Bird feathers, blood found in both engines of crashed jet in South Korea, source says

Posted by The_Stockholm_Rhino@reddit | aviation | View on Reddit | 82 comments

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truthisnothateful@reddit

How could all electrical power, including to the black boxes, just go away 4 minutes before the crash? Can you have a total blackout on a 737 like that?

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atokirina1991@reddit

Maybe? I mean, don't the generators draw the power from both engines? Explains why the recording stopped in the last 4 mins.

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Both generators are run by the engines. Engines stop, no power except for some battery essential bus systems. From other comments it seems the black boxes are directly powered by the generators with no backup in this model of 737. Later versions were required to change that.

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truthisnothateful@reddit

How could a modern aircraft even be designed without a hefty battery backup system for critical items including the boxes? What about APU? They had 4 full minutes. Am I to understand that a B-17 had a better battery system than a 737?

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Mdrim13@reddit

It takes 3 minutes to fire the APU and it’s pretty far down the list.

Sully was Sully because he understood this and fired the APU first and out of order.

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acynicalmoose@reddit

Yes but RAT should also provide minimum hydraulics and electrics no? Unless the FCR and CVR aren’t supplied?

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Mdrim13@reddit

I thought the same. Was surprised it’s absent on this generation.

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biggsteve81@reddit

737 doesn't need a RAT, as it has manual flight control cables and you can still fly the plane without any hydraulic power whatsoever. Gear can be manually dropped with no power as well. Which means, theoretically, the 737 should do better in a dual engine failure than fly-by-wire aircraft.

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Mdrim13@reddit

I think having one to back up the CVR is a pretty good use case here. The batteries obviously didn’t work here and the name of the game in aviation safety related items is redundancy.

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JimmyCarters-ghost@reddit

The CVR doesn’t keep the plane from crashing. They have battery backup on the newer models.

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Mdrim13@reddit

My comment was on electrically providing redundant power? What’s your point?

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JimmyCarters-ghost@reddit

You said the “batteries didn’t work”. There is no indication of that. The batteries don’t back up the CVR in that year model but the CVR isn’t critical equipment. It’s nice to have sure but it’s not that important.

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biggsteve81@reddit

Starting in 2010 all 737s sold to operators in the US and Europe have a RIPS system that will keep the CVR active for 10 minutes after power failure (or engine shutdown). This plane was manufactured in 2009 and so it was not required to have this option. Installing a RAT just to power the CVR is a bit much.

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NukeRocketScientist@reddit

No RAT on the 737 or at least that version.

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acynicalmoose@reddit

You learn something new everyday…. Supposedly they would have ~60 mins of battery power, wonder what happened.

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NukeRocketScientist@reddit

From what I understand, the justification for not having one is redundancy, but considering the circumstances, clearly not enough. It is interesting how similar this situation is turning out compared to the Hudson River landing with wildly different outcomes. If you assume both pilots were just as experienced and skilled, it comes down to A320 versus 737, and that is not a good look for Boeing again.

An interesting difference, though, is that since the Hudson River landing landed on water, they never tried to put the gear down. It makes you wonder if they would have had a similar outcome if they were able to turn back to LaGuardia immediately. Again, though, the A320 does have a RAT, so they may not have had any difficulty putting the gear down anyway.

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JimmyCarters-ghost@reddit

A RAT would have made zero difference. Also there is no reason to just assume that the pilots of this flight were as experienced as the cactus 1549.

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Reasonable_Lunch7090@reddit

These are not comparable situations with what we know and you're forcing this into an Airbus vs Boeing thing.

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flightist@reddit

If you assume both pilots were just as experienced and skilled

Which would be an absolutely wild thing to assume, given the 737 was landed without landing gear.

The 320 needs a RAT because you need computers and hydraulics to so much as move a control surface. If you lost both gens you’d almost certainly lose control of the aircraft before the APU is online.

A 737 can fly just fine - if not as a particularly fun experience for anybody - until the APU is on.

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Only_Razzmatazz_4498@reddit

Not 100% sure about this one but on the RAT only the captain side is powered. Apparently in this version the recorders aren’t powered by batteries or the RAT.

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biggsteve81@reddit

No 737 has a RAT; it has manual fight controls and a battery for essential avionics. For 737s made after 2010 there is an option for a battery backup on the CVR, but this airframe was manufactured before that was an option.

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Only_Razzmatazz_4498@reddit

Good point I saw that mentioned after I wrote my comment

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MBTbuddy@reddit

Question for a complete novice. Why would turning on what is essentially the emergency power in the apu be so far down a checklist for a potential loss of engine?

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Mdrim13@reddit

Not that important relative to the other tasks.

