstate their pilots, procedures and training in a good light, thus the implications of it's absence seems pretty clear.
meleagertoo is offline  
Old 10th Mar 2020, 16:36
  #9 (permalink)  
 
Join Date: Mar 2014
Location: Way north
Age: 44
Posts: 420
Originally Posted by Tobin View Post
......
Oh, wait.
I agree....

You'd think half of the people replying in here has absolutely no idea of flying, or think themselves better than other pilots.

Problem is, everyone thinks: this will never happen to me, or: I will always be able to handle this....

Too many accidents caused by that attitude.
jmmoric is offline  
Old 10th Mar 2020, 16:45
  #10 (permalink)  
 
Join Date: Dec 2015
Location: Aus
Posts: 71
The “Runaway Stabilizer” checklist has ALWAYS told you to use the trim switches before switching to cut out, always! Read the memory items again....

“Control the airplane pitch attitude manually with control column and main electric trim as needed”

That bit is in between disengage the autopilot(if engaged) and disengaging the autothrottle(if engaged)

It is not a new thing.

In both accidents, no one was flying the airplane, they were riding along until impact
Switchbait is offline  
Old 10th Mar 2020, 17:36
  #11 (permalink)  
 
Join Date: Apr 2019
Location: Toronto
Posts: 15
That was listed as a sub-step of the disable autopilot step. It didn't have its own number. If you were already flying manually when the runaway started, you'd skip that. The clear intent of the instruction was to eliminate the autopilot as a source of the runaway. If you didn't have autopilot, you wouldn't attempt that step.

Now if you're looking at this checklist instead, it does have that step listed independently. But this checklist came out after the MCAS debacle, because someone realized the original instructions did not account for an MCAS-type event.

Even though it's an improvement, I still take issue with the wording here. How long do you execute step 4 for before moving to step 5? The words "until the aircraft is back in trim" do not appear. There is no precondition for step 5 (so, why not do it as soon as possible anyway?), and once step 5 is executed, step 4 is partially invalidated (because electric trim is unavailable).

"Control the airplane pitch attitude manually with control column and main electric trim as needed" is not equal to "Adjust pitch trim with main electric trim until flight path is stable and control column forces are reduced".
Tobin is offline  
Old 10th Mar 2020, 18:23
  #12 (permalink)  
 
Join Date: Jan 2008
Location: Reading, UK
Posts: 12,614
Tobin

Your link lands a little short of the post you're referring to, so here's the checklist in question with the changes marked in the usual way:


DaveReidUK is online now  
Old 10th Mar 2020, 23:43
  #13 (permalink)  
 
Join Date: Aug 2019
Location: Rocket City
Posts: 24
Tobin

Sort of the same. Once you suspect/declare runaway trim you hit the cutouts.
Until then you use the switches to correct trim.

After few cycles you realize something is trimming out of control/inappropriately that's the runaway and you hit the cutouts.
Or you first detect a trim change at the wrong/unexpected time and hit the switches. Whether MCAS or other cause.

Either way gets you to the same point. Cutouts used before you are severely out of trim and overspeed.

ST Dog is offline  
Old 11th Mar 2020, 01:37
  #14 (permalink)  
 
Join Date: Aug 2000
Location: Monrovia / Liberia
Age: 59
Posts: 748
I was saying this from the get-go and for which I was castigated as some sort of pariah for apparently throwing fellow pilots under the bus.

Well let me speak plainly. I'm f'ing certain that I wouldn't be so f'ing gash as to allow a stab trim runaway to get so out of hand that I couldn't then control the aircraft... it's basic airmanship people.... and yet those twerps / 'children of the magenta line' did precisely that (twice) and for which I blame their innate ability (or the lack of it), along with the pilot aptitude testing & selection processes in both Lion Air and Ethiopian (or the lack of it), and also their training & checking (or the lack of it).

Aside from Boeing introducing a piece of software / hardware that caused the problem, both were preventable accidents using Boeing's own procedure / memory item for this (as exemplified by the actions of the crew on the sector that occurred immediately prior to the Lion Air crash wherein, with the precise same problem, the correct memory item procedure was actioned in a timely manner - much due to an as yet unidentified / ghost jump-seat pilot whom evidently instructed the befuddled operating crew how to rectify the problem - and that flight thereafter continued without further event or mishap. QED).
Old King Coal is offline  
Old 11th Mar 2020, 02:30
  #15 (permalink)  
 
Join Date: Dec 2015
Location: Aus
Posts: 71
Tobin

Even though it's an improvement, I still take issue with the wording here. How long do you execute step 4 for before moving to step 5? The words "until the aircraft is back in trim" do not appear. There is no precondition for step 5 (so, why not do it as soon as possible anyway?), and once step 5 is executed, step 4 is partially invalidated (because electric trim is unavailable).

"Control the airplane pitch attitude manually with control column and main electric trim as needed" is not equal to "Adjust pitch trim with main electric trim until flight path is stable and control column forces are reduced".[/QUOTE]


Sir, your assertion here that “you’d skip that step” is exactly why both airplanes speared in!

