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Comment by dmkirwan | Hacker News Reader

A lot of the reporting that I read about this event showed an astonishing lack of critical thinking. As the linked article says, two things would have to have been true:

1: The aircraft entered into free-fall (i.e. falling at ~9.81m/s) at a low altitude and recovered within 1425ft. This would mean the wings were fully stalled and there was no drag or lift forces on the airframe while it was falling.

2: None of the many passengers on board felt the need to share it on social media.

Both of which are highly unlikely. I'd like to see the report of what actually happened, but I'm not sure if that will be forthcoming since it's a voluntary safety report. I'm not sure if they're treated similarly to NTSB investigations where the reports are made public.

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I'm not sure a stalled 777 at that altitude with that rate of decent would be able to recover in time.

Since they were flying in cloud, wouldn't spatial disorientation resulting in an accidental nose-down attitude be more likely than a stall?

A dive that gradually became steeper could cause that kind of descent without feeling like freefall to the passengers. They'd sure notice have noticed the 2.7g recovery at the end, though.

Generally spatial disorientation would be pretty unlikely this close to departure, since the departure path tends to be “straight forward with a climb gradient of X” - a pretty unusual situation for pilots of that level of experience.

A possible scenario that has been discussed before is the engagement of autopilot (which often happens at this phase of flight post-departure) with an incorrect altitude entered - my guess is something like 310 rather than 31000, particularly because the language used for altitudes above 17k is in flight levels - “cleared Flight Level 310”, autopilot engages, “whoops…” disengage, recover, climb and continue with corrected autopilot setting.

Again, still odd, but very experienced humans make mistakes like this pretty regularly.

> A possible scenario that has been discussed before is the engagement of autopilot (which often happens at this phase of flight post-departure) with an incorrect altitude entered - my guess is something like 310 rather than 31000

This sounds the most plausible to me of what I’ve heard. Would also explain why “further training” was ordered.

Not an expert here, but isn't this far beyond the descent rate that autopilot would employ in normal operations?

Ceilings were 800 feet, so they were in the clouds almost immediately after departure. The weather in the area that day was terrible and extremely turbulent. I think you drastically underestimate how powerful spacial disorientation is. Given the passengers lost all visual cues just after taking off, and there was likely at least moderate turbulence on climb out, the passengers probably just felt like it was a bumpy climb out. The human body doesn't register progressive falling very well without visual cues.

That amount of freefall would absolutely register. Falling is one thing - being weightless for a few seconds is absolutely noticeable.

I am also confused about the "spatial disorientation" argument, I'm not a pilot but I know there's a good reason there's a primary flight display with an abundance of information(including vertical speed, indicated airspeed and pitch) on the 777 which should've given pilots enough indication about what's going on.

A speed of 9.81m/s is not free fall. Acceleration of 9.81m/s² is. If you're actually in free fall, you will quickly accelerate past 9.81m/s to whatever your terminal velocity is.

A typical passenger jet flies at a speed of somewhere between 100m/s and 300m/s. Just a small downward angle can add a vertical component to that vector well above 9.81m/s. That's what I think we're seeing here, not a plane dropping out of the sky.

Yeah - I think if it was an autopilot engagement, the velocity may have been gradual enough that it just felt a little weird. Add in clouds - it’s not a crazy amount of altitude to lose in a jet like this, and you prepare for some weird feelings getting on a jet in the first place.

Did the pilots just not look at the altimeter? I’m not a pilot but it seems to me once the autopilot is set you’d naturally look at the altimeter and maybe airspeed indicator to confirm it was working.

Altimeter is a secondary instrument for a climb. The primary instrument for pitch would be the airspeed indicator (for a typical constant speed climb). The fact that they noticed the descent (on the VSI and altimeter) and corrected indicates they were scanning, but doesn't tell much about what was happening that caused them to transition from a climb to descent.

Yeah, agreed here - workload on a departure (depending on the type of departure) can be pretty heavy compared to cruise phase. Arrivals and approaches are more commonly known to have heavy workloads, but there’s a lot to do just after departure, so this doesn’t feel wildly out of bounds for a scan recovery after an autopilot mistake.

> A typical passenger jet flies at a speed of somewhere between 100m/s and 300m/s. Just a small downward angle can add a vertical component to that vector well above 9.81m/s. That's what I think we're seeing here, not a plane dropping out of the sky.