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The_Stockholm_Rhino@reddit (OP)

Juan Browne - Blancolirio breaks it down here: https://youtu.be/0CgO01n1px0?si=P7ymZCmbUkuqnMU5

Of course we’ll have to wait for more info from the investigation. But if it’s a dual engine outage + stress + stupid concrete wall art the end of the runway = makes sense to me.

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truthisnothateful@reddit

Thanks for the link. IIRC, Sullenberger fired up the APU as soon as it was apparent both engines were toast. But because of this truly shitty electrical design we’ll never know if these guys even tried.

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mimicthefrench@reddit

In Sully's case one of the engines was actually functioning enough to provide electrical power, though not any meaningful thrust. It's why the plane never left normal law and the RAT never deployed. Starting the APU was definitely the right call, though. More redundancy is generally good.

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hr2pilot@reddit

…and IIRC, when in normal law, the bus will automatically and conveniently hold green dot speed with no need for PF to chase an airspeed.

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mimicthefrench@reddit

Yep. If you read William Langewiesche's book Fly By Wire, he makes a strong argument that while Sully's decision making and piloting were more or less flawless and he's certainly worthy of praise for that, much of the safe landing itself came down to the plane itself being so automated and letting him focus on the situation at hand rather than having to worry about whether the plane would stall.

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hr2pilot@reddit

Exactly…Sulley and his crew must be given much credit for saving so many lives that day, but I often wonder whether the outcome would have been different had he been operating an airplane having less automation and technology.

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Gloomy_Pick_1814@reddit

If the two survivors were in the aft jumpseats they would normally be able to hear the APU starting. Obviously with everything going on they may or may not have though.

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mattrussell2319@reddit

Very reasonable working hypothesis

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TogaPower@reddit

Because airliners have a ton of systems to run, and batteries can only power so much while still providing a reasonable amount of time to land the aircraft safely (things like basic navigational systems, avionics, etc. ).

Generally speaking, they’ll provide power to critical systems for about 30 minutes.

It obviously varies by aircraft, but I can see why an FDR wouldn’t be considered an essential item in a no-kidding dual generator failure. Fact of the matter is, it isn’t essential to the safety of that aircraft anymore.

A dual gen failure where the only thing left to power certain systems being the battery is so rare, that it isn’t surprising that designers would, in this freak scenario, decide that the battery is better reserved for other systems.

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Only_Razzmatazz_4498@reddit

The boxes aren’t critical other than after the fact. I don’t disagree that they should have battery power but I wouldn’t call it critical equipment.

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truthisnothateful@reddit

Depends on what you call critical. If the data could save lives going forward, isn’t that kind of critical?

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Only_Razzmatazz_4498@reddit

Not at all to the people on the plane. Whatever makes it more likely for the pilot to be able to control and land the plane is critical. I wouldn’t trade a data recorder for the ability to see the airspeed or being able to move the control surfaces.

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IncidentalIncidence@reddit

How could a modern aircraft even be designed without a hefty battery backup system for critical items including the boxes?

The standby power doesn't power the boxes because they aren't flight-critical. The CVR and FDR on newer planes have an independent battery backup that doesn't take power from the standby circuit.

What about APU?

The APU can provide hydraulic pressure by running the EMDPs. I would imagine it can also provide electrical power to the FDR/CVR, but I'm not sure. But we know they didn't have hydraulic pressure, so they either never fired the APU, it didn't have time to come online before they crashed, or the APU had some sort of failure.

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Qel_Hoth@reddit

But we know they didn't have hydraulic pressure,

Do we know they didn't have hydraulic pressure? Gear and flaps were up, but they also had a reverser deployed.

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IncidentalIncidence@reddit

I guess you're right, that's not 100%. I assumed it because of the flaps and gear being up.

But I think that if both engines were out and the APU for whatever reason never came online, they would have very little hydraulic pressure -- only whatever could be generated by the EDPs connected to the windmilling engines.

If the APU had been operational, the transponders and CVR/FDR should have come back online as well.

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flightist@reddit

Doesn’t take any hydraulics to drop the gear.

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11Kram@reddit

But it takes quite a bit of time to wind down the gear by hand in the floor of the cockpit.

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flightist@reddit

No it doesn’t, mainly because you don’t wind anything. You pull three cables to release the three uplocks.

Takes about 5 seconds.

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11Kram@reddit

Can these be reached from one of the pilot’s seats?

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flightist@reddit

Yes.

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IncidentalIncidence@reddit

it takes way more time than they had to do it by hand

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flightist@reddit

It takes less time than it took you to type that sentence.

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biggsteve81@reddit

It is also legal to dispatch the 737 with an inoperative APU, as long as it doesn't fly ETOPS.

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truthisnothateful@reddit

Was the reverser deployed or did it get ripped open?

