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Ethiopian airliner down in Africa

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Ethiopian airliner down in Africa

Old 6th Apr 2019, 11:12
  #3441 (permalink)  
 
Join Date: Feb 2015
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Grounded Fleet

Can anybody report whether any kind of functionality checks are being performed on the grounded fleet?
eg. Wiring/ FOD/ AoA etc. Plenty of time now for that..
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Old 6th Apr 2019, 11:46
  #3442 (permalink)  
 
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Originally Posted by George Glass View Post
The B737 is a very simple aircraft with lots of bells and whistles, most of which are nice to have, not must have.
The original B737 may have been that, the MAX is not. If it were. you wouldn't need MCAS to certify.
AFAIK, the MAX is certified as a B737 amendment. That may be wrong. If MCAS is necessary to certify, the aerodynamics are radically different.
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Old 6th Apr 2019, 11:50
  #3443 (permalink)  
 
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Originally Posted by Airbanda View Post
Was about to post same question. Have other incidents been reported?
Well, one was, just a few minutes ago:

Originally Posted by astonmartin View Post
Iíve had a false stick shaker on the B737 during rotation at take-off once. I agree with others that this is a huge distractor. After confirming that it is false, and change of controls, it is not only distracting, but also annoying.
The poster hasnít stated what caused the stick shaker at rotation, it could have been rogue AOA, but it could also have been something else.

Also didnít state whether it was a MAX and caused MCAS.
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Old 6th Apr 2019, 11:55
  #3444 (permalink)  
 
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Originally Posted by coaldemon View Post
they went through VMO within about 2 minutes. From there they kept accelerating. All the way to 500 kts
No, they didn't "keep accelerating". They flew at or around Vmo for almost 3 minutes. It was only in the last 30 seconds of the flight, as they were rapidly losing altitude, that airspeed got anywhere near 500 kts.

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Old 6th Apr 2019, 11:55
  #3445 (permalink)  
 
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Gergen,
I beg to differ. MCAS is only there to ensure the control column force required to increase pitch does not decrease at high angles of attack.
It is a certification requirement. The aircraft will fly perfectly happily without it.
Disconnect and fly the aircraft.
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Old 6th Apr 2019, 11:57
  #3446 (permalink)  
 
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Originally Posted by EDLB View Post

+1

The 737 safety philosophy means that it turns into a conventional stick and rudder aircraft once you turn the AP off. And that with redundant left and right seat set of controls. The PF assumes in AP off mode that he has full authority on the flight controls and surfaces. There are automatic flap retract in over speed left but that does not reduce his controll over the aircraft.
If you brake that philosophy by introducing ďfeaturesĒ overriding PF control inputs they need to be full FBW worth with all fail safe features needed for a FBW control.


With the two accidents it came out, that the manual trim wheel can not be actuated manually in a high elevator deflection and high speed situation.



Your first point is the heart of the matter. When faced with any aircraft control problem, the pilot needs to be able to quickly revert the aircraft to a configuration in which he knows what he is dealing with. In the old style mechanically controlled planes such as the 737, this was easily achieved with the autopilot disconnect button. Further, old guys like myself, grew up with these systems. I started flying transport category aircraft when an autopilot was simply a wing leveler and pitch or altitude hold. Manual flight was routine for climbs and descents. My generation needed to be encouraged to embrace auto flight as it matured. We were spring loaded to dump it and manually fly if we got behind. As the years moved on we started to have new/younger pilots whose only experience was systems, auto flight and flight management computers that could handle all phases of flight except initial takeoff. We were encouraged to use these systems fully to reduce workload and to increase our ability to maintain a lookout for traffic, terrain, volcanic cloud, cb, whatever. This advancement was wonderful but it also came with a problem. Over time, hand flying skill and instrument scan was degraded, especially in those who did not have a lot of experience hand flying in vertigo and anxiety inducing circumstances. This resulted in a disability where autoflight could, depending on the individual, become a crutch rather than a tool. The pilot with this disability needed, in any crisis, to first get auto flight operating. This is not a big problem in most circumstances but is a very big problem when the issue is basic aircraft control.