Don't pick on the commenter's unit mistake. The source material says "the aircraft would have dropped 1425 feet in 12 seconds maximum which requires about free fall acceleration" -- this is a 36 m/s descent; it started from a climb, and then ended in returning to 0 m/s at the minimum altitude. It's 2/3rds of a g acceleration downwards, minimum, if the data is valid.

CNN is reporting passenger accounts from the flight. I don't think the lack of social media reports is that telling.

https://lite.cnn.com/travel/article/united-777-plunge-takeof...

> I don't think the lack of social media reports is that telling.

Actually, I find it shocking that almost ten seconds of free fall plus many passengers being terrified to the point of screaming would go unmentioned on social media. That's not an experience you forget. :/

> Actually, I find it shocking that almost ten seconds of free fall plus many passengers being terrified to the point of screaming would go unmentioned on social media. That's not an experience you forget. :/

How do you know it hasn't been mentioned on social media? I have like 6 followers I could have posted my harrowing experience and nobody would see it

That’s a reasonable point. However, while things are more likely to go viral if the original poster has many followers, but it isn’t a hard requirement.

Any of those 6 followers could start things off by sending it to people that follow them at which point it can quickly go exponential.

Keep in mind that Maui in December is insanely expensive. The flight would be skewed older and richer, therefore less social media.

Unless there’s some conspiracy theory, I think it’s just a case of not everything everywhere is live-streamed by influencers (yet).

Searching Twitter for tweets with both airport codes SFO and OGG (the Maui airport code) on those dates: nothing

https://twitter.com/search?q=%22ogg%22%20%22sfo%22%20since%3...

For all messages @united with 1722 on those dates: nothing mentioning this incident

https://twitter.com/search?q=%40united%201722%20since%3A2022...

For all messages @united with SFO on those dates: nothing mentioning this incident

https://twitter.com/search?q=%40united%20sfo%20since%3A2022-...

For all messages @united with OGG on those dates: nothing mentioning this incident

https://twitter.com/search?q=%40united%20ogg%20since%3A2022-...

For all messages with the words maui flight on or around those dates: lots of messages about bad weather, turbulence injuries on a Honolulu-bound flight, delays and cancellations, a lot of complaints about sitting on the tarmac for 30-90 minutes waiting for a gate on Alaska Air flights to Maui, and the Hawaii Life Flight helicopter disappearance, but not this incident

https://twitter.com/search?q=maui%20flight%20since%3A2022-12...

Even if they did go on social media. It's like a sand in the ocean, not everything on social media get's amplified. Chances are folks were told to put away their electronic device since it was during the takeoff, so no one has a recording. That means a tweet or facebook post with no image or picture? Might get 1 or 2 thumbs up.

People pay for that kind of experience: https://www.gozerog.com/

The news cycle was pretty heavy with the other incident involving unexpected turbulence that resulted in hurt passengers.

https://www.hawaiinewsnow.com/2022/12/18/multiple-injuries-r...

Those passenger accounts sound like a word-for-word rewriting of the maybe-faulty radar reports.

Not to besmirch the fine folks at CNN, but I don't believe this article at all. Will wait for more from the pilots, who sound like they've been very open, forthcoming, and responsible here.

https://www.dailymail.co.uk/news/article-11746913/Passenger-...

It's unlikely to enter an actual free-fall by stalling the plane, but it's entirely possible to produce an acceleration of -1 G by diving - the astronaut training airplanes are doing it all the time. The question is just, why would a normal passenger aircraft do it (except maybe in an extreme emergency)?

> 1: The aircraft entered into free-fall (i.e. falling at ~9.81m/s) at a low altitude and recovered within 1425ft. This would mean the wings were fully stalled and there was no drag or lift forces on the airframe while it was falling.

It's not true that falling at 9.81m/s means no drag or lift forces were on the place, it could also mean the plane was pointing down and it was engine thrust was accelerating it downwards (not just gravity)

They presumably meant accelerating down at g (9.81 m/s/s) rather than steady velocity of 9.81 m/s.

Whether engine or gravity, that would cause an uncomfortable feeling of weightlessness in the cabin and vertical velocity would build quickly.

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