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Ethiopian airliner down in Africa

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Ethiopian airliner down in Africa

Old 3rd Apr 2019, 11:47
  #2961 (permalink)  
 
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The WSJ article quoted above says that the Ethiopian pilots were aware of the Lion Air crash and did turn off the stab trim motors but couldn't get the nose up using the manual wheels.
MCAS is inhibited as long as the flaps are down. As the flaps are retracted (at 1000 AGL per SOP) MCAS starts to push the nose down for 5 secs, maybe twice or three times, before PF realizes whats going on .
Then per EAD trim cutout.
The plane gets faster quickly, control loads higher.
Someone would need to pull the yoke and reduce thrust, but both are trying to get the nose up with the trim wheel???
Really??.
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Old 3rd Apr 2019, 12:25
  #2962 (permalink)  
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I know HS loads has been mentioned several times, but I feel this post raises the bar.

It really spells out how ordinary mortals can be trapped into a different kind of coffin corner.

Ethiopian airliner down in Africa
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Old 3rd Apr 2019, 12:28
  #2963 (permalink)  
 
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During my 737 3-400 type rating training I clearly recall a demonstration in which stab trim was allowed to go beyond the point where manual trim could be operated due to control loads. Whether this was part of a stab trim runaway drill or an extension of demonstrating the trim system I no longer recall. The purpose was to enable awareness of the condition and practice the technique of (both pilots) hauling back on the yoke and then relaxing the pull while simultaneously clawing back a little manual trim using the wheel. This has to be repeated several times before the loads reduce enough to allow continuous trimming without unloading pull on the yoke.
I was trained in the 737-200 simulator in 1977 on the technique you described. One rather crude method of demonstrating the roller coaster sequence (and I emphasize this was purely 'playing around' and not a structured planned exercise so please no criticism) was to get airborne with the stabiliser trim purposefully set full electrical forward to see what stick force was needed to get airborne.

It required full back control column to get airborne as can imagine and we passed VR plus about 20 knots before the nose would rise. The purpose was to gain enough altitude before attempting the roller coaster method of relieving aerodynamic forces on the stabiliser. With the body angle pulled hard to 10 degrees nose up, or more if possible, against the full forward stab trim, the pull force was momentarily relaxed and the aircraft 'bunts' over (for want of a better word).

During that very short period that the aircraft is transitioning from nose high to nose low the manual stab trim wheel was able to be very rapidly wound back from full forward for about five seconds before the nose dropped and height was lost.

Both pilots then again pulled back hard against the aerodynamic force until the nose was high enough to repeat the exercise. As soon as the pull was relaxed and the aerodynamic load momentarily eased, more frantic winding back of the stab trim handles was available for another five second until the nose dropped again. It is emphasized that it is extremely hard to wind the stab trim handles back unless the aerodynamic load against the stabiliser is reduced

From this rather amateur experiment it was clear that below about 1500 feet the success of the roller coaster method of using manual stab trim was very much dependent on how high the nose could be raised above the horizon before the elevator could do no more and backward pressure let go to enable the manual stab trim to be operated relatively freely for that few vital seconds you had before pulling back on the elevator to stop the ensuing dive.

Two pilots using their combined strength was needed to keep the nose from dropping but as soon as the PF took one hand from the control wheel to wind the manual stab trim, it was difficult for the other pilot to stop the nose from dropping sharply.

Once you have seen this quite dramatic exercise demonstrated in the simulator you will never forget how to fall back if necessary on the roller coaster method of using the manual stabiliser trim to relieve the aerodynamic forces on the stabiliser.
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Old 3rd Apr 2019, 12:29
  #2964 (permalink)  
 
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Originally Posted by threemiles View Post
MCAS is inhibited as long as the flaps are down. As the flaps are retracted (at 1000 AGL per SOP) MCAS starts to push the nose down for 5 secs, maybe twice or three times, before PF realizes whats going on .
Then per EAD trim cutout.
The plane gets faster quickly, control loads higher.
Someone would need to pull the yoke and reduce thrust, but both are trying to get the nose up with the trim wheel???
Really??.
So they clean up the airplane, N1 is in the 80s or 90s, MCAS kicks in and the PF for some reason is not trimming off the loads with manual electric trim. Instead the STAB TRIM CUTOUT switches iaw the EAD are set to cutout at the most unfortunate time.They bring out the trim wheel handle and try to trim via muscle power. While thrust remains in the 80s or 90s. You're now in a place where reducing thrust will make the a/c attempt to point the nose down even further and not reducing thrust/speed will make it increasingly more difficult to rotate the trim wheel. And the person next to you has 2-300hrs total flight time... Is this how it reads?
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Old 3rd Apr 2019, 13:15
  #2965 (permalink)  
 
