3 ms·

> 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

> 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
> Which is kind of leaving the territory of the AD. No, it isn't. > The way I'm reading it What it says is to restore trim to normal and then turn it off. > not fully grasping the danger of leaving that switch on normal Uncommanded stabilizer trim movement is a severe problem which is why what to do about it is a "memory item", meaning you don't have time to read the checklist. All pilots should know that runaway trim is a critical danger. > out of nowhere - entering an uncontrollable nosedive if the pilots don't properly respond within seconds There's enough time to respond. All three crews correctly restored normal trim immediately. > I still have trouble blaming the pilots because I give the pilots some of the responsibility, because they had all the information needed to counter the problem. The rest goes to Boeing for a bad MCAS design. It's a pilot's job to read, understand, and remember Emergency Airworthiness Directives. If that's unreasonable for them, they need to turn in their wings and drive an Uber. I find no fault for the pilots of the Alaska crash where the stabilizer trim jammed. There were no instructions on how to deal with that, and they were in contact with the maintenance chief who had no clue, either. The pilots kept trying to break the jam loose, doing things like engaging both trim motors to apply more torque. The result was the jackscrew nut stripped the threads, and then it slid to hard over, then broke the end of the jackscrew off, and it was game over. Now me, as an engineer who knows how that system works, I would have advised them to leave it alone, reduce airspeed to reduce the loads on it, and land ASAP. The jackscrew motors are way too powerful to let them grind away at it. Also, when it did move, it let off a very loud screech indicating that something awful was happening. But they weren't engineers or mechanics. They made a mistake, but it was reasonable considering what they knew. They did the best they could.
- chmod775 4y ago
  Give me whoever you consider the best two pilots on earth and I promise you they'll have a collective minute of suboptimal decision making at some point, especially when confronted with an extremely sudden stressful situation. Humans don't work the way you're implying they do. However we design systems and procedures such that suboptimal usually doesn't mean fatal, and in those specific instances where it would, we train humans so they perform adequately. If humans were so great, we wouldn't need a lot of the technology in modern aircraft. It's mostly there because humans suck. Taking work away from the meatbags, putting in safeguards, and designing with the human element in mind, produces more desirable outcomes. And it's not like this crew had the wrong ideas. They attempted all the right things, but execution was lacking and sadly the situation had no room for error: 1. Did use cut out, but left it on normal for a few crucial seconds without any manual input, allowing the computer to mess everything up again. 2. Did try to fix trim before cut out, but only got it halfway there to the point where they could at least achieve level flight and a slight climb. Tried to trim the rest of the way manually, but that didn't work. > There's enough time to respond. Disregarding that the situation could have been avoided, the second time this crew didn't have time to react anymore. It took only 3.5s from the automatic nose down engaging to descending at -5,000 ft/min, pitching -8° down and quickly increasing to -40°, despite the pilots pulling on their sticks full force. They had maybe a second or two to nip it in the bud, then had twenty seconds left to somehow arrest the rapid descent of an aircraft that is trimmed precisely the wrong way with the horizon in a place you don't ever want to see it in a commercial airliner. I don't think it was physically possible? It's not hard imagining situations where an aircraft doing something like that within 3.5s out of nowhere would be disastrous. There certainly wouldn't be time to respond. This crew was warned by earlier misbehavior, so the situation was theoretically avoidable, but there was little room for error and so we should be glad for all the times something didn't happen. > All three crews correctly restored normal trim immediately. Are you counting this crew? I don't think they had normal trim at any point once the incident started. They were trying to get there.
  - WalterBright 4y ago
    Yes, people make mistakes. And we should design systems to be tolerant of those mistakes. With airplanes, we try to think through all the emergencies first, figure out how to fix them at leisure, then write it down in the form of a checklist or an Emergency Airworthiness Directive. We expect pilots to pay attention to those things. They make mistakes, sure, but they are still responsible for those mistakes. The EA pilots did not follow the procedure laid out as "how to not die like the Lion Air pilots". Seems to me that should be worth reading, understanding, and remembered. Especially as there was nothing complicated about it - trim to normal, turn it off. Wouldn't you prefer to fly with pilots who did? I do.

