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 5th Apr 2019, 03:29
  #3221 (permalink)  
 
Join Date: Feb 2004
Location: Australia
Posts: 1,300
Originally Posted by Loose rivets View Post
I just can't get to grips with the concept of a weight. Counter-balance or not. My recollection of checking the vanes was that they stayed put to wherever you shoved them. Having any weight would make them subject to accelerative forces - the weight of the vane itself would be almost totally air-supported and while still affected by g, it would be minuscule compared to the pressure of the air.
Wouldn't the accelerative forces apply to the vane and the counter balance about the pivot point? So possibly no rotation due to equal forces up/down around the pivot point. I also recall the vanes stay roughly where you put them. They feel fluid-damped.
NSEU is offline  
Old 5th Apr 2019, 03:40
  #3222 (permalink)  
 
Join Date: Apr 2008
Location: Australia
Posts: 664
Not difficult to rotate the trim wheels under certain circumstances, but impossible.

IMPOSSIBLE.


Picture the stab, angled leading-edge up (trimmed for nose down) - then picture the elevator, attached to the rear of the stab, deflected up (to achieve nose up pitch).

The down force at the rear of the stab (due to the elevator deflection) makes stab movement IMPOSSIBLE above a certain speed.

IMPOSSIBLE.
FGD135 is offline  
Old 5th Apr 2019, 03:45
  #3223 (permalink)  
 
Join Date: Dec 2008
Location: PDX
Posts: 70
[Not a pilot] I note that they had time to communicate and navigate. They set altitudes and headings and communicated their intentions.

Back pressure increases, but that is not graphed, so we will have to wait eighteen months to learn how much they were exerting while they were setting altitudes, headings, etc.

Within five seconds the Captain went from climbing to 32,000 ft to requesting to maintain runway heading. Are the voice and data timestamps compatible?

Summary with points of interest:
takeoff trim 5.6
man/elec trim 4.9 to 5.9 end 5.6
trim via ?? Down from 5.6 to 4.6
auto trim Down from 4.60 to 2.1
man/elec trim Up from 2.1 to 2.4
auto trim Down from 2.4 to 0.4

"At 05:40:28 Manual electric trim in the ANU direction was recorded and the stabilizer reversed moving in the ANU direction and then the trim reached 2.3 units." [One of these ANUs is a typo, no?]

man/elec trim Up 0.4 to 2.3
Cutout

"From 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." [Approximately, 0.1 units / min.]

"At 05:41:46, the Captain asked the First-Officer if the trim is functional. The First-Officer has replied that the trim was not working and asked if he could try it manually. The Captain told him to try. At 05:41:54, the First-Officer replied that it is not working. At 05:43:04, the Captain asked the First Officer to pitch up together and said that pitch is not enough."

A minute into the two and a half minutes of nose down trim, the Captain asks a reasonable question. Within a span of eight seconds the FO answers that trim is not working, oddly suggests trying manual, gets permission, and says, Nope. What exactly was the Captain asking? What did the FO mean by manual? The nose down was gradual, but the FO only worked on whatever "manual" was for eight seconds.

They worked together on something for seven seconds. Did each have a yoke in one hand and a hand wheel in the other? So, fifteen seconds of trying did not defeat the gradual nose down of 0.2 units in two and a half minutes. Or, another interpretation: eight seconds of cranking in the wrong direction didn't seem to be helping. This interpretation is at odds with the stated "gradual" nose down.

trim Down via ?? from 2.3 to 2.1
Normal [Inferred]
manu/elec trim Up from 2.1 to 2.3
auto trim Down 2.3 to 1.0
trim via ?? 1.1 to 0.8

Last edited by fotoguzzi; 5th Apr 2019 at 21:38. Reason: add possible interpretation; clarification; disclaim
fotoguzzi is offline  
Old 5th Apr 2019, 03:53
  #3224 (permalink)  
 
Join Date: Aug 2013
Location: Washington.
Age: 70
Posts: 564
Originally Posted by dingy737 View Post
Question:
Why did Boeing give a FULL description of the NG’s , STS, in their FCOM but ONLY mention MCAS in the abbreviation section of the MAX FCOM.
A. Because a full description would highlight an unwanted flight characteristic forced onto a 1967 airframe, pushing it beyond the MAX. ( criminal)
B. It was considered better to cover up & hide this aerodynamic instability, which could open Pandora’s box and affect market $hare against the NEO. ( criminal)
C. Because their partner in crime the FAA, allowed them. ( criminal)
D. Because they thought their magic software would magically make their shoe horned design failure disappear.
E. All of the above.

