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zeke
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Re: AF66 CDG-LAX (A388-F-HPJE) diverts to Goose Bay (YYR) with reports of suspected damage to leading edge above #4 engi

Mon Oct 02, 2017 2:01 pm

TheLark wrote:
Well, if you search for "mutually exclusive independent events" you'll find nothing, because such events do not exist. This is a contradiction in terms, events are either independent or mutually exclusive, but never both.


Yes they do, an engine status is either serviceable or failed, it cannot be both, the status is mutually exclusive. They are independent as the status of one engine does not effect the status of another in the population (if one engine is serviceable does not mean the engine next to it is unservicable or serviceable). They are mutually exclusive independent events. Just look at the aircraft that landed, #4 engine failed, its status unserviceable, and the remaining engines remain serviceable as they are independent of the failed one.
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Re: AF66 CDG-LAX (A388-F-HPJE) diverts to Goose Bay (YYR) with reports of suspected damage to leading edge above #4 engi

Mon Oct 02, 2017 2:05 pm

Planetalk wrote:
I think you've misunderstood me. Yes engine failures are independent events, and one failing does not increase the odds of another failing. All anyone has said is that because there are more engines on a 4 engine plane, there is a higher chance of any one engine failing. That's basic maths. The chance of an engine failing is the sum of the individual odds across the number of engines on the plane. I thought it was clear but let me try and make it clearer. No-one said 4 engine planes are higher risk. And as you know the reasons their ETOPS rules are less strict is because losing one engine on a quad isn't an emergency as it is on a twin. All anyone said is the uncontroversial fact that is you have 4 of something, there is a higher chance something could go wrong with one of them and if you have two of it. And I think I'll leave it there because we're getting side tracked by this slightly ridiculous discussion about whether 4 times a number is bigger than 2 times a number.


As pointed out, the chance of an engine failing is NOT "the sum of the individual odds across the number of engines on the plane". If we assume that probability of a single engine failing is 0.6, then certainly for a twin-engine plane the chance of any of the engines failing is not 0.6 + 0.6 = 1.2 and for a quad not 2.4 (as probability has to be between 0 and 1).

The correct calculation is inverse of the none of the engines failing, that is 1 - (1- P)^N, where N is the number of engines and P probability for a single engine failure. This assumes that engine failures are not dependent on each other.
 
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Re: AF66 CDG-LAX (A388-F-HPJE) diverts to Goose Bay (YYR) with reports of suspected damage to leading edge above #4 engi

Mon Oct 02, 2017 2:12 pm

Planetalk wrote:
All anyone said is that there is a higher chance of one out of a set of four engines failing than one out of a set of two. You don't even needs all this maths, it's basic logic.


The logic is flawed because as you increase the number of engines, the number of hours flown also increases by the same factor, so the numerator increase is cancelled by the denominator increase.

Planetalk wrote:
Look at it like this, imagine you can either buy 4 lottery tickets or two. Each individual ticket has an extremely low chance of winning. But if you buy 4 there is a higher chance that one will win than if you only buy two, obviously. Of course with regard to engines 'winning' is losing.


That is not correct as lottery tickets are not independent events, it is a finite dependent series, it is a big series, but every unique event can be calculated. Engine failure rates are infinite independent series as the population is always growing.
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Re: AF66 CDG-LAX (A388-F-HPJE) diverts to Goose Bay (YYR) with an uncontained engine failure to #4 engine

Mon Oct 02, 2017 2:21 pm

Just curious, what are the criteria for grounding the A380 fleet ? Who makes the call ? Is it an airline-specific issue ? An Airbus issue ? Or an engine-manufacturer issue ?

I mean, first QF32, and now this. Seems to me like there would at least be a hold put on operations until the cause can be identified.

Thanks in advance for your input.
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dopplerd
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Re: AF66 CDG-LAX (A388-F-HPJE) diverts to Goose Bay (YYR) with an uncontained engine failure to #4 engine

Mon Oct 02, 2017 2:22 pm

N14AZ wrote:
peterinlisbon wrote:
It looks to me like one or more of the low-pressure blades must have come loose and cut into the cowling whilst spinning at high speed like a circular saw

But in such a scenario, wouldn't you expect some shrapnels hitting the fuselage? That's what happened in case of VH-OQA:

Anyhow, too early to speculate. They will find out...


