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 4th Apr 2019, 02:19
  #3021 (permalink)  
 
Join Date: Jul 2013
Location: Australia
Posts: 196
Originally Posted by infrequentflyer789 View Post
Since this video may not be coming back I'll post a sort of transcript from memory since I was lucky enough to get to watch it. I'll try and just describe what I saw and keep my commentary/speculation to a minimum - in <italic>. Bear in mind this is a non-pilot observer's take on it from flaky memory:


There is a fair bit of intro talk then the sim.

They are in NG sim, not MAX, no surprise there. Mentour in left seat.

They start at low altitude, I think it was commented on, not at takeoff, I can't remember if they showed putting flaps up or started with flaps up and said it was just after flaps up.

No stick shaker, that I saw.
<presume means no elevator feel shift either, and that actual AOA error is not being simulated>

IAS disagree then simulated - or they just did the memory items, I didn't notice warning light (not that I would) and he didn't note it, there was an aural alarm but I think that was for AP disconnect
<I don't think this is exactly what the accident flights faced, they had shaker and IAS disagree from takeoff>

IAS disagree memory items, AP/AT OFF, FDs OFF, 75% N1, 4degrees

Throttles are pushed forward to get 75%, he comments that at low alt with denser air this is a lot of thrust and hence speed will increase

Trim runs, obviously sim doesn't have MCAS so not sure if they are simulating runaway or if he is doing it with the column switches

Comment is made that he was _expecting_ trim to run, because speed is changing, he says it will take a couple of cycles of fighting it with the switches before being definite that it is wrong

They discuss (he raises) that he is having flight control issue, they conclude it is trim that is the problem, they now run the stab trim runaway memory items finishing by hitting the switches. At this point he is clearly holding quite a bit of pressure on the column, but not obviously losing control of pitch

Now he points out that trim has only got down to (I think) 3 degrees on the indicator (zero being full nose down, I think) and that they are now going to "try something" - video captions say "don't try this at home", like we've all got a FFS in our shed or a 737 on the drive :-)

At this point the guy in the right seat uses the handle to wind the trim further _forward_. He stops when he clearly cannot wind it further - but they point out that it's still not at full nose down

Mentour is obviously struggling to keep the nose up at this point. I noticed he didn't seem to have the shoulder straps on (right seat did), possibly because he was frequently turning round to talk to the camera. That probably didn't help, but on the other hand he didn't have stick shaker or feel shift to cope with either.

Now, with Mentour pulling back, the right seat guy tries to wind the trim back with the handle - and he struggles to move it at all

They stop the sim, I think it was after stopping that he noted that at that point they were at 310 (maybe he said 340) knots.

I think there was then some further commentary, at one point I think he mentioned the rollercoaster to unload the stab and allow trimming, but commented that close to the ground the instinct is to pull back - I may be imagining that or remembering it from another video though.

<
And that was about it. I can try to answer questions on the video if anyone has any. The eye-opener for me wasn't the force on the control column (which was held anyway), it was that the trim couldn't be moved, in either direction. From somewhere I had got the impression that those wheels had a lot of leverage, due to the gearing, which was why a lot of turns would be required, but it seems that a lot of turns would be required and a gorilla to make them...
>
From another forum.

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.
From an ex Boeing employee.
RickNRoll is offline  
Old 4th Apr 2019, 02:35
  #3022 (permalink)  
 
Join Date: Jun 2009
Location: VA, USA
Age: 55
Posts: 561
Electric trim defeats MCAS...

Ok, I have to confess Iím confused.

All this talk of manual trim forces, etc.

MCAS applies trim in increments of 2.5 degrees over 10 seconds. Any pilot pickle switch trim ceases MCAS action for 5 seconds.

If MCAS runs again, again any pilot trim action defeats MCAS.

There is is no need to manually trim against any large nose down MCAS trim surely? Electrically trim the aircraft neutral AND THEN DISABLE ELECTRIC TRIM. From then on you are tweaking trim manually and no heroic fight against aero forces is required.

Am I wrong?

- GY
GarageYears is offline  
Old 4th Apr 2019, 02:58
  #3023 (permalink)  
 
Join Date: Aug 2008
Location: Airborne
Age: 60
Posts: 31
Garage years I agree. However if you initially allow some trim rotation assuming the STS system is operating. Then when you feel the aircraft coming out of trim you identify the problem as a runaway stab. The memory items that exist do not state as you recommend. They state Disconnect AP/AT if engaged and if it continues then stab switches off, if not engaged switches OFF. Seeing that no MCAS memory items exist then they use the most relevant which is runaway stab, where no attempt to electrically trim aircraft first exist.
dingy737 is offline  
Old 4th Apr 2019, 03:34
  #3024 (permalink)  
 
Join Date: Jun 2006
Location: California
Posts: 237
Originally Posted by GarageYears View Post
Ok, I have to confess Iím confused.

