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Ethiopian airliner down in Africa

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Ethiopian airliner down in Africa

Old 26th Apr 2019, 15:13
  #4381 (permalink)  
 
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Originally Posted by HundredPercentPlease View Post
When I was trained on the 737 (classic and NG), the stab trim runaway was a runaway - where the trim wheel ran continuously. We would identify it as a runaway, because it was continuously running, and flick the switches.

1. MCAS activation is not continuous, it's bursts.
2. The 737 trim system likes to provide bursts of random trim at certain times (STS) so bursts are considered normal.
Honest question: How long does a trim wheel have to spin before you deem it "continuous" and thus subject to intervention by the pilot?

In the case of Ethiopian, the MCAS input was not like the normal Speed Trim you see during takeoff. If you take a look at the DFDR traces of the automatic trim before the flaps were retracted, you can see what these inputs look like. Short and seemingly random inputs.

When MCAS activated, it ran the trim nose down for 9 continuous seconds. Please count that out to yourself. MCAS moved the stab about 2.5 degrees. That would be about 37 spins of the flight deck trim wheel. Please imagine that white stripe on the trim wheel making 37 trips passed the Captain's knee. All this time, the Captain was holding the yoke and must have felt the changing trim pressures. This happened TWICE (one other MCAS input was interrupted by the pilot trimming nose up). Ultimately, it wasn't even the 8122-hour Captain who suggested that the trim cutout switches be used - it was the 361-hour First Officer.

So honestly, just how long does the stab have to continuously run before a fully qualified 737 type-rated Captain determines that he has runaway stab trim?
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Old 26th Apr 2019, 15:42
  #4382 (permalink)  
 
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Reviewing the charts, can someone explain to me why the N1 percentage seems to be 95-100%? This aircraft seems to be going at a very high IAS. No wonder manual trim was so difficult. Rule number 1, fly the aircraft.
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Old 26th Apr 2019, 15:45
  #4383 (permalink)  
 
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Salute!

Thanks a lot, Wonk. Best post in a very long time.

Maybe some of the “Sky Gods” here would think about some things.

And I support your criticism of Big B and FAA and so forth for letting the plane fly we lowly proles without satisfying basic aerodynamic FAR requirements. I would even go so far as to claim the Airbus FBW models could be flown in “direct law” and behave as required. After all, the AF447 debacle showed how stable the plane was despite the best efforts of the crew to keep it stalled.

Gums ......
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Old 26th Apr 2019, 16:31
  #4384 (permalink)  
 
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Gums,

As I understand it, when designing the A320 Airbus toyed with the idea of reduced stability, citing FBW as the "excuse". The whole world raised a regulatory eyebrow and Airbus designed a fully stable aircraft.

Ironically, Boeing designed a less than stable aircraft with a bit of bolt on, undocumented FBW, and the world continued to rotate, until two crashed.
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Old 26th Apr 2019, 16:41
  #4385 (permalink)  
 
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Originally Posted by 737 Driver View Post
). Ultimately, it wasn't even the 8122-hour Captain who suggested that the trim cutout switches be used - it was the 361-hour First Officer.
The reason people are bashing your skygod/airmanship analysis is hidden in your statement above.

Why do you think the captain didn't get it, but the FO did?

Really, why?

As so many are saying, this is HF. Think: volume of input and processing.

A final thought: do you think that if the ET crew had trained this scenario in the sim, then when it happened for real then they would have been fine? The comfort of the sim helps recognition, which reduces processing, which allows improved performance through lack of overload. The max is a dog, but Boeing would have got away with it (again) if pilots had been sim trained.

These pilots were overloaded, they weren't adequately prepared and the aircraft is flawed.
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Old 26th Apr 2019, 16:47
  #4386 (permalink)  
 
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Originally Posted by HundredPercentPlease View Post
.
These pilots were overloaded, they weren't adequately prepared and the aircraft is flawed.
Agree 100%. So what should be done to insure the next crew is not overloaded and unprepared the next time they are handed a flawed, but still flyable, aircraft?

