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 6th Apr 2019, 14:28
  #3461 (permalink)  
 
Join Date: Jan 2008
Location: Reading, UK
Posts: 11,140
Originally Posted by PaxBritannica View Post
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?
The 737 FCOM Runaway Stabilizer checklist reproduced in the Preliminary Report (Appendix 3) has, as Item 3: "Disengage (and do not re-engage) the autothrottle".
DaveReidUK is online now  
Old 6th Apr 2019, 14:38
  #3462 (permalink)  
 
Join Date: Feb 2019
Location: All-At-Sea
Posts: 20
The overall trim system now appears to be under scrutiny by several XAA's.

Also, what is more likely in the final dive of both crashes:

Pilots pulling with as much physical strength as they can muster to avert certain death did not think to also apply more than 2 brief blips of ANU trim to help...

Or

For the same reason manual trim is impossible in specific conditions, so is electrically operated ANU trim...

?

Seems to me that once the stab due to MCAS or runaway trim reaches a certain point it is unrecoverable without the old roller coaster manouvre few have been trained on or practiced. And possibly not just the Max.

I hope I am wrong of course, but this story may yet have further twists and turns to come.


Just the fax maam is offline  
Old 6th Apr 2019, 14:59
  #3463 (permalink)  
 
Join Date: Mar 2018
Location: Central UK
Posts: 356
Let's not forget that the manual trim may only become immovable at or near max stabiliser travel at normal airspeeds.
It is more than a bit harsh to criticise Boeing when the pilots so mishandle (overspeed) the aircraft it is completely out of all parameters for the trim to work, and neither do they take any recovery action - ie slowing down.
Additionally, Boeing would not expect or anticipate a crew allowing the trim to get so far out of position, the rollercoaster method was a confidence demo to show that even if you did let the trim go to extremes it could never normally achieve in reality it was still recoverable. These pilots did let it get there.
If the pilots don't fly the aeroplane/procedures properly how can Boeing's procedures be expected to cope with that?
There's no certification need or requirement to have manual trim operable at full deflection above VMO - how could there be?
meleagertoo is offline  
Old 6th Apr 2019, 15:05
  #3464 (permalink)  

Only half a speed-brake
 
Join Date: Apr 2003
Location: Commuting home
Age: 42
Posts: 2,710
Like a tiny little go-pro, recording a 10 minutes loop onto a titanium-encased SD card with a radio-isotope pinger. Good question why no such thing is already commonplace for at least 15 years. Asking out loud will not win you friends, but the answers are a great research material.
FlightDetent is offline  
Old 6th Apr 2019, 15:10
  #3465 (permalink)  
 
Join Date: Mar 2002
Location: Seat 0A
Posts: 7,872
It is more than a bit harsh to criticise Boeing when the pilots so mishandle (overspeed) the aircraft it is completely out of all parameters for the trim to work, and neither do they take any recovery action - ie slowing down.
So we're test pilots too now? No mention anywhere by Boeing of keeping the speed down, these guys were probably totally focussed on the MCAS issue, not your bog-standard UAS/80%. Ask yourself: when did you last pull off a handful of thrust at 1000ft above ground, straight after takeoff with the stick shaker going? I would suggest that some pilots don't even touch the thrust levers after takeoff normally, let alone have it in their muscle memory to do it when all hell has just broken loose.

I suspect watching the crew deal with the multitude of alarms and contradictory instruments readings, plus proximity to the ground, on the two Lionair and one ET flight would focus professionals minds a lot more on the human factors issues of these emergencies...
Any professional pilot would already have a very good visual concept of what happened here. Absolutely no need to watch someone dying, thanks.
Capn Bloggs is offline  
Old 6th Apr 2019, 15:24
  #3466 (permalink)  
 
Join Date: Mar 2018
Location: Central UK
Posts: 356
When all's said and done there was one thing and one thing only missing that on it's own would have totally prevented all this, from LionAir onwards.

I hope I'm not banned for using foul and profane language but the followiing contains adult concepts that some may find deeply offensive and disturbing.

Spoiler
 

Last edited by meleagertoo; 6th Apr 2019 at 16:25.
meleagertoo is offline  
Old 6th Apr 2019, 15:31
  #3467 (permalink)  
 
Join Date: Dec 2004
Location: Southern England
Posts: 109
Originally Posted by Capn Bloggs View Post
So what are we doing here, flying by memo? Boeing should have revised the Stabiliser Runway memory procedure
It's in my memory items, right under disconnect autothrottle. Do you fly the 737? Next time you're in the sim put the stab forward to 2 units and leave it there. See how you get on, I doubt you'll consider it to be controlling the aircraft.

