5 ms·

> Turning it off with the STAB TRIM CUTOFF switch turned it off. > The pilots in the second crash did not follow that procedure. "At 05:40:35, the First-Off

> Turning it off with the STAB TRIM CUTOFF switch turned it off. > The pilots in the second crash did not follow that procedure. "At 05:40:35, the First-Officer called out 'stab trim cut-out' two times. Captain agreed and First-Officer confirmed stab trim cut-out."[1] However they were unable to correct the trim of the aircraft without help of the electrical systems (still being on full takeoff power didn't help). So around 3 minutes later stab trim cutout was switched back to normal. Pretty much the moment they did that the aircraft pitched down hard, the situation becoming unrecoverable within seconds, followed by the aircraft impacting the ground. There were possibly ways to save the aircraft (reduce aerodynamic forces that prevented trim by hand by, for instance, reducing thrust), but those weren't detailed in any ADs. [1]https://leehamnews.com/wp-content/uploads/2019/04/Preliminary-Report-B737-800MAX-ET-AVJ.pdf https://leehamnews.com/wp-content/uploads/2019/04/Preliminar...

WalterBright 4y ago
The instructions in the Emergency Airworthiness Directive said: 1. restore trim to normal with the electric thumb switches on the column 2. then turn off the stab trim The electric trim overrides MCAS. Boeing Emergency Airworthiness Directive: "Initially, higher control forces may be needed to overcome any stabilizer nose down trim already applied. Electric stabilizer trim can be used to neutralize control column pitch forces before moving the STAB TRIM CUTOUT switches to CUTOUT. Manual stabilizer trim can be used before and after the STAB TRIM CUTOUT switches are moved to CUTOUT." https://theaircurrent.com/wp-content/uploads/2018/11/B737-MAX-AD-1107.pdf https://theaircurrent.com/wp-content/uploads/2018/11/B737-MA...
- chmod775 4y ago
  > 1. restore trim to normal with the electric thumb switches on the column That's probably not an easy thing with a computer undoing your work every few seconds and fighting you for control. And they did try to correct the trim before moving to 2. 5:40:00 AND (here automatic nose down) activates for 9 seconds, computer trimming from 4.60 to 2.1 units, crew trying to counteract by pitching up. 5:40:14 Pilot begins adjusting trim up. Gets to 2.4 units. 5:40:22 AND activates yet again (7s), also pushing trim all the way down to 0.4 units. DON'T SINK warning and PULL UP. 5:40:29 Captain asks the First-Officer to trim up with him. They reach 2.3 units (9s). This interrupts AND. 5:40:38 stab trim cut-out 5:40:43 AND activates again, but at least now it leaves the stabilizer alone. All in they did fine, considering all this happened in 40 seconds. They regained control of the aircraft and now have time to asses what even happened. However they still have to apply up to 100lbs of force to keep the nose somewhat pointed up. Only at times when both of them are actually pulling on the stick does the plane gain altitude. On top of that they're getting a MASTER CAUTION "anti-ice left alpha vane", adding to their workload. In the next three minutes they're discussing the warnings they're getting, informing ATC of their problem, and are trying to manually trim the plane (which doesn't work). I'd imagine their arms are getting tired. So the understandable next step is to switch stab trim cut out back to normal, then trying to correct the trim further. 