Because there will be a next time.



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Old 26th Apr 2019, 16:57
  #4387 (permalink)  
 
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Simple.

Remove the flaw. Either remove the aerodynamic stability problem or make the FBW fix a proper one (like an Airbus, triple inputs, 14 computers, multiple layers of automatic or selectable degraded flight modes).

Train the pilots. If a single failure (here AoA) causes a monster, then prepare the pilots by training.

As someone who has moved back and forth, twice, between the 737 and A320, I can't begin to describe how lowly I view the Renton tractor. Boeing made a flawed aircraft and failed to mandate sufficient training. The pilots are as much victims as the passengers. No doubt at all.
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Old 26th Apr 2019, 17:07
  #4388 (permalink)  
 
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Originally Posted by 737 Driver View Post
Wonkazoo,
Ultimately, these planes were flyable using some pretty basic airmanship skills, but that did not happen.
No.
Look I agree with most of what you're saying. Good airmanship, hand flying practice, all the other great points.

But this is different to any other aircraft system failure that I can think of.

Eg loss of pitot. Loss of static. Engine fire. "QF32" uncontained failure causing multiple control system failures. Flap/slat wrong config at takeoff. Dual engine out after bird strike... Etc.

These are all single events that put the aircraft in a new and interesting state. Now use good airmanship to recover. Fine.

Why is MCAS different?
1) It's intermittent. Not just a single event. Pops up unexpectedly for a few seconds then disappears. These are always the hardest faults to diagnose.
2) It's insidious - hidden by noise and by human expectation (hiding in plain sight - bursts of trim are normal).
3) It's fast - it can put you in serious trouble in a few seconds flat
4) Like a bacterial complication to a viral infection, it creeps in and hits you when you're dealing with another problem (airspeed unreliable/stick shaker)
I'm not saying that the ET302 pilots had no room for improvement. Like you I think their repeated autopilot engagement is a red flag. But dealing with MCAS failure is in test pilot league, not 'basic airmanship skills'.
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Old 26th Apr 2019, 18:31
  #4389 (permalink)  
 
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Inherent stability and "help

Salute!

@ 100% We went thru a lot of the issue concerning stability and such on the 447 thread.

The more we saw of the AB330, and the FDR traces, the more it was apparent that the thing was and is a good design. So smooth an entry to the stall that the crew did not understand why the sucker wasn't reponding to stick commands.

Many of the bent wing designs have obvious clues when you are gettiing to high AoA. Buffet, wing rock, maybe aileron reversal and so forth. Others are smooth and stick shakers or pushers can save the day.

The AB330 does not appear to be statically neutral from what we saw, but the control laws make it appear so. If you use a gee command for pitch, then you will not have speed stability WRT AoA or Q. Duhhhh? Then I see the 737 with the STS kludge and I cannot find enuf early 737 data to indicate a need for the STS when the dinosaur model was certified.

One and not the only reason that a good FBW implementtion helps the $$$, is you can fly with less trim drag by using the stab to keep the tail up than forcing the nose down. My trusty Viper was and is the classic case. However, I do not think that Airbus developed the 320 and subsequent FBW models to be inherently speed neutral or have much longitudinal stability issues. Sure, you could get away with some aft cee gee, but could always fly the plane as you would any other. I"m not even sure if the USAF F-22 and F-35 have the same longitudinal stability properties as the F-16. Their demo routines show stuff that we Viper drivers couldn't dream of, primarily the really high AoA stuff.

Gums sends...



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Old 26th Apr 2019, 20:45
  #4390 (permalink)  
 
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Learned a lot

Amazing thread. I always believed that the 737NG was a redesigns similar to the 747-400 - shocking to here it is still FBC.
I saw that reference was made to the AF447 crash - truly shocking. And very helpfull. The AF crash makes very clear that problematic pilot skills are not at all related to the mother country of the airline in question. And that makes the discussion about possible pilot shortcomings in relation to the 737Maxs crash bearable, because one thing is clear: Nothing becomes worse than errors made during the AF crash, and this was a true European airline’s crash.
(Same goes for AirEgypt 990 and Germanwings 9525)

Written by a surprised Pax.
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Old 26th Apr 2019, 21:18
  #4391 (permalink)  
 
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Fly the damn aircraft....