Originally Posted by MemberBerry View Post
He does try to use the thumb switches to control the trim, but then so did the Ethiopian crew.
From the trace they blipped it a couple of times with one slightly larger correction before the cutouts were used. If i've got this wrong then I apologise but as I see it they retained full control of the stabilizer with electric trim at all times (apart from when they cut it out) and it would have overridden any MCAS AND command. After the initial AND command the aircraft is never put back into trim.
Albino is offline  
Old 6th Apr 2019, 15:52
  #3468 (permalink)  
 
Join Date: Mar 2018
Location: Central UK
Posts: 356
Originally Posted by Capn Bloggs View Post
So we're test pilots too now? No mention anywhere by Boeing of keeping the speed down, these guys were probably totally focussed on the MCAS issue, not your bog-standard UAS/80%. Ask yourself: when did you last pull off a handful of thrust at 1000ft above ground, straight after takeoff with the stick shaker going?
The last time I pulled a handful of power 1000ft-ish from the ground with stickshaker going was probably the last time I got one in the sim - as I accelerated towards flap limiting speed having already determined on which side the error lay, with correct pilot flying and confidence in my airspeed. How 'bout you?

You must know by now that MCAS didn't (couldn't) start it's tricks until flap was retracted...er...don't you?
Question is, would Test Pilot Bloggs actually retract flap in that situation? Even if you were climbing to 4-5000agl to complete the troubleshooting what would you be doing with the power at that point? Leaving it at climb thrust like these guys? Climbing at 200Kts, Flap 5 at 6000fpm and a pitch angle of 15degrees, with a stickshalker going???? But they were flying level-ish, not climbing!
Does Boeing actually need to tell you that?

See my post #3515 above...

Last edited by meleagertoo; 6th Apr 2019 at 16:21.
meleagertoo is offline  
Old 6th Apr 2019, 16:13
  #3469 (permalink)  
 
Join Date: Dec 2018
Location: 8th floor
Posts: 0
Originally Posted by Albino View Post
From the trace they blipped it a couple of times with one slightly larger correction before the cutouts were used. If i've got this wrong then I apologise but as I see it they retained full control of the stabilizer with electric trim at all times (apart from when they cut it out) and it would have overridden any MCAS AND command. After the initial AND command the aircraft is never put back into trim.
No, I agree, they didn't fully reverse the MCAS AND trim before using the cutout switches. I was just saying that they did use the switches in the ANU direction, to reverse part of the trim applied by MCAS, not that they fully reversed it.

I can only guess why they didn't fully reverse the AND trim applied by MCAS. Maybe it was the fear of MCAS doing it again, so they hurried to use the cutout switches. Maybe it was the fear of being close to a stall, and didn't want to make any large adjustments in the ANU direction.

Also, the trim adjustment speed available to MCAS is higher than the speed available to the pilots, 0.27 units/s for MCAS vs 0.18 units/s for the thumb switches. So, if MCAS trims for 9 seconds AND, you would then need to trim with the thumb switches for 14 seconds in the ANU direction to fully reverse the 2.5 units of AND trim introduced by MCAS. Anything less than that, and you will lose the fight at some point.

Last edited by MemberBerry; 6th Apr 2019 at 16:29. Reason: corrected error about the trim direction applied by MCAS
MemberBerry is offline  
Old 6th Apr 2019, 16:45
  #3470 (permalink)  
 
Join Date: Jun 2006
Location: Brisbane
Posts: 5
Best as I can piece together from the report, the successful 11-second (approx) electric ANU trim from 0.4 to 2.3 units took place at 325-330 kts (05:40:28 to 39). Capt control column aft displacement during this time varied from 12 to 5 degrees.

The two “blips” of electric trim (suggested by some as failure of electric trim) from 2.1 to 2.3 units took place at 360-365 kts (05:43:11). Capt control column aft displacement during this time varied from 9 to 6 degrees.

Airspeeds deduced from the narrative based on the F/O’s airspeed (the presumed correct one). VMO for is aircraft is 340 kts. Control column inputs based on the FDR chart.

A question then becomes, is the difference between 325-330 kts and 360-365 kts enough to overwhelm the electric stab trim with these kind of control column displacements?

Obviously the second case is outside of design parameters, and therefore may not even be able to be tested in a simulator (unless the simulator is certified to 365 kts).

On another note: some have suggested that the “blips” would be due to severe G-forces resulting from each blip. I don’t buy it. G-forces are mapped in the FDR plot (vertical acceleration), and they are insignificant - certainly much less than the pilot-induced G-forces of the previous couple of minutes. And let’s get serious for a moment - is a bit of trim-G going to bother you if you’ve had two pilots pulling on the column for dear life for the past few minutes?

