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PcarSBA
Posts: 18
Joined: Sun Mar 17, 2019 8:08 am

Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Sun Apr 14, 2019 10:01 pm

Ray,

I see the 2nd long electric trim ANU input lasting about 10 seconds. The STAB angle appears to follow the command for the entire time at a stable rate (slope of graph is constant)

The graph resolution isn’t very high but I can’t say this looks like the stabilizer didn’t react to the electric trim. Even the last short blibs labeled “manual electric trim commands” seem to have an albeit small effect on the stab angle.

I wonder if the FDR records things like switch actuations, current draw of the trim motor, etc. so one could tell what forces were in play and whether the jack screw was jammed and wasn’t able to pass 2.4 units later in flight.
 
asdf
Posts: 696
Joined: Tue Mar 18, 2014 12:03 am

Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Sun Apr 14, 2019 10:04 pm

MSPNWA wrote:
WIederling wrote:
it is mechanical and follows the laws of physics.
Every reduction in force will call for an increase in revolutions required for the same effect.
so: either you can't turn it or you don't make enough progress ( in the obviously limited amount of time available.)

What has not been answered: With full stick back / full elevator travel : does the electric trim still work effectively ( in the right direction reducing tailplane incidence.)


The mistake is making a statement that assumes no other changes were made to the system except a smaller trim wheel. It is entirely possible for a smaller trim wheel to be easier to turn and quicker to adjust.

Unless a person intimately knows the mechanics of the manual trim, there can be no assertive statements made.


its sufficient to understand the basics of physic

if a wheel is from smaller diameter
and there is no other external power applied in the rotation
the same force on the stab will need more power at the wheels to move them if the diameter is smaller

its simply physics
no surprises
Last edited by asdf on Sun Apr 14, 2019 10:05 pm, edited 1 time in total.
 
speedbird52
Posts: 1012
Joined: Sat Nov 26, 2016 5:30 am

Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Sun Apr 14, 2019 10:05 pm

Out of curiosity, why didn't the pilots leave electric trim off and use manual trim?
 
asdf
Posts: 696
Joined: Tue Mar 18, 2014 12:03 am

Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Sun Apr 14, 2019 10:38 pm

speedbird52 wrote:
Out of curiosity, why didn't the pilots leave electric trim off and use manual trim?


following the documents because manual trim had not enough authority to bring the nose up
maybe because of overspeeding the forces where to high
 
PcarSBA
Posts: 18
Joined: Sun Mar 17, 2019 8:08 am

Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Sun Apr 14, 2019 10:38 pm

speedbird52 wrote:
Out of curiosity, why didn't the pilots leave electric trim off and use manual trim?

It’s speculation but the (deleted) Mentor video suggests that the aerodynamic load on the stabilizer made cranking the hand-wheel extremely difficult if not impossible.
 
patplan
Posts: 37
Joined: Sun Nov 11, 2018 1:38 pm

Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Sun Apr 14, 2019 10:45 pm

morrisond wrote:
smartplane wrote:
MSPNWA wrote:

The mistake is making a statement that assumes no other changes were made to the system except a smaller trim wheel. It is entirely possible for a smaller trim wheel to be easier to turn and quicker to adjust.

Unless a person intimately knows the mechanics of the manual trim, there can be no assertive statements made.

Boeing used grandfathering scaling rules to reduce it's size, and did what to compensate? Nothing?


Who knows - they might have increased the gearing meaning that it takes more turns to move the stabilizer the same distance. Making it easier or They might not have - I can't find anything discussing the system in that much detail.


It was discussed and admitted by one of Boeing's ex-engineers in the other forum: They make the wheels smaller and had to put a dampening mechanism on the NG's, and, get this..., it was to accommodate the space needed to install a more "modern looking" PFD's for the pilots.

...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...
Original post


As it was mentioned many times before, this modified manual trim wheel is also another classic case of "grandfathering" that eventually bites back.
 
MSPNWA
Posts: 3698
Joined: Thu Apr 23, 2009 2:48 am

Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Sun Apr 14, 2019 11:08 pm

smartplane wrote:
Boeing used grandfathering scaling rules to reduce it's size, and did what to compensate? Nothing?


Good question. Maybe you can answer them?

asdf wrote:
its sufficient to understand the basics of physic

if a wheel is from smaller diameter
and there is no other external power applied in the rotation
the same force on the stab will need more power at the wheels to move them if the diameter is smaller

its simply physics
no surprises


What you state is fine. Nobody is disputing that. But you're also not understanding the problem with the assertive statements being made that cannot be made without intimate knowledge of the system.

speedbird52 wrote:
Out of curiosity, why didn't the pilots leave electric trim off and use manual trim?

One of the big unanswered questions from the preliminary report. We don't know yet.
 
Saintor
Posts: 60
Joined: Wed Mar 13, 2019 10:35 pm

Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Sun Apr 14, 2019 11:22 pm

One possible reason is that they wanted to turn off MCAS, same circuit? This article suggests it is;
https://leehamnews.com/2019/04/03/et302 ... stop-mcas/
 
asdf
Posts: 696
Joined: Tue Mar 18, 2014 12:03 am

Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Sun Apr 14, 2019 11:34 pm

MSPNWA wrote:
smartplane wrote:
Boeing used grandfathering scaling rules to reduce it's size, and did what to compensate? Nothing?


Good question. Maybe you can answer them?

asdf wrote:
its sufficient to understand the basics of physic

if a wheel is from smaller diameter
and there is no other external power applied in the rotation
the same force on the stab will need more power at the wheels to move them if the diameter is smaller

its simply physics
no surprises


What you state is fine. Nobody is disputing that. But you're also not understanding the problem with the assertive statements being made that cannot be made without intimate knowledge of the system.

speedbird52 wrote:
Out of curiosity, why didn't the pilots leave electric trim off and use manual trim?

One of the big unanswered questions from the preliminary report. We don't know yet.


actually it is not fine
it was too late do change it

it should have said:

„if a wheel is from smaller diameter
and there is no other external power applied in the rotation
the same force on the stab will need more power at the wheels to move them if the diameter is smaller
or it will need more rotations to gain the same result“

but anyway ....
 
morrisond
Posts: 2715
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Mon Apr 15, 2019 12:27 am

patplan wrote:
morrisond wrote:
smartplane wrote:
Boeing used grandfathering scaling rules to reduce it's size, and did what to compensate? Nothing?


Who knows - they might have increased the gearing meaning that it takes more turns to move the stabilizer the same distance. Making it easier or They might not have - I can't find anything discussing the system in that much detail.


It was discussed and admitted by one of Boeing's ex-engineers in the other forum: They make the wheels smaller and had to put a dampening mechanism on the NG's, and, get this..., it was to accommodate the space needed to install a more "modern looking" PFD's for the pilots.

