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 23rd Apr 2019, 12:48
  #4221 (permalink)  
 
Join Date: Dec 2015
Location: Cape Town, ZA
Age: 59
Posts: 424
Originally Posted by Alchad View Post
came across this thread, relevant quote from it below. Obviously no way of knowing if genuine or not, but given what else has been posted on the difficulty of operating the manual trim wheel, it does sound plausible.


Shutdown caused Boeing crash. - Page 4 - International Skeptics Forum

Quote...

"I agree it's a flawed design. And I used to work there. I'm glad I don't now.

Regarding the trim wheels: When the NG was being introduced, I happened to be the Lead Engineer in charge of them and a whole lot of other stuff. There were some issues. The new display system created a pinch point between the dash and the wheel. We had to make the wheel smaller. And the new trim motor resulted in the wheel, which is directly connected to the stabilizer by a long cable, springing back when electric trim was used. It was an undamped mass on the end of a spring. We had to add a damper.
Result: Depending on the flight conditions, the force to manually trim can be extremely high. We set up a test rig and a very fit female pilot could barely move it.
As I said, I'm glad I'm no longer there."

Alchad
Posted a few (hundred?) pages back in this thread: https://www.pprune.org/rumours-news/619272-ethiopian-airliner-down-africa-post10438165.html
GordonR_Cape is offline  
Old 23rd Apr 2019, 12:51
  #4222 (permalink)  
 
Join Date: Nov 2004
Location: UK
Posts: 403
Originally Posted by Alchad View Post
We set up a test rig and a very fit female pilot could barely move it.
Accepting that beauty is in the eye of the beholder, surely how much one fancies a lady has little if any bearing upon her ability to trim the 737 manually...
pilotmike is offline  
Old 23rd Apr 2019, 13:13
  #4223 (permalink)  
 
Join Date: Apr 2019
Location: USA
Posts: 217
Originally Posted by FullWings View Post
Scenario 1: In the simulator, doing a “runaway trim exercise”. There you are at 6,000’ straight and level, 220kts, nothing happening. Oh look, the trim has started moving on its own, can’t stop it, I wonder if this is right? No? OK, do the runaway checklist. Sim passed! Easy, this trim runaway.

Scenario 2: In the aeroplane, cleaning up. Trim starts moving forward, then stops. Is that MCAS gone wrong (or even possibly functioning correctly), is it STS doing its job or is it the other guy who’s flying it trimming the aircraft? Hmmm. There goes the trim again...

Scenario 3: All the above plus continuous stick shaker, aural warnings and UAS symptoms.

Honestly, I’m not quite sure how you would train an MCAS runaway in the sim, if disconnecting the trim when there wasn’t an actual runaway = fail. It’s easy to say “they should have done the trim runaway checklist” but how do you tell NORMAL operation of MCAS/STS from ABNORMAL in a very limited timeframe? If you disconnect the trim every time it moves, you’re going to be doing lots of very short flights...
I understand what you are trying to say, but let me make this observation.

We know that the MCAS input stops if any pilot puts in manual electric trim. It then restarts after a 5 second delay. If a pilot is regularly responding to the changing trim pressures by inputting nose up trim (MCAS trims some nose down, pilot trims some nose up, MCAS trim nose down, pilot trims nose up, repeat), then yes, it looks a lot different than a classic runaway trim.

In the case of ET302, however, the MCAS input lasted 9 continuous seconds which equates to around 37 spins of the manual trim wheel. The entire time, the Captain has the yoke in his hands and the control pressures increase dramatically. This happened at least twice. What about this does not scream runaway trim?
737 Driver is offline  
Old 23rd Apr 2019, 14:31
  #4224 (permalink)  
 
Join Date: Dec 2003
Location: Tring, UK
Posts: 1,494
Originally Posted by 737 Driver View Post
In the case of ET302, however, the MCAS input lasted 9 continuous seconds which equates to around 37 spins of the manual trim wheel. The entire time, the Captain has the yoke in his hands and the control pressures increase dramatically. This happened at least twice. What about this does not scream runaway trim?
I agree that’s a bit more obvious but we are now in the “end game” where the goose is close to being irreversibly cooked. What it screams to me is that the pilot(s) were so overloaded by control forces / stick shake / aural and visual warnings / general confusion that they had reverted to “pull back to make the houses look smaller” and had fixated on this due to saturation of their input channels. The trim running could well be the gorilla in the room, if you’ve seen the video.

