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The explanation put forward (which seems reasonable) is that the cutouts were disengaged because the aerodynamic forces were stronger than could be overcome by

The explanation put forward (which seems reasonable) is that the cutouts were disengaged because the aerodynamic forces were stronger than could be overcome by the manual control, so they had to turn the electrics back on in an attempt to move it (which allowed the MCAS to continue pushing the stabilizer to the extreme)

treis 8y ago
>The explanation put forward (which seems reasonable) is that the cutouts were disengaged because the aerodynamic forces were stronger than could be overcome by the manual control, so they had to turn the electrics back on in an attempt to move it (which allowed the MCAS to continue pushing the stabilizer to the extreme) But the only way it would end at the total extreme is if they were within 2.5 degrees of max when they re-enabled electric trim and they crashed within 5 seconds. Otherwise, they should have been able to at least get some adjustment. >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. https://www.theguardian.com/business/2019/apr/03/ethiopian-airlines-crash-boeing-software-engaged-repeatedly https://www.theguardian.com/business/2019/apr/03/ethiopian-a... 4 cycles should have gotten them to 7-10 degrees away from the extreme. So something else was going on.
sokoloff 8y ago
Ah. They'd have had to "roller coaster" the airplane (pitch up, then move the elevator surface towards neutral [so a net nose down]) to get the trim to move manually [the last step on the checklist]. Repeat as needed until the stab is trimmed within a range where it can move manually in unaccelerated flight. That's an interesting possibility, which if they didn't know about it (I don't blame them), they may have felt they had no choice but to go "off checklist" and re-engage the electric trim system. I'd expect that would be in the context of "PF commands nose up pitch trim continuously while PNF engages the trim cutout to normal and monitors." That's a tougher hand dealt the crew than I previously contemplated and if that's what they did, it's one for which I will owe them a retraction.
- JshWright 8y ago
  They never had the altitude to do that...
- gomijacogeo 8y ago
  It's a shame that MCAS behavior wasn't fully explained after the first crash. If it had, they might have remembered that flaps disable MCAS. If I had to go "off checklist", I'd go: stab trim off -> flaps 1st detent -> stab trim on -> trim to neutral -> stab trim off for duration of flight -> flaps up -> manual flight for the duration. Still, that's all while you're pulling on the column like mad, all the indicators are lit, all the annunciations are going on, the stick shaker is going, you're going like a bat out of hell, and the ground is coming up at you. In the final seconds of flight, there was so much nose-down that they were pulling -2g.
- gomijacogeo 8y ago
  Another thing we know now about MCAS is that it's locked out for 5 seconds after each trim switch operation. So, if you never have stab trim engaged for longer than 5 seconds a shot, you should be able to trim up the plane.

treis 8y ago

>The explanation put forward (which seems reasonable) is that the cutouts were disengaged because the aerodynamic forces were stronger than could be overcome by the manual control, so they had to turn the electrics back on in an attempt to move it (which allowed the MCAS to continue pushing the stabilizer to the extreme) But the only way it would end at the total extreme is if they were within 2.5 degrees of max when they re-enabled electric trim and they crashed within 5 seconds. Otherwise, they should have been able to at least get some adjustment. >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. https://www.theguardian.com/business/2019/apr/03/ethiopian-airlines-crash-boeing-software-engaged-repeatedly https://www.theguardian.com/business/2019/apr/03/ethiopian-a... 4 cycles should have gotten them to 7-10 degrees away from the extreme. So something else was going on.

sokoloff 8y ago

Ah. They'd have had to "roller coaster" the airplane (pitch up, then move the elevator surface towards neutral [so a net nose down]) to get the trim to move manually [the last step on the checklist]. Repeat as needed until the stab is trimmed within a range where it can move manually in unaccelerated flight. That's an interesting possibility, which if they didn't know about it (I don't blame them), they may have felt they had no choice but to go "off checklist" and re-engage the electric trim system. I'd expect that would be in the context of "PF commands nose up pitch trim continuously while PNF engages the trim cutout to normal and monitors." That's a tougher hand dealt the crew than I previously contemplated and if that's what they did, it's one for which I will owe them a retraction.

JshWright 8y ago
They never had the altitude to do that...
gomijacogeo 8y ago
It's a shame that MCAS behavior wasn't fully explained after the first crash. If it had, they might have remembered that flaps disable MCAS. If I had to go "off checklist", I'd go: stab trim off -> flaps 1st detent -> stab trim on -> trim to neutral -> stab trim off for duration of flight -> flaps up -> manual flight for the duration. Still, that's all while you're pulling on the column like mad, all the indicators are lit, all the annunciations are going on, the stick shaker is going, you're going like a bat out of hell, and the ground is coming up at you. In the final seconds of flight, there was so much nose-down that they were pulling -2g.
gomijacogeo 8y ago
Another thing we know now about MCAS is that it's locked out for 5 seconds after each trim switch operation. So, if you never have stab trim engaged for longer than 5 seconds a shot, you should be able to trim up the plane.