...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...
Original post


As it was mentioned many times before, this modified manual trim wheel is also another classic case of "grandfathering" that eventually bites back.


Good information - Thanks
 
dampfnudel
Posts: 588
Joined: Wed Oct 04, 2006 9:42 am

Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Mon Apr 15, 2019 12:48 am

patplan wrote:
morrisond wrote:
smartplane wrote:
Boeing used grandfathering scaling rules to reduce it's size, and did what to compensate? Nothing?


Who knows - they might have increased the gearing meaning that it takes more turns to move the stabilizer the same distance. Making it easier or They might not have - I can't find anything discussing the system in that much detail.


It was discussed and admitted by one of Boeing's ex-engineers in the other forum: They make the wheels smaller and had to put a dampening mechanism on the NG's, and, get this..., it was to accommodate the space needed to install a more "modern looking" PFD's for the pilots.

...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...
Original post


As it was mentioned many times before, this modified manual trim wheel is also another classic case of "grandfathering" that eventually bites back.

And in this case, resulted in the senseless deaths of 346 people. I sincerely hope this is a watershed event for both Boeing and the FAA.
A313 332 343 B703 712 722 732 73G 738 739 741 742 744 752 762 76E 764 772 AT5 CR9 D10 DHH DHT F27 GRM L10 M83 TU5
 
planecane
Posts: 1568
Joined: Thu Feb 09, 2017 4:58 pm

Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Mon Apr 15, 2019 1:30 am

XRAYretired wrote:
PcarSBA wrote:
SheikhDjibouti wrote:

Unlike JT610, these Ethiopian pilots correctly identified and applied runaway stab trim procedure. :thumbsup:
So why on earth would they re-engage electric trim, unless they were in desperate hole?



The FO identified the runaway issue but I respectfully disagree they applied the procedure correctly. Else they would have trimmed the AC and only then opened the STAB TRIM CUTOUT switches. The FDR suggests the AC wasn’t trimmed when the FO called stab trim cut-out at 5:40:35 and the captain agreed. The trim was at 2.3 units at that point and speed was building. That’s pretty far away from 4 - 5.

So they were in a desperate hole and that’s why they re-engaged the switches to get the electric motors to help.


Respectfully, what I see is a total of 4 attempts of trim switch up. The first got to 2.4 and the other three all stopped at 2.3. Too much of a coincidence for me. I dont believe in coincidence. I would be looking for a common factor, and I dont think the pilots could be quite that accurate on purpose.

Ray

The first attempt they only held the switch for maybe 3 seconds. Then 5 seconds later MCAS commanded to almost full nose down. Then they we trimming and the trim was moving ANU but they hit the cutoff switches after about 9 seconds. The last two commands they tried were only a second or less each. It is possible that due to over speed the electric motor didn't move the stabilizer but they didn't hold the switch very long.

The proper procedure would have been to keep pressing the trim switch on the first attempt until the forces we're balanced and then hit the cutoff. That is what the procedure says to do and they didn't. They allowed MCAS to activate again after the first manual trim. They cut off electric trim before they finished trimming the second time.
 
hivue
Posts: 2076
Joined: Tue Feb 26, 2013 2:26 am

Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Mon Apr 15, 2019 2:03 am

morrisond wrote:
they were just trying to meet the FAR that required a steady increase in control column force as you approached stall.


That required a steady increase in control column force as airspeed increases. This sort of imprecise language just tends to perpetuate the myth that MCAS is an aniti-stall system.
"You're sitting. In a chair. In the SKY!!" ~ Louis C.K.
 
morrisond
Posts: 2715
Joined: Thu Jan 07, 2010 12:22 am

Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Mon Apr 15, 2019 3:11 am

hivue wrote:
morrisond wrote:
they were just trying to meet the FAR that required a steady increase in control column force as you approached stall.


That required a steady increase in control column force as airspeed increases. This sort of imprecise language just tends to perpetuate the myth that MCAS is an aniti-stall system.


Intersting. I've been arguing all along that MCAS wasn't an anti-stall system.

Maybe I didn't say it quite right - but I keep getting bashed whenever I post the MCAS description from 737.org.uk. Here it is http://www.b737.org.uk/mcas.htm

Is there a better description that talks about the need for increasing control column force as speed increase vs getting close to the stall?

This is a bad joke - but I hope that FAR didn't apply to the manual trim wheel either.....
 
planecane
Posts: 1568
Joined: Thu Feb 09, 2017 4:58 pm

Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Mon Apr 15, 2019 3:25 am

patplan wrote:
morrisond wrote:
smartplane wrote:
Boeing used grandfathering scaling rules to reduce it's size, and did what to compensate? Nothing?


Who knows - they might have increased the gearing meaning that it takes more turns to move the stabilizer the same distance. Making it easier or They might not have - I can't find anything discussing the system in that much detail.


It was discussed and admitted by one of Boeing's ex-engineers in the other forum: They make the wheels smaller and had to put a dampening mechanism on the NG's, and, get this..., it was to accommodate the space needed to install a more "modern looking" PFD's for the pilots.

...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...
Original post


As it was mentioned many times before, this modified manual trim wheel is also another classic case of "grandfathering" that eventually bites back.

I wonder if it would have made any difference if the trim wheel was still the original size. The 737-200 FCOM referenced the "roller coaster" procedure for using the manual wheel. I don't think it was ever an easy thing to do if the aircraft was way out of trim and the control column was held opposite the trim.
 
hivue
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Joined: Tue Feb 26, 2013 2:26 am

Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Mon Apr 15, 2019 4:28 am

morrisond wrote:
Is there a better description that talks about the need for increasing control column force as speed increase vs getting close to the stall?


I think the requirement applies to scaling the control column force for both nose up and nose down column movement. The pilot needs the right feedback (even if it is contrived) from the control column whenever maneuvering.
"You're sitting. In a chair. In the SKY!!" ~ Louis C.K.
 
User avatar
zeke
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Mon Apr 15, 2019 6:13 am

planecane wrote:
I wonder if it would have made any difference if the trim wheel was still the original size. The 737-200 FCOM referenced the "roller coaster" procedure for using the manual wheel. I don't think it was ever an easy thing to do if the aircraft was way out of trim and the control column was held opposite the trim.


I think assuming the hinge moments and forces required to move the stab are the same for all 737 variants are the same is misguided. Fact that procedure has been removed from later variants suggest to me the forces are different.

Boeing engineers would be very well aware of the forces required and can easily make changes which are not visible to the pilots.
Human rights lawyers are "ambulance chasers of the very worst kind.'" - Sky News
 
XRAYretired
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Mon Apr 15, 2019 6:32 am

PcarSBA wrote:
Ray,

I see the 2nd long electric trim ANU input lasting about 10 seconds. The STAB angle appears to follow the command for the entire time at a stable rate (slope of graph is constant)

The graph resolution isn’t very high but I can’t say this looks like the stabilizer didn’t react to the electric trim. Even the last short blibs labeled “manual electric trim commands” seem to have an albeit small effect on the stab angle.

