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Ethiopian airliner down in Africa

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Ethiopian airliner down in Africa

Old 5th Apr 2019, 10:56
  #3281 (permalink)  
 
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Aviate, navigate, communicate?
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Old 5th Apr 2019, 10:57
  #3282 (permalink)  
 
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Originally Posted by spornrad View Post
In the prelim. report is a clear statement by the FO that the manual trim attempt did not work as advertised in the AD.
There is also a subtle hint that probably shows why the pilots in a last desperate attempt did reengage the trim motors, and how the pilots were desperately trying to follow the AD and manually resetting the trim, which was most likely aerodynamically blocked:
After the cutout, there is a very slow, long, subtle nose-down movement of the fin according to the report. What do you do when the crank is blocked, instinctively? You're rattling it! And then in this phase it moves only a few hairs nose-down, but not a bit Nose-Up.
Then, in desperation, they probably switched on the electric motors again, only to find out now, with two very short trim-up switch attempts, that in the meantime, electric trim quit working too (speed has meanwhile increased further). A nightmare.

This last attempt to implement the AD has now reset MCAS. And then comes design-wise (but is not in the FCOM or the AD, was never mentioned in training), while they still think about what to do next, after 5 s the final death blow of MCAS ...

The plane systems (MCAS and Trim) and the AD procedure just did not give them a fair chance IMHO.

An excellent overview over these 60 year old speed issues with the 737 trim system can be found in many old manuals and here: https://www.satcom.guru/2019/04/stab...and-range.html
excellent article with diagrams- all thanks to Peter Lemme. Its a pity that level of schematic is not easily available to lone pilots.
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Old 5th Apr 2019, 11:05
  #3283 (permalink)  
PJ2
 
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Yanrair, all 5 points well-worth reading and memorizing. Thank you for a fellow aviator's recollections from those days - they remain as valuable and potentially life-saving as ever. I don't know what happened to them in the last two or three decades but there weren't too many wheels left that needed re-inventing, yet here we are. Another guy worth reading, just like Centaurus in Tech.

PJ2
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Old 5th Apr 2019, 11:07
  #3284 (permalink)  
PJ2
 
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. . . so 250 is quite credible.
Thanks, Alpine Flyer, yes, that seemed reasonable to me too.
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Old 5th Apr 2019, 11:12
  #3285 (permalink)  
fdr
 
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Originally Posted by BluSdUp View Post
Let one thing be clear, we now have facts.
The crew was extremely inexperienced :
The FO had grand total 361hrs of wich 207 the last 3 months.
The captain was 29 years. Had an impressive career!
Had 8122hrs total

July 23 2010 he graduated
FO 737-800 31 jan 2011
Then FO 757/767 777 and 787.
BUT!
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!

BLU, do we stop using captains that have less than 1.5 years in command?
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Old 5th Apr 2019, 11:13
  #3286 (permalink)  
 
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Update

It looks like the FAA has decided to postpone the Certification of the Software update past April, according memo!
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Old 5th Apr 2019, 11:15
  #3287 (permalink)  
 
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Also

No Max for RYR this summer schedule!
Summer in Ireland is April to end of October!

Max
RIP
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Old 5th Apr 2019, 11:21
  #3288 (permalink)  
 
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That said do disagree with statements on manual trim, pretty strong evidence that at the speed and trim they were in it would be physically very hard or impossible to trim manually without unloading maneuvers that the did not have the altitude for and/or knowledge/training of.
MurphywasRight
If the column forces were too high, one option (if you hadn't worked out how to engage the manual trim, which these guys hadn't) is to turn the trim back on, correct it with the normal electric trim switches, and then turn it off again before MCAS kicks back in. You asked what I would do, that's what I would do.
PaperHanger

They decide to cut out the trim switches at 0540:35, 35 seconds after first MCAS activation.N1 remains at 94% throughout leading to loss of speed control. But If ANU manual trim had been ordered immediately following cutout of stab trim switches, or better still, PF had trimmed back to 5 units(which has a visual marking on the trim index) and then disabled the trim switches,can we calculate if the aerodynamic loads were already too much for manual trim to work.What was the speed at 0540:35?
Captain asks if trim is functional at 0541:46,so that's 71 seconds after trim cutout where no attempt is made to relieve control forces and speed is allowed to build.

Last edited by Rananim; 5th Apr 2019 at 11:32.
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Old 5th Apr 2019, 11:21
  #3289 (permalink)  
 
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Originally Posted by DaveReidUK View Post
Nope, sorry, you assume incorrectly - I don't speak gobbledygook either. You would need to ask EASA.