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...while pulling 60 pounds with the left hand only on the control column and then manually turn the aerodynamically loaded (from high speed) STAB TRIM wheel with the right hand at least a hundred revolutions, within seconds?
So are you saying there was only one pilot on the flight deck?
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Old 3rd Apr 2019, 13:34
  #2966 (permalink)  
 
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Originally Posted by threemiles View Post
MCAS is inhibited as long as the flaps are down. As the flaps are retracted (at 1000 AGL per SOP) MCAS starts to push the nose down for 5 secs, maybe twice or three times, before PF realizes whats going on .
Then per EAD trim cutout.
The plane gets faster quickly, control loads higher.
Someone would need to pull the yoke and reduce thrust, but both are trying to get the nose up with the trim wheel???
Really??.
I am not a pilot, but have read enough to think we are all seeing the same story now. Once they had passed 250kts at low altitude, they really had run out of options. This is despite what Boeing and the FAA confidently told us with the emergency AD in November. Nothing there about lowering speed or releasing the elevator, to reduce stabiliser loading under manual trim.

They also didn't have the option of putting flaps down (due to overspeed), which would have immediately inhibited MCAS. Enabling auto-pilot was equally impossible because of IAS disagree.

A reminder of the exact AD wording, which sounds so easy:
Initially, higher control forces may be needed to overcome any stabilizer nose down trim already applied. Electric stabilizer trim can beused to neutralize control column pitch forces before moving the STABTRIM CUTOUT switches to CUTOUT. Manual stabilizer trim can beused before and after the STAB TRIM CUTOUT switches are movedto CUTOUT.
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Old 3rd Apr 2019, 13:49
  #2967 (permalink)  
 
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If the reports of the Ethiopian pilot’s difficulties after following the procedure are correct, either being unable to trim manually or the perception of ineffectiveness - high force slow trim rate, this would increase pressure on Boeing and the FAA.

Furthermore, if the FAA knew of this inability (NTSB rep), then how could they issues a special approval for repositioning flights with empty 737 Max.
Might the operators / unions have a view on this.

Control force discussion and EASA views (#25) in Boeing advice on "aerodynamically relieving airloads" using manual stabilizer trim


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Old 3rd Apr 2019, 14:16
  #2968 (permalink)  
 
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Correct me if I'm wrong, but as far as I am aware, there was/is nothing stopping the crew from electrically trimming the aircraft nose-level (or high even) and THEN hitting the trim cutout switches?

Notwithstanding speed or any other factors?

Yes, I'm sitting here with 20/20 hindsight as many are happy to point out, but assuming Ethiopian WAS an AOA sensor high issue (which we still have no confirmation) leading to an MCAS issue, why wouldn't the crew trim NU electrically and then in the 5 seconds before MCAS would run again, hit the cut-outs?

- GY
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Old 3rd Apr 2019, 14:44
  #2969 (permalink)  
 
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GarageYears, #3001, there is much conjecture as to a crew’s ability to detect a malfunction, where initially the trim - MCAS function is working as designed, so that it might take at least two cycles to deduce a problem (less so with increasing stick force, but this is not directly associated with trim).
Thus why fly / trim nose high if everything appears normal (except distracting stick shake, air-data alerts, low speed awareness, all of which might suggest keep the nose low).

More recently, from the EASA certification documents ‘Simulation has demonstrated that the thumb switch trim does not have enough authority to completely trim the aircraft longitudinally in certain corners of the flight envelope, e.g. gear up/flaps up, aft center of gravity, near Vmo/Mmo corner, … this description appears to relate to conventional trim assessment of trim force vs speed in level flight and not the the failure condition, (and to what extent does this simulation represent the real aircraft if the aircraft had never experienced the condition, MCAS induced extreme trim setting, + stick shake, + increased feel)
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Old 3rd Apr 2019, 14:45
  #2970 (permalink)  
 
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Originally Posted by safetypee View Post
Furthermore, if the FAA knew of this inability (NTSB rep), then how could they issues a special approval for repositioning flights with empty 737 Max.Might the operators / unions have a view on this.
My understanding (not a pilot) is that if the stabiliser trim is set on the ground, and the trim cutoff switches activated before takeoff, then the aircraft should be controllable under normal flight conditions. Keeping airspeeds below 250kts would be an extra precaution.

The FDR readout for the Lion Air flight (JT043) prior to the crash (posted on previous page) looks mostly unremarkable (stick shaker notwithstanding). Following the initial oscillations, and after the cutoff switches were activated, trim adjustments were handled manually as per normal flight parameters.

Originally Posted by GarageYears View Post
Correct me if I'm wrong, but as far as I am aware, there was/is nothing stopping the crew from electrically trimming the aircraft nose-level (or high even) and THEN hitting the trim cutout switches?

Notwithstanding speed or any other factors?