I wonder if the FDR records things like switch actuations, current draw of the trim motor, etc. so one could tell what forces were in play and whether the jack screw was jammed and wasn’t able to pass 2.4 units later in flight.


Indeed. I think we need to keep an open mind and look for common factor.

Ray
 
rheinwaldner
Posts: 1859
Joined: Wed Jan 02, 2008 4:58 pm

Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Mon Apr 15, 2019 6:35 am

OldAeroGuy wrote:
The airplane is way too fast. Pulling the throttles back to idle would have been a good choice.

Having unreliable speed indications? Insisting on the strict compliance to the stab runaway NNC and the AD on one hand and asking to set zero thrust while having lost reliable speed indications sounds like comical to me.
Many things are difficult, all things are possible!
 
XRAYretired
Posts: 870
Joined: Fri Mar 15, 2019 11:21 am

Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Mon Apr 15, 2019 6:47 am

planecane wrote:
XRAYretired wrote:
PcarSBA wrote:

The FO identified the runaway issue but I respectfully disagree they applied the procedure correctly. Else they would have trimmed the AC and only then opened the STAB TRIM CUTOUT switches. The FDR suggests the AC wasn’t trimmed when the FO called stab trim cut-out at 5:40:35 and the captain agreed. The trim was at 2.3 units at that point and speed was building. That’s pretty far away from 4 - 5.

So they were in a desperate hole and that’s why they re-engaged the switches to get the electric motors to help.


Respectfully, what I see is a total of 4 attempts of trim switch up. The first got to 2.4 and the other three all stopped at 2.3. Too much of a coincidence for me. I dont believe in coincidence. I would be looking for a common factor, and I dont think the pilots could be quite that accurate on purpose.

Ray

The first attempt they only held the switch for maybe 3 seconds. Then 5 seconds later MCAS commanded to almost full nose down. Then they we trimming and the trim was moving ANU but they hit the cutoff switches after about 9 seconds. The last two commands they tried were only a second or less each. It is possible that due to over speed the electric motor didn't move the stabilizer but they didn't hold the switch very long.

The proper procedure would have been to keep pressing the trim switch on the first attempt until the forces we're balanced and then hit the cutoff. That is what the procedure says to do and they didn't. They allowed MCAS to activate again after the first manual trim. They cut off electric trim before they finished trimming the second time.



Yes, I appreciate the procedure and the argument, but is does not resolve the coincidence for me. 'The pilot was not not aware enough to hold the trim switch long enough but was to stop at 2.3 in each case'? As a mind game, with regard to the last two attempts, if I pressed the thum switch and the wheeel did not move exceptmay be very briefly, I release it and press again it does not move, I start thinking what to do next.....

Ray
 
MRMR12
Posts: 2
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Mon Apr 15, 2019 9:10 am

First post here :), this post says it could not be AoA senbsor since so many other systems where affected? Mostly about Lion Air but says even ET302 had similar errors?

Boeing does not understand the cause of this 737MAX problem themselves.

Because the AOA sensor on the Lion Air aircraft was replaced after it flew JT775 and was BITE tested twice before the crash flight (JT610) we can be confident that JT610’s crash was not caused by a faulty AOA sensor.

Boeing’s software patch however is entirely based on Boeing’s belief that the AOA sensor was the cause.

Boeing seems to lack engineering competence for reasons which I can only guess at. Both Boeing and FAA are locked in a form of psychosis of denial.

It now turns out Lion Air 737MAX in flights on three days before the accident suffered multiple failures that cannot be attributed to MCAS nor to AOA sensor.

For example failure of the Left PFD, failure of the Left Radar altimeter, Left anti-ice, Left AOA sensor and activation of the Left Stick Shaker. Ethiopian ET302 is reported by Flight Global to have suffered similar instrument failures on left side instruments & systems.

These systems cannot be influenced by the AOA sensor, nor by MCAS. They suggest the root cause is either a voltage instability in the Left DC bus relay or a TRU failure.

Voltage irregularity for example could affect how the data is signaled from the AOA sensor to the ADIRU/DFDAU along the ARINC 429 data bus by altering signal encoding.


Link: https://www.quora.com/Why-doesn-t-Boeing-fix-the-MCAS-software-immediately Simon Gunson
 
xmp125a
Posts: 292
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Mon Apr 15, 2019 9:31 am

XRAYretired wrote:

Yes, I appreciate the procedure and the argument, but is does not resolve the coincidence for me. 'The pilot was not not aware enough to hold the trim switch long enough but was to stop at 2.3 in each case'? As a mind game, with regard to the last two attempts, if I pressed the thum switch and the wheeel did not move exceptmay be very briefly, I release it and press again it does not move, I start thinking what to do next.....

Ray


Yeah. This answers the question "what will they do between now and the time final report is released". This small detail is a nice catch!
 
RawSushi
Posts: 89
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Mon Apr 15, 2019 10:03 am

morrisond wrote:
hivue wrote:

That required a steady increase in control column force as airspeed increases. This sort of imprecise language just tends to perpetuate the myth that MCAS is an aniti-stall system.


Intersting. I've been arguing all along that MCAS wasn't an anti-stall system.

Maybe I didn't say it quite right - but I keep getting bashed whenever I post the MCAS description from 737.org.uk. Here it is http://www.b737.org.uk/mcas.htm

Is there a better description that talks about the need for increasing control column force as speed increase vs getting close to the stall?


Boeing claims it's not an anti-stall system, but they clearly designed it to behave like one. It even makes the stabilizer move by the same amount regardless of air speed. How does a system that can't even differentiate between a nudge and a slap be an effective "feel" system? It does one thing and one thing only, push the nose down until a satisfactory AoA is reached. That is a behaviour of an anti-stall system, not that of a "feel" system.
 
flybucky
Posts: 376
Joined: Tue Apr 17, 2018 7:44 pm

Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Mon Apr 15, 2019 10:44 am

Saintor wrote:
Why just pulling on the yoke wouldn't raise the nose via rear elevators?

The main reason is because the horizontal stabilizer is a much larger surface than the elevator. The horizontal stabilizer is the entire "tail wing", whereas the elevator is a flap at the trailing edge of the "tail wing". (See this image.) When the stabilizer is in trim, then the elevator works great. But if they are in opposition, then the stabilizer effect will dominate over the elevator effect.
 
flybucky
Posts: 376
Joined: Tue Apr 17, 2018 7:44 pm

Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Mon Apr 15, 2019 10:59 am

speedbird52 wrote:
Out of curiosity, why didn't the pilots leave electric trim off and use manual trim?

