Jeju Air737-800 Crash at MWX (Muan International Airport, South Korea)

[Evan]

Extremely unlikely. First of all smoke needs some time to enter the cabin and then you need the cabin crew to call the cockpit to inform the guys up front.
(Don't know if this works with the 737 PA without generator power)
With a total electrical failure and an (at least assumed) double engine failure, smoke removal is the very last thing to consider and this procedure takes a loooong time.

Yeah, that theory doesn't add up.

[Evan]

To release the landing gear on the 737, the Copi needs to move his seat to the aftmost position, open the hatch and pull three handles. I don't think that this was an option, that close to the runway, at that low altitude and low speed.
Curious if they find out at what position the flaps/slats were. As mentioned before, clean config isn't a GA setting.

Another possibility, though remote, is the the CB "ALTN EXTEND SOL" (P6-3 D16) was left open after maintenance and the alternate gear failed to function. This was the issue with the LOT 767. Maybe that panel survived the crash so they could rule it out. I'm still thinking they simply got overwhelmed and spaced out the gear extension. The landing appears to me like an attempt at a main gear touchdown. As Gabriel said, we may never know.

[Gabriel]

Another possibility, though remote, is the the CB "ALTN EXTEND SOL" (P6-3 D16) was left open after maintenance and the alternate gear failed to function. This was the issue with the LOT 767. Maybe that panel survived the crash so they could rule it out.

Did you forget the blue font or was that a serious comment?

[Evan]

Did you forget the blue font or was that a serious comment?

You mean about the survival aspect?

[Gabriel]

You mean about the survival aspect?

All of it!!!

The 737 and 767 shear the same landing gear logic
And the same CB with the same number / coordinate
In the same CB panel
Located in the same place where it can be subject to accidental disconnecting
And that also happened here
And that the panel survived with the CB's in their pre-impact position

[Evan]

All of it!!!

The 737 and 767 shear the same landing gear logic
And the same CB with the same number / coordinate
In the same CB panel
Located in the same place where it can be subject to accidental disconnecting
And that also happened here
And that the panel survived with the CB's in their pre-impact position

The 737 and 767 don't share the same logic that I'm aware of, but they both have a CB on the P6 panel that controls the uplock release. On the 737NG it is ALTN EXTEND SOL" (P6-3 D16).
They probably both have a maintenance procedure that involves opening this CB and then closing it again when completed. They are both subject to the same human error. This is an oversight that can go a long time without being detected.
I have no idea what the state of the wreckage is, but if the part of the P6 panel having this CB was recovered, it might rule out this possibility. If it was found open or collared, that might rule it in.
And, if you read all my words, will see the words 'remote' and 'possibility'. I don't think this is likely to have occurred. But it is one that has occurred.

Edit: I have an image of that CB on the 737-700 P6 panel, but this infernal forum software won't let me upload it.

[Evan]

737-700NG P6 Panel

[Gabriel]

Interesting. I need to go and re-read that 767 accident report to understand the logic. And then also check the 737 system. Why would a CB interfere with you pulling some cables to release the up locks? And how to extend the gear if there is a total electrical failure? It doesn't make immediate sense to me.

[Evan]

Interesting. I need to go and re-read that 767 accident report to understand the logic. And then also check the 737 system. Why would a CB interfere with you pulling some cables to release the up locks? And how to extend the gear if there is a total electrical failure? It doesn't make immediate sense to me.

The uplocks are released by motors that are on that circuit. If the circuit is unpowered, they won't unlock.

[Gabriel]

Ok. alternate gear extension, if I am understanding correctly:

In the 757 and 767 there is a guarded switch next to the landing gear lever that, when flipped, activated a DC motor (fed byt he essential bus) that unlocks the up-locks, and the gear extends by gravity.

In the 737 you have the 3 pull cables that unlock the up-locks mechanically. No amount of CB's and electrical failures would impede that.

What is the function of the P3-6 D16 ALTN EXTEND SOL circuit breaker, then? I couldn't figure it out.

[Gabriel]

The uplocks are released by motors that are on that circuit. If the circuit is unpowered, they won't unlock.

In the 767, yes. In the 737, apparently not.

[Gabriel]

CVR and FDR...

https://www.youtube.com/watch?v=1TKoCI9kVtc

I am still looking at it. Very detailed but it seems that nothing new.

[Gabriel]

737 Landing Gear system (link points to the timestamp where the alternate manual extension starts)

https://youtu.be/6CZk8outH6U?si=gwuQcqGRkZxJQmZN&t=1612

[Evan]

Gabriel, that circuit on the 737 may just power a solenoid that protects the hydraulic system from locking if the hydraulics are restored when (after?) using the alternate gear extension. Apparently that microswitch on the alternate gear hatch is what prevents this. If that hatch is open, normal gear retraction will not work. Ditto if the CB is open (or unless that CB is open?). I don't have time right now for the video. Does it mention the purpose of that microswitch?

[Gabriel]

Gabriel, that circuit on the 737 may just power a solenoid that protects the hydraulic system from locking if the hydraulics are restored when (after?) using the alternate gear extension. Apparently that microswitch on the alternate gear hatch is what prevents this. If that hatch is open, normal gear retraction will not work. Ditto if the CB is open (or unless that CB is open?). I don't have time right now for the video. Does it mention the purpose of that microswitch?

I don't remember exactly but it was something like that. But in that case the position of the CB would not impede alternate extension. It could impede normal extension/retraction though. But in any case I agree with you that the likelihood of this being a factor is remote. So I think we can let this dead horse rest in peace (at least by now).