I’ve never hand-flown a B737 at 365 kts before, but I have hand-flown one at 320 kts plenty of times - and trimming is not an G-force inducing event at that speed.
Derfred is offline  
Old 6th Apr 2019, 16:51
  #3471 (permalink)  
 
Join Date: Jun 2006
Location: Brisbane
Posts: 5
Anything less than that, and you will lose the fight at some point.
That’s not entirely true, as soon as MCAS starts trimming you can stop it with a reverse blip. You don’t need to wait for it to punish you for 9 seconds.
Derfred is offline  
Old 6th Apr 2019, 16:57
  #3472 (permalink)  
 
Join Date: Dec 2018
Location: 8th floor
Posts: 0
To stop it yes. But your "blip" still needs to be 50% longer than the "blip" from MCAS, to fully reverse it.

For example if you let MCAS run for 2 seconds, your "blip" needs to be 3 seconds long to not just stop MCAS, but fully reverse what it did.
MemberBerry is offline  
Old 6th Apr 2019, 17:05
  #3473 (permalink)  
 
Join Date: Mar 2006
Location: England
Posts: 860
yo gums, F16 Guy,
Slightly off topic, but an an analogy of the 737 situation.
The only F16 experience I have, apart from sitting in the prototype at Edwards, was to fly the T33 simulation with side stick, and fixed centre stick (equally effective).
In that time frame the problem of restricting flight envelopes was being evaluated (F16?); thus with increasing AoA, at some point the nose up control was restricted and commanded nose-down preventing limit excursion. However, a high g turning departure / flick with associated roll-coupling put the aircraft above the AoA limit - now what.
The aerodynamics place the aircraft beyond a limit, the software prevents recover (situation not known).

The converse, analogy with the 737 Max is that the software puts the aircraft beyond the limit, and the aerodynamics / mechanics prevent recovery (situation not known).
PEI_3721 is offline  
Old 6th Apr 2019, 17:24
  #3474 (permalink)  
 
Join Date: Jun 2006
Location: Brisbane
Posts: 5
Originally Posted by MemberBerry View Post
To stop it yes. But your "blip" still needs to be 50% longer than the "blip" from MCAS, to fully reverse it.

For example if you let MCAS run for 2 seconds, your "blip" needs to be 3 seconds long to not just stop MCAS, but fully reverse what it did.
Correct, or you could do 3x 1-second "blips", each 4 seconds apart. Or 6x half-second "blips". Or instead of counting, just trim repeatedly and/or continually until the elevator force is neutral, like a pilot. Which he never did.

He did say one strange thing though: if it is correct in translation, he asked the F/O "to trim up with him". This was after the second MCAS. He had only responded to the first MCAS with a relatively short "blip" (2.1 to 2.4 units). The response to the second MCAS (presumably with the F/O "helping") was around 11 seconds and took it from 0.4 to 2.3 units (if only they'd kept going another 11 seconds).

So why did he need the F/O's help to activate main electric trim? It's a thumb switch. Was the stick-shaker that annoying he couldn't activate the thumb switch? Could this mystery have anything to do with the two fatally short "blips" near the end of the flight?
Derfred is offline  
Old 6th Apr 2019, 17:39
  #3475 (permalink)  
 
Join Date: Jan 2008
Location: Hotel Sheets, Downtown Plunketville
Age: 72
Posts: 0
Here is an interesting piece on the STM :


"• Boeing 737NG • Improve field reliability of the Horizontal Stabilizer Trim Motor (STM) • Solder joint fatigue of the memory chip • 6355C0001-01 to 6355C0001-02
""Joint investigation into the STM’s field reliability with Boeing, along with lessons learned from 737MAX qualification, have yielded design improvements to the Control PWA.".

The link is at:

file:///C:/Users/Tony/Downloads/Jay%...A302_FINAL.pdf
Chronus is offline  
Old 6th Apr 2019, 17:41
  #3476 (permalink)  
 
Join Date: Nov 2010
Location: Denver
Age: 52
Posts: 45
Originally Posted by Majorbyte View Post
This constant assumption by aircraft manufacturers that the pilots don't know f*** all about flying and insist on installing complicated systems to act as a safety pilot is crazy, how often do pilots stall airliners?? very very rarely is the answer, and if they were stupid enough to stall the aircraft, recovery is relatively simple, assuming some altitude is available. A message to Boeing and Airbus, please let the pilots fly the aicraft you build and stop confusing them with unnecessary and untimately dangerous technology.