All this talk of manual trim forces, etc.

MCAS applies trim in increments of 2.5 degrees over 10 seconds. Any pilot pickle switch trim ceases MCAS action for 5 seconds.

If MCAS runs again, again any pilot trim action defeats MCAS.

There is is no need to manually trim against any large nose down MCAS trim surely? Electrically trim the aircraft neutral AND THEN DISABLE ELECTRIC TRIM. From then on you are tweaking trim manually and no heroic fight against aero forces is required.

Am I wrong?

- GY
I agree. When did we stop becoming pilots?
TriStar_drvr is offline  
Old 4th Apr 2019, 03:42
  #3025 (permalink)  
 
Join Date: Dec 2015
Location: Cape Town, ZA
Age: 59
Posts: 424
Originally Posted by GarageYears View Post
Ok, I have to confess Iím confused.

All this talk of manual trim forces, etc.

MCAS applies trim in increments of 2.5 degrees over 10 seconds. Any pilot pickle switch trim ceases MCAS action for 5 seconds.

If MCAS runs again, again any pilot trim action defeats MCAS.

There is is no need to manually trim against any large nose down MCAS trim surely? Electrically trim the aircraft neutral AND THEN DISABLE ELECTRIC TRIM. From then on you are tweaking trim manually and no heroic fight against aero forces is required.

Am I wrong?

- GY
If the runaway MCAS is countered early enough, then nose up trim, and disabing the cutoff switches is sufficient. That was the official version from Boeing and the FAA, until shortly after the second MAX crash. If left too long, the situation enters uncharted territory, and nobody has come out alive (except those in the simulator).

Several sources indicate that electric trim was intentionally limited in scope, to avoid unintentional runaway nose up trim (whether by the pilot or by a wiring fault). Runaway nose up trim may be just as deadly as nose down trim, so there was logical justification for this restriction.

It has been suggested that pitted against runaway MCAS, the electric trim never wins enough authority to recover from severe nose down trim, where there is aerodynamic loading of the horizontal stabiliser. Whether electric trim would be sufficient against the upgraded MCAS is not clear, and that risk needs to be scrutinised.

Several tests, leaks, and EASA documentation have knocked a huge hole in the initial assertions. I don't have detailed references handy for all of those points, but they have been interspersed throughout the last few days posts. I expect to see more media articles and blogs on these topics.

Edit: The link posted by ProPax gives the latest overview: https://www.flightglobal.com/news/ar...ses-ne-457224/

The FAA is presumably not happy with all of this contradictory information, and being made to look sheepish by ongoing media revelations. The certification review should require detailed evidence, rather than the bland reassurances we had last November after the first MAX crash.
GordonR_Cape is offline  
Old 4th Apr 2019, 04:39
  #3026 (permalink)  
 
Join Date: Feb 2018
Location: Canberra
Posts: 1
Originally Posted by GordonR_Cape View Post
Don't you just love the spin Boeing are putting out, right now its:

Boeing warns against drawing conclusions before investigators release more details
You can bet your bottom dollar after the findings are released it'll all be:

"We don't want to comment on the past, we want to look to the future, as we make a safer aircraft even safer, and we've ALREADY released software to do that, nothing to see here, move along"........
Dee Vee is offline  
Old 4th Apr 2019, 05:01
  #3027 (permalink)  
gmx
 
Join Date: Nov 2018
Location: Brisbane
Posts: 25
Originally Posted by GordonR_Cape View Post

Edit: The link posted by ProPax gives the latest overview: https://www.flightglobal.com/news/ar...ses-ne-457224/

The FAA is presumably not happy with all of this contradictory information, and being made to look sheepish by ongoing media revelations. The certification review should require detailed evidence, rather than the bland reassurances we had last November after the first MAX crash.
The article doesn't seem to know what it's talking about. MCAS is (temporarily) disabled by pilot use of the electric trim. There's no two steps down, one step up scenario at play here, where MCAS has greater authority over the stabiliser than the pilot. The only way MCAS puts the aircraft in an unrecoverable dive is if the pilot fails to trim out MCAS nose down inputs and then activates the stab trim cutout switches, leaving the pilot with manual trim only.
gmx is offline  
Old 4th Apr 2019, 05:09
  #3028 (permalink)  
 
Join Date: Mar 2015
Location: Washington state
Posts: 209
Originally Posted by ecto1 View Post
This is my understanding also, based on the schematic posted before:

737MAX Stab Trim architecture


When MCAS is engaged, control column "extreme deflection" towards pull will NOT disable MCAS trim down, but it will NOT disable your thumb switch trim up either, so you still win.

