[bsdbsd]

Well, did you all know that passengers were put back on the exact plane that sufferred the exact fate two years back on SFO-HNL route?! What are the chances of this?!

[aashishnb]

Somewhat off topic, attaching a 'differently honest' cockpit safety video

https://youtu.be/SZB4_-tiRt0

[GRAND23]

Originally Posted by BoneCollector

https://Youtu.be/sBxe4cQzUIY

It's great to see that no lives were lost in air or on ground.

There is no cowl on engine. Scary scenes indeed. Good that they have diverted the flight back to base (and that's what manual says too).

I work for aviation industry (specifically on engines). It looks like a fan blade failure for me. But wait! Blade failure can be contained and engine is designed for this. But if there are multiple blades failure then it cannot be contained and will lead to catastrophic failure.

Root cause of failure is something we need to wait until investigation completes. In aviation engines, even slightest things matter. There is something called "Hazard path". Means = Number of defects line up and they lead to catastrophic failure. There might be few/combination of defects in the engine which has lead this failure. Because, one defect cannot cause this large impact.

Almost all engines are designed to fly back with single engine and this is mandatory requirement from EASA approval. From this video, it looks like bad engine was still running or may be it was shut down later? Generally during blade failures, engine will be shut down immediately. Reason = uncontrolled fire will lead to further damages on aircraft.

Good that Boeing has stepped up the inspection on all P&W engines. You never want your entire fleet to be impacted.

[Jeroen]

Originally Posted by GRAND23

There is no cowl on engine. Scary scenes indeed. Good that they have diverted the flight back to base (and that's what manual says too).

There is no requirement to fly back to base, the pilots assess the situation and based on protocol and their own judgement decide where they want to land in essence. Obviously, if you have just taken off, the nearest airport is likely to be the one you have just departed from. But that is certainly not a given. Depending on how the pilots assess the situation they might want to give preference to another airport nearby.

Originally Posted by GRAND23

I work for aviation industry (specifically on engines). It looks like a fan blade failure for me. But wait! Blade failure can be contained and engine is designed for this. But if there are multiple blades failure then it cannot be contained and will lead to catastrophic failure.

The whole definition of a catastrophic failure is currently discussed on the various pilot forum. In layman terms, when the blades are breaking of and leaving the engine perpendicular and thus potentially can pierce the cabin it tends to be called catastrophic. Engine have special protective measure and some re-informcements in place to minimise damage by blades coming of the engine.

It looks that in this case most of the bits came out of the back of the engine. Still very serious, but a very different kind of failure it appears. We will have to see and hear more.

Originally Posted by GRAND23

Almost all engines are designed to fly back with single engine and this is mandatory requirement from EASA approval.

Not just EASA. I can’t think of a any aviation authority that doesn’t mandate the ability to loose one engine (on a twin) and even multiple engine failure on 3-4 engine planes.

In general, on twins, it is mandatory to be able to loose an engine during take off and still take to the air, and obviously stay cruising on one engine. It does come with substantial performance reduction, obviously.

Originally Posted by GRAND23

From this video, it looks like bad engine was still running or may be it was shut down later? Generally during blade failures, engine will be shut down immediately. Reason = uncontrolled fire will lead to further damages on aircraft.
.

It looks like the engine is simply windmilling. The pilots will have shut it down, which means no fuel is going to the engine. But part of the turbine is still in place and it is just the wind/air flow through the engine that makes it spin. You can observe the same effect on airplanes on the ground. Look at their engine, if there is some wind, you are likely to see them spinning around slowly.

Not quite sure what it is we see glowing/burning. Most likely some components that got very hot, or hydraulic oils spilling out.

Jeroen

[NevGin]

Originally Posted by Jeroen

It looks like the engine is simply windmilling. The pilots will have shut it down, which means no fuel is going to the engine. But part of the turbine is still in place and it is just the wind/air flow through the engine that makes it spin. You can observe the same effect on airplanes on the ground. Look at their engine, if there is some wind, you are likely to see them spinning around slowly.

Not quite sure what it is we see glowing/burning. Most likely some components that got very hot, or hydraulic oils spilling out.

Jeroen

Engine was announced as being secured so my understanding is extinguishing detergent was released from the extinguishers. Engine is certainly wind-milling. Flames would be from leaking fuel lines that would have been damaged by shrapnel.

[Jeroen]

Originally Posted by NevGin

Engine was announced as being secured so my understanding is extinguishing detergent was released from the extinguishers. Engine is certainly wind-milling. Flames would be from leaking fuel lines that would have been damaged by shrapnel.

Correct, they will have thrown the so called fuel cut off switches. That ensures no fuel will be go to the engine. And they will have pulled the fire engine handle which releases halon, pressurised by nitrogen.

Actually by pulling the fire engine handle a number of things, other than releasing the halon, are initiated as well. The generator is effectively tripped, fuel spar valve get closed, thrust reverser system gets disabled and a bunch more.

A couple of simplified diagrams”





Jeroen

[NevGin]

Originally Posted by Jeroen

Correct, they will have thrown the so called fuel cut off switches. That ensures no fuel will be go to the engine. And they will have pulled the fire engine handle which releases halon, pressurised by nitrogen.

Jeroen

Which makes me wonder what is the failback mechanism if the halon lines and nozzle are also impacted by the shrapnel and do not function as a result.

[Jeroen]

Originally Posted by NevGin

Which makes me wonder what is the failback mechanism if the halon lines and nozzle are also impacted by the shrapnel and do not function as a result.

None to my knowledge. Both bottles can be released to either engine I believe, to what extend they would have their individual plumbing, from bottle to respective engine, I don’t know.

Not sure if there has ever been a case where this has happened though.
If anything, you want to get back to mother earth even quicker!

[Typhoon]

The National Transportation Safety Board (NTSB) has attributed the incident to metal fatigue (caused due to excitations/vibrations). It can be seen from the image below (released by NTSB) that there are two fan-blades that are severed, one at the root and other around mid-span.



It is very likely that pieces of metal might have embedded in the Turbine section which is very hot and caused the fire. Usually these engines are designed to contain such debris and foreign particles (that is normally encountered in sandy conditions), but perhaps in this case the debris were one full fan blade and a half. Each fan blade is about 1.5 times taller than an average human.
Pilots have switched off the engine (or in other words cut fuel supply), so this engine was not running when the video is captured.

What remains to be answered is what might have caused to continue to propagate a fire, is it remaining fuel in pipes or oxygen at low altitudes as they were descending?