51–60 of 269 posts
So a single point of failure (malfunctioning sensor) can engage the horizontal stabilizer without notifying pilots, in a way that the control yoke can't override. What the hell did Boeing think was going to happen?
But the normal way of stopping it (the yoke) doesn't necessarily work, and the pilots wouldn't necessarily think to physically stop the wheel with their hands.
The headline is really confusing; I thought I was perhaps reading it wrong, but it's sort of impossible to read correctly until you realize they are talking about a separate incident than the well-known crash. It would have been clearer if they had written something simpler, like "Lion Air 737 Nearly Crashed One Day Before Deadly Accident"
Earlier quoted context omitted.
Do we have a confirmed source that it can't be override by pilot input? My understanding was that using the stick could overcome it with other control surfaces and that the controls for trim can be set/reset by the pilot. I think Boeing has handled the aftermath (and much of the lead up since the release of the plane) very, very poorly. I, as a layman to aviation, am not willing to bet that Boeing knew the true likel…
>safety critical systems should always be redundant. That's east to say from an armchair but on an aircraft everything is "safety critical" to some extent and you have to choose what gets redundancy. Something where without it you can't fly the plane sure, that make sense. The argument for considering MCAS, a system which is not necessary to fly the plane safely, to be "safety critical" is much weaker. The Lion Air c…
In flight entertainment, non-emergency lighting, food prep, &c aren't "safety critical" any more than the TVs in hospital rooms are.
As a layman, I'd've imagined that all avionics and control surface control was redundant. Don't most large planes have redundant hydraulic systems and even a deployable wind turbine to run avionics and hydraulic systems under total power loss scenarios? (And hasn't that turbine been used a few times?)
Yes, weight is always a factor, but that doesn't mean that there aren't already multiple redundant, heavy, systems on aircraft.
What puzzels me is that there are 2 angle of attack sensors, but they're only connected to one of the flight computers each, with the other flight computer being the redundant one. What's more Southwest ordered the optional disagree alert, so there is some way to tie and compare these sensors.
Edit:
> The argument for considering MCAS, a system which is not necessary to fly the plane safely, to be "safety critical" is much weaker.
It controls the control surfaces; I'm not sure how it wouldn't count.
Earlier quoted context omitted.
>safety critical systems should always be redundant. That's east to say from an armchair but on an aircraft everything is "safety critical" to some extent and you have to choose what gets redundancy. Something where without it you can't fly the plane sure, that make sense. The argument for considering MCAS, a system which is not necessary to fly the plane safely, to be "safety critical" is much weaker. The Lion Air c…
I'm fairly certain that the characteristic "If this component malfunctions loss of life is one potential outcome" is a solid case for the component actually being safety critical. The pilots would never have needed to disable MCAS had it not malfunctioned in this manner. I'm not sure what redundancy has to do with this, but clearly there was a failure in a safety-critical system.
The same thing can be said for literally tons of components on a plane. You can't have them all be redundant. At some point you have to pick and choose. A sensor for an obviously supplemental feature seems like a pretty obvious one to choose not to be redundant.
>I'm not sure what redundancy has to do with this,
I think the part in the GP comment where he/she state that "no matter the likelihood of failure, safety critical systems should always be redundant" has something to do with it.
From my point-of-view, two opinion points: 1. I am glad that 737 MAX has been grounded. May it stay that way, globally, until this issue is provably resolved. 2. The entire Boeing chain of management that resulted in these crashes should be publicly flogged, their remuneration & benefits clawed back & subject to a mandatory minimum prison sentence. Who the hell am I kidding! Neither is very likely to happen in the pr…
Runaway trim is supposed to be part of the "memory checklist" for pilots. The symptoms of MCAS are the same as runaway trim and the fix is the same (which is why Boeing didn't feel like extra pilot training was needed), so I'm curious to see the most recent investigation and hear the black box voice recorder. Did they not know they were dealing with runaway trim? Did they think it was something else? Did they forget…
You are correct. And if two crews in 5 months had the same issue either identifying or dealing with the same problem, then perhaps there is an design or training problem error here.
Earlier quoted context omitted.
>safety critical systems should always be redundant. That's east to say from an armchair but on an aircraft everything is "safety critical" to some extent and you have to choose what gets redundancy. Something where without it you can't fly the plane sure, that make sense. The argument for considering MCAS, a system which is not necessary to fly the plane safely, to be "safety critical" is much weaker. The Lion Air c…
> That's east to say from an armchair but on an aircraft everything is "safety critical" to some extent and you have to choose what gets redundancy. In flight entertainment, non-emergency lighting, food prep, &c aren't "safety critical" any more than the TVs in hospital rooms are. As a layman, I'd've imagined that all avionics and control surface control was redundant. Don't most large planes have redundant hydraulic…
Earlier quoted context omitted.
that sounds like the engineers are at fault for not refusing to stamp the thing.
The ones at fault at the people at the FAA who let Boeing certify their own planes.
An extra set of eyes saved them, it's a shame that there wasn't any way for them to include a reminder in the next crews flight plans.
The headline is really confusing; I thought I was perhaps reading it wrong, but it's sort of impossible to read correctly until you realize they are talking about a separate incident than the well-known crash. It would have been clearer if they had written something simpler, like "Lion Air 737 Nearly Crashed One Day Before Deadly Accident"
I still can't tell if it says whether or was actually the same individual aircraft.