To your second point. I do not know if this is a fact and it seems like it should have been a certification issue if it is. I would not accept any simulator demonstration but would expect that it has been demonstrated in the actual aircraft that the manual, hand crank, stab trim is operable throughout the envelope of the aircraft, speed up to Vmo, altitude, thrust setting, g loading, Cg. If this was not done, it is a problem. If there is a speed limit to manual stab operation, the pilots should be told, even it is just a note that it was not demonstrated to work in excess of Vmo , or whatever speed it was tested to.
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Old 6th Apr 2019, 11:58
  #3447 (permalink)  
 
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Originally Posted by Derfred View Post


Well, one was, just a few minutes ago:



The poster hasnít stated what caused the stick shaker at rotation, it could have been rogue AOA, but it could also have been something else.

Also didnít state whether it was a MAX and caused MCAS.
If you had the shaker on rotate, you wouldn't be raising the flaps in a hurry so at least MCAS wouldn't start retrimming the plane at low altitude.
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Old 6th Apr 2019, 12:01
  #3448 (permalink)  
 
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Originally Posted by Albino View Post
You need to go and read step 2 again. It wasn't completed, at any point after the MCAS AND.
One could argue that you can skip step 2 when the A/P is not engaged.

I don't think the runway stabilizer memory items cover all possible runway situations properly, especially when MCAS is involved. A step 2.5 asking you to try to bring the trim back to neutral using the thumb switches, before applying the cutoff switches, wouldn't hurt, in my opinion.

And having in mind that the current version of MCAS will re-activate in 5 seconds, it should also tell you to use the cutoff switches as soon as possible after you bring the trim to neutral, in under 5 seconds after your last electric trim use. With the new MCAS version that will hopefully no longer be needed.

There are plenty of things the accident crew could have done better, and they clearly made mistakes. I think using the cutoff switches before bringing the trim to neutral was one of their smallest mistakes, if you can even consider it a mistake.

Boeing and the FAA claiming, after the Lion Air crash, that the existing procedures for dealing with a runway stabilizer are sufficient to address the MCAS issues is a much larger mistake, in my opinion.

And the elephant in the room is that manual trimming with the trim wheels can be extremely hard, or even impossible to do, when you apply a lot of nose up elevator depending on the airspeed.

In addition to the MCAS fixes, I think this is one of the problems the FAA and Boeing need to address, not only for the MAX, but for previous models as well.

Unfortunately I don't see an easy solution for that particular problem. Some complex changes might be needed. For example an additional electric trim circuit and motor as a backup for the main one.
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Old 6th Apr 2019, 12:02
  #3449 (permalink)  
 
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Originally Posted by George Glass View Post
Gergen,
I beg to differ. MCAS is only there to ensure the control column force required to increase pitch does not decrease at high angles of attack.
It is a certification requirement. The aircraft will fly perfectly happily without it.
Disconnect and fly the aircraft.
That seems to be the problem - you can't disconnect MCAS without defeating the trim motors and there now appears (from the ET report) to be a problem in retrimming manually with a lot of back-stick. The other way would be to run down a stage of flap, which should stop MCAS interfering but it's hard to see a procedure which called for that getting approval.
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Old 6th Apr 2019, 12:13
  #3450 (permalink)  
 
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One could argue that you can skip step 2 when the A/P is not engaged.
Seriously?

Aircraft is trimming badly forward when you donít want it to. Try trimming it back then trim cutout. If that doesnít work then trim cutout anyway. Youíre a pilot.
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Old 6th Apr 2019, 12:36
  #3451 (permalink)  
 
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Originally Posted by Derfred View Post
Seriously?

Aircraft is trimming badly forward when you don’t want it to. Try trimming it back then trim cutout. If that doesn’t work then trim cutout anyway. You’re a pilot.







I'm not saying it's a correct argument, personally I don't think you should skip step 2, but I've seen some people arguing that. So there is some confusion about those memory items.

But, in any case, the problem is you have only 5 seconds to use the cutout switches before MCAS does it again. If you delay that by only a few seconds, you end up with an out of trim aircraft. No matter how you look at it, that is not ideal.

And the Ethiopian crew did trim it back partially before using the cutout switches. They probably felt the trim they applied was sufficient to make the aircraft controllable enough at that point, and didn't want to risk applying more with the stick shaker active.

And assuming it's not MCAS, but a regular trim runaway that can't be stopped or reversed with the thumb switches, you will be out of trim after using the cutout switches. Both on the MAX and also on older models. Not easily being able to then correct the trim with the trim wheels in that situation is a big problem.