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Flaxinator@reddit

The thrust reversers on on the 737 can be deployed without hydraulic pressure

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66hans66@reddit

Modern aircraft? A 737?

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truthisnothateful@reddit

Compared to a B-17, I’d say so!

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66hans66@reddit

Hey, only 32 years between first flights :-)

Also, are we really going to compare the technical needs of heavy bombers with airline transport planes?

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truthisnothateful@reddit

No, we’re not. I’m just a pilot/plane nerd with a passion for electronics. So naturally I’m fascinated by the battery systems on those old bombers and the APUs they had that were powered by a pull-start Briggs & Stratton or Tecumseh engine. Coming from that perspective, it just feels silly to me that back then they were able to muster enough battery power to turn over a cold 18 cylinder radial engine, now they don’t have enough extra battery to power a CVR and FDR. That’s just how my brain works.

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drakanx@reddit

Wouldn't exactly call a 737 a modern aircraft.

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truthisnothateful@reddit

Well, compared to the B-17 I mentioned…

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JFlyer81@reddit

The 737 can run critical systems for I think 30 minutes on the battery backup (more than enough time to get the APU running or even just get down on the ground.) The FDR/CVR were, at the time this aircraft was built, simply not required to be connected to that backup bus.

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TheDrMonocle@reddit

Can't tell ya. Only think I can think of is black boxes arent essential to the safety of flight. They're just essential in determining what happened. And there are plenty of other things that can help determine that.

That being said, it is silly they aren't on some backup power. Just as this scenario proves. Why it was like that, who knows. Tho it's probably money. Its always money

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Qel_Hoth@reddit

For the FDR specifically, there's not much point backing it up unless you are also backing up all the things it draws data from.

For the CVR, they are required to have a backup since a few years after this plane was built. Retrofits weren't required though.

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evthrowawayverysad@reddit

I do not understand how on god's green earth they didn't decide to add some level of battery powered redundancy into or in line with the black boxes power supply at the time.

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Qel_Hoth@reddit

Generators are connected the the engine shaft though, right? So if the engines are turning (even windmilling) the generators are working.

The only thing that kills the generators if the engines are still turning sufficiently fast is the fire handles.

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fly_awayyy@reddit

No there is a minimum speed for generator engagement if it can’t spin fast enough to generate power it will drop off line.

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TheDrMonocle@reddit

I'm not personally familiar with the 737 specifics but I'd be surprised if the generators work with just windmilling. I would think there would be an electrical disconnect as the system senses engine shutdown to remove any sort of load on the engine to facilitate a restart. Again, I don't know, but thats my thought as an A&P who only worked on CRJs for 2 years.

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beachletter@reddit

A 20+year 737 captain made this analysis: Based on how the plane executed the go around, how smoothly it climbed and turned back to land (no way to do it that smoothly with just muscle and steel cables), plus the fact that the pilots made last minute cabin announcements after birdstrike (as revealed by passangers' phone messages), there was no way this plane has completely lost power in the last 4mins.

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Joehansson@reddit

What strikes me most is that the gear wasn’t extended, even though there is the gravitational option for the 737.

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beachletter@reddit

They didn't extend any flaps, the plane was not in a landing config, there would be no gear related warning as the plane assumed they were not landing.

It was possible that they though the gear was down, so they made a typical approach, assuming the gears would start touching ground at the appropriate touchdown zone, yet there were no gear and they floated on air. When they finally touched ground with the belly they've already used half the runway.

In fact, even if the gears were down they were still doomed because at zero flaps they touched down way too fast. It would be impossible to stop on that short runway with or without landing gears.

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The_Stockholm_Rhino@reddit (OP)

Wrote this further down, copypasta:

Juan Browne - Blancolirio - breaks it down here: https://youtu.be/0CgO01n1px0?si=P7ymZCmbUkuqnMU5

Of course we’ll have to wait for more info from the investigation. But if it’s a dual engine failure + stress + stupid concrete wall at the end of the runway = makes sense to me.

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hookahsmokingladybug@reddit

That concrete wall was the killer. Can't wait for the Mayday Air Disaster ep on this one

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Agent_of_talon@reddit

There's really a gruesome and twisted sense of irony to all of this. They managed to touch down (in one piece) despite everything, ...and then got obliterated anyway.

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Jambi1913@reddit

It’s truly tragic.

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ludicrous780@reddit

It's a tiny chance but can still happen. 1/50 doesn't mean never.

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1401_autocoder@reddit

"Stopped recording" and "data missing" are not specific enough to say the black boxes lost power or stopped functioning. All those statements say for sure is that the boxes didn't receive any data to record. "Data missing" sort of implies that they were recording, but had nothing to record, IMO.

If you have seen a reliable statement that says the black boxes stopped, I would like to see it.