The theory is that it was not possible to manual trim nose up due to the stabilizer load.
https://www.satcom.guru/2019/04/stabili ... range.html
https://leehamnews.com/2019/04/05/bjorn ... -analysis/

Another evidence is that over a period of 2.5 minutes, while the Stab Trim was Cutout, the Stab Trim gradually moved nose DOWN by 0.2º. That would be an indication that the pilots tried to wrestle the manual trim wheel, but it did not budge towards nose UP, and they actually "lost ground".

From the Preliminary Report:
"05:40:42 to 05:43:11 (about two and a half minutes), the stabilizer position gradually moved in the AND direction from 2.3 units to 2.1 units."
 
JibberJim
Posts: 152
Joined: Tue Nov 08, 2016 1:33 pm

Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Mon Apr 15, 2019 11:03 am

asdf wrote:
if a wheel is from smaller diameter
and there is no other external power applied in the rotation
the same force on the stab will need more power at the wheels to move them if the diameter is smaller


Unless gearing is introduced, however that would of course require more turns on the wheel for the same movement of the trim, and I believe we know that not to have happened?
 
morrisond
Posts: 2715
Joined: Thu Jan 07, 2010 12:22 am

Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Mon Apr 15, 2019 11:20 am

JibberJim wrote:
asdf wrote:
if a wheel is from smaller diameter
and there is no other external power applied in the rotation
the same force on the stab will need more power at the wheels to move them if the diameter is smaller


Unless gearing is introduced, however that would of course require more turns on the wheel for the same movement of the trim, and I believe we know that not to have happened?



There is no evidence one way or another.
 
morrisond
Posts: 2715
Joined: Thu Jan 07, 2010 12:22 am

Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Mon Apr 15, 2019 11:23 am

flybucky wrote:
speedbird52 wrote:
Out of curiosity, why didn't the pilots leave electric trim off and use manual trim?

The theory is that it was not possible to manual trim nose up due to the stabilizer load.
https://www.satcom.guru/2019/04/stabili ... range.html
https://leehamnews.com/2019/04/05/bjorn ... -analysis/

Another evidence is that over a period of 2.5 minutes, while the Stab Trim was Cutout, the Stab Trim gradually moved nose DOWN by 0.2º. That would be an indication that the pilots tried to wrestle the manual trim wheel, but it did not budge towards nose UP, and they actually "lost ground".

From the Preliminary Report:
"05:40:42 to 05:43:11 (about two and a half minutes), the stabilizer position gradually moved in the AND direction from 2.3 units to 2.1 units."


Entirely possible - however the aerodynamic loads might have been so great on the Horizontal Stabilizer above VMO that just the movement in the control columns back and forth could have caused the same effect.

Above Vmo it really is unknown territory.
 
flybucky
Posts: 376
Joined: Tue Apr 17, 2018 7:44 pm

Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Mon Apr 15, 2019 11:36 am

New article by Scott Hamilton of Leeham News: https://leehamnews.com/2019/04/15/train ... x-crashes/

Broadly, the following points appear to be contributory factors to the two accidents:

  1. Bad MCAS design.
  2. Single point of failure—linking to one AOA instead of two.
  3. Failure to tell the airlines/pilots of the MCAS.
  4. Failure to have warning systems as standard equipment in cockpit.
  5. Possible poor maintenance at Lion Air.
  6. Possible poor communication at Lion Air between the crew on the preceding flight and subsequent crews.
  7. Pilot actions at Ethiopian.
 
morrisond
Posts: 2715
Joined: Thu Jan 07, 2010 12:22 am

Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Mon Apr 15, 2019 11:36 am

RawSushi wrote:
morrisond wrote:
hivue wrote:

That required a steady increase in control column force as airspeed increases. This sort of imprecise language just tends to perpetuate the myth that MCAS is an aniti-stall system.


Intersting. I've been arguing all along that MCAS wasn't an anti-stall system.

Maybe I didn't say it quite right - but I keep getting bashed whenever I post the MCAS description from 737.org.uk. Here it is http://www.b737.org.uk/mcas.htm

Is there a better description that talks about the need for increasing control column force as speed increase vs getting close to the stall?


Boeing claims it's not an anti-stall system, but they clearly designed it to behave like one. It even makes the stabilizer move by the same amount regardless of air speed. How does a system that can't even differentiate between a nudge and a slap be an effective "feel" system? It does one thing and one thing only, push the nose down until a satisfactory AoA is reached. That is a behaviour of an anti-stall system, not that of a "feel" system.


Agreed - but there was no FAR that required an Anti-stall system (That I know of). In a properly functioning MCAS as you got close to the stall the controls would have gotten heavier as MCAS put the aircraft out of trim. I suspect that's why they had to increase the speed of MCAS as it did not impart enough heavier feel at .6 units fast enough.

I don't believe MCAS was needed to make the plane safer - I don't believe any Pilot in the world would have been bad enough to pull through the area of light feel, the stick shaker, the Audio alarms and the frame buffeting and actually put it in a stall.

It's easier to pull through that area of light wheel - but also easy to push the control back to the right angle.

Controls can get pretty light when you are flying through turbulence or downdrafts as well which is why Pilots are taught not to rely on the feel of the controls (you can't on most FBW aircraft anyways) and constantly scan your instruments and visual references outside the plane to ensure you know what the plane is doing.

The MAX would have been better off without it and probably would have flown absolutely safely for many years.
 
morrisond
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Mon Apr 15, 2019 11:51 am

flybucky wrote:
New article by Scott Hamilton of Leeham News: https://leehamnews.com/2019/04/15/train ... x-crashes/

Broadly, the following points appear to be contributory factors to the two accidents:

  1. Bad MCAS design.
  2. Single point of failure—linking to one AOA instead of two.
  3. Failure to tell the airlines/pilots of the MCAS.
  4. Failure to have warning systems as standard equipment in cockpit.
  5. Possible poor maintenance at Lion Air.
  6. Possible poor communication at Lion Air between the crew on the preceding flight and subsequent crews.
  7. Pilot actions at Ethiopian.


That article just got going then it stopped without presenting any facts or thesis's. I disagree that it's only a third world training issue - Experienced pilots on these forums have shared stories of bad training in the West as well.

I recall a western 737 pilot with 1,000's and 1,000's of hours mentioning that he only had to use the Manual trim wheel in the simulator once since his initial type rating.

If the article is right - then I would suggest we either go full automatic (not let the crews have manual control) and accept that X numbers of crashes will occur until we get it absolutely right - or increase training standards worldwide (by legislation so all airlines are in the same boat) so Crews spend a lot more time dealing with unusual situations and learning a lot more about how to fly with degraded systems vs just being button pushers.

Computers are a lot better at executing automatic procedures - until we get good AI though - nothing will replace a well trained Human when the S**t hit's the fan and you have to improvise - and the S**t will hit the fan in even the most perfectly designed system as parts can fail.
 