My point is that, even if you don't skip step 2, and I don't think you should skip it, you can end up in the same situation they did, depending on the type of runaway you are experiencing.
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Old 6th Apr 2019, 12:40
  #3452 (permalink)  
gmx
 
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Originally Posted by GordonR_Cape View Post
2. In the event of AOA failing nose up and MCAS activating (25% odds), there is an overwhelming fatality rate. There are no known survivors other than the preceding Lion air flight, and unfortunately that airframe was destroyed the very next day, so there is little evidence to strip down and examine (apart from the FDR).
Does this provide some context on the relative scarcity of such occurrences?
​​​​​​A disconcerting mystery is why the crew of the preceding LionAir flight didn't feel like they had miraculously dodged an insidious malfunction, and instead handed the aircraft to the next crew with little warning of the mortal danger that lay ahead. And why the airline allowed the vehicle back into the air after an emergency had been declared on that preceding flight, without fully understanding the nature and source of the flight control issues experienced.

For some reason I'm less concerned about the automated flight control issue than the fragility of the safety processes enacted in the event of a declared emergency. If that Lion aircraft had been grounded immediately following the pre-accident flight ...
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Old 6th Apr 2019, 12:49
  #3453 (permalink)  
 
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Originally Posted by MemberBerry View Post
One could argue that you can skip step 2 when the A/P is not engaged.
Just to confirm, I'm talking about 'Control airplane pitch manually with control column and main electric trim as needed'

This is pretty basic stuff.
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Old 6th Apr 2019, 12:53
  #3454 (permalink)  
 
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Originally Posted by GordonR_Cape View Post
I agree that such data would be very useful, but suggest two reasons why it has not been forthcoming:
1. If AOA fails nose down (50% odds), there will be no stick shaker or stall warning or MCAS activation, and it would probably be a non event, written up for maintenance, or reported to the NASA hotline. Conversely if AOA fails nose up on the 'non-MCAS' side (25% odds), there will be stick shaker activation, but it will not be flight critical, and the fault will be repaired. In neither case will the airframe be examined in any detail.
2. In the event of AOA failing nose up and MCAS activating (25% odds), there is an overwhelming fatality rate. There are no known survivors other than the preceding Lion air flight, and unfortunately that airframe was destroyed the very next day, so there is little evidence to strip down and examine (apart from the FDR).
Does this provide some context on the relative scarcity of such occurrences?
As was stated before the AoA vanes are not new equipment and are the same on all the NGs and probably the Classic. There are vast numbers of these flying and as you state they would be just maintenance issues, but all those issues go into analytics and Boeing would have known their failure rate on designing the Max. In knowledge of that failure rate they felt failures were improbable to highly improbable. They also felt that a crew given significant uncommanded nose down trim would immediately trim back nose up and a second uncommanded nose down would result in the crew trimming back nose up then switching off the Stab Trim. It was certainly not expected that a crew would attempt to fly with significant pull force and _not_ trim back. As someone upthread stated trimming is second nature. So add to your probabilities extremely rare failure of AoA vane and Full expectation that 99.9% of PF would trim back to in trim if MCAS did operate incorrectly giving significant uncommanded nose down trim and after 2 or at worst 3 trim back would switch off Stab Trim.
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Old 6th Apr 2019, 12:54
  #3455 (permalink)  
 
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The MCAS put the aircraft into an almost (or totally) unrecoverable situation at low altitude and no BS about untrained inexperienced pilots is worth a pinch of rocking horse poo.
Sunfish

I cannot concur here.
The Boeing software design error is proven and accepted. Thats not the point here though.This crew did not fly the plane. Single side UAS after takeoff is not difficult.The stick shaker is a huge distraction but they are commercial aircrew acutely aware of the Lionair precedent.They know about MCAS and how it can be triggered in manual flight with flaps UP.Like all good aircrew they will have formulated a plan of action which will help them focus and overcome the danger of the stick shaker and its effect on the human brain's ability to think.
They will brief on what they will do....for every departure!
ISFD and FO ASI are functioning and in agreement.The Captain need only hand control to the FO and instruct him to fly a manual visual pattern at 1500 keeping takeoff flap
setting and land immediately..Right hand on the stick,left hand on the thrust levers,feet guarding the rudders.Fly the plane.
Boeing UAS NNC not applicable here! Just land the plane.
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Old 6th Apr 2019, 12:56
  #3456 (permalink)  
 
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Good info here:

https://theaircurrent.com/aviation-s...nvestigations/
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Old 6th Apr 2019, 13:20
  #3457 (permalink)  
 
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Originally Posted by CodyBlade View Post
Thanks for the link - very disturbing info.
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Old 6th Apr 2019, 13:46
  #3458 (permalink)  
 
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Humble SLF here, wondering if there's a general rule about speed/autothrottle in a runaway stabiliser situation?