The answer is always “ all of the above”.
I won't pretend to know the answer, but suggest one other possibility, supported by previous posts. Boeing needed to minimize the training load, as a selling point and commitment to its airline customers. The more that goes into the FCOM that is unique to the Max, the more pilot training must address it. It would seem that when assessing the need for FCOM documentation and training, Boeing (and FAA?) focused on how MCAS works when fully operational (no malfunctions), requiring no pilot response. Its function is to make the handling of the Max in pitch at high AoA so similar to the 737NG (not prevent stall as the media seem to be so hooked on).

I can't imagine that Boeing anticipated the combination of conditions the pilots encountered, or even the repeated MCAS trim actions that accumulated so much. If they had, I am confident they would have done something different with the either the Max design, the FCOM and/or the pilot training. Furthermore, I doubt Boeing anticipated notion that the MCAS would create such an adverse trim condition at higher speeds than normally encountered during the takeoff climb. The higher speeds the accident aircraft reached would have made manually correcting the trim practically impossible for the pilots to achieve (ref the Mentor video).
GlobalNav is offline  
Old 5th Apr 2019, 04:15
  #3225 (permalink)  
 
Join Date: May 2008
Location: us
Posts: 16
Originally Posted by FGD135 View Post
Not difficult to rotate the trim wheels under certain circumstances, but impossible.
IMPOSSIBLE.

Picture the stab, angled leading-edge up (trimmed for nose down) - then picture the elevator, attached to the rear of the stab, deflected up (to achieve nose up pitch).that
The down force at the rear of the stab (due to the elevator deflection) makes stab movement IMPOSSIBLE above a certain speed.
IMPOSSIBLE.
Hard to imagine that Boeing didn't include a WARNING in the flight manual advising that above certain speeds manual trimming of the stab would be extremely difficult, if not impossible. Surely they must have encountered this situation during flight testing. In their efforts to hide the MCAS system, they failed to make operators aware of a potentially deadly scenario.
runner1021 is offline  
Old 5th Apr 2019, 04:18
  #3226 (permalink)  
 
Join Date: Jan 2006
Location: Sydney Australia
Posts: 2,170
Originally Posted by FrequentSLF View Post
thanks, yes i meant that would be pretty hard to operate the manual,trim under high loads, sorry for the confusion i might have created
No worries mate.

Glad we cleared that up.
KRUSTY 34 is offline  
Old 5th Apr 2019, 04:40
  #3227 (permalink)  
 
Join Date: Oct 2007
Location: Here
Posts: 776
Originally Posted by NSEU View Post
Wouldn't the accelerative forces apply to the vane and the counter balance about the pivot point? So possibly no rotation due to equal forces up/down around the pivot point. I also recall the vanes stay roughly where you put them. They feel fluid-damped.
Yes.

That is what happens when everything is working correctly.

The suggestion is that the observed changes to the AoA signal recorded by the FDR can be explained if it is assumed that the vane has fallen off thereby unbalancing the system and making it susceptible to AoA signal changes with changing Vertical Acceleration (g).
jimjim1 is offline  
Old 5th Apr 2019, 04:47
  #3228 (permalink)  
 
Join Date: Apr 2008
Location: Australia
Posts: 664
Hard to imagine that Boeing didn't include a WARNING in the flight manual advising that above certain speeds manual trimming of the stab would be extremely difficult, if not impossible. Surely they must have encountered this situation during flight testing. In their efforts to hide the MCAS system, they failed to make operators aware of a potentially deadly scenario.
Boeing did include exactly that warning in the flight manuals, but deleted it - no doubt, due product liability concerns.
FGD135 is offline  
Old 5th Apr 2019, 04:56
  #3229 (permalink)  
 
Join Date: Aug 2005
Location: EDLB
Posts: 205
Seems to me that the final hole in the cheese which dictated the outcome of both flights is, that at higher speeds the trim is jammed (in the direction of nose up) if trimmed nose down. On the Ethopian flight a single nose down command by the MCAS system was enough to seal their fate.

I do not believe that in the time where they clinged on the column for nose up, that they did not try to use the trim switches to unload the back pressure. Elevator trimming you learn from day one in your SEP trainer.

On the Lion air you can see that the PF did constant fight the MCAS AND trim with nose up. As soon as he transferred command there are only few blips of nose up trim to see on the FDR. Same here on the Ethopian flight.

I can’t believe that you only try with two short blips if the landscape becomes larger fast.