As many have worked out, the stabiliser is a very powerful pitch control on the 737 and the elevator is just a trim, really. I’m not sure how much emphasis is put on that in training these days.
FullWings is offline  
Old 23rd Apr 2019, 14:48
  #4225 (permalink)  
 
Join Date: Jul 2009
Location: France
Age: 58
Posts: 44
Originally Posted by Loose rivets View Post
RatherBeFlying #2447
is a tad confusing but blue surely must be thumb switch inputs. If so, where did this microscopic data come from?
It is just a magnified screen shot from the prelim. report of the Lionair crash

Reason I posted this is the weird question of the ET captain to the FO to help him with the electric, manual trim, plus the (way too) short trim blips late in the traces of ET as well as the too short trim blips late in the Lionair traces. I was simply wondering if there could be a hint here to a common ergonomic problem due to artificial feel stick force and shaker.

spornrad is offline  
Old 23rd Apr 2019, 15:04
  #4226 (permalink)  
 
Join Date: Apr 2008
Location: back of beyond
Posts: 115
Originally Posted by Bergerie1 View Post
How many of us would have diagnosed the problem correctly in the time available?
At least three if these columns are anything to go by
fizz57 is offline  
Old 23rd Apr 2019, 15:55
  #4227 (permalink)  
 
Join Date: Jun 2008
Location: London
Age: 64
Posts: 353
Most people would find it reasonable to expect a pilot to have experienced flight conditions in the area outside the certification limits, if it is reasonably probable that the aircraft will be in this condition.
I don't find it reasonable at all. Unless you are a qualified test pilot, you should not be going outside the certification envelope.
Fortissimo is offline  
Old 23rd Apr 2019, 16:18
  #4228 (permalink)  
 
Join Date: Apr 2015
Location: Under the radar, over the rainbow
Posts: 707
In response to this:
Most people would find it reasonable to expect a pilot to have experienced flight conditions in the area outside the certification limits, if it is reasonably probable that the aircraft will be in this condition.
Fortissimo posted this:
Originally Posted by Fortissimo View Post
I don't find it reasonable at all. Unless you are a qualified test pilot, you should not be going outside the certification envelope.
That's fine, as long as non-test pilots can be reasonably confident that it is not "reasonably probable" that the aircraft will end up outside the envelope on any given flight.

Last edited by OldnGrounded; 23rd Apr 2019 at 16:19. Reason: Formatting (but I thought it was right the first time)
OldnGrounded is offline  
Old 23rd Apr 2019, 16:43
  #4229 (permalink)  
 
Join Date: Apr 2009
Location: A place in the sun
Age: 79
Posts: 939
fizz,

It's very easy to sort these things out with hindsight and when sitting comfortably in an armchair!
Bergerie1 is offline  
Old 23rd Apr 2019, 17:42
  #4230 (permalink)  
 
Join Date: Apr 2019
Location: USA
Posts: 217
Originally Posted by Bergerie1 View Post

How many of us would have diagnosed the problem correctly in the time available?
If any of the accident pilots had simply flown the aircraft and kept the aircraft in a reasonably in-trim state (the thumb switch will trump the automation every single time), then the time available would have been equal to the fuel available. There was no ticking time bomb here.

Last edited by 737 Driver; 23rd Apr 2019 at 19:34. Reason: typo
737 Driver is offline  
Old 23rd Apr 2019, 18:14
  #4231 (permalink)  
 
Join Date: Apr 2019
Location: USA
Posts: 217
-
Originally Posted by FullWings View Post
What it screams to me is that the pilot(s) were so overloaded by control forces / stick shake / aural and visual warnings / general confusion that they had reverted to “pull back to make the houses look smaller” and had fixated on this due to saturation of their input channels. The trim running could well be the gorilla in the room, if you’ve seen the video.
Yes, I’ve seen the video, and yes I agree that it appears the Captain had achieved cognitive overload. Where I differ is that I feel the circumstances were not so extreme that cognitive overload would have been a reasonable expectation of a 737 type-rated Captain.

I used to do basic flight instruction, and I’ve seen many types of students. I would often tell them that flying an aircraft on a nice day really wasn’t that difficult once you had a little time under your belt, not too unlike learning to drive an automobile. The huge difference between a car and a plane, of course, is that you just can’t pull an aircraft over on the shoulder when things go wrong. You have to take whatever comes, work with whatever you have, and do your damnedest to get the aircraft safely back on the ground. I would tell my students that if they could not deal with that reality, then they should not become a pilot.

