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Comment by philip1209 | Hacker News Reader

I'm skeptical of this account - Newton's First Law says that an object in motion stays in motion. Losing instruments for a second doesn't cause a change in momentum - that would have needed to be a stall, a change in trim, or an external weather event such as a downdraft. A stall would have been accompanied by a stall recovery procedure involving attitude + thrust changes, and nobody seems to be reporting that in the article.

I'm no professional, but if I had to guess - the plane got hit by a hard gust, and the gust triggered a short in some electronics that caused the screens to go blank. (So, the opposite direction of causality).

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>Newton's First Law says that an object in motion stays in motion.

How is this relevant? There is turbulence and gravity, this isn't "empty" space.

> Losing instruments for a second doesn't cause a change in momentum

No, but modern jets need computer-aided control of flight control surfaces to keep the aircraft stable.

If the account is accurate sounds like quite literally everything had a blip for a second, which would have prevented computer-intervention when encountering severe turbulence, or worse, flight control surfaces became "stuck."

Nitpicking. I agree with your broader point.

> No, but modern jets need computer-aided control of flight control surfaces to keep the aircraft stable.

Most aircraft outside of fighter jets are aerodynamically stable. Loss of powered flight would mean the airplane will glide (in nominal operation). Even the 737MAX7/9 aircraft are still stable (although that brings up defining exactly what we mean by aerodynamically stable... )

>Most aircraft outside of fighter jets are aerodynamically stable.

Sure, but there is significant overlap between being stable and throwing around passengers, unfortunately.

Dropping 500 feet is perfectly okay for the aircraft and it will largely continue to not simply fall out of the sky past that.

That's not what aerodynamically stables means. Anything external that would cause a 787 to drop 500 feet is probably going to do that with or without the flight computers working.

In the case of military aircraft, they quite literally can't glide or maintain stable flight without the flight computer actively managing the control surfaces.

A 787 is perfectly capable of flying in steady state should the computer glitch.

modern jets need computer-aided control of flight control surfaces to keep the aircraft stable

Small nitpick, commercial jets are designed to be aerodynamically stable. If controls froze briefly, the plane would continue to be stable, flying as it was when the controls froze. You'd need to add in the turbulence or some external force for it to be a problem. That said, the 787 is 100% dependent on electronic controls, so anything more than brief loss of controls would lead to a crash.

>You'd need to add in the turbulence or some external force for it to be a problem.

Which is what I said :). The computer controlled flight control surfaces aren't just keeping the aircraft aerodynamically stable, they're keeping it comfortable/safe which is what "stable" means in this context (since it's a passenger jet).

Dropping 500 feet is nothing for the aircraft. That's a different story for the passengers.

Yes, I wanted to draw the distinction between other types of aircraft, like some military jets, which compromise stability (either for performance or stealth), and need the computer controlled surfaces to fly straight. I take stable to mean, not unexpectedly changing speed and direction, not just smooth.

If passengers were touching the ceiling, it would have required either a very powerful downdraft or control surface inputs leading to greater-than gravity acceleration downwards. Very interested to hear the investigation into this.

Murphy's law, "anything that can go wrong (eventually) will go wrong". Gusts triggering a short that blocks out fly-by-wire would be even more worrying than poor coding. You know landings generally have lots of gusts and would be a terrible time to locked out.

Better make sure nothing can gonwrobg then with robust systems

> and the gust triggered a short in some electronics that caused the screens to go blank

That is a hilariously complex first guess.

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