I think that a rough translation is "when electric trim runs out, pray you have enough time, strength and altitude left to start winding ..."
This is a master piece of an aviation agency output. Could be any, this is not sepcific to EASA: It is the result of lawyers writing tech statements or manuals. The 737MAX emergency AD is no better. It is contradictary, leaves open questions and is not the smart wording standard other industries have reached in the past 40 years, partially because of tough consumer laws.
The peak is the FAA "Continued Airworthiness Notification to the International Community" dated March 12, a document type that was non existant before this date, is not based on ICAO rules and had just one obvious purpose. CMA.

Too often I sit in front of aviation regulations, rulings and manuals and think: damn sh.., what is it they want to tell me? And the obvious questions that every semi-intelligent guy/gal would have from a paragraph are never raised in the document nor answered. Still in this modern world people are too often ashamed to ask the obvious. There is no shame if it can save lifes.
Commercial aviation is stuck in the late 60s.
It is the answer to thick pants mentality and low management quality; as long as knee-jerk reactions dictate it will never change.
I have been there. For more than 30 years and unsuccessful to change that.
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Old 5th Apr 2019, 11:22
  #3290 (permalink)  
 
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Originally Posted by 42go View Post
DaveReidUK


I assume from your post that you understand what this gobbledygook means? Can you explain it in English?
Maybe I can try, EASA's sentence was: "The increased safety provided by the Boeing design limits on the thumb switches (for out-of-trim dive characteristics) provides a compensating factor for the inability to use the thumb switches throughout the entire flight envelope."

This seems to be in reference to the thumb switches not being able to trim the stabilizer until the mechanical stop limit.

They seem to mean that the safety added by not being able to trim with the thumb switches until you hit the mechanical stops compensates not being able to do that when you actually need it.

For example, if a thumb switch gets stuck, the resulting runaway won't be able to bring the trim to the full nose down mechanical limit, so it decreases the risk of getting the aircraft in an unrecoverable dive, they consider that an advantage.

The disadvantage is that, if you really need to bring the trim full nose down, to the mechanical limit, you won't be able to do that with the thumb switches.

So they are saying the advantages and disadvantages compensate each other.

Also, a lot of people seem to interpret those EASA's statements as saying you are not able to use the thumb switches at all in those conditions. But the trim limit switches are designed to prevent you from reaching the mechanical limits, not going away from them, so electric trim attempts going in the opposite direction, away from the mechanical limit, should still work, even if you are outside the designed trim limits for manual electric trim.

So I think it's unlikely the trim limit switches were a factor in this accident.

Last edited by MemberBerry; 5th Apr 2019 at 11:37. Reason: grammar
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Old 5th Apr 2019, 11:26
  #3291 (permalink)  
 
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Preliminary report, pristine quality

For reference
- preliminary report on EA302 (source: Washington Post)
and pristine extracts of images in appendix 1 (improving on these in post 3161)
- preliminary FDR data
- general overview of the flight
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Old 5th Apr 2019, 11:35
  #3292 (permalink)  
 
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FDR
NO No, we have all been there!
I am just stating a FACT.
This Young Commander was experienced , just not as a Commander.

And according to Ethiopian propaganda he did all correct.
NO he did not!!
Engage AP at 400 feet with the stick shaker going : WRONG
Never controlling PWR and Speed WRONG
Retracting Flaps as per standard Ops when possible in a stall : WRONG
I feel so bad for him!

But sad to say, he was set up by Murphy, FAA and Boeing and I see only panic in the action and reaction.
After 4000+ hrs in 4 sims I have seen a bit, and it is all down to a confusing flight deck with this fail mode!
Something like this I have never encountered in a Sim

But , please
Were do You see experience? . Sorry to be so blunt.

Sincerely
Cpt B
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Old 5th Apr 2019, 11:38
  #3293 (permalink)  
 
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Originally Posted by spornrad View Post
Then, in desperation, they probably switched on the electric motors again, only to find out now, with two very short trim-up switch attempts, that in the meantime, electric trim quit working too (speed has meanwhile increased further). A nightmare.
If you look carefully at the FDR traces it seems to me that the electric trim did in fact work after apparently re-enabling it. The line goes up ever so slightly around 5:43:15, just before MCAS trims nose-down again. About back to where it was when the trim cutout switches were set to cutout.

I wonder, since the next page (27) has much higher-resolution graphs of some parameters, why the graph showing the flight control parameters (p. 26) is only low-resolution (looks like a screenshot).

The scenario painted on Bjorn's corner at Leeham News seems very plausible and extremely scary, especially the take on why only short trim blips were used. One of the most scary parts is that even at a moderately out-of-trim situation, where the PF could hold the control column forces for several minutes, that mechanical trim would not work, if that turns out to be true.

