AF66 CDG-LAX diverts - uncontained engine failure over Atlantic

[EEngr]

Originally Posted by RatherBeFlying

Possibly a fan blade, but can't say for sure from the available photos. Cowl pieces are the other possibility, some fragments in the vanes look like composite.

It does look like a blade, with the spline that engages in the fan hub slot near the top (#176). I'd guess that if the fan did come loose and move forward, getting tangled in the cowling's Kevlar containment band made short work of the integrity of the fan. If they go looking for it, it won't be a fan stuck in the ice of Greenland. More likely a 20 mile trail of blades and pieces of cowling.

[Nonbiased]

I have a video on my youtube account which has all the details from my perspective as a passenger in row 12 of LAST Class, the unlucky ones who went to ATL on the second flight. I can't post links though as I'm a noob. Does anyone want to DM me and put the link up to share the experience with you guys?

[ManInJapan]

Originally Posted by lomapaseo

I take it that some have not noted what looks to be an intact fan blade and its attachments lodged in the vanes behind the fan?

That doesn't look like a fan blade to me, and if the fan blades (even just one) hit the guide vanes behind them, I think you'd see a lot more damage to the guide vanes. They look almost untouched. The debris in the photo could be anything really.

[ManInJapan]

Originally Posted by EEngr

Just guessing here: The fan hub to shaft coupling is designed to withstand quite a bit of thrust (produced by the fan). But the fan hub to LP compressor barrel coupling not nearly so much. It's more for the torque of spinning the compressor. So an initial failure of the shaft to fan (where a jagged piece remains) would allow the fan to pull forward. The 24 (?) bolts holding the compressor stage failed under tension (photo in #194). That may be by design. To let the fan go forwardvwithout trying to pull the compressor rotor through the stator.

Like 'lomapaseo' I'm inclined to think that purposeful design of the fan to separate is unlikely, but to me your sequence of failure sounds right. I do find it surprising however that the bolts at the compressor flange all failed.

My armchair opinion is that the bolts in the flange were not tightened / sized / put in correctly.

A failure of the driveshaft would pull the whole LP compressor forward which would either pull it through the guide vanes and out the front of the engine with the fan. Or the guide vanes (stators) would hold (as they have done) and prevent the LP compressor from moving out of the engine. In this case the deceleration of the LP compressor and the fan would be high, but I doubt high enough to severe the bolts at the LP compressor flange as cleanly as what has occurred.

[pax2908]

Still, perhaps it is the latter ... if the core comes to an "instant" stop, the choice might have been to let the fan "snap" off, rather than overstressing the engine attachment to the wing. But what do I know

[procede]

Originally Posted by Barnsbury

The suggested failure modes still don't fully add up. The fan would have been producing a leisurely five or six tons or so of thrust, which wouldn't have troubled anything compared to the previous take-off loads, so this isn't an overload failure.

It probably happened during a step climb, thus at higher thrust levels.

The total load case is not just thrust, but also torque and centrifugal loads.

I would think that with the lower air density, the rotational speed of the fan will be considerably higher at altitude than at ground level for the same amount of thrust.

[wrighar]

Originally Posted by ManInJapan

That doesn't look like a fan blade to me, and if the fan blades (even just one) hit the guide vanes behind them, I think you'd see a lot more damage to the guide vanes. They look almost untouched. The debris in the photo could be anything really.

Difficult to say with these pictures.

[DaveReidUK]

Originally Posted by procede

I would think that with the lower air density, the rotational speed of the fan will be considerably higher at altitude than at ground level for the same amount of thrust.

No engine is capable of producing the same amount of thrust at cruise level compared to SL.

But of course it doesn't need to.

For a large turbofan, N1 in the cruise will typically be in the region of 80%.

[procede]

I agree. Maximum thrust levels decrease with altitude.
During a step climb N1 will probably get close to 100% (max climb).
One more thing to mention is thermal stress, which could be higher at altitude. And then there are acoustic stresses...

Does the GP7000 have heating in the cone? Could well be that that failed...

[Stumpy Grinder]

If it waddles like a duck and goes Quack then it's probably a duck......


That there is a fan blade, of that there can be no doubt.

[Onceapilot]

Originally Posted by DaveReidUK

No engine is capable of producing the same amount of thrust at cruise level compared to SL.

This is, of course, incorrect. It would be correct to say that modern civil turbofans produce their highest or limiting thrust at low altitude.