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PW100
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Mon Apr 15, 2019 12:33 pm

planecane wrote:
The first attempt they only held the switch for maybe 3 seconds. Then 5 seconds later MCAS commanded to almost full nose down. Then they we trimming and the trim was moving ANU but they hit the cutoff switches after about 9 seconds. The last two commands they tried were only a second or less each. It is possible that due to over speed the electric motor didn't move the stabilizer but they didn't hold the switch very long.

The proper procedure would have been to keep pressing the trim switch on the first attempt until the forces we're balanced and then hit the cutoff. That is what the procedure says to do and they didn't. They allowed MCAS to activate again after the first manual trim. They cut off electric trim before they finished trimming the second time.

Do wo know for a fact that they didn't?
Could the system have stopped trimming**, while the pilot(s) kept pressing the thump switch?
** Perhaps because of overload? Is there an overload cut-out on the trim motor?
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PW100
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Mon Apr 15, 2019 12:44 pm

morrisond wrote:
flybucky wrote:
The theory is that it was not possible to manual trim nose up due to the stabilizer load.
https://www.satcom.guru/2019/04/stabili ... range.html
https://leehamnews.com/2019/04/05/bjorn ... -analysis/

Another evidence is that over a period of 2.5 minutes, while the Stab Trim was Cutout, the Stab Trim gradually moved nose DOWN by 0.2º. That would be an indication that the pilots tried to wrestle the manual trim wheel, but it did not budge towards nose UP, and they actually "lost ground".

From the Preliminary Report:
"05:40:42 to 05:43:11 (about two and a half minutes), the stabilizer position gradually moved in the AND direction from 2.3 units to 2.1 units."


Entirely possible - however the aerodynamic loads might have been so great on the Horizontal Stabilizer above VMO that just the movement in the control columns back and forth could have caused the same effect.

Above Vmo it really is unknown territory.


Things were already (very) problematic before Vmo was reached.
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PW100
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Mon Apr 15, 2019 12:46 pm

RawSushi wrote:
morrisond wrote:
hivue wrote:
That required a steady increase in control column force as airspeed increases. This sort of imprecise language just tends to perpetuate the myth that MCAS is an aniti-stall system.

Intersting. I've been arguing all along that MCAS wasn't an anti-stall system.
Maybe I didn't say it quite right - but I keep getting bashed whenever I post the MCAS description from 737.org.uk. Here it is http://www.b737.org.uk/mcas.htm

Is there a better description that talks about the need for increasing control column force as speed increase vs getting close to the stall?

Boeing claims it's not an anti-stall system, but they clearly designed it to behave like one. It even makes the stabilizer move by the same amount regardless of air speed. How does a system that can't even differentiate between a nudge and a slap be an effective "feel" system? It does one thing and one thing only, push the nose down until a satisfactory AoA is reached. That is a behaviour of an anti-stall system, not that of a "feel" system.


Shall we call it a pilot-induced-stall preventing system ?
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XRAYretired
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Mon Apr 15, 2019 12:58 pm

MRMR12 wrote:
First post here :), this post says it could not be AoA senbsor since so many other systems where affected? Mostly about Lion Air but says even ET302 had similar errors?

Boeing does not understand the cause of this 737MAX problem themselves.

Because the AOA sensor on the Lion Air aircraft was replaced after it flew JT775 and was BITE tested twice before the crash flight (JT610) we can be confident that JT610’s crash was not caused by a faulty AOA sensor.

Boeing’s software patch however is entirely based on Boeing’s belief that the AOA sensor was the cause.

Boeing seems to lack engineering competence for reasons which I can only guess at. Both Boeing and FAA are locked in a form of psychosis of denial.

It now turns out Lion Air 737MAX in flights on three days before the accident suffered multiple failures that cannot be attributed to MCAS nor to AOA sensor.

For example failure of the Left PFD, failure of the Left Radar altimeter, Left anti-ice, Left AOA sensor and activation of the Left Stick Shaker. Ethiopian ET302 is reported by Flight Global to have suffered similar instrument failures on left side instruments & systems.

These systems cannot be influenced by the AOA sensor, nor by MCAS. They suggest the root cause is either a voltage instability in the Left DC bus relay or a TRU failure.

Voltage irregularity for example could affect how the data is signaled from the AOA sensor to the ADIRU/DFDAU along the ARINC 429 data bus by altering signal encoding.


Link: https://www.quora.com/Why-doesn-t-Boeing-fix-the-MCAS-software-immediately Simon Gunson

Frankly, I cant see anything in either Preliminary Report that ties up with anything in the write up on this link?

Ray
 
planecane
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Mon Apr 15, 2019 1:34 pm

PW100 wrote:
planecane wrote:
The first attempt they only held the switch for maybe 3 seconds. Then 5 seconds later MCAS commanded to almost full nose down. Then they we trimming and the trim was moving ANU but they hit the cutoff switches after about 9 seconds. The last two commands they tried were only a second or less each. It is possible that due to over speed the electric motor didn't move the stabilizer but they didn't hold the switch very long.

The proper procedure would have been to keep pressing the trim switch on the first attempt until the forces we're balanced and then hit the cutoff. That is what the procedure says to do and they didn't. They allowed MCAS to activate again after the first manual trim. They cut off electric trim before they finished trimming the second time.

Do wo know for a fact that they didn't?
Could the system have stopped trimming**, while the pilot(s) kept pressing the thump switch?
** Perhaps because of overload? Is there an overload cut-out on the trim motor?

The FDR traces shows the command. Based on the block diagram posted at some point the only thing that cuts off power to the command signal is the cutout switches.
The other line on the chart shows the stabilizer trim position.
 
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Mon Apr 15, 2019 1:35 pm

flybucky wrote:
New article by Scott Hamilton of Leeham News: https://leehamnews.com/2019/04/15/train ... x-crashes/

What a load of dreck that article is; a bunch of words with no substance. And, Scott Hamilton's sense of self-importance is nauseating. It's an article with zero new information, and nothing but weak conjecture, yet the first sentence is "This column will no doubt light up the blog-o-sphere." Unlikely. :roll:
 
mzlin
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Mon Apr 15, 2019 1:55 pm

aerolimani wrote:
flybucky wrote:
New article by Scott Hamilton of Leeham News: https://leehamnews.com/2019/04/15/train ... x-crashes/

What a load of dreck that article is; a bunch of words with no substance. And, Scott Hamilton's sense of self-importance is nauseating. It's an article with zero new information, and nothing but weak conjecture, yet the first sentence is "This column will no doubt light up the blog-o-sphere." Unlikely. :roll:


Scott didn't provide his own insights but rather just referred the reader to an aviation week article which is very detailed and does provide an excellent narrative summary of the things that went wrong in that flight: https://m.aviationweek.com/commercial-a ... detachment
 