Not that simple. As stated already hundreds of times, MCAS is required because of aerodynamic differences with the older model (bigger nacelle, further forward), making the required pull to increase AOA at high AOA too light (best way I can phrase it). You could blame Boeing for not designing a new aircraft, but based on all their other new designs i am sure it would have more, not less envelope protection.
hans brinker is offline  
Old 6th Apr 2019, 17:51
  #3477 (permalink)  
 
Join Date: Nov 2010
Location: Denver
Age: 52
Posts: 45
Originally Posted by astonmartin View Post

But they stayed in ‘level change’ mode all the time. That means that the autothrottle kept the engines at climb thrust all the time.

Both altitude and speed were uncontrolled.
Agree, I meant they had the intent to level of and reduce speed. Because the never got to ALT hold and Speed mode (or whatever Boeing calls it) they remained at full thrust.
hans brinker is offline  
Old 6th Apr 2019, 17:53
  #3478 (permalink)  
 
Join Date: Oct 2011
Location: Lower Skunk Cabbageland, WA
Age: 69
Posts: 354
Originally Posted by Chronus View Post
Here is an interesting piece on the STM :


"• Boeing 737NG • Improve field reliability of the Horizontal Stabilizer Trim Motor (STM) • Solder joint fatigue of the memory chip • 6355C0001-01 to 6355C0001-02
""Joint investigation into the STM’s field reliability with Boeing, along with lessons learned from 737MAX qualification, have yielded design improvements to the Control PWA.".

The link is at:

file:///C:/Users/Tony/Downloads/Jay%...A302_FINAL.pdf
Sorry, link is bad. Looks as if it's a local file on your puter.
Organfreak is offline  
Old 6th Apr 2019, 19:42
  #3479 (permalink)  
 
Join Date: Jan 2008
Location: Hotel Sheets, Downtown Plunketville
Age: 72
Posts: 0
Originally Posted by Organfreak View Post
Sorry, link is bad. Looks as if it's a local file on your puter.
Apologies for that, it is a pdf file on www.eaton.eu

Here is the slide :
Boeing 737NG • Improve field reliability of the Horizontal Stabilizer Trim Motor (STM) • Solder joint fatigue of the memory chip • 6355C0001-01 to 6355C0001-02 5 © 2018 Eaton. All Rights Reserved.. Background Part history • Eaton has been the provider of the Stabilizer Trim Motor used on the Boeing 737NG since 1996. • 6355B0001-02/-03:1996 - 2003 • 6355C0001-01: 2003 - 2017 • 6355C0001-02: 2017 - Present • 6355D0001-01: 2016 - Present • Unique to the 737MAX and not interchangeable with 6355B/C configurations 6 © 2018 Eaton. All Rights Reserved.. Background • Stabilizer Trim Motor (STM) exceeds Boeing’s reliability requirements. However, in partnership with Boeing and using Eaton’s continuous improvement process and operator feedback, design improvements have been made to further improve field reliability. • Primary failure mode is solder joint fatigue of the non-volatile memory (NVM) chip due to a combination of uncontrolled environmental conditions causing bending, vibration and thermal expansion stresses. • Eaton implemented a shimming procedure that will ensure the control printed wire assembly (PWA) is held flat, so that all component leads, including the NVM, are free from mechanical bending stress. This change is identified on 6355C0001-01 units as Modification 9 (“Mod 9”). • Boeing has performed an in-depth analysis of the Horizontal Stabilizer Trim System Wiring design to include ships wiring, switches and production breaks and splices. The results of the Boeing Study show that operators may reduce the No Fault Found test results for the STM by checking the airplane wiring and switching components prior to removal. 7 © 2018 Eaton. All Rights Reserved.. Solution • Joint investigation into the STM’s field reliability with Boeing, along with lessons learned from 737MAX qualification, have yielded design improvements to the Control PWA. • Modifications to the NVM chip package which is significantly more robust to vibration and thermal expansion. • Control PWA changes include NVM component replacement, component land pattern optimization, component height spacers, copper balancing of the PWB, reduction of hand soldering operations and addressing potential obsolescence concerns. • An upgrade of a 6355C0001-01 to a 6355C0001-02 will require a new Control PWA (the PWA itself can not be upgraded). • Long term lab testing of the 6355C0001-02 shows that the failure mode of solder joint fatigue of the Non-Volatile Memory (



Chronus is offline  
Old 6th Apr 2019, 19:58
  #3480 (permalink)  
 
Join Date: Oct 2011
Location: Lower Skunk Cabbageland, WA
Age: 69
Posts: 354
THANK YOU!
Organfreak is offline  

Thread Tools
Search this Thread

Contact Us - Archive - Advertising - Cookie Policy - Privacy Statement - Terms of Service - Do Not Sell My Personal Information

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