In other words, this battle will not be affected by too much pull.
So that is a selonoid on the column cutout override switch, right? What happens if it sticks ON, perhaps because someone installed the wrong one? (I have seen this.). Since MCAS is never engaged normally such a fault could lie in wait a long time. What woukd be the consequence, there is not much detail in that schematic.
Water pilot is offline  
Old 4th Apr 2019, 05:33
  #3029 (permalink)  
 
Join Date: Dec 2015
Location: Cape Town, ZA
Age: 59
Posts: 424
Originally Posted by gmx View Post
The article doesn't seem to know what it's talking about. MCAS is (temporarily) disabled by pilot use of the electric trim. There's no two steps down, one step up scenario at play here, where MCAS has greater authority over the stabiliser than the pilot. The only way MCAS puts the aircraft in an unrecoverable dive is if the pilot fails to trim out MCAS nose down inputs and then activates the stab trim cutout switches, leaving the pilot with manual trim only.
I agree the article is badly worded. The point is, do you believe anything that Boeing and the FAA tell you at this stage? More proof is needed to regain trust, rather than assertions and paper circuit diagrams. Since MCAS cannot be independently turned on or off, there is no way for a maintenance technician to test any of this, nor a pre-flight check on a specific aircraft.

Originally Posted by Water pilot View Post
So that is a selonoid on the column cutout override switch, right? What happens if it sticks ON, perhaps because someone installed the wrong one? (I have seen this.). Since MCAS is never engaged normally such a fault could lie in wait a long time. What woukd be the consequence, there is not much detail in that schematic.
More questions for each answer in this thread! Having a non-redundant column cutout switch solenoid would be another single point of failure. Presumably the fact that there are two control columns has something to do with it. Since MCAS is wired into both columns, then either one can be used to control the stabiliser trim in the event that the other fails.
GordonR_Cape is offline  
Old 4th Apr 2019, 06:10
  #3030 (permalink)  
gmx
 
Join Date: Nov 2018
Location: Brisbane
Posts: 25
Originally Posted by GordonR_Cape View Post
I agree the article is badly worded. The point is, do you believe anything that Boeing and the FAA tell you at this stage? More proof is needed to regain trust, rather than assertions and paper circuit diagrams. Since MCAS cannot be independently turned on or off, there is no way for a maintenance technician to test any of this, nor a pre-flight check on a specific aircraft.
I will wait for the official report. MCAS is clearly an unintuitive and potentially lethal system when triggered by faulty AoA data. I'm not going to blame Boeing, the FAA, the pilots or airlines until we know the exact failure modes triggered in these two accidents.
gmx is offline  
Old 4th Apr 2019, 06:25
  #3031 (permalink)  
 
Join Date: Dec 2015
Location: Cape Town, ZA
Age: 59
Posts: 424
Originally Posted by gmx View Post
I will wait for the official report. MCAS is clearly an unintuitive and potentially lethal system when triggered by faulty AoA data. I'm not going to blame Boeing, the FAA, the pilots or airlines until we know the exact failure modes triggered in these two accidents.
I am not a pilot, and probably being adversarial, but the question that might be asked is: Will waiting for the grounding to be lifted be enough, or the FAA oversight review, or until either or both of the accident reports, which ever comes later?

The FDR readouts provide a lot of information, but the state of the AOA sensor, cutoff switches, and flight computers is impossible to determine after the crashes. We may never know the the full answers, given the complex fault tree. Could this saga take years, like the Comet metal fatigue investigation?
GordonR_Cape is offline  
Old 4th Apr 2019, 06:38
  #3032 (permalink)  
 
Join Date: Jun 2003
Location: UK
Posts: 2,423
It could take years, but it may be more like the rudder hardover problem. Two fatal accidents, keep the thing flying, quite a few hairy moments, then find and fix the problem years later.
HundredPercentPlease is offline  
Old 4th Apr 2019, 06:39
  #3033 (permalink)  
 
Join Date: Aug 2005
Location: EDLB
Posts: 213
Originally Posted by GordonR_Cape View Post
Could this saga take years, like the Comet metal fatigue investigation?
Very unlikely. The modern digital FDR used store lots of parameters and with the CVR synced there will be enough data to come up with a very good picture of what happened why. There are lots of grounded MAX too where you can look into and test fly them to check your assumptions about the events.
EDLB is offline  
Old 4th Apr 2019, 06:42
  #3034 (permalink)  

Keeping Danny in Sandwiches
 
Join Date: May 1999
Location: UK
Age: 73
Posts: 1,290
Boeing's mistake was to use the stabiliser to actuate MCAS. If they had followed the example of the BAC 1-11 and the deep stall problem in the 1960's they would have had a stick shaker followed by a stick pusher on the elevators. At least the pilot was in the loop throughout the period of designed operation, even if as I suspect like MCAS the pusher was there to satisfy the certification regime and unlike the 737 probably never actuated in flight.