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Mon Apr 15, 2019 2:11 pm

mzlin wrote:
aerolimani wrote:
flybucky wrote:
New article by Scott Hamilton of Leeham News: https://leehamnews.com/2019/04/15/train ... x-crashes/

What a load of dreck that article is; a bunch of words with no substance. And, Scott Hamilton's sense of self-importance is nauseating. It's an article with zero new information, and nothing but weak conjecture, yet the first sentence is "This column will no doubt light up the blog-o-sphere." Unlikely. :roll:


Scott didn't provide his own insights but rather just referred the reader to an aviation week article which is very detailed and does provide an excellent narrative summary of the things that went wrong in that flight: https://m.aviationweek.com/commercial-a ... detachment

Scott Hamilton just spouted his opinion, and with nothing solid to back it up. The Aviation Week article doesn't bring any new information to light either. It's an opinion piece which tries to draw conclusions based on scant evidence. Even so, the article concludes with "The source indicates the crew appeared to be overwhelmed and, in a high workload environment, may not have followed the recommended procedures for re-trimming." While I wouldn't exactly call that total exoneration, it's not supportive of Scott Hamilton's conclusions either.
 
planecane
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Mon Apr 15, 2019 2:35 pm

XRAYretired wrote:
planecane wrote:
XRAYretired wrote:

Respectfully, what I see is a total of 4 attempts of trim switch up. The first got to 2.4 and the other three all stopped at 2.3. Too much of a coincidence for me. I dont believe in coincidence. I would be looking for a common factor, and I dont think the pilots could be quite that accurate on purpose.

Ray

The first attempt they only held the switch for maybe 3 seconds. Then 5 seconds later MCAS commanded to almost full nose down. Then they we trimming and the trim was moving ANU but they hit the cutoff switches after about 9 seconds. The last two commands they tried were only a second or less each. It is possible that due to over speed the electric motor didn't move the stabilizer but they didn't hold the switch very long.

The proper procedure would have been to keep pressing the trim switch on the first attempt until the forces we're balanced and then hit the cutoff. That is what the procedure says to do and they didn't. They allowed MCAS to activate again after the first manual trim. They cut off electric trim before they finished trimming the second time.



Yes, I appreciate the procedure and the argument, but is does not resolve the coincidence for me. 'The pilot was not not aware enough to hold the trim switch long enough but was to stop at 2.3 in each case'? As a mind game, with regard to the last two attempts, if I pressed the thum switch and the wheeel did not move exceptmay be very briefly, I release it and press again it does not move, I start thinking what to do next.....

Ray

I understand what you are saying. One of my best talents as an engineer was root cause analysis. With respect to the first two post-MCAS manual trim attempts, the first one the switch was pressed for around 2 seconds and the trim moved ANU slightly.

The second attempt, the trim was moving linearly ANU from the moment the thumb switch was pressed until the cutout switches were moved. We know they cut off the electric trim at that point from the CVR excerpt.

There is no evidence that the trim wouldn't have continued to move ANU if they left the electric trim enabled for another 10 seconds while giving ANU manual trim inputs.
 
morrisond
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Mon Apr 15, 2019 2:38 pm

aerolimani wrote:
mzlin wrote:
aerolimani wrote:
What a load of dreck that article is; a bunch of words with no substance. And, Scott Hamilton's sense of self-importance is nauseating. It's an article with zero new information, and nothing but weak conjecture, yet the first sentence is "This column will no doubt light up the blog-o-sphere." Unlikely. :roll:


Scott didn't provide his own insights but rather just referred the reader to an aviation week article which is very detailed and does provide an excellent narrative summary of the things that went wrong in that flight: https://m.aviationweek.com/commercial-a ... detachment

Scott Hamilton just spouted his opinion, and with nothing solid to back it up. The Aviation Week article doesn't bring any new information to light either. It's an opinion piece which tries to draw conclusions based on scant evidence. Even so, the article concludes with "The source indicates the crew appeared to be overwhelmed and, in a high workload environment, may not have followed the recommended procedures for re-trimming." While I wouldn't exactly call that total exoneration, it's not supportive of Scott Hamilton's conclusions either.


Yes - The Aviation Week article wasn't that great either.

However there were a lot of comments from Pilots below the article though. I found this one interesting.

"Yes, In 30 years I have had trims jam, freeze and a trim jack outright fail.
To handle these frozen controls, yes most failures required the reduction of pilot or aerodynamic forces...in order to move these frozen trims...or props?..
But...These problems did not compare to the difficulty of working with low time inexperienced pilots.
To add to this dilemma...add the language barrier, low flight hours, PLUS just plain bad attitude, is sometimes willingly!...causing deadly situations.
Also to mention...my pilot skills degraded badly nearing retirement...direct result of flying mostly with auto pilot "on"....the company SOP (manufacture's)..sales?... standard?
Noticed pilots benefit enormously, when allowed to train just a few more hours, (after basic training), handling the ship by hand flying...500 ft circuits is a good start.."dark ship" with all electrics turned off...is another good practice...
"Feel and listen"... To the airflow around your machine...(pressure instruments failed) Have your required, flashlight handy!
These few extra training hours...will all help experienced AND inexperienced pilots ..but the company is always too cheap to give extra (unusual or emergency type) flying training practice...
So depending on more automation is nice...(for sales)...but hazardous!...for everyone when the lights finally start to blink in the storm.....
Best interest, is to expect it all to fail....(the airplane)...forget training all the pilots to depend fully on the automation, they need regular, real hands on flying, with basic handling skills honed to basic standard."

This is a Worldwide issue - not just third world.
 
kalvado
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Mon Apr 15, 2019 2:39 pm

aerolimani wrote:
mzlin wrote:
aerolimani wrote:
What a load of dreck that article is; a bunch of words with no substance. And, Scott Hamilton's sense of self-importance is nauseating. It's an article with zero new information, and nothing but weak conjecture, yet the first sentence is "This column will no doubt light up the blog-o-sphere." Unlikely. :roll:


Scott didn't provide his own insights but rather just referred the reader to an aviation week article which is very detailed and does provide an excellent narrative summary of the things that went wrong in that flight: https://m.aviationweek.com/commercial-a ... detachment

Scott Hamilton just spouted his opinion, and with nothing solid to back it up. The Aviation Week article doesn't bring any new information to light either. It's an opinion piece which tries to draw conclusions based on scant evidence. Even so, the article concludes with "The source indicates the crew appeared to be overwhelmed and, in a high workload environment, may not have followed the recommended procedures for re-trimming." While I wouldn't exactly call that total exoneration, it's not supportive of Scott Hamilton's conclusions either.

On one hand, accident rates in US support the message.
On the other hand, designing for an average pilot means that the half of pilots, who are below average, are unfit to fly the airplane. Remember - average means just that, average - some are better, some are worse.
And this approach may save Boeing short term, but will bite long term. Insurance will consider Boeing as a more risky brand, and sales price would need either to offset premium difference, or orders from outside of first world will dry out. No fanfare, no bold statements, no headlines - just no orders.
 