As professional pilots, we ought to meet an even much higher standard. When things started to go wrong, at least one of these pilots needed to look past the noise, place their hands firmly on the yoke and throttles, set the proper attitude and power settings, keep the aircraft in trim, and stay away from the rocks. That was all that was required. Everything else could have waited. The plane wasn’t on fire, the wing didn’t fall off, there were no bombs on board. This plane was flyable.

Yes, Boeing fracked up. Yes, the FAA and the airlines were culpable of going along with the fiction that the MAX wasn’t really that much different from the NG. But you know what? On any given day someone else could screw up and give us an aircraft that will malfunction in a unique and potentially dangerous way. And as always, the pilots are the last line of defense. We need to be mentally prepared for that reality or find another line of work.


Last edited by 737 Driver; 23rd Apr 2019 at 18:16. Reason: typo
737 Driver is offline  
Old 23rd Apr 2019, 18:26
  #4232 (permalink)  
 
Join Date: Mar 2015
Location: Washington state
Posts: 209
Originally Posted by GordonR_Cape View Post
Many pages back, in another thread LEOCh posted a schematic chart showing a nasty inflection between 10 and 15 degrees AOA, which is when MCAS kicks in. Once AOA is below 10 degrees, MCAS unwinds the nose-down trim (unless the pilots intervene with electrical trim inputs
This seems like rather complex behavior for the pilots not to be informed about or trained on, especially in a plane that is not advertised as a fly by wire plane. When exactly does MCAS start to unwind the trim and in the worst case scenario how much uncommanded nose down trim does the pilot have to unwind if they happen to have blipped the trim switch at the wrong point in the unwind scenario?
Water pilot is offline  
Old 23rd Apr 2019, 19:31
  #4233 (permalink)  
 
Join Date: Dec 2015
Location: Cape Town, ZA
Age: 59
Posts: 424
Originally Posted by Water pilot View Post
This seems like rather complex behavior for the pilots not to be informed about or trained on, especially in a plane that is not advertised as a fly by wire plane. When exactly does MCAS start to unwind the trim and in the worst case scenario how much uncommanded nose down trim does the pilot have to unwind if they happen to have blipped the trim switch at the wrong point in the unwind scenario?
I am not a pilot, but interesting questions (some of which I may have hinted at very early in this thread). The simple answer is that the amount of nose down trim should be limited to 2.5 degrees, and the trim unwind process should only begin once AOA is below 10 degrees.

The assumption must be that the pilot would not "porpoise" the aircraft with the elevator, alternately crossing the MCAS 10 degree AOA threshold. This criterion requires time-smoothing, to avoid random fluctuations of the AOA values (as per the new specification).

Blipping the electric trim (either up or down) during the unwind process, could theoretically put the aircraft in a semi-unstable situation, since MCAS would be disabled, and cannot reactivate again (as per the new specification). Again we must assume that the pilot intentionally wants to keep the nose high for specific reasons (such as high-altitude terrain proximity avoidance). In this scenario MCAS should not try to second guess the flight situation, but rather wait for the pilot to release the elevator yoke (and sort out any trim issues later).

Presumably the MCAS system will be clearly documented to the point where pilots are assured that:
- MCAS will not inhibit the necessary elevator yoke authority during escape maneuvers
- The overall flight system will not produce an out of trim condition when exiting from a maneuver

I seems obvious that Boeing and the FAA will flight test all of this in great detail. Whether an average pilot needs to experience this in a simulator, is an entirely different question (conditions outside the normal flight envelope). The time-delay feedback process is indeed new, and somewhat uncharted territory.
GordonR_Cape is offline  
Old 23rd Apr 2019, 19:56
  #4234 (permalink)  
 
Join Date: Jan 2008
Location: Hotel Sheets, Downtown Plunketville
Age: 73
Posts: 0
Originally Posted by 737 Driver View Post
-

Yes, I’ve seen the video, and yes I agree that it appears the Captain had achieved cognitive overload. Where I differ is that I feel the circumstances were not so extreme that cognitive overload would have been a reasonable expectation of a 737 type-rated Captain.