Bernd
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Old 5th Apr 2019, 11:44
  #3294 (permalink)  
fdr
 
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Originally Posted by yanrair View Post
So. MCAS being sorted. Good thing. Does that leave us still with a much bigger problem? The elephant in the room! What’s going to happen next time an automated function badly misbehaves- and it will.
Y
Having done reversion testing, I was wondering what I had missed in the wording, so have dusted off the manual and had another look at the FCTM wording for the runaway stabiliser and the follow on manual trim. In the latter it mentions excessive airloads, and then discusses having both pilots applying effort to the system....in extreme cases airloads have to be relieved, and the next sentence covers returning the aircraft to the actual in-trim speed while attempting to trim using the manual trim wheels.

... the problem with the wording is that having the aircraft now trimmed to an undesired speed (....Mach 2 etc from the runaway trim case...) then the crew are to match the trim case while using both pilots if needed to manually change the trim. So, the crew bunt over to match the in trim speed for the nose down runaway case... which is all well and good except that is generally where planet earth is also located. If you are in an A-10, that is possibly second nature, or if you are current on Stukas, but for an RPT aircraft, that seems to be rather light on reasonableness. If this is reasonable, then perhaps the OEM should load up one of their aircraft with the management and DERs involved, and go demonstrate the technique at low level and high speed and determine how reasonable that is in the real world where the crew are confronted with an unexpected surprise in close proximity to the ground or water. On second thought, it would appear unfair to ask the OEM to do that... or anyone else for that matter, pilots, cabin crew and passengers.

The 737 is the worlds most prolific jet transport, by a sizeable margin, the manner that the trim issue is worded, and the limited protection that exists with the Part 25 wording for compliance doesn't seem to be impressive, particularly for a design where current activity is making "a safe aircraft safer". Perhaps runaway trims just don't happen and there is no risk from the underlying design, but I'm pretty sure that the last person who tried to pass an FAA check ride with two pilots having all hands on the controls at the same time ended up with more than just a discussion item.

25.255 provides for a 3 second trim error to be introduced... that is not what either of the recent crews experienced. Perhaps 3 seconds is perfectly fine as a value, in which case, the crew just need the chicken entrails to know when the system may exceed 3 seconds of uncommanded motion.

Humans are adept at adaptation, we can find workarounds for almost anything, but some 50 years on, if the cure for the system is as described, it may be time to look closely at grandfather rights vs public safety. Boeing builds a good plane, however perhaps it deserves some more thought into the system architecture, and at the very least some reinforcement training for crews that may need to deal with the issues related to the design.
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Old 5th Apr 2019, 11:51
  #3295 (permalink)  
 
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Originally Posted by MemberBerry View Post
Maybe I can try, EASA's sentence was: "The increased safety provided by the Boeing design limits on the thumb switches (for out-of-trim dive characteristics) provides a compensating factor for the inability to use the thumb switches throughout the entire flight envelope."

This seems to be in reference to the thumb switches not being able to trim the stabilizer until the mechanical stop limit.

They seem to mean that the safety added by not being able to trim with the thumb switches until you hit the mechanical stops compensates not being able to do that when you actually need it.

For example, if a thumb switch gets stuck, the resulting runaway won't be able to bring the trim to the full nose down mechanical limit, so it decreases the risk of getting the aircraft in an unrecoverable dive, they consider that an advantage.

The disadvantage is that, if you really need to bring the trim full nose down, to the mechanical limit, you won't be able to do that with the thumb switches.

So they are saying the advantages and disadvantages compensate each other.

Also, a lot of people seem to interpret that EASA's statements as saying you are not able to use the thumb switches at all in those conditions. But the trim limit switches are designed to prevent you from reaching the mechanical limits, not going away from them, so electric trim attempts going in the opposite direction, away from the mechanical limit, should still work, even if you are outside the designed trim limits for manual electric trim.

So I think it's unlikely the trim limit switches were a factor in this accident.
My take would be that the aircraft could not comply with the 3 second trim operation, no load, required for electric trims for (CS 25.255(a)(1)).
So they declared that the manual trim wheel was the "main trim'. This only requires a 30 lbf mistrim, but allowed trimming throught the entire flight envelope.
The electric stops were then reset so maximum electric trim deflection was sufficient for the "normal airline operational" envelope, manual trim picks up the rest.
So now we can claim how conservative we are.
Now, where does a stability augmentation system failure morph into a trim runaway?