5:43:11 stab trim back to normal, followed by some short manual electric trim inputs 5:43:21 AND triggers yet again (5s), stab to 1.0 units. Within the first 3.5s the aircraft pitches -8° down, descent rate increases to -5,000 ft/min. If they had caught and interrupted the AND/flipped stab trim back immediately, maybe this could've been saved. But since the computer got to do its thing for a few seconds, it's pretty much too late to do anything. The pilots are applying up to 180lbs of force, which accomplishes nothing. The plane keeps pitching further down. 5:43:44 Plane impacts the ground at an angle of 40° nose down. That whole timeline was 3 minutes, 44 seconds. The only way you can reasonably expect a human to deal with a situation like that, which requires a quick response, is if you train them for it. You don't just give a vague warning, a bunch of steps with three IFs attached, and hope for the best. More complete, interim, report: https://reports.aviation-safety.net/2019/20190310-0_B38M_ET-AVJ_Interim.pdf https://reports.aviation-safety.net/2019/20190310-0_B38M_ET-...
  - WalterBright 4y ago
    I did read the EAD. I even quoted it. > That's probably not an easy thing with a computer undoing your work every few seconds and fighting you for control. Having the trim start running again every few seconds is EXACTLY WHY there's a trim cutout switch. A few seconds is enough time to hit the thumb trim switches right on the column under your thumb, and the then hit the cutoff switch which is right there on the center console. I don't dispute the timeline. But the fact remains, using the electric trim switches to return trim to normal, then turning it off, would have worked. The stab trim does not move that fast, they had time to turn it off after trimming to normal. Thanks for the link. At one point, it was clear the EA pilots did use the electric trim switches to override MCAS. They did turn off the trim at one point. What they did not do was follow the instructions in the EAD. > maybe this could've been saved The first incident shows the procedure works. Trim to normal, turn it off. That's all there is to it. The thing about the Emergency Airworthiness Directive is it came out after the first MAX crash, and was about how to not die if it happens to you. If you were a MAX pilot, wouldn't you take extra care to read that EAD, understand it, and remember it? I cannot fathom ignoring it.
    - chmod775 4y ago
      > I cannot fathom ignoring it. I can see why it they wouldn't have recalled it in the first 40s of that situation. However they got the situation stabilized to a point where they could've kept going for a while and maybe came up with a better plan of action before attempting to correct the trim again (which is what ultimately doomed the flight). > Having the trim start running again every few seconds is EXACTLY WHY there's a trim cutout switch. A few seconds is enough time to hit the thumb trim switches right on the column under your thumb, and the then hit the cutoff switch which is right there on the center console. Which is kind of leaving the territory of the AD. The way I'm reading it, it advises to leave the switch set to cutout for the remainder of the flight. They'd have had to come up with that approach (or an approach that would have enabled manual trim) on their own once they had the aircraft flying somewhat straight without immediate danger. Their main mistake may have been to not take more time to assess their situation when they had the chance and not fully grasping the danger of leaving that switch on normal for even the 5s it took the plane to become unrecoverable at the end. But all those factors pale in the face of inadequate training and the fact that there could hardly be a more dangerous problem with an aircraft than it - out of nowhere - entering an uncontrollable nosedive if the pilots don't properly respond within seconds. I'd maybe rate complete loss of control/"wings fell off" higher. I still have trouble blaming the pilots because - with the benefit of hindsight - I would have expected such crashes to happen as much as they did, maybe more. The aviation industry generally avoids expected mistakes that result in loss of life and someone was bound to make this one.