VV
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Mon Apr 15, 2019 2:40 pm

I am pretty sure you can see the trim wheel turn when the MCAS gives the order to trim.

I recall there's a painting on that wheel to enhance the visibility when it's turning.
 
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Mon Apr 15, 2019 2:45 pm

VV wrote:
I am pretty sure you can see the trim wheel turn when the MCAS gives the order to trim.

I recall there's a painting on that wheel to enhance the visibility when it's turning.

How often do you look at your feet while you're driving your car at highway speeds?
 
hivue
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Mon Apr 15, 2019 3:07 pm

PW100 wrote:
Shall we call it a pilot-induced-stall preventing system ?


The problem with that is that MCAS doesn't prevent stalls. In a situation where MCAS is legitimately activated with no bad AoA data, etc. the pilot would still be able to stall the airplane. MCAS is not alpha prot or alpha floor as in AB FBW airplanes. In the case of AF447, if the airplane had been able to remain in normal law with all envelope protections in place the FO would not have been able to stall the airplane and crash it. MCAS is not an anti-stall system.
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kalvado
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Mon Apr 15, 2019 3:12 pm

morrisond wrote:
aerolimani wrote:
mzlin wrote:

Scott didn't provide his own insights but rather just referred the reader to an aviation week article which is very detailed and does provide an excellent narrative summary of the things that went wrong in that flight: https://m.aviationweek.com/commercial-a ... detachment

Scott Hamilton just spouted his opinion, and with nothing solid to back it up. The Aviation Week article doesn't bring any new information to light either. It's an opinion piece which tries to draw conclusions based on scant evidence. Even so, the article concludes with "The source indicates the crew appeared to be overwhelmed and, in a high workload environment, may not have followed the recommended procedures for re-trimming." While I wouldn't exactly call that total exoneration, it's not supportive of Scott Hamilton's conclusions either.


Yes - The Aviation Week article wasn't that great either.

However there were a lot of comments from Pilots below the article though. I found this one interesting.

"Yes, In 30 years I have had trims jam, freeze and a trim jack outright fail.
To handle these frozen controls, yes most failures required the reduction of pilot or aerodynamic forces...in order to move these frozen trims...or props?..
But...These problems did not compare to the difficulty of working with low time inexperienced pilots.
To add to this dilemma...add the language barrier, low flight hours, PLUS just plain bad attitude, is sometimes willingly!...causing deadly situations.
Also to mention...my pilot skills degraded badly nearing retirement...direct result of flying mostly with auto pilot "on"....the company SOP (manufacture's)..sales?... standard?
Noticed pilots benefit enormously, when allowed to train just a few more hours, (after basic training), handling the ship by hand flying...500 ft circuits is a good start.."dark ship" with all electrics turned off...is another good practice...
"Feel and listen"... To the airflow around your machine...(pressure instruments failed) Have your required, flashlight handy!
These few extra training hours...will all help experienced AND inexperienced pilots ..but the company is always too cheap to give extra (unusual or emergency type) flying training practice...
So depending on more automation is nice...(for sales)...but hazardous!...for everyone when the lights finally start to blink in the storm.....
Best interest, is to expect it all to fail....(the airplane)...forget training all the pilots to depend fully on the automation, they need regular, real hands on flying, with basic handling skills honed to basic standard."

This is a Worldwide issue - not just third world.

I will comment on more than your words. Frankly speaking, our approach is really very moderate. More training for unusual situations? Likely good idea. Depending on that training? Probably bad.
We have some pilots on this forum who has an ego barely fitting in their pants as they want to be reliant on themselves. Makes me scared that I may end up with those guys hauling me around.
Issue is that even trained human is a fairly unrealiable link in the chain, and if those skills have to be invoked - situation is already very problematic. IUnvestment in not getting there provides better return of investment in terms of accident losses at this point.
One can appeal to the well-known graph of crash rates. 737MAX is actually not that bad on a grand scheme of things. It has a typical record for the early jet age - when The Pilots used to be at the controls.
Today those high skills are not generally required - until we're talking flying relics like Tu-134/154 or 707s; and even those did improve over the years.
We can go back to highly trained pilots, but-we-did-our-best! designed planes and monthly crashes.. But probably that is a bad idea.
 
morrisond
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Mon Apr 15, 2019 3:41 pm

kalvado wrote:
morrisond wrote:
aerolimani wrote:
Scott Hamilton just spouted his opinion, and with nothing solid to back it up. The Aviation Week article doesn't bring any new information to light either. It's an opinion piece which tries to draw conclusions based on scant evidence. Even so, the article concludes with "The source indicates the crew appeared to be overwhelmed and, in a high workload environment, may not have followed the recommended procedures for re-trimming." While I wouldn't exactly call that total exoneration, it's not supportive of Scott Hamilton's conclusions either.


Yes - The Aviation Week article wasn't that great either.

However there were a lot of comments from Pilots below the article though. I found this one interesting.

"Yes, In 30 years I have had trims jam, freeze and a trim jack outright fail.
To handle these frozen controls, yes most failures required the reduction of pilot or aerodynamic forces...in order to move these frozen trims...or props?..
But...These problems did not compare to the difficulty of working with low time inexperienced pilots.
To add to this dilemma...add the language barrier, low flight hours, PLUS just plain bad attitude, is sometimes willingly!...causing deadly situations.
Also to mention...my pilot skills degraded badly nearing retirement...direct result of flying mostly with auto pilot "on"....the company SOP (manufacture's)..sales?... standard?
Noticed pilots benefit enormously, when allowed to train just a few more hours, (after basic training), handling the ship by hand flying...500 ft circuits is a good start.."dark ship" with all electrics turned off...is another good practice...
"Feel and listen"... To the airflow around your machine...(pressure instruments failed) Have your required, flashlight handy!
These few extra training hours...will all help experienced AND inexperienced pilots ..but the company is always too cheap to give extra (unusual or emergency type) flying training practice...
So depending on more automation is nice...(for sales)...but hazardous!...for everyone when the lights finally start to blink in the storm.....
Best interest, is to expect it all to fail....(the airplane)...forget training all the pilots to depend fully on the automation, they need regular, real hands on flying, with basic handling skills honed to basic standard."

This is a Worldwide issue - not just third world.