The only issue then would be the small size of the elevators on the 737 but that could have been resolved.

Last edited by sky9; 4th Apr 2019 at 08:38.
sky9 is offline  
Old 4th Apr 2019, 06:53
  #3035 (permalink)  
 
Join Date: Apr 2004
Location: near EDDF
Posts: 775
Originally Posted by Water pilot View Post

So that is a selonoid on the column cutout override switch, right? What happens if it sticks ON, perhaps because someone installed the wrong one? (I have seen this.). Since MCAS is never engaged normally such a fault could lie in wait a long time. What woukd be the consequence, there is not much detail in that schematic.
The system (stabilizer trim control column switching module) must be checked every 6000 FH according MPD.

IFixPlanes is offline  
Old 4th Apr 2019, 06:58
  #3036 (permalink)  
 
Join Date: Aug 2005
Location: EDLB
Posts: 213
I have a simple question:
What happens if the trim cutoff switches are in on position (electrical trim possible), MCAS wan’t to trim the stabiliser nose down while the pilot holds his dual trim switches on the colom for nose up?

Who wins?

According to water_pilot the PF win’s but is it verified?

With the outcome of ET302 I have my doubts.
EDLB is offline  
Old 4th Apr 2019, 07:15
  #3037 (permalink)  
 
Join Date: Feb 2008
Location: victoria bc
Age: 79
Posts: 36
Originally Posted by RatherBeFlying View Post
It appears that MCAS can in ten seconds move the stab whenever it's in the mood, but the pilots need considerably longer to bring back the stab with dozens of cranks of manual trim - provided that airload allows them to move the trim.

Very much an unequal contest.

​​​​​​MCAS really shouldn't be putting in more trim than can be corrected by the crew in the interval before it reactivates.

But then, limiting MCAS authority might fail to achieve required stick force increase approaching stall. The software will have to get even fancier to satisfy 10E-9 reliability.

I'm with gums. Dump MCAS and fix the nacelle aerodynamics.
Me too, and I would be willing to bet quite a few Boeing engineers long before anyone else ever heard of it.
ferry pilot is offline  
Old 4th Apr 2019, 07:49
  #3038 (permalink)  
 
Join Date: Nov 2018
Location: madrid
Posts: 47
Originally Posted by EDLB View Post
I have a simple question:
What happens if the trim cutoff switches are in on position (electrical trim possible), MCAS wanít to trim the stabiliser nose down while the pilot holds his dual trim switches on the colom for nose up?

Who wins?

According to water_pilot the PF winís but is it verified?

With the outcome of ET302 I have my doubts.
PF wins, see FDR traces.

On a different topic, failure of control column deflection cutoff override to always closed would mean that if the trim thumb button is pressed nose down, or fails to that position, it will not be cut if the pilot pulls.

Very rare coincidence, but previous posters are right in that periodical check would be needed.

It is in my eyes as dangerous and as rare as the control column defection switches failing to always open, and they installed an override for that (before mcas)
ecto1 is offline  
Old 4th Apr 2019, 08:05
  #3039 (permalink)  
 
Join Date: Feb 2016
Location: S.E.Asia
Posts: 1,807
Apart from Boeing the FAA will be left holding the legal responsibility here.

Trying to get the Max back in the air and fully certified will not be easy.

This is not a quick fix and rubber stamp job.

Added to that the passenger viewpoint of an old design past its sell by date and clearly not safe and you have a whole bundle of problems for the manufacturer.
Mike Flynn is offline  
Old 4th Apr 2019, 08:27
  #3040 (permalink)  
Pegase Driver
 
Join Date: May 1997
Location: Europe
Age: 70
Posts: 2,967
I was talking this week end with a senior from one of the European airline affected, they had last week decided stop training on the Max, transfer all the pilots to their other types for upgrade and strike out the type from their summer schedule. Whether the airline will survive this financially is in the balance now as the Summer season is where the money is made... this will have rippling effect on the industry well beyond Boeing..
ATC Watcher is offline  

Thread Tools
Search this Thread

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

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