Based on the very little we know about AF incident, no. AF 380 failure appears to have happened in the fan/LP compressor half of the engine. The QF 380 failure happened in the HP turbine half of the engine. The difference is that compressors get energy from the shaft while turbines give energy to the shaft. When a compressor separates from the shaft it looses its source of energy but in a turbine separation it looses a place to put energy and rapidly accelerates to the point of exploding with a tremendous amount of force. This is what happened with the QF32 and the American 767 at O'Hare last year. At O'Hare parts of the exploded disk were found thousands of feet away inside a UPS freight hanger.
 
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Re: AF66 CDG-LAX (A388-F-HPJE) diverts to Goose Bay (YYR) with an uncontained engine failure to #4 engine

Mon Oct 02, 2017 2:27 pm

dik909 wrote:
Just curious, what are the criteria for grounding the A380 fleet ? Who makes the call ? Is it an airline-specific issue ? An Airbus issue ? Or an engine-manufacturer issue ?

I mean, first QF32, and now this. Seems to me like there would at least be a hold put on operations until the cause can be identified.

Thanks in advance for your input.


An airline can always ground its own fleet. A Civil (or Federal) Aviation Authority can ground airplanes under its jurisdiction. For example, in Boeing 787 battery problems, first the Japanese airline affected grounded its own fleet, then Japanese CAA grounded Japanese carriers, and then other aviation authorities (including US FAA) grounded the 787 fleets worldwide. FAA really should have revoked the Airworthiness Certificate in that case (as the plane was clearly not airworthy any more), but it was deemed too a drastic action.
 
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Re: AF66 CDG-LAX (A388-F-HPJE) diverts to Goose Bay (YYR) with reports of suspected damage to leading edge above #4 engi

Mon Oct 02, 2017 2:29 pm

TheLark wrote:
zeke wrote:
Have a search for yourself for the mathematical proof of mutually exclusive independent events and you will see that the probability is zero.


Well, if you search for "mutually exclusive independent events" you'll find nothing, because such events do not exist. This is a contradiction in terms, events are either independent or mutually exclusive, but never both.

The correct way to describe it is: if you have a fully redundant system of two completely independent components, and each component has a very low but finite probability of failure within a given interval, say 1 in a million per day, then the probability of both failing within this interval is 1 in a million squared, which is one in a trillion. In a quad, the probability is 1 in a million to the fourth power, whatever this tiny number is called. That's the theory. In practice you'll often find that many failures are not completely independent, often there are subtle dependencies you don't think about, and the combined probability is higher.

We are discussing two different scenarios here: (1) ALL engines fail, (2) ANY engine has an uncontained failure. In the second case the risk is much lower to begin with, say one in a trillion, but redundancy does not help here. In a twin the risk is then two in trillion, and in a quad four in a trillion.

Both scenarios have very low, but non-zero probabilities, in twins as well as in quads. I've made the numbers up, you'd have to do thorough risk analysis to get real numbers, but you get the idea. In any aircraft either scenario may be more likely than the other, or both risks may be of the same magnitude.

But now I have to go back to doing risk analysis for medical devices, because that's what I do for a living.


As an engineer, I truly appreciate the sound comment about the debate in place. Thank you
 
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Re: AF66 CDG-LAX (A388-F-HPJE) diverts to Goose Bay (YYR) with reports of suspected damage to leading edge above #4 engi

Mon Oct 02, 2017 2:43 pm

Finn350 wrote:
Planetalk wrote:
I think you've misunderstood me. Yes engine failures are independent events, and one failing does not increase the odds of another failing. All anyone has said is that because there are more engines on a 4 engine plane, there is a higher chance of any one engine failing. That's basic maths. The chance of an engine failing is the sum of the individual odds across the number of engines on the plane. I thought it was clear but let me try and make it clearer. No-one said 4 engine planes are higher risk. And as you know the reasons their ETOPS rules are less strict is because losing one engine on a quad isn't an emergency as it is on a twin. All anyone said is the uncontroversial fact that is you have 4 of something, there is a higher chance something could go wrong with one of them and if you have two of it. And I think I'll leave it there because we're getting side tracked by this slightly ridiculous discussion about whether 4 times a number is bigger than 2 times a number.


As pointed out, the chance of an engine failing is NOT "the sum of the individual odds across the number of engines on the plane". If we assume that probability of a single engine failing is 0.6, then certainly for a twin-engine plane the chance of any of the engines failing is not 0.6 + 0.6 = 1.2 and for a quad not 2.4 (as probability has to be between 0 and 1).