WalterBright 4y ago

> Which is kind of leaving the territory of the AD. No, it isn't. > The way I'm reading it What it says is to restore trim to normal and then turn it off. > not fully grasping the danger of leaving that switch on normal Uncommanded stabilizer trim movement is a severe problem which is why what to do about it is a "memory item", meaning you don't have time to read the checklist. All pilots should know that runaway trim is a critical danger. > out of nowhere - entering an uncontrollable nosedive if the pilots don't properly respond within seconds There's enough time to respond. All three crews correctly restored normal trim immediately. > I still have trouble blaming the pilots because I give the pilots some of the responsibility, because they had all the information needed to counter the problem. The rest goes to Boeing for a bad MCAS design. It's a pilot's job to read, understand, and remember Emergency Airworthiness Directives. If that's unreasonable for them, they need to turn in their wings and drive an Uber. I find no fault for the pilots of the Alaska crash where the stabilizer trim jammed. There were no instructions on how to deal with that, and they were in contact with the maintenance chief who had no clue, either. The pilots kept trying to break the jam loose, doing things like engaging both trim motors to apply more torque. The result was the jackscrew nut stripped the threads, and then it slid to hard over, then broke the end of the jackscrew off, and it was game over. Now me, as an engineer who knows how that system works, I would have advised them to leave it alone, reduce airspeed to reduce the loads on it, and land ASAP. The jackscrew motors are way too powerful to let them grind away at it. Also, when it did move, it let off a very loud screech indicating that something awful was happening. But they weren't engineers or mechanics. They made a mistake, but it was reasonable considering what they knew. They did the best they could.

chmod775 4y ago
Give me whoever you consider the best two pilots on earth and I promise you they'll have a collective minute of suboptimal decision making at some point, especially when confronted with an extremely sudden stressful situation. Humans don't work the way you're implying they do. However we design systems and procedures such that suboptimal usually doesn't mean fatal, and in those specific instances where it would, we train humans so they perform adequately. If humans were so great, we wouldn't need a lot of the technology in modern aircraft. It's mostly there because humans suck. Taking work away from the meatbags, putting in safeguards, and designing with the human element in mind, produces more desirable outcomes. And it's not like this crew had the wrong ideas. They attempted all the right things, but execution was lacking and sadly the situation had no room for error: 1. Did use cut out, but left it on normal for a few crucial seconds without any manual input, allowing the computer to mess everything up again. 2. Did try to fix trim before cut out, but only got it halfway there to the point where they could at least achieve level flight and a slight climb. Tried to trim the rest of the way manually, but that didn't work. > There's enough time to respond. Disregarding that the situation could have been avoided, the second time this crew didn't have time to react anymore. It took only 3.5s from the automatic nose down engaging to descending at -5,000 ft/min, pitching -8° down and quickly increasing to -40°, despite the pilots pulling on their sticks full force. They had maybe a second or two to nip it in the bud, then had twenty seconds left to somehow arrest the rapid descent of an aircraft that is trimmed precisely the wrong way with the horizon in a place you don't ever want to see it in a commercial airliner. I don't think it was physically possible? It's not hard imagining situations where an aircraft doing something like that within 3.5s out of nowhere would be disastrous. There certainly wouldn't be time to respond. This crew was warned by earlier misbehavior, so the situation was theoretically avoidable, but there was little room for error and so we should be glad for all the times something didn't happen. > All three crews correctly restored normal trim immediately. Are you counting this crew? I don't think they had normal trim at any point once the incident started. They were trying to get there.
- WalterBright 4y ago
  Yes, people make mistakes. And we should design systems to be tolerant of those mistakes. With airplanes, we try to think through all the emergencies first, figure out how to fix them at leisure, then write it down in the form of a checklist or an Emergency Airworthiness Directive. We expect pilots to pay attention to those things. They make mistakes, sure, but they are still responsible for those mistakes. The EA pilots did not follow the procedure laid out as "how to not die like the Lion Air pilots". Seems to me that should be worth reading, understanding, and remembered. Especially as there was nothing complicated about it - trim to normal, turn it off. Wouldn't you prefer to fly with pilots who did? I do.