The primary role of the PF is to fly the bloody airplane! FLY THE AIRPLANE!!!!!!!!!

Why on earth would you “skip that step”??? The only step that matters at that point is controlling the flight path of the airplane. If you don’t do that, it doesn’t matter how many checklists you write.....
Switchbait is offline  
Old 11th Mar 2020, 03:32
  #16 (permalink)  
Administrator
 
Join Date: Apr 2015
Location: The Gulf Coast
Posts: 873
I appeal to you all to approach this interim report with professionalism as our guiding principle.
Please don't turn this into a hamsterwheel.
T28B is offline  
Old 11th Mar 2020, 06:25
  #17 (permalink)  
 
Join Date: Apr 2019
Location: Toronto
Posts: 15
Originally Posted by Switchbait View Post
Why on earth would you “skip that step”???
Because the instructions look like this:


Now, I can stand to be corrected. Is the format of the checklist officially described anywhere? How are the indented statements to be read? Are they simply independent instructions to be executed always?

They don't look like it to me. They each look like a dependency or continuation of the numbered step immediately above. My natural reading is to get through "2. Autopilot (if engaged) ....." and think Okay, autopilot is definitely disengaged. The rest of this is irrelevant. What's step 3? Then move onto step 3.

I don't fly planes but I have dealt with crappy instructions, which I have followed, gotten a bad result, and then when I asked about it I had someone tell me, "Oh, well, that part's technically wrong, but everyone knows you just do this other thing instead." I'm left to wonder: If the instructions are wrong, then what's the point of having them at all? If "everyone knows" what the wrong steps should be, why were they written down?

If all one needs to do is "fly the plane" and "possess airmanship", why have a checklist?

The interim report starting at section 1.16 strongly suggests that the pilots were unable to manually trim because the forces on the manual trim wheel are too great to move it with the aircraft 2.5 units out-of-trim. Did the pilots expect that would be the case? It's a difficult case to make. Let us remember, these people did not want to crash their plane. They did not want to die. They did what they thought was correct in the circumstances presented to them, based on their knowledge and training.

The old Runaway Stabilizer checklist sure looks like a hole in the cheese to me. And the new one is a distinctly smaller, but still present, hole.
Tobin is offline  
Old 11th Mar 2020, 07:52
  #18 (permalink)  
 
Join Date: Dec 2015
Location: Aus
Posts: 71
”I don't fly planes”

That’s why you don’t understand the importance of it.
Switchbait is offline  
Old 11th Mar 2020, 08:34
  #19 (permalink)  
 
Join Date: Jan 2008
Location: Reading, UK
Posts: 12,614
Originally Posted by ST Dog View Post
Sort of the same
If the two versions of the checklist are "sort of the same", why (in your view) was it considered necessary to make the amendment at all ?
DaveReidUK is online now  
Old 11th Mar 2020, 08:49
  #20 (permalink)  
 
Join Date: Jul 2003
Location: An Island Province
Posts: 1,172
T28B

Its shameful that 'Bully Boy' posts from self-claiming professionals flame alternative points of view to the point of exclusion.

Non flying, non aviation views are important, if only that the 'insiders' provide reasoned explanation and eduction for alternative thoughts, and more often they, as passengers, are the people paying your wage.

As I recall the recently (self) deleted post had merit, with logical explanation of the limitations of human behaviour; I would urge the post to be reinstated to challenge and seek professional response.

Recent posts focus on a specific checklist, discussing what could or should be done; this is cherry picking a subject and biasing a viewpoint to error and covertly blaming the crew.

A similar discussion could follow for Boeing's involvement in testing and approving the system, but this too might only conclude 'error', without opportunity for learning.

These views rely on assumption, that a crew would assess the situation as trim runaway and choose that checklist - and execute it correctly. PPRuNe has discussed the piloting view extensively, and further debate is unlikely to changed 'fixed' minds.

The interim report enables a better view from a Boeing test and evaluation perspective, if only we look.

The various test simulations lacked all possible alerts and distractions, or separately did not enable full trim range.

The components of the real situation were never tested, and likely never considered because of the limitations of the ground test conditions.

I posit that the checklist would not have been used in an engineering simulation, thus any deficiency or hidden assumption not reviewed.

The three second trim runaway was a valid engineering judgement, but perhaps overlooked the normally accepted 1sec addition for human reaction.

The maximum trim deviation simulated was significant less than could be achieved in the aircraft, thus the judgement of 'just manageable' high trim force for recovery could have mistakenly be extrapolated to greater trim deviation, again assuming that the crew would manage a surprising control malfunction having already managed an apparent unreliable airspeed situation.

There was no assessment of other system interactions with AoA malfunction; no consideration of a situation with changing displays, inputs, alerts, distractions, and physical stress.
Time to put the checklist down, state the assumptions in the argument, and try really hard to place yourself in the position accident crews - without the comfort of hindsight.

'I don't fly airplanes' any more,but I try to think.

Last edited by alf5071h; 11th Mar 2020 at 09:25.
alf5071h 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.