Yes, I'm sitting here with 20/20 hindsight as many are happy to point out, but assuming Ethiopian WAS an AOA sensor high issue (which we still have no confirmation) leading to an MCAS issue, why wouldn't the crew trim NU electrically and then in the 5 seconds before MCAS would run again, hit the cut-outs?

- GY
Sources differ, and that was the advice from Boeing and the FAA (see my earlier post). There is a strong suggestion that the electric trim was intentionally restricted in power, specifically to prevent runaway nose up trim. This meant that overpowering MCAS this way was not possible, though it might have made a few degrees difference before they hit the cutoff switches. The recent simulator run reported by the NY Times last week, was not encouraging: https://www.nytimes.com/2019/03/25/b...ion-error.html

Edit: safetypee has the EASA warning.
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Old 3rd Apr 2019, 15:09
  #2971 (permalink)  
 
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Very interesting video from Mentour Pilot where he simulates the Ethiopian accident in a real simulator:
Pilots did right and it went MAX wrong - MCAS

Bjørn Ferhm at Leeham:
ET302 used the Cut-Out switches to stop MCAS
The crew of Ethiopian Airlines ET302, which crashed with 157 people on board, used the prescribed Stabilator Trim Cut-Out switches to stop MCAS according to an article by Wall Street Journal today. Yet still, they crashed. We’ve had the information this could indeed be the case for several days, but we didn’t want to speculate in such a sensitive matter.The Wall Street article sites information coming from the investigation. By it, we can now reveal how it’s possible the aircraft can crash despite using the Cut-Out switches. To verify, we ran it all in a simulator together with MentourPilot Youtube channel over the last days.
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Old 3rd Apr 2019, 15:13
  #2972 (permalink)  
 
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I've flown an aircraft with constant and continuous stick shaker operation, and I can tell you it's quite disconcerting. especially when IMC and hand flying, as we were.

It's certainly going to absorb a big chunk of the reasoning power available in any flight deck.
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Old 3rd Apr 2019, 15:14
  #2973 (permalink)  
 
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From the Reuters wire a report that the MCAS may have reactivated with the stab trim switches off:

Ethiopian Airlines crash: anti-stall system 'engaged repeatedly'

Software may have redeployed without human input before plane went down, say sources
Reuters Wed 3 Apr 2019 07.02 EDT

Boeing’s anti-stall software on a doomed Ethiopian Airlines jet re-engaged up to four times after the crew initially turned it off due to suspect data from an airflow sensor, two people familiar with the matter have said.

It was not immediately clear whether the crew had chosen to redeploy the system, which pushes the nose of the
Boeing 737 Max downwards, but one person with knowledge of the situation said investigators were studying the possibility that the software had kicked in again without human intervention.

A Boeing spokeswoman declined to comment. Ethiopian investigators were not immediately available for comment.

Investigators 'believe Ethiopian 737 Max's anti-stall system activated'
Boeing’s anti-stall software, known as MCAS, is at the centre of investigations into both the Ethiopian Airlines crash last month and a Lion Air
crash in Indonesia in October, which together killed nearly 350 people.

People familiar with the investigation said the anti-stall software – which automatically pushes the aircraft’s nose down to guard against a loss of lift – was activated by erroneous “angle of attack” data from a single sensor.

The investigation has now turned towards how MCAS was initially disabled by pilots following an emergency checklist procedure, but then appeared to repeatedly start working again before the jet plunged to the ground, they said.

A directive issued after the Indonesian crash instructed pilots to use cutout switches to disengage the system in the event of problems, and leave it switched off.

Doing so does not shut down the MCAS system completely, but severs an electrical link between the software and aircraft systems, a person familiar with the technology said.

Investigators are studying whether there are any conditions under which MCAS could reactivate itself automatically, without the pilots reversing the cutout manoeuvre. Boeing is in the process of upgrading the software while adding extra training.

A preliminary report is expected within days.

The pilots manoeuvred the plane back upwards at least two times before pressing the stabiliser cutout switches to disable the system, the other person familiar with the matter said.

However, initial flight data indicates the aircraft was not in a “neutral” attitude when pilots used the stabiliser cutout switches to disable the MCAS system, the person added, making the situation harder to manage.

After the pilots turned off MCAS, the plane gained roughly 2,000ft over the next few minutes, but dived to the ground after the renewed succession of nose-down inputs from MCAS.

None of the parties involved in the investigation was available for comment.

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Old 3rd Apr 2019, 15:17
  #2974 (permalink)  
 
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Originally Posted by GordonR_Cape View Post
Sources differ, and that was the advice from Boeing and the FAA (see my earlier post). There is a strong suggestion that the electric trim was intentionally restricted in power, specifically to prevent runaway nose up trim. This meant that overpowering MCAS this way was not possible, though it might have made a few degrees difference before they hit the cutoff switches.
If I've read your post correctly I think you are getting confused with the wording. The bulletin (the one I read anyway) specifically states that MCAS can be stopped and reversed with use of the electric trim switches on the control column. The note in the Operating Instructions implies that the electric trim should be used to neutralise the pitch force required to maintain controlled flight - then placing the stab trim switches to cutout. So position the stabilizer exactly where you want it and then cut power to the system.

