Announcement

Collapse
No announcement yet.

Breaking news: Ethiopian Airlines flight has crashed on way to Nairobi

Collapse
X
 
  • Filter
  • Time
  • Show
Clear All
new posts

  • Evan
    replied
    Originally posted by Gabriel View Post
    They were more than 10 knots beyond 250 just a few seconds after the 1st MCAS activation.
    About 25 seconds after flap retraction and 10 seconds after the first MCAS activation, there were around 280kts. Is that going to damage anything? Are they going to be at that speed if they had reduced thrust 10 seconds earlier?

    This isn't normal ops. Something has to give. Shutting down the pitch trim doesn't seem to save the day. Extending the flaps a bit over the placard speed almost cerrtainly will. But only as part of a simple, four-step memory procedure.

    Leave a comment:


  • Schwartz
    replied
    Originally posted by Gabriel View Post
    The data shows, separately:
    1) The inputs of the thumb switch
    3) The inputs of the automation (without distinguishing whether it was triggered by the AP, the MCAS or the speed trim)
    4) The position of the stabilizer.

    And what we can see is (colors correlate with the color of the trace in the FDR plot)
    a) Several thumb switch trim inputs after take-off, that are correlated with change in the stabilizer position (flaps were extended, so no MCAS)
    b) Several automation inputs after the AP is engaged, that are correlated with change in stabilizer position (MAS doesn't act when AP)
    c) Flaps handle moved to retracted, flaps start to retract
    d) In the middle of the flaps retraction the AP disengages (don't know if by itself or commanded)
    e) Flaps complete the retraction and, as soon as they get to the retracted position...
    f) Automation nose-down trim input, about 9 seconds, correlated with a stabilizer motion of about 2.5 units in the nose-down direction. Hello MCAS.
    g) About 3 seconds of nose-up thumb switch correlated with about 1 unit of nose-up stabilizer motion.
    h) 5 seconds after the thumb switch is released, another long automated nose-down input, correlated with another 2 units of nose-down stabilizer motion.
    i) A long nose-up thumb switch input correlated with an immediate stop of the MCAS automated input and immediately reversing of stabilizer motion, going up some 2 units.
    i) The CVR records the pilot discussing and confirming the use of the cutout switches.
    j) There is a 9-seconds nose-down input from the automation that is NOT correlated with any stabilizer motion, indication that the cutout switches had been turned off.
    k) A long (more than 2 minutes) lack of activity with the trim.
    l) 2 fraction-of-a-second nose-up thumb-switch clicks correlated with the stabilizer moving up a fraction of a unit (indication that they put the cutout switch back in the operative position)
    m) 5 seconds after the last thumb switch click, a 5 or 6 seconds automated nose-down trim input (must be MCAS) correlated with the stabilizer going about 1.5 units in the nose-down direction. That happen when they were at 7000 ft above the ground. They crashed some 20 seconds later.

    [ATTACH=CONFIG]23352[/ATTACH]

    This article is quite interesting and it explains one theory of why they only briefly thumbed the switches near the end.

    https://leehamnews.com/2019/04/05/bj...irst-analysis/

    The insufficient trim mystery after re-activation of Electric Trim
    After 7 PF commands Electric Trim Nose Up in two short cycles. I asked my selves (as did others) why these short trims? They are fighting to get the nose up to the extent they risk switching in the Electric Trim again. Then why not trim nose up continuously or for at least long cycles once Electric Trim is there? It took me several hours to find an explanation. Here my take:

    To understand the blip trims one must have flown fast jets at low altitude. At the speed ET302 is flying, 360kts, itís hypersensitive to trim. The least trim action and the aircraft reacts violently. Any trimming is in short blips.

    As PF holds the nose up with a very high stick force, now for a long time, heís sensitivity to release stick with trim is not there (this is what Pilots do when they trim nose up, otherwise the aircraft pitches up fast). He trims therefore in short blips and has difficulty to judge the trim effect he has achieved. His is not flying on feel. He canít, he is severely out of trim, holding on to the Yoke with a strong pull force.

