Uncontained RR Trent fan blade failure

[DIBO]

https://cimg1.ibsrv.net/gimg/pprune.org-vbulletin/675x1200/gaaoas8wyaaymns_dfe9ddb87a011de840b138c665dbc5cff503153c.jpg
source: X
https://twitter.com/JacdecNew/status/1731229652557926657



(already a day or two old, hope not a double post, but didn't see this coming by, nor found it while forum-searching)

[DaveReidUK]

Notwithstanding what sources such as Jacdec and Avherald would have us believe. there's no evidence that it was uncontained.

No way did a blade and a half exit through a hole that small.

[tdracer]

Media reports say that it was uncontained (and we all know the media is never wrong :rolleyes:).
However, in fairness, "uncontained failure" means parts escaped radially from the engine - it doesn't mean they were big pieces. So the size of the hole(s) doesn't matter - that there is a hole suggests that bits exited.

[Uplinker]

Judging by the marks on some of the other blades around the leading edge bends about 1/3 out from the hub; it looks as though some FOD has hit the fan disc ?

[MechEngr]

I'd guess one of the blades fractured, thrust from inertia initially pulled it forward before it got slowed and laid down in the housing by contact with the housing, and then got tossed around for a bit until it wedged and took out it's buddy. I'm expecting the nearly entire blade was the first to go, leaving a gap to wedge under the half blade and the half blade was the one that exited the flight. There looks to be a torn up blade behind the fan.

Maybe there was some FOD, but it isn't required to explain the damage. This failure could have been initiated by a fatigue crack starting at a nick or a tiny inclusion smaller than x-ray techs were looking for. Hoping for the nick.

[DaveReidUK]

Media reports say that it was uncontained (and we all know the media is never wrong :rolleyes:).
However, in fairness, "uncontained failure" means parts escaped radially from the engine - it doesn't mean they were big pieces. So the size of the hole(s) doesn't matter - that there is a hole suggests that bits exited.

The generally-accepted meaning of "uncontained" is that high-energy rotating parts (blade/disk/etc) escaped radially.

Word on the street is that the P/T probe underneath that access panel is what went through it, likely liberated by the shock that went through the engine when the fan blades impacted the containment ring (and were contained).

[DaveReidUK]

Judging by the marks on some of the other blades around the leading edge bends about 1/3 out from the hub; it looks as though some FOD has hit the fan disc ?

The blade failure reportedly occurred at around FL340, though of course that doesn't necessarily preclude prior damage sustained at a lower level.

[PPRuNeUser0203]

Go watch some of the fan blade off test videos on YouTube and you’ll see jet engines doing exactly what they’re supposed to do in this situation.

The thing the regs and designers worry about is “high energy debris”, namely large chunks of fan blade that could puncture the wing or fuselage with catastrophic consequences.

The containment system is primarily designed to capture the fan blade root. It’s basically having Thor’s hammer thrown at it. This incident isn’t a root failure, so we’re well within the casing’s capability.

As for the aerofoil, by time the first blade hits the containment casing, it’s been turned almost 90 degrees by contact with the trailing blade so it hits side-on. This makes the containment system’s job a bit easier, since it has to catch and stop a barn door side-on rather than a throwing knife tip-first.

Anything else that gets thrown out is most likely fragments of the blades blown forward during the engine surge. That debris could easily rip out the P2T2 probe, if the engine vibration doesn’t do the job first.

Looks to me like this engine has dealt with the FBO exactly as planned, with no high energy debris release.

[procede]

The blade failure reportedly occurred at around FL340, though of course that doesn't necessarily preclude prior damage sustained at a lower level.

There has to be a somewhat increased load to make it fracture exactly at that moment and not earlier or later, so it was probably during a step climb.

[dixi188]

It could be earlier damage and vibration caused a crack to extend and then fail.
Do Trent engines have fan vibration monitoring? Our old CF6s had the vibration pick-ups removed due to too many false warnings.

[NutLoose]

Media uncontained = blown out the arse end.. ;)

[DaveReidUK]

Media uncontained = blown out the arse end.. ;)

While we can perhaps cut the mainstream media a bit of slack, aviation-oriented sites like JACDEC and Avherald really ought to know better ...

[tdracer]

The generally-accepted meaning of "uncontained" is that high-energy rotating parts (blade/disk/etc) escaped radially.

Word on the street is that the P/T probe underneath that access panel is what went through it, likely liberated by the shock that went through the engine when the fan blades impacted the containment ring (and were contained).
While I certainly understand and accept the fundamental difference between 'high energy' and 'low energy' debris exiting the engine, the fact remains that something came out the side.
While low energy is highly unlikely to do any secondary damage, we would still have bookkept it as 'uncontained'.
BTW, for certification purposes, low energy debris could cause damage, but we could take credit for 'shielding' to protect particularly vulnerable stuff like wiring. Low energy was typically stuff like turbine/compressor blades that didn't weigh much and rapidly lost energy once out of the engine. Turbine disc debris was 'high energy' and no credit could be taken for shielding - you needed things like physical separation. It was assumed fan disc debris would go wherever it damn well pleased...
There was one particular fan disc scenario that we started accounting for after the Sioux City DC-10 - a fan disc fragment goes through the aircraft floor beams side-to-side. This was messy, because lots of critical systems have traditionally been routed through the floor beams since they provided so much protection. After Sioux City, we started moving redundant stuff either through the cargo floor or the main deck overhead.

[MechEngr]

A similar secondary ejection killed a woman on a Southwest flight and required a rapid change of course to get much closer to the ground and higher air pressure.