Last edited by zzuf; 5th Apr 2019 at 12:30.
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Old 5th Apr 2019, 11:58
  #3296 (permalink)  
 
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Originally Posted by PJ2 View Post
Is that what it is?...250 turns of the trim wheel from stop to stop? That info wasn't available anywhere in the AMM, the FCOM or even the FCTM. Like some, I wondered how many turns it was, so thanks.

The full range (from the AMM) of the stab is 17. This range is not available to all controls, (electric, manual, wheel), as noted in this thread, but let us assume the available range is -1 AND to 16 ANU using the big wheel.

Now we can calculate turns and degrees of trim, (remembering the comments on the difficulty of turning the wheel under some circumstances).

250 turns / 17 degrees = 14.7 turns per degree, or,
17 degrees / 250 turns = 0.07 per turn.

If the thinking and the math is correct, we can see that there is a lot of work and time to manually modify the stab trim using the wheel. In fact, those who fly/flew the B727/B737 will recall just how fast the wheel goes around when electrically-trimming in normal flight, flaps-up; the white mark on the wheel is almost a blur...

PJ2
Do you know how many hand inputs from the pilot will take to complete one turn? Three, four? Supposing the answer is three, the pilot will have to make 44 hand movements to change one degree. If the pilot is able to execute one turn in 4 seconds (fast), a change of only one degree will take 59 seconds, or one degree per minute.
Not enough time to recover from a dive. If my math is correct, the only way to counteract MCAS input is with electric trim. But if you need to cut off trim motors to "kill" MCAS, how the pilot will manually turn the trim wheel to achieve enough amplitude to cancel MCAS inputs?
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Old 5th Apr 2019, 12:02
  #3297 (permalink)  
 
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MemberBerry
They seem to mean that the safety added by not being able to trim with the thumb switches until you hit the mechanical stops compensates the not being able to do that when you actually need it.
I'm sorry, but you and DRUK obviously do have a Masters in gobbledygook. DRUK says it "Might be a good time to reiterate the relevant part from the document:" - WHY I ask? Does he/she understand it? What is 'relevant'?

You 'explain' it in a way I do not, as a native English speaker, begin to understand.

What chance an Ethiopian or Indonesian pilot?
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Old 5th Apr 2019, 12:13
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Not too important, but there are 2 typos in the interim report which already misguided 2 PPRuNe posters.
By comparing the report text with the DFDR diagram, it is obvious that these are typos.
They may be caused by a translation from Amharic to English ?

So please read:
...
At 05:39:22 and about 1,000 feet the left autopilot (AP) was engaged (it disengaged about 33 seconds later), the flaps gear was retracted and the pitch trim position decreased to 4.6 units.
...
At 05:40:12, approximately three seconds after AND stabilizer motion ends, electric trim (from pilot activated switches on the yoke) in the Aircraft nose up (ANU) direction is recorded on the DFDR and the stabilizer moved in the ANU direction to 2.4 units. The Aircraft pitch attitude remained about the same as the back pressure on the column increased decreased.
...
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Old 5th Apr 2019, 12:20
  #3299 (permalink)  
 
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Originally Posted by Rob21 View Post
Do you know how many hand inputs from the pilot will take to complete one turn? Three, four?
That's why the trim wheel has a flip-out handle, so you can crank it quickly: See also The video, around 14:05:

.

Looking at that, I'd say at least at low loads one can do two to three turns per second.

Bernd

Last edited by bsieker; 5th Apr 2019 at 12:35.
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Old 5th Apr 2019, 12:41
  #3300 (permalink)  
 
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Originally Posted by 42go View Post
MemberBerry


I'm sorry, but you and DRUK obviously do have a Masters in gobbledygook. DRUK says it "Might be a good time to reiterate the relevant part from the document:" - WHY I ask? Does he/she understand it? What is 'relevant'?

You 'explain' it in a way I do not, as a native English speaker, begin to understand.

What chance an Ethiopian or Indonesian pilot?
Sorry, I went through multiple revisions while composing that reply, and doing that resulted in some small grammar errors I didn't notice before posting it, like that not deleting an instance of "the", that was no longer needed after rephrasing it.

Without the needless "the", it reads: "They seem to mean that the safety added by not being able to trim with the thumb switches until you hit the mechanical stops compensates not being able to do that when you actually need it."

I fixed those errors more than an hour ago, unfortunately you somehow managed to reply to the version containing that grammar error after I already fixed it. If there are any more grammar errors in my post let me know, and I'll correct them.

I'm not a native English speaker and maybe I could have rephrased it better, I realize it could be hard to understand. That's why I then detailed what I mean by that.

I'll make another attempt, in case it's still not clear: They were saying that the designed electric limits, preventing you from reaching the mechanical limits using electric trim, have both advantages and disadvantages.
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