Incident: United B772 at Kahului on Dec 18th 2022, pilots filed safety report

by hugh-avherald • 3 years ago

75 44 3 years ago

sokoloff4• 3 years ago

The voluntary safety reporting system is well-designed IMO, with some details here: https://www.asias.faa.gov/apex/f?p=100:43:::NO::P43_REGION_V...

It’s administered by NASA (not the FAA or NTSB) and I trust them to do what the program claims. I’ve submitted a few reports over the years. One received follow up from a program administrator to ensure they understood the details*. None of the incidents were subject to any FAA follow up, so I never had to test the immunity parts.

* This was a case where the Automated Terminal Info recording was advising pilots to remain clear of a local MLB stadium by reference only to the name of the stadium and not any navigational data to help find it.

dmkirwan• 3 years ago

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.

hugh-avherald• 3 years ago

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...

thaumasiotes• 3 years ago

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. :/

throwayyy4790872• 3 years ago

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.

rpeden• 3 years ago

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.

jcutrell4• 3 years ago

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.

shawabawa32• 3 years ago

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)

sokoloff4• 3 years ago

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.

rob74• 3 years ago

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)?

kijin• 3 years ago

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.

jcutrell4• 3 years ago

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.

mlyle• 3 years ago

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.

nyc_pizzadev• 3 years ago

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

bmitc• 3 years ago

It is curious to me as to why there are zero details as to what actually happened or what additional training was assigned.

dboreham• 3 years ago

Because the details are bad?

sammalloy• 3 years ago

There were at least two separate incidents that day due to three frontal systems moving into the islands at that time. This led to turbulence thought to impact flights UA1722 and HA35, but there were actually three incidents if you expand and widen the timeframe to December 15.

On December 15, N13G7, a Hawaii Air ambulance, took off from OGG on route to the island of Hawaii when it descended from 8000 ft and spiraled into the Maui Channel where it impacted the water.

https://www.civilbeat.org/2023/01/air-ambulance-crash-expose...

https://www.documentcloud.org/documents/23565244-report_anc2...

jcutrell4• 3 years ago

Lots of speculation as to why people didn’t talk about the experience.

A few points should be made: - We don’t feel velocity, we feel acceleration/deceleration. While a sudden drop would feel crazy, if the jet rolled out and into the dive it may be subtle enough initially that the free fall was hard to feel. The pull-up out of the dive probably would have been felt, but! If the pilot came on the intercom and talked about weather, or if the attending crew didn’t act odd after the event, people are less likely to assume something weird happened.

Add to this the likelihood of IMC, as well as the likelihood that the crew warned of potential light turbulence - you’ll have a plane full of well-primed people who accepted the experience as “mostly normal.”

Add to that that there wasn’t likely wifi for another 10min or so, people may forget pretty quickly…

The graph looks wild, but people don’t feel that raw data. Perception is everything, and it is not that surprising that accounts of this event aren’t popping up like crazy.

colinmorelli2• 3 years ago

This makes sense, but during takeoff in a plane of 100+ people, none of them happened to be looking out a window and notice that they were falling below the cloud cover and getting a lot closer to the ocean? Or were they still in the clouds?

EDIT: Someone in another comment mentioned that ceilings were 800 feet, so passengers likely would not have noticed they were getting closer to the ocean at all.

mh-• 3 years ago

This CNN article suggests people definitely did feel it.

“It felt like you were climbing to the top of a roller coaster. It was at that point,” Williams said. “There were a number of screams on the plane. Everybody knew that something was out of the ordinary, or at least that this was not normal.”
The experience was harrowing for passengers.
“When the plane started to nosedive, multiple screams are being let out, at that point,” Williams said. “You’re trying your best to maintain your composure – there’s obviously kids on the flight – nobody really knows what’s going on, but at the same time, you’re concerned. You don’t know if this is an issue, but it was certainly out of the ordinary.”
“Someone from the cockpit got on the intercom and said, ‘Alright, folks, you probably felt a couple G’s on that one, but everything’s gonna be OK. We’re gonna be alright,’ ” Williams said.

https://www.cnn.com/travel/article/united-777-plunge-takeoff...

kashunstva• 3 years ago

The lack of communication with ATC about the incident is odd. Surely an altitude loss of that magnitude should have caught the controller’s attention.

I don’t know the meteorological details but heavy rain was reported; so low-level wind shear during climb-out is a possibility. But why would the crew not make a PIREP once they were stabilized? It’s something other aircrews would like to know. And were that the case, why would the airline need to subject them to additional training, unless their LLWS escape procedures were improper?

blantonl2• 3 years ago

That airplane snitched on that crew when this incident happened via FOQA datalinks. The 777 is equipped with a real time data modem via Inmarsat that sends back to the United operations home base data on each flight. The SFO United chief pilot was probably waiting for them at the gate when they landed. Airlines will use FOQA data to notify them when overspeed actions or other quality problems occur in flight and will ding the pilots. It's very common.

Also, spacial disorientation is a thing, and the body doesn't typically sense falling very well without visual cues. It is entirely possible that the drop coupled with turbulence on the climb out didn't register with passengers (nor the pilots!) as much as you think. If you've ever experienced unusual attitude recovery training as a pilot, you'll know that it's somewhat shocking what your body is telling vs what you see when you pull your head up and look outside. It is a jarring experience when you learn that your body is straight up lying to you.

thehappypm• 3 years ago

Yeah, elevators are like that too! Get into an elevator in a skyscraper and drop 500 feet in a short time, your brain has almost no cue.

martopix• 3 years ago

the body doesn't typically sense falling very well without visual cues

the post talks about freefall (-1g) and +2.7g. These would be very noticeable.

cmurf• 3 years ago

Noticeable, but not translatable into any sort of spacial awareness. I'm a commercial pilot with an instrument rating, but as a passenger with the only information being a sequence of variable forces, I absolutely can't tell you what our orientation is at the end of that sequence.

~2.6G is a severe hard landing. A 60-degree bank in level flight produces 2G's. One is really jolting because it happens in an instant, the other is certainly noticeable but also a more docile because it happens over time. If the 2.7G force is over a few seconds, my guess is I'd associate it with moderate to severe turbulence and not give it another thought. Do we know the duration of these forces?

Edit: Also from Avherald, Simon writes From my editorial point of view it is clear however, that the occurrence did not happen along the lines of the report that surfaced on Sunday. And I tend to agree with that, the original reporting is confused how serious the event was. Something happened, pilots self-reported, and received training.

ngcc_hk• 3 years ago

Wonder is this also on airbus and whether this is a new requirement after the loss of the Malaysian airplane?

jlmorton• 3 years ago

In addition, if indeed 2.7G were encountered, passengers would certainly have reacted and this occurrence would have been all over the media the next day at the very latest.

While it must have been a scary ten seconds, you can't show g-forces very well on video, especially when it lasts a few seconds. If anyone from this flight had shown up on social media recounting the tale, they would be met with a chorus of voices telling them it's just normal turbulence.

loser777• 3 years ago

What is a bit concerning is the speculation that the flight continued to the intended destination in an effort to avoid having the incident captured by cockpit voice recorder (which apparently only have a recording window of 2 hours???!?).

sokoloff4• 3 years ago

If the problem was understood and corrected, I don't see any operational reason to not continue to the destination. (Same story on the AA runway incursion in NY. They knew what happened; it was corrected; they called company and continued the trip.) The CVR over-write is a side-effect of those correct decisions.

Incident: United B772 at Kahului on Dec 18th 2022, pilots filed safety report

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