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, 08:20
  #3261 (permalink)  
 
Join Date: Apr 2007
Location: Bristol
Age: 73
Posts: 45
I have read all the comments made on this forum concerning the Lion Air, and now the Ethiopian 737 Max crashes. It seems to me that the majority of comments focus on what could, or should, have been done by the crews involved. The Ethiopian pilots especially, whilst doubtless fully knowledgeable of the previous incident, were faced with the extraordinary and bizarre coincidence of a 2nd failure on the Max of the AOA vane, supplying erroneous data to the MCAS. This happened at the worst possible time where they were at their busiest, and with no height or time to play with. Whilst we all now have the benefit of knowledge, hindsight and time to analyse the situation . . . they didn’t. Of course they did their best, attempting to follow the memory items and new procedures as this crisis developed, but who, hand on heart, can lay any blame on them for not getting it exactly right? They may have been an average crew, with maybe less than average experience, but they were a trained and qualified crew and presumably signed off to fly the Max.

Even Boeing chief executive Dennis Muilenburg has publically stated: “As pilots have told us, erroneous activation of the MCAS function can add to what is already a high workload environment”. The Max, and in fact all commercial aircraft, simply have to be designed, built and certified to be within the flying ability of all pilots deemed qualified by their authorities to fly the Max. Two crews have shown sadly that the Max was outside their ability, particularly the 302 crew even with prior knowledge of the potential failure, and the industry therefore has to assume that this is the norm, not the exception.

SRMman is offline  
Old 5th Apr 2019, 08:23
  #3262 (permalink)  
 
Join Date: Apr 2008
Location: back of beyond
Posts: 93
Originally Posted by ecto1 View Post
...

My point is: most probably ANY of those mods would have saved the day, and all of them are pretty evident.

...
Disagree. May address the issues that caused the latest accident, but contradicts the entire concept of the 737's instrumentation system, and will invalidate the safety calculations on which certification is based, as well as possibly opening the doors to other failure modes.

The 737 instrumentation is a dual-redundant system, comprising two completely separate systems such that in the event of a single failure one completely operational system is still available. With the aid of appropriate disagreement monitors, standby instruments and checklists, pilots are trained to detect and diagnose such failures and take appropriate action.

This system was state-of-the-art at the time the 737 was launched and is still in use in smaller, non-FBW airliners. It is totally adequate for its stated task, that is to provide information to a well-trained human crew. It should never have been allowed to provide inputs to a system that will automatically drive flight control surfaces.
fizz57 is offline  
Old 5th Apr 2019, 08:40
  #3263 (permalink)  
 
Join Date: Jan 2008
Location: Reading, UK
Posts: 10,642
Originally Posted by AfricanSkies View Post
Do you really need an electric trimmer to move a stabilizer in a 15 degree range?
Of course not, you simply turn the manual trim wheel.

About 250 revolutions from full ANU to full AND ...
DaveReidUK is offline  
Old 5th Apr 2019, 08:56
  #3264 (permalink)  
 
Join Date: Apr 2019
Location: Cape Town
Posts: 1
trim blips

Originally Posted by EDLB View Post
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 clung 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.
Not a pilot, my field is electronic engineering. The FDR traces on both Lion Air & Ethiopia show short electrical trim ANU blips when longer trim activation would be expected.

I am curious as to where the FDR data for the stabilizer trim is read from - yoke trim switches or the motor drive electronics? Most high power motor drives have feedback that detects if the power demand is exceeded. If this happens, power to the motor is disabled, in order to protect it. Therefore a situation could arise where even though the pilot is activating ANU trim, it results in just a short ANU motor movement, before the motor power limit is exceeded. So if the FDR records from the drive electronics, the trim ANU 'request' by the pilot, will be seen as just a 'blip' although the trim switch is still activated,

This would account for AND trim running the full period as motor power demand is not exceeded (low aerodynamic load), but ANU trim is fighting against high aerodynamic load, which activates the motor protection. Thoughts?
onsoutherntip is offline  
Old 5th Apr 2019, 09:09
  #3265 (permalink)  
 
Join Date: Nov 2018
Location: madrid
Posts: 47
Originally Posted by fizz57 View Post
Disagree. May address the issues that caused the latest accident, but contradicts the entire concept of the 737's instrumentation system, and will invalidate the safety calculations on which certification is based, as well as possibly opening the doors to other failure modes.

.
I read your post and reflected about it. I see your point. We musn't have knee jerk reactions. But open your mind for a second:

Disregarding AOA for speed calculation (for example) will contradict which concept? Which safety calculation will it invalidate? Which other failure mode can you imagine if we do that? (note that the difference is about 5knt at takeoff speed between correct and batshit crazy AOA, so the error between fixed assumed AOA value and real AOA may be as low as 2knts).

Advicing the crew of inability to trim at high speed will harm how? We think it is worthy to throw them an alarm about the AOA heater not heating, and keep the stick shaker all along, but we believe it would be too distracting to remind them that he will loose trim ability due to high speeds?