[scifi]

What is left of the engine should be able to spin without causing much vibration.
However, the passengers felt a lot of vibration for several seconds.
This seems to imply that the fan broke up in sequence... First one blade detached, then the vibration caused all the bolts to fail, and what was left of the fan disk spun off forwards.
.

[DaveReidUK]

Originally Posted by Onceapilot

This is, of course, incorrect. It would be correct to say that modern civil turbofans produce their highest or limiting thrust at low altitude.

Hmmm. It sounds like we're saying the same thing in two different ways.

That aside, since maximum thrust on any jet engine is achieved at zero TAS, I think we can safely say that's not available at altitude.

[Musician]

looks like that's a fan blade

Comparing these details (taken from the big twitter images that tricityb linked in post #175) with the picture of posted by Stumpy Grinder in #185 that shows a worker assembling the fan, I can identify the curved line separating the two types of surface on the blade and the rounded ridge that locks the blade to the hub.

[CAAAD]

I think it may well be a fan blade.

The dovetail root length from the very useful GA is about half the span of the fan OGV, and the leading edge of the fan blade is about one OGV span from root to change of curvature in profile. Also , the root is the correct colour.

And a bit of containment on the blade tip.

Fan failures are very chaotic affairs and we cannot possibly predict the sequence of events from the limited material available.

I'm sure East Hartford will have a very good idea by now.

[slip and turn]

Originally Posted by scifi

What is left of the engine should be able to spin without causing much vibration.

Might you mean pie in the sky?

However, the passengers felt a lot of vibration for several seconds.

Yes.

This seems to imply that the fan broke up in sequence... First one blade detached, then the vibration caused all the bolts to fail, and what was left of the fan disk spun off forwards.
.

Yes a sequence as long as your arm and more! For my money, and admittedly it is a statement of the bleedin' obvious, I reckon the bright sparks will eventually compute from the available remains that there was a lot more going on after the first thing broke than had previously been computer-modelled. And personally from a little reading around the subject, I have little doubt that at some stage - milliseconds or possibly whole seconds after the first thing broke - a somewhat massive lump came off in a dizzying non axi-symmetric whirl, having long since (well a few seconds anyway!) given up the momentum of its original purpose to something more of a sling shot effect, and in passing gave the wing leading edge (some distance behind the fan case not forward of it) quite a ding!

I really would love to see that tail fin video - but will we ever? Anyone know if footage is retained informally other than by passengers who happen to be filming the screens on the backs of seats?

[Stumpy Grinder]

The post fan blade off (FBO) vibration is 2 phased, firstly a High Level Short Duration (HLSD) followed by (normally) Low Level Long Duration as the unbalanced engine windmills. All gas turbine and airframe parts are subjected to either test or analysis to demonstrate that they can remain attached and if necessary functional during and after a FBO event.

[DType]

It could have been even more exciting if the fan had detached when still on the ground during take off. When they drop to the ground, they zip v v rapidly sideways, bouncing as they go. I've seen a few holes in test bed roofs, and liberated (turbine) discs in distant fields.

[G-CPTN]

If, as is suggested, that the fan 'broke up', what chance of it being due to FOD damage?

Birdstrike or drone?

[slip and turn]

Originally Posted by DaveReidUK

Notwithstanding the fan blade(s) embedded in the guide vanes, the engine did still satisfy that particular FAR, in that it neither caught fire nor detached from its mounting attachments.

Well now we're venturing into the bounds of semantics - when I studied the subject of how power is delivered, we sat down and opened learned reference works titled "propulsion" as opposed to "engines".

As I understand it, an aircraft engine these days comprises several modules each and every one of which is mounted in a obligatory fixed sense in relation to each adjacent module and at sundry well chosen points directly to the airframe. Plenty of suitable elasticity is built in, of course.

So the plan is that the collection of major engine bits on landing should still ideally be reasonably complete even after an FBO. That's as opposed to a scenario where the fan and fan containment module are merely expected to self-adhere to their master's heel through the worst of the thick and thin, but having given up their angular antics, are allowed to pop off in some as yet undeciphered direction when the final urging to leave gets overwhelming!

Bearing in mind that the few hundred kilo module delivering 80% of the propulsion is indeed our Elvis in this case, one wonders if the purport of § 33.94 seriously allows for an exit like that ... methinks not.

For the pernickety and legal-minded, the question might be 'What is meant by "mounting attachments" in § 33.94?', but I am sure more serious-minded engineers are somewhat beyond that.