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> And finally we don't even know the level of instability It'd approach criminal liability if the FAA certified a plane they didn't know the level of instabili
by ethbro 8y ago
> And finally we don't even know the level of instability
It'd approach criminal liability if the FAA certified a plane they didn't know the level of instability of. This is why test flights are performed.
As the other commenter mention, something that gets lost in this discussion is the fact that MCAS was there to make the control feel approximate other airframes.
The same aero adjustments could be accomplished by the pilot, but regulations prohibit their being necessary. So, MCAS.
We're talking 'stability that adheres to control forces required by regulation' rather than 'F-117 drop out of the sky' instability.
- pedrocr 8y ago> It'd approach criminal liability if the FAA certified a plane they didn't know the level of instability of. The question isn't if they didn't know, it's if this is an unusual level of instability for an airliner. >We're talking 'stability that adheres to control forces required by regulation' rather than 'F-117 drop out of the sky' instability. Hopefully yes, but we don't know how much instability there is. If you assume the answer there's no point having the discussion.
- mikeash 8y agoAerodynamically unstable aircraft cannot be flown purely by humans. They require a fly by wire system. The 737 is not fly by wire, thus we can pretty trivially conclude that the 737 is aerodynamically stable.
- pedrocr 8y agoThat's pithy. MCAS is definitely fixing something.
- mikeash 8y agoOf course, but it’s not fixing aerodynamic instability.
- pedrocr 8y agoHow does that change anything? If the instability is not aerodynamic and instead is runaway pitch up on power, how is that any different?
- mikeash 8y agoYou keep insisting that we don’t know if this airplane is unstable. My point is that we do know. If you want to argue that some other aspect of it makes it equally dangerous, be my guest. I’m just correcting that one thing.
- pedrocr 8y ago>You keep insisting that we don’t know if this airplane is unstable. Because we don't. You've only corrected a strawman, that we know this plane isn't a fully aerodynamic unstable design like an F-16. No one thought that. I never even specifically said aerodynamically unstable, just that we don't know the level of instability MCAS is correcting for to know if it is unusual for an airliner design. From what I had read I had assumed it was actually a power-on issue and not aerodynamic. But as it turns out the issue is indeed apparently aerodynamic from the engine shape generating more lift at higher angle of attack and thus leading to pitch up. And no, we don't know. We the public at least. We don't know how big the flight envelope is where MCAS is needed or how much of an issue it would be if MCAS didn't exist. From public information we don't know if without MCAS the plane wouldn't enter an unrecoverable pitch up attitude in normal flying conditions. That's not knowing if the plane isn't inherently unstable.
- mikeash 8y agoJust a few comments up, your response to the idea of being totally aerodynamically unstable was “hopefully yes.” Not “of course it’s stable, that’s obvious.” https://news.ycombinator.com/item?id=19556911 https://news.ycombinator.com/item?id=19556911 I’m not responding to a straw man, I’m responding to what you wrote. If it’s not what you meant, well, I can’t really do anything about that.
- ams6110 8y agoRead mhandley's post upthread. It explains what MCAS does: it addresses a certification requirement for handling control forces at high angles of attack.