Originally Posted by HundredPercentPlease View Post
Simple.

Remove the flaw. Either remove the aerodynamic stability problem or make the FBW fix a proper one (like an Airbus, triple inputs, 14 computers, multiple layers of automatic or selectable degraded flight modes).

Train the pilots. If a single failure (here AoA) causes a monster, then prepare the pilots by training.

As someone who has moved back and forth, twice, between the 737 and A320, I can't begin to describe how lowly I view the Renton tractor. Boeing made a flawed aircraft and failed to mandate sufficient training. The pilots are as much victims as the passengers. No doubt at all.
There will never be a flawless aircraft or flawless maintenance or flawless training or flawless pilots. But at the end of the day, it is the pilots and their passengers who will be on the receiving end of these inevitable flaws. Thus our focus and our determination to overcome those flaws ought to be greater.

Throughout the history of aviation, pilots have been handed unique malfunctions or adverse situations for which there was no prior history, no procedure, no checklist. Many of these situations were also initially confusing, mentally taxing, and potentially paralyzing. Some crews performed, if not flawlessly, at least well enough to stabilize the situation and get the aircraft safely back to earth. Some crews did not.

In a remarkable number of these events, the difference between success and failure came down to the exact same answer - the crew's ability to overcome the startle effect, look past the distractions, and focus on the basics of flying the aircraft. Turn off the automation, set the proper attitude, set the power, trim out the control forces, monitor the performance, move the aircraft away from the threat. The pilots don't have to be perfect or diagnose the problem right away. Fly the aircraft and buy some time. Very, very few of our non-normals need to be executed so fast that we can't first devote the majority of our attention and the necessary time to flying the aircraft.

Training is key, but it has to be the right kind of training. Training scripts in the simulator where you pretty much know not only the problem but the answer ahead of time do little to prepare a pilot for the visceral challenges of the unexpected. Overemphasis on automation to the point that even seasoned pilots feel that tad bit of discomfort when the autopilot and autothrottles click off is a definite warning sign. When all goes to hell, do you have a good idea - right now - where the aircraft pitch and power and airspeed should be for takeoff? low altitude? high altitude? missed approach? Do you know your memory items and limitations cold? If not, you have some homework to do.

It is too late to save the crew and passengers of these two accident, but it is not too late to learn from them. Some commercial pilots have stated here that they could not have done any better, and I'm here to say that is a cop out. If you are a commercial pilot and feel that you cannot - under the duress of distracting warnings and information - turn off the automation, set a reasonable pitch and power setting, establish a climb, hold a heading, and trim the controls as necessary, then you need to do something about that right now.
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Old 26th Apr 2019, 21:58
  #4392 (permalink)  
 
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Originally Posted by HundredPercentPlease View Post
When I was trained on the 737 (classic and NG), the stab trim runaway was a runaway - where the trim wheel ran continuously. We would identify it as a runaway, because it was continuously running, and flick the switches.

1. MCAS activation is not continuous, it's bursts.
2. The 737 trim system likes to provide bursts of random trim at certain times (STS) so bursts are considered normal.

This is why the Boeing excuse "they should have done the runaway stab QRH to fix the MCAS problem" is a load of utter nonsense. 737 Driver - pinning this on lack of airmanship will costs lives in the future.
Back in November 2018 Boeing issued a bulletin about the MCAS Stab Trim problem and many airlines responded by removing the word “CONTINUOUS” from the Runaway Stabilizer checklist.



Last edited by Lost in Saigon; 27th Apr 2019 at 03:24. Reason: Photo of checklist added
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Old 26th Apr 2019, 22:01
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Originally Posted by Lost in Saigon View Post


Back in November 2018 Boeing issued a bulletin about the MCAS Stab Trim problem and many airlines responded by removing “continuous” from the Runaway Stabilizer checklist.