If the information leaked is accurate and the system was behaving as Boeing expected it to in the bulletin, this was misunderstood by the pilots.
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Old 3rd Apr 2019, 15:30
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Originally Posted by Airbubba View Post
From the Reuters wire a report that the MCAS may have reactivated with the stab trim switches off:
How is this possible? MCAS is still operational with the trim system disabled????
If this is true Boeing not only designed the MCAS system and installed it without telling the pilots, but they also failed to tell pilots it can’t be switched off, even after Lion Air crashed?
They made a procedure to deal with a runaway MCAS that is completely worthless and will not take care of the problem?

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Old 3rd Apr 2019, 15:37
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Originally Posted by ManaAdaSystem View Post
How is this possible? MCAS is still operational with the trim system disabled????
Or, were the column forces in pitch so great with the stab trim switches off that the crew turned them back on momentarily to retrim, not realizing that they could trim manually with the trim wheels?
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Old 3rd Apr 2019, 15:44
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If the 'fix' advised by Boeing post Lion Air turns out to be have been followed by the Ethiopian crew that will not reflect well on either Boeing or the FAA.

If they have got it wrong twice what else is out there? The questions will go way beyond MCAS implementation.



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Old 3rd Apr 2019, 15:46
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Albino, #3008, further to the post Ethiopian airliner down in Africa
and EASA text via Boeing advice on "aerodynamically relieving airloads" using manual stabilizer trim there could be questions about the validity of the AD procedure, at least if it was evaluated in the abnormal conditons or only in theory.

Also see the video (via SteinerN) https://www.youtube.com/watch?v=EzgBft-79U8&feature=youtu.be
Whilst it appears easier to set nose down trim, it is less so to recover back to a trimmed condition. The nose down direction might be aided by the aerodynamic forces, whilst nose up the trim wheel has to overcome them.
Also, MCAS could run the trim nose down after flap retraction - lower stab trim loads, but if speed increases due to descending flight, then back trim at a higher speed is less achievable, having to overcome much higher stab trim loads.

This is a dynamic, escalating situation. And for those following the ‘40secs time to react’ theme, consider that recognition might take two MCAS cycles 10sec trim, 5 sec pause / back trim, 15 x 2 = 30 sec, only leaves 10secs for action - select trim inhibit, then apply back trim wheel. See the video, move seat back, pull the handle out, then wind - how much, how long, if able.



Last edited by safetypee; 3rd Apr 2019 at 15:58. Reason: dynamic, 40 secs
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Old 3rd Apr 2019, 15:51
  #2979 (permalink)  
 
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Originally Posted by ManaAdaSystem View Post


How is this possible? MCAS is still operational with the trim system disabled????
If this is true Boeing not only designed the MCAS system and installed it without telling the pilots, but they also failed to tell pilots it can’t be switched off, even after Lion Air crashed?
They made a procedure to deal with a runaway MCAS that is completely worthless and will not take care of the problem?

The poster you’re responding to didn’t read the article critically enough. It says ‘may have re-activated up to four times after INITIALLY being switched off.’

It was poorly written to begin with or written to elicit reaction from people who don’t read well.
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Old 3rd Apr 2019, 15:53
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Salute!

Looking more and more like Big B needs to bite the bullet and do something with the engine mounting design and possibly the stabilizer/elevator configuration. Screw MCAS. Fix the aero problem for certification and general good handling characteristics.

It can be done, and was long ago by Lockheed, but......

Back when the earth was still cooling, Lockheed had to modify all of the Electra airliners due to harmonic vibrations and such. Hell, the wings were being ripped off! The public relations war was lost, however, and even though the fix cured the problem, had great results and the legendary P-3 Orion resulted. the damage had been done and folks wouldnt fly the thing.

I can't unnerstan why slots or slats on the nacelles wouldn't help with the pitch moments. Maybe small cannards. Reshape the nacelles?. And so forth. With many features of the old design already certified, doesn't seem to me that re-certifying without the MCAS kludge would not be as expensive as a complete new design, although the billions about to be paid for the lawsuits could influence that proposal.
_____________________________________
I tried to imagine the roller coaster procedure posted here to regain useable trim and had to laugh. Imagine the pax barfing and screaming, plus flight attendants bouncing off the overhead bins and more. And just when it seems to the SLF in seat 23A that things are under control, whooo hooo one more time!!

Gums sends...

Last edited by gums; 3rd Apr 2019 at 16:38. Reason: added rationale
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