I used to do basic flight instruction, and I’ve seen many types of students. I would often tell them that flying an aircraft on a nice day really wasn’t that difficult once you had a little time under your belt, not too unlike learning to drive an automobile. The huge difference between a car and a plane, of course, is that you just can’t pull an aircraft over on the shoulder when things go wrong. You have to take whatever comes, work with whatever you have, and do your damnedest to get the aircraft safely back on the ground. I would tell my students that if they could not deal with that reality, then they should not become a pilot.

As professional pilots, we ought to meet an even much higher standard. When things started to go wrong, at least one of these pilots needed to look past the noise, place their hands firmly on the yoke and throttles, set the proper attitude and power settings, keep the aircraft in trim, and stay away from the rocks. That was all that was required. Everything else could have waited. The plane wasn’t on fire, the wing didn’t fall off, there were no bombs on board. This plane was flyable.

Yes, Boeing fracked up. Yes, the FAA and the airlines were culpable of going along with the fiction that the MAX wasn’t really that much different from the NG. But you know what? On any given day someone else could screw up and give us an aircraft that will malfunction in a unique and potentially dangerous way. And as always, the pilots are the last line of defense. We need to be mentally prepared for that reality or find another line of work.


I couldn`t disagree more. To fly the modern airliners you fly the automatics. If for whatever reason you cannot do that then its very much up to the avionics to do whatever they have been setup to do. These guys did not have a cats in hell chance of persuading the automatics to allow them to interfere. They simply lost the very short argument with the machine. What sort of last line of defense is that, is it a bit like the Maginot Line, invincible until proven otherwise and how many times does it need to be demonstrated before someone realises it aint working. Give me human error any day, I can understand that, computers, electronics and all that wizardry that goes with them, let the kids addicted to them play with it all, that would be a whole load safer.
Chronus is offline  
Old 23rd Apr 2019, 20:16
  #4235 (permalink)  
 
Join Date: Sep 2006
Location: here and there
Posts: 167
Originally Posted by Chronus View Post
I couldn`t disagree more. To fly the modern airliners you fly the automatics. If for whatever reason you cannot do that then its very much up to the avionics to do whatever they have been setup to do. These guys did not have a cats in hell chance of persuading the automatics to allow them to interfere. They simply lost the very short argument with the machine. What sort of last line of defense is that, is it a bit like the Maginot Line, invincible until proven otherwise and how many times does it need to be demonstrated before someone realises it aint working. Give me human error any day, I can understand that, computers, electronics and all that wizardry that goes with them, let the kids addicted to them play with it all, that would be a whole load safer.
And I couldn't disagree any more with this. You're basically endorsing no airmanship.
formulaben is offline  
Old 23rd Apr 2019, 20:26
  #4236 (permalink)  
 
Join Date: Nov 2012
Location: New York
Posts: 11
Originally Posted by 737 Driver View Post
As professional pilots, we ought to meet an even much higher standard. When things started to go wrong, at least one of these pilots needed to look past the noise, place their hands firmly on the yoke and throttles, set the proper attitude and power settings, keep the aircraft in trim, and stay away from the rocks. That was all that was required. Everything else could have waited. The plane wasn’t on fire, the wing didn’t fall off, there were no bombs on board. This plane was flyable.

Yes, Boeing fracked up. Yes, the FAA and the airlines were culpable of going along with the fiction that the MAX wasn’t really that much different from the NG. But you know what? On any given day someone else could screw up and give us an aircraft that will malfunction in a unique and potentially dangerous way. And as always, the pilots are the last line of defense. We need to be mentally prepared for that reality or find another line of work.
I couldn't agree more. With modern airliners, it is part of the pilot's job to be able to fly the plane when the automatic systems fail. Otherwise, what are we doing? If the automatics always work, pilots are out of a job. And if we can't get the plane out of trouble, we might as well not be sitting up front, either. Yes, in this instance Boeing, etc. made the job harder. And they need to fix that. In the Ethiopian case, they had stick shaker shortly after liftoff. Had one minute and 15 seconds to absorb that. Then an uncommanded, continuous nose-down trim for 9 seconds. Count that out, it's a long time. I don't fly the B737, but I would hope I would catch that in my aircraft!