What exactly was the MCAS Stab Trim problem?
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Old 26th Apr 2019, 22:37
  #4394 (permalink)  
 
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Originally Posted by 737 Driver View Post
..., and I'm here to say that is a cop out. If you are a commercial pilot and feel that you cannot - under the duress of distracting warnings and information - turn off the automation, set a reasonable pitch and power setting, establish a climb, hold a heading, and trim the controls as necessary, then you need to do something about that right now.
Of course everyone here can do that. The ET crew could do that. Do you really think that an 8000 hour 737 captain didn't know how to do that?

You are missing the point - which is why they didn't do that. Or maybe why they couldn't do that. Or most importantly, why you may not do that as some point in the future.

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Old 26th Apr 2019, 23:15
  #4395 (permalink)  
 
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Originally Posted by Bend alot View Post
What exactly was the MCAS Stab Trim problem?
The “problem” was explained in the Boeing Bulletin issued back in November 2018 after the Lion Air accident.

“Uncommanded nose down stabilizer trim due to erroneous Angle of Attack during Manual flight only”

Ethiopian airliner down in Africa
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Old 26th Apr 2019, 23:26
  #4396 (permalink)  
 
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Originally Posted by HundredPercentPlease View Post
Of course everyone here can do that. The ET crew could do that. Do you really think that an 8000 hour 737 captain didn't know how to do that?
There is no practical difference between a pilot who does not have certain skills and a pilot who cannot demonstrate those skills when needed.

You are missing the point - which is why they didn't do that. Or maybe why they couldn't do that. Or most importantly, why you may not do that as some point in the future.
Actually, this is exactly my point. I'm sure on nice sunny day with no distractions, or maybe with a jumpseater who could provide a third set of eyes, or perhaps during a pre-briefed sim session when they knew the malfunction was coming, either the Captain or First Officer could have parked the pitch at 10 degrees, set the power to 80% N1, trimmed the stab up to neutral no matter what spurious inputs the automation was making, and flown safely away from the ground. Unfortunately, in the real world we do not always have the luxury of being free from distractions, or having that jumpseater, or having our emergencies pre-briefed.

Why indeed could these crews not perform to the standards expected of a commercial pilot? Perhaps automation dependency and lack of hand-flying experience? Maybe an airline and training culture that emphasized rote procedures or systems management over basic airmanship skills? Sim training that was long on following scripts and checklists and short on big picture flying? First Officers that were light on experience and/or discouraged from speaking up when necessary? Perhaps some personal issues with the specific individuals? I could go on, but this would be a good start. I suspect the various accident boards will be looking at all these issues.

Yes, they could have and they should have but they didn't. That is why the human factor element of these accidents cannot and should not be ignored.

Last edited by 737 Driver; 26th Apr 2019 at 23:37.
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Old 26th Apr 2019, 23:44
  #4397 (permalink)  
 
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Originally Posted by Lost in Saigon View Post


The “problem” was explained in the Boeing Bulletin issued back in November 2018 after the Lion Air accident.

“Uncommanded nose down stabilizer trim due to erroneous Angle of Attack during Manual flight only”

Ethiopian airliner down in Africa
It is interesting that the revised runaway trim card in the official emergency AD is significantly different from the one in above, the note about using manual electrical trim was moved to the bottom and is not directly below the 'action' items. See page 7:

http://rgl.faa.gov/Regulatory_and_Gu...2018-23-51.pdf

Would a pilot converting to MAX in November have seen the Boing bulletin or just the revised per emergency AD manual?
Are the bulletins typically discarded when an official AD is issued?