The responsibility for the shroud (housing?) is the aircraft designer and for containment falls to the engine maker; there seems to be a sliver of opportunity between the two where a containment event can eject part of the housing with enough energy to breach the fuselage or some other part of the aircraft.

[Tom Sawyer]

Seems very similar to this event; https://www.atsb.gov.au/publications/investigation_reports/2017/aair/ao-2017-066 .

[Rebus]

If memory serves me well, that hole is forward of the kevlar containment belt.

[PPRuNeUser0203]

If memory serves me well, that hole is forward of the kevlar containment belt.

Yep the P2T2 probe is in the inlet, forward of the fan case front flange.

Well, it was…

[MechEngr]

Suspiciously similar failure Feb 9, 2018, considering the nearly identical radial position of the blade failure:

https://twitter.com/JacdecNew/status/961858322272890880

From avherald:

On Sep 30th 2019 Singapore's AIB released their final report concluding the probable causes of the incident were:

- The failure of the fan blade with more than 75% missing material originated from a fatigue crack that initiated at the acute corner of the inner convex surface bond.

[tdracer]

If memory serves me well, that hole is forward of the kevlar containment belt.
Parts exiting forward of the fan containment is something we started to see with the increasing high bypass engines that started appearing in the late 1980s. Back with the original JT9D/CF6-50 engines, we never saw that, but we did started seeing damage forward of the containment ring in the 1990s. I suspect the higher bypass ratios - along with the move toward wide cord fan blades - meant that more fan debris was of the size, shape, and mass that meant the aero forces could more readily overcome the inertia forces acting on released blade fragments and pulling them forward of the containment ring before they lost enough energy to prevent them damaging/penetrating the inlet. I believe this was a factor in a few blade out events on Boeings that released the inlet.
I was in a meeting long ago where this was discussion of requiring additional protection for blade debris forward of the requirements for the containment ring, but I don't know what ever became of that.

[PPRuNeUser0203]

Well there’s more energy in an individual wide chord fan blade than the narrow-chord ones of previous generations, and they’re more likely to get chewed up too.

Also as bypass ratio has gone up, so has overall pressure ratio (last stage of compressor pressure divided by compressor inlet pressure).

At takeoff a JT9D’s OPR is 25 ish versus the Trent 700’s OPR of 36. And it’s even higher at ToC, 45ish.

Later generation engines have an ever higher OPR: The Trent XWB’s is over 50, and the GE9X should be 60.

So when the fan blade goes, it’s followed by one seriously powerful surge. The bits at the top of the pressure gradient are at the back of the HP compressor, and now have 14 stages of compressor and what’s left of the fan to get back through, generating more and more debris as they go.

So it’s not bypass ratio as such that’s the cause, more the OPR that’s risen with it.

And yes it’s all moving at Mach 0.82, your brain says everything should go backwards at high speed with the incident airflow.

But in the surge, that incident airflow is reversed temporarily, causing the ejection of debris forwards through the compressor, then radially outwards by the fan. Plenty of low-energy debris to make a mess of the intake and wing, but nothing that could cause serious damage.

I have to admit though, if the P2T2 probe has been taken out that would be unusual.

[NutLoose]

This may help.

https://cimg7.ibsrv.net/gimg/pprune.org-vbulletin/675x900/image_4ad162e37388c68b29e03a8d578ee78730f1314d.jpeg

[NutLoose]

Film in the cabin, a fair bit of vibration there from the engine failure.

https://weibo.com/2084223127/NvsnKpNXS?pagetype=profilefeed


https://s.weibo.com/weibo?q=%23东航mu721航班故障机舱画面曝光%23 (https://weibo.com/2084223127/NvsnKpNXS?pagetype=profilefeed)

[MechEngr]

It may not be the energy of a single blade that does the damage, but the outward impulse from a broken blade getting plowed outward by the remaining blades in the fan. A similar effect happens in explosions from IEDs where the blast and fragments from the IED doesn't penetrate, but it gives the vehicle hull a sharply rising deformation that leads to pulverizing or kicking loose anything on the other side. The deformation doesn't have to be large if the item on the other side has not gap and has good conduction from the impulse. Given that it separated part of a second blade and split a third, the initial blade fragment got a pretty good smack before the containment ring let it escape.

[DaveReidUK]

the initial blade fragment got a pretty good smack before the containment ring let it escape.

We don't actually know that the containment ring didn't perform its intended function.

[PPRuNeUser0203]

We don't actually know that the containment ring didn't perform its intended function.

In fact we know that it DID.

Remember this aircraft has suffered one of the most violent failures possible. And it flew and landed safely.

Job done.

[MechEngr]

We don't actually know that the containment ring didn't perform its intended function.

The "it" was the impulse. The impulse clearly escaped.

[tdracer]

Film in the cabin, a fair bit of vibration there from the engine failure.

Airframe vibration is a big concern - it can be almost unimaginably violent. There have been reports of the vibrations after a Fan Blade Out event being so severe that the crew can't see the flight deck instruments.

I can't think of any FBO events that have resulted in an extended diversion time before they were able to land, but there are serious concerns that if one occurred in the middle of a 180 (or longer) ETOPS flight, the extended exposure to that level of vibration could have highly adverse effects on both the aircraft and the flight crew performance. And the move to ever larger fans means that the FBO vibration levels are just going to get worse.

[NutLoose]

Airframe vibration is a big concern - it can be almost unimaginably violent. There have been reports of the vibrations after a Fan Blade Out event being so severe that the crew can't see the flight deck instruments.



I have had that in real life when the aircraft we were running spat out the IGV’s through the turbine and up the detuner coming out the top like a mushroom cloud, we couldn’t read a damned thing and it stopped seized in a couple of turns when we managed to chop the fuel.