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South Korea plane crash kills 179 with investigation into cause under way (www.bbc.com)

submitted 5 days ago* (last edited 4 days ago) by [email protected] to c/world

22 comments fedilink hide all child comments

cross-posted from: https://rss.ponder.cat/post/81292

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[–] [email protected] 42 points 5 days ago* (last edited 4 days ago) (5 children)

This crash is very strange to me. No flaps (even if hydraulics fail, there's electrical backup), no gear (there's gravity extension backup), landed way down the runway (9000' should have been plenty, gear up landing has been done in shorter distances)... what happened?

My guess at the moment: bird strike made the pilots panic, they didn't ensure the plane was in the correct configuration when attempting the second landing, and tried to put it down soft and ended up going long?

What do I know though, I'm not a pilot, just a fan of disasters and flight simulation. Guess I'll have to see what blancolirio has to say.

Edit: Juan Browne, aka Blancolirio on YouTube finally posted a video on this, probably some of the best insight we'll get at this early stage.

[–] CMahaff 12 points 4 days ago (1 children)

I don't know enough to say if it's a valid theory, but I saw one commenter suggest this scenario:

Bird strike takes out 1 engine.
Wrong engine is shut off by the pilots by mistake (now both engines aren't operating)
Without engine power, hydraulic systems stop working properly
Pilots realize their mistake too late while trying to do a go around, try to land instead farther down the runway since they can't climb.

[–] [email protected] 5 points 4 days ago* (last edited 4 days ago)

I’m inclined to believe hydraulics were functioning based on the stabilized approach. The recent Azeri plane crash is what it looks like when you have no hydraulics. Granted, different planes, 737 NG has manual control, but it’d be difficult. Aside from a little shimmy the approach was good, especially considering they whipped a 180 after that first landing attempt on runway 01. The plane seemed to be well in control.

Also of note, there doesn’t appear to be any rudder applied on the approach, so one engine out seems to not be the case. They also tracked straight down the centerline so no asymmetric thrust. This would imply they either had both engines or no engines. I’m hesitant to believe both engines were out due to the speed they had after scraping down the runway, with the nose in the air.

I’m wondering if they got task saturated after the bird strike and quick go around 180, didn’t hear the “too low, gear” warning, then got spooked from the scrape and attempted a go around like that PIA crash. The initial tail strike happened way earlier on the runway, they floated for a long time after that initial contact.

Altogether very strange. Definitely a lot of Swiss cheese holes aligning in a terrible way. Very curious to see what’s recovered from the FDR and CVR.

[–] krimson 9 points 4 days ago

Way too fast as well it looks like. Maybe both engines failed and it was the last possibility to get it down. RIP. Last moments must have been awful, especially for the pilots who saw that wall coming ..

[–] [email protected] 6 points 5 days ago (2 children)

I don’t think whatever electrical backup has enough power to deploy flaps at landing or near landing speeds.

[–] [email protected] 9 points 4 days ago* (last edited 4 days ago) (1 children)

737 NG alt flaps work up to 230 knots, well above landing speed. Landing with hydraulics out is the primary function of the alt flaps system. It's really slow, however, so flaps 15 is typically the most they use.

[–] [email protected] 4 points 4 days ago (1 children)

I didn't find the speed rating for the alt flaps, but I was able to verify that it is an electrical system backup

https://www.airliners.net/forum/viewtopic.php?t=1481455

[–] [email protected] 3 points 4 days ago* (last edited 4 days ago) (1 children)

There's a placard in the cockpit with flap speed limits.

[–] [email protected] 1 points 4 days ago

You know what? I like the C152 better. It’s color coded around the speedometer.

[–] Blackrook7 3 points 5 days ago (1 children)

That's unfortunate if true

[–] [email protected] 2 points 4 days ago

Looks like I'm wrong.

[–] Maggoty 1 points 4 days ago

I'm wondering if they were even able to setup properly for the second landing. Assume competent pilots and the wheels, flaps, and reversers cannot deploy. Was the second engine even actually working? The video we have is them already on the ground. So it makes me wonder if we're looking at the alternate scenario of having landed in the Hudson.

[–] kautau 1 points 4 days ago

Not a 737 Max, but again, another Boeing plane whereas I haven’t seen a fatal airbus accident in ages. It may not have been the plane at all and may have completely been pilot error, but still doesn’t look great to see another fatal 737 accident

[–] [email protected] 22 points 4 days ago (1 children)

Definitely a strange crash, although it sounds like there was some mechanical stuff going on as a result of multiple bird strikes on the previous approach.

Lots of airports around the world have EMAS which is designed to stop an airplane in this situation. Unfortunately this airport has a concrete wall instead. Google maps has it labeled as "Walls of death", although I don't know if that was recently added or if they've had that nickname for a while. https://maps.app.goo.gl/eX9Fp9RXeVkRB94L9

[–] [email protected] 3 points 4 days ago* (last edited 4 days ago) (1 children)

EMAS requires a certain pressure to break through the surface. It’s designed for gear down overruns, not belly landings. I don’t think it’d do much if it were installed in this case.

From skybrary.aero:

Additional assumptions for all designs are that:

an aircraft is still attempting to stop as the runway is exited

reverse thrust / reverse pitch is not being used as the runway is exited

the surface area leading to the EMAS bed has poor braking characteristics

there is minimal or no structural damage to the landing gear

there is no aircraft braking or use of reverse thrust / reverse pitch once an aircraft enters the EMAS

That penultimate point is key. It’s not designed for a no gear landing, or even damaged gear landing. It adds friction by the gear sinking into the materials.

[–] [email protected] 1 points 4 days ago (1 children)

Typically yeah, but I think there was likely enough weight on the engine cowls to make the engines dig in to EMAS. I wonder if it has ever been tested.

[–] [email protected] 3 points 4 days ago

Certainly wouldn't have hurt, but I don't think it would have done that much.

From skybrary:

Most installations to date have used a maximum 70 knots bed-entry speed.

...and thats with gear down. I believe the Jeju plane was doing something like 130+ kts off the end of the runway.

[–] werefreeatlast 12 points 4 days ago

The world's brick laying standards have now been updated to "when asked to build a brick, stone or cement concrete by an airport agency to be located at the end of the roadway, you are legally and morally bound to beat the living bejisus out of whoever's idea that was.