Both of them talk of 'higher control forces may be needed' they do not specifically state that the manual trim might be unusable in a significantly mistrimed state.
Would be easy to read that as referring to column forces, especially by a someone not trained in the 'unloading'/ roller coaster maneuver

Last edited by MurphyWasRight; 27th Apr 2019 at 00:07. Reason: Added Comment on forces
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Old 27th Apr 2019, 00:03
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Originally Posted by MurphyWasRight View Post
It is interesting that the revised runaway trim card in the official emergency AD is significantly different from the one in above, the note about using manual electrical trim was moved to the bottom and is not directly below the 'action' items. See page 7:

http://rgl.faa.gov/Regulatory_and_Gu...2018-23-51.pdf

Would a pilot converting to MAX in November have seen the Boing bulletin or just the revised per emergency AD manual?
Are the bulletins typically discarded when an official AD is issued?
Also with the inclusion of "up to 10 seconds" clearly directed at MCAS - by MCAS not reference in either document.

Seems like a cover up - a non cover up would have given pilots more tools, like a L/H AoA failure can cause...............
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Old 27th Apr 2019, 00:21
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Originally Posted by MurphyWasRight View Post
Both of them talk of 'higher control forces may be needed' they do not specifically state that the manual trim might be unusable in a significantly mistrimed state.
I don't know for sure, but I think this statement might be a reference to activation of the Elevator Feel Shift Module (EFSM). This module is one of the 737 systems that may be activated by a stall signal from the Stall Management Yaw Damper (SMYD) computer. Activation is accompanied by annunciation of the FEEL DIFF PRESS light which is one of the symptoms mentioned in the AD.

Relevant quote from the 737 Aircraft Maintenance Manual (AMM)

EFSM Operation

At stall onset, either SMYD sends a signal to energize the dual coil solenoid valve on the EFSM. The EFSM operation occurs when all of these conditions occur:
• Stick shaker is active
• AOA is 8 to 11 degrees more than thermal anti-ice (TAI) biased stick shaker AOA
• EFSM is not inhibited due to low altitude or the airplane is on the ground.

When all of these conditions occur, the SMYDs energize the dual coil solenoid valve. The solenoid valve sends 3000 psi system A pressure to the pressure-operated mode valve. The mode valve opens and sends pressure between 820 psi to 880 psi from the pressure reducer to the system A side of the dual feel actuator. This increases the control column feel forces up to four times nominal feel. The increased feel force makes sure the pilots cannot easily override automatic stabilizer movement to nose down pitch of the airplane.
The FCOM has similar (though less detailed) information, though oddly it states the control forces only double.

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Old 27th Apr 2019, 01:37
  #4400 (permalink)  
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I've tried to look into the minds of the pilots in the latter part of this thread. I've even suggested that the ET PF's prior knowledge may have been counterproductive. The realisation that he is experiencing the same set of issues that were disastrous only months ago may have been truly alarming, countering any advantage he could have gained by having prior knowledge.

Suppose he was fixating on the attitude - he knows it's what he's supposed to do in this scenario. But he's also learned the autopilot could take the technical problem away and so frantically stabs at that a few times. Remember, things are very, very unreal to him at this time. Someone retorted that he didn't remember the flaps shouldn't be raised. Fair comment, but only recalling part of a briefing is not surprising at this moment.

So what's happening if he was focussing on the attitude? One thing's reasonably certain - he will* experience some tunnel vision. Not optical, but a kind of narrowed visual processing. Could it conceivably be enough to stop him seeing the wheel's white flashes? It seems impossible but how else is that protracted period of automatic spining explained? Is it the STS working harder, since the power is still high? I doubt he was that analytical with his hands full and being deluged with bad news.

*Being human is having more sub-processing going on that in the Boeing. We've all seen the spinning radar head change direction, despite knowing it hasn't. Or the Necker wire frame cube. We know that a sudden change happens, but what is incredible is that in most humans, it happens after a given number of seconds. That is very serious interference with our concious processing. Just an amusing bit of psychology, until you realise just how susceptible we are to our minds doing their own thing. A lot goes on that we can not escape from. Training around illusionary effects of acceleration and the products of fear is all we can do, and that's easier said than done.
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Last edited by Loose rivets; 27th Apr 2019 at 12:50. Reason: Cranking changed to Spining as former implies hand cranking
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