    Anyone who has flown a grossly out of trim aircraft at high speeds knows your feel is compromised. The sensors you have to rely on are your eyes, not your hands.

    PF has the horizon glued to read the aircraft. The result is the short nose-up trims we see. The nose goes up and the stick force needed is reduced. His judgment is; this is enough for now, it was a powerful response. Any MCAS attack I now trim against, then I correct my trim if I need to.

    But the aggressive MCAS, trimming with a speed 50% higher than the pilot and for a full nine seconds, kicks in at 8 with a force they didnít expect. Speed is now at 375kts and MCAS was never designed to trim at these Speed/Altitude combinations. Dynamic pressures, which governs how the aircraft reacts to control surface movements, is now almost double it was when last MCAS trimmed (Dynamic pressure increases with Speed squared).

    The Pilots are thrown off their seats, hitting the cockpit roof. Look at the Pitch Attitude Disp trace and the Accel Vert trace. These are on the way to Zero G and we can see how PF loses stick pull in the process (Ctrl Column Pos L). He can barely hold on to the Yoke, let alone pull or trim against.

    His reduced pull increases the pitch down further, which increases the speed even more. At 05.45.30 the Pilots have hit the seats again (Accel Vert trace and Ctrl Columns force trace) and can start pulling in a desperate last move. But itís too late. Despite them creating the largest Control Column movement ever, pitch down attitude is only marginally affected.
    I think the two key parts are that he claims in an overspeed state, trim adjustments are made very carefully, and the second point is that the MCAS trim is extremely aggressive and fast. By the time it kicked in, there were only seconds before it was nearly impossible to recover from even at that altitude.

    Leave a comment:


  • Gabriel
    replied
    Originally posted by Evan View Post
    You can safely extend flaps 1 at 250kts. That procedure I suggest lists 'reduce thrust' before 'extend flaps'. Even if you are 10kts fast at that point, it's better to risk flap damage (unlikely unless you are well above that speed) than to risk losing pitch trim authority.
    They were more than 10 knots beyond 250 just a few seconds after the 1st MCAS activation.

    Leave a comment:


  • Gabriel
    replied
    Originally posted by Evan View Post
    This is what really bothers me. Boeing saw what MCAS could do with the Lion Air crash and responded with this fatal procedure that removes a key system that is perfectly functional instead of simply using the MCAS on/off lever (the flap lever). And so another one bites the dust.

    Why didn't they write the emergency AD procedure to be: restore pitch/counter-trim/reduce thrust/extend flaps?

    I mean, why is nobody thinking this thing through?
    And what if the trim runaway was not due to MCAS? Then you lost valuable time with something that will not work.

    Leave a comment:


  • Gabriel
    replied
    Originally posted by flashcrash View Post
    Thinking outside the box a little here - do we actually _know they didn't use the thumb switches more than a perfunctory couple of times? I get that the data shows the stab only moved a couple of clicks after they re-engaged the electric trim. But that's not quite the same thing. Given their overspeed condition, is it possible that even the motor driving the jackscrew was unable to fight the aerodynamic forces on the stab to move it nose up? In contrast, MCAS found it easy to move it nose-down?
    The data shows, separately:
    1) The inputs of the thumb switch
    3) The inputs of the automation (without distinguishing whether it was triggered by the AP, the MCAS or the speed trim)
    4) The position of the stabilizer.