The emergency AD issued by the FAA doesn't appear to say anything about speed. Is this just a matter of common sense among pilots, or would the PF have felt that it was sensible to keep the speed high to counter nose-down and hopefully gain altitude? Did he disobey the AD?
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Old 6th Apr 2019, 13:54
  #3459 (permalink)  
 
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Originally Posted by Albino View Post
Just to confirm, I'm talking about 'Control airplane pitch manually with control column and main electric trim as needed'

This is pretty basic stuff.
Yes, and I agree. But then you could then argue it shouldn't even be included in the memory items, and all the discussion about step 2 is irrelevant here.

It's not exactly the same situation but, I looked again at Mentour's video that demonstrates the runaway stabilizer memory items. They already have the A/P disconnected when the runaway starts, and the thumb switches are not working at all during the runaway. He does try to use the thumb switches to control the trim, but then so did the Ethiopian crew.


This is how it went (some small details omitted):

17:18 - runaway starts
17:28 - Mentour (PF) - "I'm not doing that"
17:40 - F/O (PM) identifies the issue as a runway stabilizer
17:50 - Mentour asks the F/O to perform the runway stabilizer memory items
17:55 - F/O - "control column: hold firmly"
17:57 - Mentour - "holding firmly"
17:59 - F/O - "auto pilot - disengage"
18:01 - Mentour - "autopilot is disengaged"
18:04 - F/O - "auto throttle - disengage"
18:07 - Mentour - "if you can do that for me please"
18:09 - F/O - "disengaged"
18:11 - F/O - "if it continues, I will go with the stab trim cutout switches"
18:13 - Mentour - "ok, let's evaluate this to see if it's moving"
18:20 - F/O - "memory items for the runaway stabilizer complete"
18:21 - Mentour - "yeah, let's evaluate"
18:25 - Mentour - "I have no authority of the trim at the moment"
18:29 - F/O - "roger"
18:32 - Mentour - "I can't control it manually, so it doesn't really work, so if you can continue with the memory items please"
18:37 - F/O - "memory items - stab trim cutout switches to cutout"
18:40 - Mentour - "Continue"
18:41 - F/O moves the switches to the cutout position
18:42 - F/O: "Cutout"

So, between the start of the runaway and using the cutout switches it takes them 83 seconds to perform the runaway stabilizer memory items. With no additional failures and alarms that can distract them and increase their workload. With that in mind, do you think the stabilizer runaway memory items are adequate for dealing with an MCAS failure induced by an AOA sensor failure?

My guess is the Ethiopian crew was aware they could be dealing with MCAS, so they actually skipped some memory items and other procedures to stop MCAS as soon as possible:

05:40:00 - first MCAS AND trim
05:40:12 - pilot ANU trim
05:40:20 - second MCAS AND trim
05:40:27 - the Captain advised the First-Officer to trim up with him
05:40:28 - pilot ANU trim
05:40:35 - the First-Officer called out “stab trim cut-out” two times. Captain agreed and First-Officer confirmed stab trim cut-out.
05:40:41 - third MCAS attempt to apply AND trim, but it doesn't affect trim anymore

They did all that in under 40 seconds.

It's funny. Until the preliminary report was released many people were arguing that the cut-out switches should be used as soon as possible when you are dealing with an MCAS failure. Now people say that you should first bring the aircraft is in perfect trim before doing it. So basically that you should use the cutout switches in a 5 second interval, not too soon, and not too late, or it's pilot error. I disagree. This is not a fighting video game when you have to mash the right sequence of buttons with the right timing to produce a "combo". That's not OK when the lives of hundreds of people are at stake.
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Old 6th Apr 2019, 13:57
  #3460 (permalink)  
 
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Originally Posted by Albino
Just to confirm, I'm talking about 'Control airplane pitch manually with control column and main electric trim as needed'
So what are we doing here, flying by memo? Boeing should have revised the Stabiliser Runway memory procedure!

It knew it had a deathtrap on it's hands, why didn't it insert a line into the memory procedure about trimming to neutral and then switch off the stab trim?

All the background is lovely stuff, but Boeing, you're the experts, give me a couple of lines to hang my hat on and I will not crash the aeroplane. That's what memory items are for, are they not? Certainly, the current Stab Runaway is not appropriate in these cases where the stab had already lost the plot.
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