Originally Posted by Chronus View Post
I couldn`t disagree more. To fly the modern airliners you fly the automatics. If for whatever reason you cannot do that then its very much up to the avionics to do whatever they have been setup to do. These guys did not have a cats in hell chance of persuading the automatics to allow them to interfere. They simply lost the very short argument with the machine. What sort of last line of defense is that, is it a bit like the Maginot Line, invincible until proven otherwise and how many times does it need to be demonstrated before someone realises it aint working. Give me human error any day, I can understand that, computers, electronics and all that wizardry that goes with them, let the kids addicted to them play with it all, that would be a whole load safer.
I would hope any aircraft has some way of overriding the automatics and flying by hand, in case of multiple unmodeled failures. Be it cables, direct law, or whatever. And I would hope to train to be proficient in flying in that mode as well. I'm not trying to argue whether or not any plane is up to that standard, but that would be my goal. Either that or an ejection seat, but that doesn't work so well with pax.
hawk76 is offline  
Old 23rd Apr 2019, 20:26
  #4237 (permalink)  
 
Join Date: Jan 2008
Location: Hotel Sheets, Downtown Plunketville
Age: 73
Posts: 0
Originally Posted by formulaben View Post
And I couldn't disagree any more with this. You're basically endorsing no airmanship.
Try as one might, to endorse airmanship, computer says Nooo and coughs .
Chronus is offline  
Old 23rd Apr 2019, 21:11
  #4238 (permalink)  
 
Join Date: Apr 2019
Location: East Coast
Posts: 11
Originally Posted by 737 Driver View Post
- When things started to go wrong, at least one of these pilots needed to look past the noise, place their hands firmly on the yoke and throttles, set the proper attitude and power settings, keep the aircraft in trim, and stay away from the rocks. That was all that was required. Everything else could have waited. The plane wasn’t on fire, the wing didn’t fall off, there were no bombs on board. This plane was flyable.
On any given day someone else could screw up and give us an aircraft that will malfunction in a unique and potentially dangerous way. And as always, the pilots are the last line of defense. We need to be mentally prepared for that reality or find another line of work.

Thank you 737 Driver. Your sentiment is exactly what we the flying public expects.
EPHD75 is offline  
Old 23rd Apr 2019, 23:48
  #4239 (permalink)  
 
Join Date: Jan 2004
Location: Far West Wessex
Posts: 2,550
I am amazed at the continued "any real airman could have handled this... obvious trim runaway... follow the procedures" drumbeat from people who identify as US- or Euro-based pilots. (I say "identify" because at least one such got outed as a sim player.)

People! So far we know of only three occurrences of the basic failure (AoA sensor is bad from the start of roll, falsely high reading, high enough for stall warning, and it's the one driving MCAS today). Two resulted in total loss. The third was saved by a jumpseat rider who had attention to spare and a better view of the trim wheels. That is stark evidence that this failure sequence is dangerous in the extreme.

Moreover, airlines all over the world have, in recent years, contributed to the industry's excellent safety record. Not too many signs that (not to put too fine a point on it) the ethnicity of the pilots or management is a big deal.
LowObservable is offline  
Old 24th Apr 2019, 00:10
  #4240 (permalink)  
Psychophysiological entity
 
Join Date: Jun 2001
Location: Tweet Rob_Benham Famous author. Well, slightly famous.
Age: 81
Posts: 4,894
Quote:
Originally Posted by GordonR_Cape
Many pages back, in another thread LEOCh posted a schematic chart showing a nasty inflection between 10 and 15 degrees AOA, which is when MCAS kicks in. Once AOA is below 10 degrees, MCAS unwinds the nose-down trim (unless the pilots intervene with electrical trim inputs
.





Water pilot: #4242 My bold.
This seems like rather complex behavior for the pilots not to be informed about or trained on, especially in a plane that is not advertised as a fly by wire plane.
Water pilot continues below, but a point I've been wondering about for ages. MCAS winds back after it's done its thing? So little has been made of this - apart from me - that I wondered if I'd misunderstood. However, it seems that if the PF uses the electric trim, this will not happen. Since there was extensive use of the thumb switch trim, I guess this is why MCAS at no stage put things back where it found them. Erm, did it?

When exactly does MCAS start to unwind the trim and in the worst case scenario how much uncommanded nose down trim does the pilot have to unwind if they happen to have blipped the trim switch at the wrong point in the unwind scenario?
What a vital observation.

GordonR carries the logic forward in the next thread.
Loose rivets 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 © 2018 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.