Those are the official excuses. I don't buy them. It was honestly a very reasonable system when safety was important but not as important as today, data buses did not exist and pilots came from the military.

Not any more.We have better tools now and even if we break concepts and need to recertify things, it is simply too easy today to fool a 737 computer.
ecto1 is offline  
Old 5th Apr 2019, 09:21
  #3266 (permalink)  
 
Join Date: Apr 2002
Location: HK
Posts: 690
https://leehamnews.com/2019/04/05/bj...is/#more-29839

Thinks that the force when electric tirm/ MCAS was switched back on probably bounced the crew out of their seats, causing them to lose/ weaken grip on the controls
Freehills is offline  
Old 5th Apr 2019, 09:25
  #3267 (permalink)  
PJ2
 
Join Date: Mar 2003
Location: BC
Age: 71
Posts: 2,408
Originally Posted by DaveReidUK View Post
Of course not, you simply turn the manual trim wheel.

About 250 revolutions from full ANU to full AND ...
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
PJ2 is offline  
Old 5th Apr 2019, 09:34
  #3268 (permalink)  
PJ2
 
Join Date: Mar 2003
Location: BC
Age: 71
Posts: 2,408
Originally Posted by Freehills View Post
https://leehamnews.com/2019/04/05/bj...is/#more-29839

Thinks that the force when electric tirm/ MCAS was switched back on probably bounced the crew out of their seats, causing them to lose/ weaken grip on the controls
While the gee is slightly less than 0g, the arms may fly up momentarily, but the crew would be belted-in, perhaps with the shoulder-straps still on, (though they may have been removed for greater mobility). "Hitting the ceiling"? Hm.
PJ2 is offline  
Old 5th Apr 2019, 09:44
  #3269 (permalink)  
 
Join Date: Jul 2009
Location: France
Age: 57
Posts: 23
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
spornrad is online now  
Old 5th Apr 2019, 09:44
  #3270 (permalink)  
 
Join Date: Feb 2011
Location: Grand Turk
Age: 56
Posts: 64
Originally Posted by SLFstu View Post
(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.
I agree, but this anomaly is only part of the story. There is also the question of why there are so few electric trim corrections considering the circumstances? MCAS has massive authority despite massive AoA disagreement. Surely, the obvious solution is for MCAS to be automatically disabled but not electric trim? Why would the engineers even contemplated MCAS continuing to operate with significant AoA disagree? What is the effect of a constant input on the pickle switch? Does it give continuous control authority or intermittent authority?

It is fairly obvious that the automated system should have disabled MCAS authority as soon as there was significant disagreement with the two AoA sensors. Blaming the pilots is not sufficient, the more fundamental defect is plainly a Boeing issue and seemingly inexcusable. I feel that the pilots needed to act within the first 15 or 20 seconds of stick shaker but failed to recognize the issue quickly enough. The question is how many crews would have acted quickly enough and why should they have to react at all? It is all so unnecessary.

It is suggested that Boeing provided the MCAS system to overcome approval considerations. However, it does not make sense to leave it to the pilots to disable MCAS when it could be handled automatically. Neither does it make any sense to disable electric trim completely in order to disable MCAS.

...Just touching the surface of the negligent design and certification issues...
wheelsright is offline  
Old 5th Apr 2019, 09:51
  #3271 (permalink)  
 
Join Date: Aug 2010
Location: sussex
Posts: 42
DaveReidUK
"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."
I assume from your post that you understand what this gobbledygook means? Can you explain it in English?
42go is offline  
Old 5th Apr 2019, 09:56
  #3272 (permalink)  
 
Join Date: Apr 2008
Location: back of beyond
Posts: 93
Originally Posted by ecto1 View Post
...
Those are the official excuses. I don't buy them. It was honestly a very reasonable system when safety was important but not as important as today, data buses did not exist and pilots came from the military.
...
They're not "official excuses". The dual redundant system has been thoroughly analysed and its consequences known and calculated to a nicety.

What you're proposing is a hybrid system (disabling an input to a good system in case of a single failure on the other system) which will have its own consequences.

There is a solution, as has been implemented in FBW aircraft - if you are going to patch FBW onto a dinosaur, then its sensor suite must also be upgraded to meet those requirements and not rely on more patching to a grandfathered certification.
fizz57 is offline  
Old 5th Apr 2019, 10:11
  #3273 (permalink)  
 
Join Date: Jun 2002
Location: east ESSEX
Posts: 3,301
From what I`ve read ,the MCAS operates when flaps are `UP`...What is the flap limiting speed,and does the system(MCAS) depend on the flap lever position only...?
I used to fly C-130,which had power controls,but power to the rudderboost was limited when the flaps were UP,but full hydraulic power beyond 20 deg,primarily to prevent overstressing the fin at `high speed`,but cover the lower speed asymmetric case requiring more rudder...
However,if one was doing `tactical/fighter affiliation/more aggressive flying,one could `cheat` by pulling a c/b for the FLAP hydraulics,and then select the flap lever to 20 deg.This then gave the rudder full hyd.,but the flaps were still `UP`..