I will comment on more than your words. Frankly speaking, our approach is really very moderate. More training for unusual situations? Likely good idea. Depending on that training? Probably bad.
We have some pilots on this forum who has an ego barely fitting in their pants as they want to be reliant on themselves. Makes me scared that I may end up with those guys hauling me around.
Issue is that even trained human is a fairly unrealiable link in the chain, and if those skills have to be invoked - situation is already very problematic. IUnvestment in not getting there provides better return of investment in terms of accident losses at this point.
One can appeal to the well-known graph of crash rates. 737MAX is actually not that bad on a grand scheme of things. It has a typical record for the early jet age - when The Pilots used to be at the controls.
Today those high skills are not generally required - until we're talking flying relics like Tu-134/154 or 707s; and even those did improve over the years.
We can go back to highly trained pilots, but-we-did-our-best! designed planes and monthly crashes.. But probably that is a bad idea.


I wouldn't disagree - making airplanes safer is a good idea - but even the most perfectly designed plane can have things fail - that is why we need pilots until Artificial Intelligence can handle non-normal situations (probably a lot better than pilots).

We should be expecting more out of pilots these days in unusual situations vs less as Automation has made the job a lot easier and instead of decreasing training hours - maintain them or increase them so Pilots have time to get comfortable and familiar with things in the SIM going wrong so if they are faced with them in real life - the odds of a successful outcome are a lot higher.
 
dragon6172
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Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Mon Apr 15, 2019 3:47 pm

XRAYretired wrote:
At 05:39:57, the Captain advised again the First-Officer to request to maintain runway heading and that they are having flight control problems.

What was the flight control problem at this point? There had not been any MCAS inputs yet. Up to this point there was stick shaker, Anti-ice Master Caution, and the autopilot had just kicked off at 5:39:55.

If I make the assumption that this was said in conjunction with the first MCAS input around the 05:40:00, does that mean the pilots had properly diagnosed that they had a situation similar to LionAir, and if so why not trim to neutral and turn off electric trim IAW the AD now instead of waiting 30-40 seconds and two AND / MNU trim cycles.

PW100 wrote:

The uptrim just did not reach the "neutral" condition. And we do not know why that is. Perhaps that was an incompetent crew, as some repeatingly suggest as their favourite explanation (and then mumbling on about declining pilot standards worldwide . . . ).

It didn't reach neutral because the switch wasn't held long enough. Why wasn't the switch held long enough is the question. I do not think it is incompetence. I think it may come down to something physical or mental. In other words, if you are suddenly pulling 15-20 lb force to maintain level flight, then MCAS kicks in for round two and you are pulling 25-30 lb force, when you trim nose up you may stop around the 15-20 lb force mark cause that is what feels normal. Possible. Another thing to think is how long does a pilot normally hold the trim switch? It would appear that they would have to hold the trim switch for 15-20 seconds to return to neutral. All other manual inputs earlier in the takeoff sequence are in the 2-3 second range. Trimming for 15-20 seconds probably doesn't seem normal. Easy to see why a pilot may stop trimming, especially when the forces on the controls maybe don't seem to be improving.
Just some ideas on the "why" they wouldn't hold the trim switch for long enough.

PW100 wrote:
That semi-controlled may not have been sustainable for much longer, if the crew needed most of their physical strength to keep the nose up. Having seen the infamous MentourPilot video, it can be very understandable that workload was so high that communication with Maintenance would have become very difficult.

Most of their physical strength may be an exaggeration. Even in the video you mention, it is only one pilot who is holding the control column. In the ET crash the FO was doing other things for a lot of the event: attempting manual trim, making heading and altitude changes on the FDs (still not sure why these were important in this emergency). They probably could have continued a climb for a while longer.

I think there may be a bit of urgency to land in these two crashes, because there is a sensation of not being in control. Understandable with all the bells and whistles and control problems happening. But in both cases I think they were in control, and would have eventually come to the same result as the first LionAir incident, with some patience. Easy to say now I know.

speedbored wrote:
The fact that this is not included in the "procedure above", and includes the wording "can be used" clearly suggests that this is optional.

Of course it is optional. If you would rather pull 25-50 lbs of force on the control column for the remainder of the flight, you have that option as well.

OldAeroGuy wrote:
2) Some pitch control is still available via the yoke. If it wasn't, the airplane would have accelerated more during its 5500' climb. Excess energy was being converted into climb rather than acceleration. This could only be done by controlling pitch attitude.

I think the aircraft would have kept accelerating if the auto-throttles were not engaged. It is my understanding that AT engaged will not allow exceeding Vmo. This can be seen in the FDR plots. Once the LH (master FCC in this case) reaches Vmo, there is a slight reduction in N1.
xmp125a wrote:
So perhaps "fiddle with the trim and never let 5 seconds elapse" would be far better advice (since you don't lose electric control), but I understand that sounds ridicolous for EAD for a modern airplane.

This is essentially what LionAir crew did for 7 minutes. MCAS trims down, pilot trims up. Repeat 20 times.
Phrogs Phorever
 
9Patch
Posts: 578
Joined: Wed Mar 13, 2019 10:38 pm

Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Mon Apr 15, 2019 3:55 pm

Leeham news goes there:

Training is a factor in the MAX crashes

It’s fair to say that the four pilots were probably trapped into making mistakes. Boeing didn’t tell the airlines about the MCAS, so no training was possible. But mistakes were made by pilots, nevertheless.

Those who pointed to poorer training in Third World countries aren’t wrong.


Pilot skills and training in the First World are extraordinary. The accident rates in the US, Canada and First World Europe have been lower than anywhere else since the dawn of modern aviation.


That the definition of the “average pilot” may need a rethink is a thesis that has emerged from these two MAX accidents.

It looks like a thesis that has merit.

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freakyrat
Posts: 2010
Joined: Fri Aug 22, 2008 1:04 pm

Re: Ethiopian Airlines 737MAX crashes enroute to Nairobi

Mon Apr 15, 2019 3:57 pm

Ok folks after reading all the reports and opinions about this accident one that I read sticks out. Mainly that thius aircraft could have been initially saved with the correct pilot actions. The aircraft lost AOA sensor data due to a possible bird strike ripping the sensor vane off of the aircraft. This happened moments after takeoff. The aircraft was climbing out with 100% of N1 power with flaps extended when the Captain's stick shaker activated due to loss of the sensor followerd by an overspeed alarm. The correct procedure which should be ingrained in every pilots memory would have been to reduce power to leave the flaps down, reduce backpressure on the control column to a 10% nose up on the PFD and reduce power to 85% of N1. All of which this crew did not do. From what I understand when reading about MCAS is that it doesn't operate with flaps extended. Should have, would have in hindsight. The crew should have corrected the overspeed situation, left the flaps extended and returned to the airport. MCAS would not have activated in this siutation. When they raised the flaps up MCAS kicked in and the series of trim events leading to an out of control airplane and subsequent crash occured. I'm just throwing this out there as it is one 737 pilots opinion that I read. Yes MCAS as it currently is designed is a poor system and software and hardware fixes should correct it so this never happens again. Also better pilot training in the SIM and more hands on flying will improve pilot skills so they can correctly respond to problem situations.

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