EDLB is offline  
Old 5th Apr 2019, 05:14
  #3230 (permalink)  
 
Join Date: Aug 2013
Location: Hong Kong, Scotland, Slovakia
Age: 57
Posts: 37
Originally Posted by FGD135 View Post
Not difficult to rotate the trim wheels under certain circumstances, but impossible.

IMPOSSIBLE.


Picture the stab, angled leading-edge up (trimmed for nose down) - then picture the elevator, attached to the rear of the stab, deflected up (to achieve nose up pitch).

The down force at the rear of the stab (due to the elevator deflection) makes stab movement IMPOSSIBLE above a certain speed.

IMPOSSIBLE.
The more this subject is examined the more convinced I am that it will be IMPOSSIBLE for the MAX to retain its certification in current form. A quick fix is not going to cut it. No regulator will put their head on a chopping block over it.
rmac2 is offline  
Old 5th Apr 2019, 05:28
  #3231 (permalink)  
 
Join Date: Aug 2005
Location: EDLB
Posts: 205
Originally Posted by Takwis View Post
Lots more discussion of manual trim, here: https://www.satcom.guru/2019/04/stab...and-range.html
Thanks for the link. So Boeing added at least two more lined up holes in the cheese on the MAX. MCAS much more powerful with 2.5 degree steps. Removal of the Autopilot+MCAS trim cut out switch. You now go direct to manual wheel crank trim only, if you have to cut out the influence from any automation to the trim.
And as a third hole that manual trim wheel is jammed if MCAS did his job on false data from a single sensor.

How did they get this changes through certification?

We know now with 20/20 hindsight that you are in deep trouble if any of your flight automation systems goes rough and you have to cut out trim.

Unfortunately for Boeing I do not see the Max getting back in the air soon.
EDLB is offline  
Old 5th Apr 2019, 05:52
  #3232 (permalink)  
 
Join Date: Jun 2006
Location: Brisbane
Posts: 109
At 05:43:04, the Captain asked the First Officer to pitch up together and said that pitch is not enough.

At 05:43:11, about 32 seconds before the end of the recording, at approximately 13,4002 ft, two momentary manual electric trim inputs are recorded in the ANU direction. The stabilizer moved in the ANU direction from 2.1 units to 2.3 units.
This bit baffles me. Apart from the question of why didn't they get the aircraft back in trim earlier, at this point in time the situation looked just salvageable.

Presumably somewhere in-between these two time-stamps, the stab trim cutout switches were turned back on.

There is no mention of any cockpit discussion taking place from the CVR about turning them back on, so perhaps the Captain just reached down and reactivated the stab trim in desperation.

But why only two short blips of trim? They worked! It is stated the trim moved from 2.1 to 2.3 units. Re-engaging the stab trim was working! So why stop there? If only they'd trimmed it back to around 5 units and then hit the cutout switches again it would have become a manageable problem again. Surely every Max pilot in the world would have briefed themselves on this after Lion Air?

This makes the event seem all the more tragic - so close to solving the problem.
Derfred is offline  
Old 5th Apr 2019, 06:22
  #3233 (permalink)  
THUNDERTAILED
 
Join Date: Nov 1999
Location: L200
Posts: 318
With respect to Why didn't they use the yoke trim switches effectively?
How much or how little, rather, hand flying experience did they have?
Captain was cadet from the start at ET, operated from the get go in an "AP on at 200' and off at 1000'/500' " SOP environment, and the FO was brand new in just such an environment. Unfamiliar with using trim switches whilst flying .. unfamiliar with hand flying, and having to do it with the stick shaker on max continuous with unreliable airspeeds. Ouch
AfricanSkies is offline  
Old 5th Apr 2019, 06:36
  #3234 (permalink)  
 
Join Date: Jun 2001
Location: at the edge of the alps
Posts: 375
Originally Posted by BluSdUp View Post
And here comes the problem: In 26 Okt 2017 he made Cpt 737-800 , SO less then 1.5 years Command.
There is a total of 1477hrs 738 and 103hrs Max.
Of which a lot is FO time!!
So, a low timer indeed!

This is a warning on so many levels!
Someone who's flown 8000 hours from 2011 to 2019 can hardly be called a "low-timer", that's more than most people flying in Europe (or even the US would rack up in that time).
Most Commanders flew as FOs before (and the saying goes that those who didn't aren't the best to fly with). Every time there's a new type out there, someone's gonna have to start flying it with zero hours on this type.
Where would you procure "ready-made" commanders with experience and command time on type?