I would have thought that the immediate actions drill would have also stated to have reduced speed to perhaps below 300 kts..
sycamore is offline  
Old 5th Apr 2019, 10:16
  #3274 (permalink)  
Gender Faculty Specialist
 
Join Date: Mar 2002
Location: Stop being so stupid, it's my turn
Posts: 1,703
Originally Posted by ManaAdaSystem View Post


Chesty, we discussed this earlier, and you said you have flown the 737 with manual trim and it was no problem.
I’ve only tried this a few times, but found the manual trim to be pretty hard. A friend of mine got «Stab out of trim» enroute and diverted because he thought he had a jammed stab. This after he tried manual trim and found it so hard he concluded he had a jammed stab.
It now looks like manual trim is nearly impossible at higher speeds.
It puzzels me a bit that the stab can be trimmed so far it will bring the aircraft out of the pilot’s control. And then you can’t manually bring it back under control because the trim forces are too high.

How Boeing will solve this is beyond me. MCAS is a killer and if they restrict it it will affect the certification. In order to get rid of MCAS they have to redesign the aircraft.
IMHO the MAX will stay on ground for a long time.
Yes but that's a function of aerodynamic load.

My point was that anyone can turn a wheel regardless of hours (obviously if it's not prevented by aerodynamic load) so to suggest that the FO couldn't turn it because he had only 200 hours was and is total nonsense (and I know you didn't make that point).
Chesty Morgan is offline  
Old 5th Apr 2019, 10:17
  #3275 (permalink)  
 
Join Date: Jan 2008
Location: Reading, UK
Posts: 10,642
Originally Posted by 42go View Post
DaveReidUK
"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."
I assume from your post that you understand what this gobbledygook means? Can you explain it in English?
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 ..."
DaveReidUK is offline  
Old 5th Apr 2019, 10:28
  #3276 (permalink)  
 
Join Date: Nov 2007
Location: dublin
Posts: 1
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
having done manual trim on 707-737:-800 during sim training and air test over thirty years - a few points
1 stop wheel turning before you get way out of trim is the drill. But you have to notice. I note in the video posted here it took 10 seconds to disable STAB. Lion air struggled for 10 ?? minutes. In other words STAB is off so quickly that all these situations we speak of here don’t occur. And if they do, go to next step >>
2 old trick as mentioned earlier- off load stab by releasing back pressure for a few seconds allows you to trim ANU in any load situation . Both pilots both wheels with handles extended. Very quick. It’s the elevator loads against the STAB jackscrew that causes the high loads . But you have to know this and I think it’s not taught any more.
3 Stab is three times more powerful than elevators - they don’t ‘blow back’- just not designed to overcome STAB.
4 if you’ve turned off STAB ELECTRICS you can turn them on to enable ANU trim. Thumb switches. Then when back in green range - safe range- STAB OFF and trim manually.

5 But- and this all gets back to training- you have to know all this. Not look in manuals. It has to be in the core of your airplane skill base. Trained by the trainers. And if the trainers don’t have it ........
Summary. Are pilots new to 737 aware of the dangers posed by the stabiliser?
They do runaway stab, jammed stab and manual reversion during type rating training- at least did until recently! So they know how tough an animal the STAN can be but manageable.
MCAS
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
yanrair is offline  
Old 5th Apr 2019, 10:48
  #3277 (permalink)  
 
Join Date: Jun 2001
Location: at the edge of the alps
Posts: 330
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.
Having been on the jumpiest of a classic or NG (never been in a MAX), those trim wheels seemed to turn quite a lot even for very short bursts of trim input, so 250 is quite credible.
Alpine Flyer is offline  
Old 5th Apr 2019, 10:48
  #3278 (permalink)  
 
Join Date: Dec 2014
Location: Nz
Posts: 273
5 But- and this all gets back to training- you have to know all this. Not look in manuals. It has to be in the core of your airplane skill base. Trained by the trainers. And if the trainers don’t have it ........
Years and years of drift towards ‘lean operations’ where training gets faster and shallower and faster and shallower as the decades slide by.
Why keep 10 sim sessions for a type rating when you can get away with 9 and collect a $10,000 KPI bonus?
Two years later........ why keep 9 sim sessions for a type rating when you can get away with 8 and collect a $15,000 KPI bonus?
Two years later.........why do 8 full flight sim sessions for a type rating when you can get away with 6 + 2 cheaper ‘motion off’ sessions and collect a $20,000 KPI bonus?
73qanda is online now  
Old 5th Apr 2019, 10:56
  #3279 (permalink)  
 
Join Date: Aug 2006
Location: Around here
Age: 43
Posts: 38
Aviate, navigate, communicate?
lancs is offline  
Old 5th Apr 2019, 10:57
  #3280 (permalink)  
 
Join Date: Nov 2007
Location: dublin
Posts: 1
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. It’s a pity that level of schematic is not easily available to lone pilots.
yanrair is offline  

Thread Tools
Search this Thread

Contact Us Archive Advertising Cookie Policy Privacy Statement Terms of Service

Copyright © 2018 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.