WalterBright 4y ago

The instructions in the Emergency Airworthiness Directive said: 1. restore trim to normal with the electric thumb switches on the column 2. then turn off the stab trim The electric trim overrides MCAS. Boeing Emergency Airworthiness Directive: "Initially, higher control forces may be needed to overcome any stabilizer nose down trim already applied. Electric stabilizer trim can be used to neutralize control column pitch forces before moving the STAB TRIM CUTOUT switches to CUTOUT. Manual stabilizer trim can be used before and after the STAB TRIM CUTOUT switches are moved to CUTOUT." https://theaircurrent.com/wp-content/uploads/2018/11/B737-MAX-AD-1107.pdf https://theaircurrent.com/wp-content/uploads/2018/11/B737-MA...

chmod775 4y ago
> 1. restore trim to normal with the electric thumb switches on the column That's probably not an easy thing with a computer undoing your work every few seconds and fighting you for control. And they did try to correct the trim before moving to 2. 5:40:00 AND (here automatic nose down) activates for 9 seconds, computer trimming from 4.60 to 2.1 units, crew trying to counteract by pitching up. 5:40:14 Pilot begins adjusting trim up. Gets to 2.4 units. 5:40:22 AND activates yet again (7s), also pushing trim all the way down to 0.4 units. DON'T SINK warning and PULL UP. 5:40:29 Captain asks the First-Officer to trim up with him. They reach 2.3 units (9s). This interrupts AND. 5:40:38 stab trim cut-out 5:40:43 AND activates again, but at least now it leaves the stabilizer alone. All in they did fine, considering all this happened in 40 seconds. They regained control of the aircraft and now have time to asses what even happened. However they still have to apply up to 100lbs of force to keep the nose somewhat pointed up. Only at times when both of them are actually pulling on the stick does the plane gain altitude. On top of that they're getting a MASTER CAUTION "anti-ice left alpha vane", adding to their workload. In the next three minutes they're discussing the warnings they're getting, informing ATC of their problem, and are trying to manually trim the plane (which doesn't work). I'd imagine their arms are getting tired. So the understandable next step is to switch stab trim cut out back to normal, then trying to correct the trim further. 5:43:11 stab trim back to normal, followed by some short manual electric trim inputs 5:43:21 AND triggers yet again (5s), stab to 1.0 units. Within the first 3.5s the aircraft pitches -8° down, descent rate increases to -5,000 ft/min. If they had caught and interrupted the AND/flipped stab trim back immediately, maybe this could've been saved. But since the computer got to do its thing for a few seconds, it's pretty much too late to do anything. The pilots are applying up to 180lbs of force, which accomplishes nothing. The plane keeps pitching further down. 5:43:44 Plane impacts the ground at an angle of 40° nose down. That whole timeline was 3 minutes, 44 seconds. The only way you can reasonably expect a human to deal with a situation like that, which requires a quick response, is if you train them for it. You don't just give a vague warning, a bunch of steps with three IFs attached, and hope for the best. More complete, interim, report: https://reports.aviation-safety.net/2019/20190310-0_B38M_ET-AVJ_Interim.pdf https://reports.aviation-safety.net/2019/20190310-0_B38M_ET-...
- WalterBright 4y ago
  I did read the EAD. I even quoted it. > That's probably not an easy thing with a computer undoing your work every few seconds and fighting you for control. Having the trim start running again every few seconds is EXACTLY WHY there's a trim cutout switch. A few seconds is enough time to hit the thumb trim switches right on the column under your thumb, and the then hit the cutoff switch which is right there on the center console. I don't dispute the timeline. But the fact remains, using the electric trim switches to return trim to normal, then turning it off, would have worked. The stab trim does not move that fast, they had time to turn it off after trimming to normal. Thanks for the link. At one point, it was clear the EA pilots did use the electric trim switches to override MCAS. They did turn off the trim at one point. What they did not do was follow the instructions in the EAD. > maybe this could've been saved The first incident shows the procedure works. Trim to normal, turn it off. That's all there is to it. The thing about the Emergency Airworthiness Directive is it came out after the first MAX crash, and was about how to not die if it happens to you. If you were a MAX pilot, wouldn't you take extra care to read that EAD, understand it, and remember it? I cannot fathom ignoring it.
  - chmod775 4y ago
    > I cannot fathom ignoring it. I can see why it they wouldn't have recalled it in the first 40s of that situation. However they got the situation stabilized to a point where they could've kept going for a while and maybe came up with a better plan of action before attempting to correct the trim again (which is what ultimately doomed the flight). > Having the trim start running again every few seconds is EXACTLY WHY there's a trim cutout switch. A few seconds is enough time to hit the thumb trim switches right on the column under your thumb, and the then hit the cutoff switch which is right there on the center console. Which is kind of leaving the territory of the AD. The way I'm reading it, it advises to leave the switch set to cutout for the remainder of the flight. They'd have had to come up with that approach (or an approach that would have enabled manual trim) on their own once they had the aircraft flying somewhat straight without immediate danger. Their main mistake may have been to not take more time to assess their situation when they had the chance and not fully grasping the danger of leaving that switch on normal for even the 5s it took the plane to become unrecoverable at the end. But all those factors pale in the face of inadequate training and the fact that there could hardly be a more dangerous problem with an aircraft than it - out of nowhere - entering an uncontrollable nosedive if the pilots don't properly respond within seconds. I'd maybe rate complete loss of control/"wings fell off" higher. I still have trouble blaming the pilots because - with the benefit of hindsight - I would have expected such crashes to happen as much as they did, maybe more. The aviation industry generally avoids expected mistakes that result in loss of life and someone was bound to make this one.