If I got you wrong, please elaborate.
Alpine Flyer is offline  
Old 5th Apr 2019, 06:38
  #3235 (permalink)  
 
Join Date: Sep 2009
Location: 64N, 020E
Age: 52
Posts: 36
Elec trim about 230 knots impossible?

EASA document from Feb 2016 allegedly states that electric trim would not work above 230 knots. That might explain why they re-engaged trim (if the indication that they did re-engage trim is correct)...

The undated EASA certification document, available online, was issued in February 2016, an agency spokesman said.

It specifically noted that at speeds greater than 230 knots (265mph, 425kph) with flaps retracted, pilots might have to use the wheel in the cockpit’s center console rather than an electric thumb switch on the control yoke.
https://www.reuters.com/article/us-e...-idUSKCN1RA0DP
NiclasB is offline  
Old 5th Apr 2019, 06:46
  #3236 (permalink)  
 
Join Date: Jul 2013
Location: Norway
Age: 53
Posts: 127
Originally Posted by NSEU View Post
The Maintenance Manual has upper and lower limits when there are no airloads:

The torque required to turn the wheel is somewhere between 22 and 62pound-inches (2.5 and 7 newton-meters).

What's the radius of the trim wheel at the handle position?
I would say the radius at the handle is between 10 and 15cm. So, that would give a force required to manually crank - WITHOUT any air loads - of 2,5 to 7 kg for a 10 cm radius and 1,67 to 4,67 kg for a 15 cm radius wheel.
I am fairly sure that the radius at the handle is closer to 10 cm than to 15 cm.
SteinarN is offline  
Old 5th Apr 2019, 06:59
  #3237 (permalink)  
 
Join Date: Oct 2010
Location: EASA land
Posts: 26
Trim Runaway C/L

C/L is actually trying to do the troubleshooting - first step is to eliminate autopilot false inputs and then if that does not help - trim motor switches go to cut-out.
Should it be the other way around - trim motor switches to cut out first and then troubleshoot if you want.

Especially after the Lion crash when it was widely known that disengaging the autopilot is a pre-condition for erroneous MCAS trim input.
TOGA Tap is offline  
Old 5th Apr 2019, 07:02
  #3238 (permalink)  
 
Join Date: Feb 2015
Location: Gold Coast, QLD, Australia
Posts: 21
MCAS fired a blank

(From an ex hardware/software tech writer) - a comment about software rather than aeronautics. If the timeline story (CVR derived) in comparison to the FDR traces is accurate, here is something weird from the preliminary report's data nobody has commented on.

The third MCAS activation lasting 9 or so seconds starting at 05:40:41 did not alter stab pitch trim because the FO had just cut power to the stabilizer jackscrew motor. The report glibly notes that fact. But why did MCAS even try to activate, as if sitting there fat, dumb and stupid? Exactly what type of coding allows the FCC to attempt to command AND trim when both STAB TRIM switches are already set to CUTOUT? Seems the designed use case never anticipated this sequence.

So it appears that this bolted on chunk of MAX-only software was not monitoring real-time trim motor electrics. Hell no, you cannot do that - a loom change might be required and that would disturb the production line and possibly delay certification! Or better yet, a few lines of more rigorous code were required.

Way up in the thread at least 2 incredulous posters suggested, sarcastically I think, that an intern might have programmed MCAS_1? Makes you wonder.

Last edited by SLFstu; 5th Apr 2019 at 07:09. Reason: fixed formatting of special characters
SLFstu is offline  
Old 5th Apr 2019, 07:02
  #3239 (permalink)  
 
Join Date: Apr 2009
Location: Hotel Gypsy
Posts: 2,831
Is it not a bit quaint that a 21st century airline manufacturer still believes that a hand-cranked pulley is the best final solution to a complex systems problem?

Surely the biggest lesson to learn from this event is that the Max should be the last of the 737 family? (No disrespect to the 737 which has been an outstanding aircraft......... but is rather long in the tooth).

Interesting fact. The 737 first flew about 50 years ago and, to date, there have been about 11000 manufactured and 4000 on order. The A320 range first flew 30 years ago and there have been about 8500 built and 6000 on order. Sort of explains why Boeing need to stay in the game.
Cows getting bigger is offline  
Old 5th Apr 2019, 07:04
  #3240 (permalink)  
Gender Faculty Specialist
 
Join Date: Mar 2002
Location: Stop being so stupid, it's my turn
Posts: 1,718
Originally Posted by Rananim View Post
units but FO couldnt get the manual trim working.FO has 200 hours
so this is not surprising
I'm sorry but how many hours does one require before one can turn a wheel?
Chesty Morgan 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.