    And what we can see is (colors correlate with the color of the trace in the FDR plot)
    a) Several thumb switch trim inputs after take-off, that are correlated with change in the stabilizer position (flaps were extended, so no MCAS)
    b) Several automation inputs after the AP is engaged, that are correlated with change in stabilizer position (MAS doesn't act when AP)
    c) Flaps handle moved to retracted, flaps start to retract
    d) In the middle of the flaps retraction the AP disengages (don't know if by itself or commanded)
    e) Flaps complete the retraction and, as soon as they get to the retracted position...
    f) Automation nose-down trim input, about 9 seconds, correlated with a stabilizer motion of about 2.5 units in the nose-down direction. Hello MCAS.
    g) About 3 seconds of nose-up thumb switch correlated with about 1 unit of nose-up stabilizer motion.
    h) 5 seconds after the thumb switch is released, another long automated nose-down input, correlated with another 2 units of nose-down stabilizer motion.
    i) A long nose-up thumb switch input correlated with an immediate stop of the MCAS automated input and immediately reversing of stabilizer motion, going up some 2 units.
    i) The CVR records the pilot discussing and confirming the use of the cutout switches.
    j) There is a 9-seconds nose-down input from the automation that is NOT correlated with any stabilizer motion, indication that the cutout switches had been turned off.
    k) A long (more than 2 minutes) lack of activity with the trim.
    l) 2 fraction-of-a-second nose-up thumb-switch clicks correlated with the stabilizer moving up a fraction of a unit (indication that they put the cutout switch back in the operative position)
    m) 5 seconds after the last thumb switch click, a 5 or 6 seconds automated nose-down trim input (must be MCAS) correlated with the stabilizer going about 1.5 units in the nose-down direction. That happen when they were at 7000 ft above the ground. They crashed some 20 seconds later.

    Click image for larger version

Name:	ethiopian_b38m_et-avj_190310_7.jpg
Views:	1
Size:	193.2 KB
ID:	1034201

    Leave a comment:


  • TeeVee
    replied
    Originally posted by Evan View Post
    These two crashes will already cost Boeing billions in terms of restitution settlements and lost revenue. We don't wan't to destroy Boeing. We want to repopulate the management. We want to see the top executives responsible for leading Boeing astray go to jail, as we did with the Volkswagen and Audi emissions scandals. We want to a bunch more reduced to flipping burgers. We don't want to do anything detrimental to society or to see good, talented people lose their jobs.

    We want to see the 797 rolled out over the coming decade, and for Boeing to reclaim the trust of the people who depend on it.
    "restitution settlements" what is that exactly?

    lost revenue? they brought that shit on themselves.

    i didn't say shutter boeing. but i would narrow the investigation down to every punkass that had anything to do with the max program, grill the hell out of them in public hearings, including the low level folks that only NOW seem to think speaking out is a good idea, when they would have been protected by state and federal whistleblower protection laws and make them at least FEEL partially responsible for the 364 dead. make them look at pictures of every dead passenger and read their names out loud on national TV. i could care less if they flipped burgers or shoveled shit for the rest of their lives. engineers are a dime a dozen...like lawyers. get rid of the shitty ones and keep the good ones.

    Leave a comment:


  • Evan
    replied
    Originally posted by Black Ram View Post
    Wouldn't reducing thrust make the nose go down when you are fighting with MCAS? I guess it should work if you immediately concentrate on the trim switches to control the nose, and then you can reduce thrust if it's working well enough
    You lose some pitch-thrust coupling. You are already getting nose down from the MCAS, so it's irrelevant: you have to pull up and trim-switch up (steps 1 and 2). Then, extending flaps to flaps 1 (step 4) terminates the MCAS problem, so you can lay off the trim. From there, you just COMMUNICATE and NAVIGATE back to the terra firma under complete control. I don't understand why this wasn't the emergency AD procedure.

    Originally posted by elaw
    I semi-agree, but at this point turning off MCAS doesn't seem to be the biggest issue. It can be disabled via the cutoff switches and the Ethiopian pilots did exactly that - the big problem seems to be that even with it turned off, you can find yourself in an unrecoverable situation.
    Exactly. You're not following me. Turning off the electric trim is a BIG mistake. Turning off the MCAS without turning off the pitch trim is LESS COMPLICATED.

    Leave a comment:


  • Black Ram
    replied
    Originally posted by Evan View Post
    It's a bit late in the day for Boeing to avoid complicting things significantly, but the least complicated solution is still the best one. You can safely extend flaps 1 at 250kts. That procedure I suggest lists 'reduce thrust' before 'extend flaps'. Even if you are 10kts fast at that point, it's better to risk flap damage (unlikely unless you are well above that speed) than to risk losing pitch trim authority.
    Wouldn't reducing thrust make the nose go down when you are fighting with MCAS? I guess it should work if you immediately concentrate on the trim switches to control the nose, and then you can reduce thrust if it's working well enough

    Leave a comment:


  • elaw
    replied
    I semi-agree, but at this point turning off MCAS doesn't seem to be the biggest issue. It can be disabled via the cutoff switches and the Ethiopian pilots did exactly that - the big problem seems to be that even with it turned off, you can find yourself in an unrecoverable situation.

