3 ms·

>the airplane did not have stable flight characteristics because of its physical design. This is a gross oversimplification of the problem. In most of the fli

by na85 7y ago

>the airplane did not have stable flight characteristics because of its physical design. This is a gross oversimplification of the problem. In most of the flight envelope the aircraft is stable. At high alpha the aircraft has pitch problems. There are myriad ways to address this, and MCAS was one (bad) choice of many available to Boeing.

leoc 7y ago
That's the devilish thing, I think. Making the plane unstable then patching things up with MCAS, or something else, isn't a fault in any straightforward way. But it is taking a risk, and the source of risk isn't simply the risk that eg. MCAS will fail on any given flight, it's also the higher-order risk that eg. the MCAS system will have a faulty design. (A bit like rewriting code in C for performance, or keeping on generally unloved code to satisfy a paying customer, presumably.) I assume that makes the ethical and safety decisions a lot more murky for the engineers than having a specific fault to point to, especially in an organisation afflicted with go fever.
sokoloff 7y ago
I believe the airplane is aerodynamically stable even at high alpha. What it fails in certification is the requirement to have continually increasing pitch feedback forces. I believe the pitch feedback forces are still in the stable region, just too low. This is not a flying wing or intentionally unstable airplane (as the F-16).
- leoc 7y ago
  >> [...] In most of the flight envelope the aircraft is stable. >> At high alpha the aircraft has pitch problems. > I believe the airplane is aerodynamically stable even at high alpha. [...] This is not a flying wing or intentionally unstable airplane (as the F-16). In some ways that's likely worse news than an airplane that's inherently unstable in general, no? A corner case, and one that evidently isn't actually all that uncommon. If you're building something like an F-16 you know that you absolutely have to make the fly-by-wire correct and robust, and the ground crews similarly know that if anything affects its performance the plane isn't fit to fly.
- inferiorhuman 7y ago
  I believe the airplane is aerodynamically stable even at high alpha. That would put you at odds with Boeing's test pilots.
  - sokoloff 7y ago
    No it wouldn't (or "citation needed" if so). The issue is not that the airplane shows negative or neutral aerodynamic pitch stability, it's that it does not exhibit an increasing stick force gradient, as required by certification rules. https://airfactsjournal.com/2019/03/can-boeing-trust-pilots/ https://airfactsjournal.com/2019/03/can-boeing-trust-pilots/

by na85 7y ago

leoc 7y ago

That's the devilish thing, I think. Making the plane unstable then patching things up with MCAS, or something else, isn't a fault in any straightforward way. But it is taking a risk, and the source of risk isn't simply the risk that eg. MCAS will fail on any given flight, it's also the higher-order risk that eg. the MCAS system will have a faulty design. (A bit like rewriting code in C for performance, or keeping on generally unloved code to satisfy a paying customer, presumably.) I assume that makes the ethical and safety decisions a lot more murky for the engineers than having a specific fault to point to, especially in an organisation afflicted with go fever.

sokoloff 7y ago

I believe the airplane is aerodynamically stable even at high alpha. What it fails in certification is the requirement to have continually increasing pitch feedback forces. I believe the pitch feedback forces are still in the stable region, just too low. This is not a flying wing or intentionally unstable airplane (as the F-16).

leoc 7y ago
>> [...] In most of the flight envelope the aircraft is stable. >> At high alpha the aircraft has pitch problems. > I believe the airplane is aerodynamically stable even at high alpha. [...] This is not a flying wing or intentionally unstable airplane (as the F-16). In some ways that's likely worse news than an airplane that's inherently unstable in general, no? A corner case, and one that evidently isn't actually all that uncommon. If you're building something like an F-16 you know that you absolutely have to make the fly-by-wire correct and robust, and the ground crews similarly know that if anything affects its performance the plane isn't fit to fly.
inferiorhuman 7y ago
I believe the airplane is aerodynamically stable even at high alpha. That would put you at odds with Boeing's test pilots.
- sokoloff 7y ago
  No it wouldn't (or "citation needed" if so). The issue is not that the airplane shows negative or neutral aerodynamic pitch stability, it's that it does not exhibit an increasing stick force gradient, as required by certification rules. https://airfactsjournal.com/2019/03/can-boeing-trust-pilots/ https://airfactsjournal.com/2019/03/can-boeing-trust-pilots/