    And there's no limit to how much things can be complicated! Sure the "MCAS situation" creates complication for pilots, but that's no excuse for introducing more complication.

    Leave a comment:


  • Evan
    replied
    Originally posted by elaw View Post
    But the reality is there are hard-and-fast rules about when flaps should and should not be used, and how much. Adding in "do this if MCAS is going nuts and you want to stop it" to those rules complicates things significantly. And when working a multiple-serious-failure scenario, the last thing pilots need is more complexity.
    It's a bit late in the day for Boeing to avoid complicting things significantly, but the least complicated solution is still the best one. You can safely extend flaps 1 at 250kts. That procedure I suggest lists 'reduce thrust' before 'extend flaps'. Even if you are 10kts fast at that point, it's better to risk flap damage (unlikely unless you are well above that speed) than to risk losing pitch trim authority.

    From everything that has been explained about MCAS thus far, the flap lever is a de facto on/off switch for MCAS.

    Leave a comment:


  • elaw
    replied
    Uh... maybe because the flaps lever is NOT an "MCAS-off switch"?

    Yes, if you have complete situational awareness, which is very unlikely in events like those we're discussing here, you could consider using the flap lever to disable MCAS... if you happen to think of it.

    But the reality is there are hard-and-fast rules about when flaps should and should not be used, and how much. Adding in "do this if MCAS is going nuts and you want to stop it" to those rules complicates things significantly. And when working a multiple-serious-failure scenario, the last thing pilots need is more complexity.

    Leave a comment:


  • Evan
    replied
    Originally posted by BoeingBobby View Post
    And THIS is where experience comes into play. Not ALL of us sit back "fat dumb and lazy" like the nub thinks
    This is what really bothers me. Boeing saw what MCAS could do with the Lion Air crash and responded with this fatal procedure that removes a key system that is perfectly functional instead of simply using the MCAS on/off lever (the flap lever). And so another one bites the dust.

    Why didn't they write the emergency AD procedure to be: restore pitch/counter-trim/reduce thrust/extend flaps?

    I mean, why is nobody thinking this thing through?

    Leave a comment:


  • flashcrash
    replied
    Originally posted by Gabriel View Post
    It was a last resource, they were dead if they didn't re-engage it. And re-engaging it could have saved them if they had actually used the frigging thumb switch to trim nose-up.
    Thinking outside the box a little here - do we actually _know they didn't use the thumb switches more than a perfunctory couple of times? I get that the data shows the stab only moved a couple of clicks after they re-engaged the electric trim. But that's not quite the same thing. Given their overspeed condition, is it possible that even the motor driving the jackscrew was unable to fight the aerodynamic forces on the stab to move it nose up? In contrast, MCAS found it easy to move it nose-down?

    Leave a comment:


  • Gabriel
    replied
    Originally posted by Evan View Post
    The #2 Fire handle? No... no... no.

    Actually, if you really know the afflicted system, this is where you want to go:
    Yes, but they should have done that immediately after the flaps fully retracted and the MCS activated the 1st time. Shortly later they were already way beyond flaps speed.
    At the time that they could have done it, they could have also done other more "procedural" things, like trim with thumb switch BEFORE using the cutout switches (as recommended in the Boeing procedures) and use the trim wheel earlier (before they got so fast and the wheel got so hard), not to mention pulling back on the throttles and pulling more nose-up to keep the speed in check instead of overspending.

    Leave a comment:


  • BoeingBobby
    replied
    Originally posted by Gabriel View Post
    It would have done more than that. It would have killed the MCAS just like the trim cutout buttons but without killing the thumb switch and without needing to rely on a manual wheel that gets stuck.
    And THIS is where experience comes into play. Not ALL of us sit back "fat dumb and lazy" like the nub thinks

    Leave a comment:

Working...
X