The correct calculation is inverse of the none of the engines failing, that is 1 - (1- P)^N, where N is the number of engines and P probability for a single engine failure. This assumes that engine failures are not dependent on each other.


I would hope the probability isn't 0.6! Anyway, thank you for confirming that there is a higher chance of an individual engine failing on a quad than a twin. Can't really believe there is a debate about this...
 
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Re: AF66 CDG-LAX (A388-F-HPJE) diverts to Goose Bay (YYR) with an uncontained engine failure to #4 engine

Mon Oct 02, 2017 2:52 pm

Here is a little thought experiment: there is one A380 and two B777 flying with all the engines having the same failure rate. Now is there same probability that one of the four engines in the A380 fails as that one of the four engines in the two B777 fails?
 
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Re: AF66 CDG-LAX (A388-F-HPJE) diverts to Goose Bay (YYR) with an uncontained engine failure to #4 engine

Mon Oct 02, 2017 2:55 pm

dik909 wrote:
Just curious, what are the criteria for grounding the A380 fleet ? Who makes the call ? Is it an airline-specific issue ? An Airbus issue ? Or an engine-manufacturer issue ?


It would normally be the FAA or EASA who would issue an emergency directive. However I do not think that will happen. A similar event last year on a different type received very little attention from the regulators.

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Re: AF66 CDG-LAX (A388-F-HPJE) diverts to Goose Bay (YYR) with an uncontained engine failure to #4 engine

Mon Oct 02, 2017 3:05 pm

Similar, but at least the fan is still there.
 
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Re: AF66 CDG-LAX (A388-F-HPJE) diverts to Goose Bay (YYR) with an uncontained engine failure to #4 engine

Mon Oct 02, 2017 3:11 pm

EK413 wrote:
zeke wrote:
EK413 wrote:
The choice of airport for a diversion definitely up to the Operations Control based on the situation at hand.

EK413


The diversion decision is only up to the captain, they have the final authority, control, and responsibility. They will take onboard the input from others, but they have the final call to make.


I agree the captain has final say. In this instance AF66 was an emergency & captain would've made the decision but in the event of medical or weather operations control would have an influence on the decision based on alternate airports, ground support, customer recovery etc.

EK413


The captain can contact the operations center, who will then contact the station manager (assuming it's a staffed outstation) or the operations dept of whatever airport they're planning on going to.

In the case of most diversions, the captain makes the decision based on what those people have to say. There are times when even a company staffed outstation will advise that no, diverting here is not recommended. Find somewhere else. But in the end, it's the captain's plane, and his decision. He's the one on the line for the decision, good or bad.

In the case of this incident, he most likely wanted a nice long runway, and wanted to get it down as quickly as possible. In this case no ground manager or airport would advise them to keep looking.
 
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Re: AF66 CDG-LAX (A388-F-HPJE) diverts to Goose Bay (YYR) with reports of suspected damage to leading edge above #4 engi

Mon Oct 02, 2017 3:14 pm

Planetalk wrote:

An engines status is considered to be serviceable or unserviceable, not both, ie the engine status is mutually exclusive. Engines are also considered to be independent, because the status of each engine is independent of the status of another engine, if you have a failure of one engine it does not mean the other will fail (some engines need to be removed a number of times from the wing for repair over their life, and some engines do not get removed at all).


That's not entirely true. The design objective is to make engine failures entirely independent events, but that is not totally true. For example one factor could be a mechanic accidentally using APU oil instead of engine oil and the result of successive engine failures is higher due to a common cause. Contaminated fuel can also increase the probability of engine failures, since if one engine gets contaminated fuel, others will be getting the same fuel. There's also the possibility of one engine causing damage to the other with an uncontained failure. A manufacturing defect (often referred to as an escapement) can affect multiple engines and the same airplane may have close to sequential serial number engines. Fuel leaks can affect multiple engines. There's a reason for all the enhanced ETOPS procedures regarding maintenance.

Any failure modes that can cause multiple engines to fail will likely be catastrophic under a failure mode and effects analysis and therefore be required to have probabilities lower than 1E-9. A single engine failure is not a catastrophic event so it can have a higher probability like 1E-7 or 1E-5, but a common failure cause will have the highest risk and therefore must have the lowest probability of happening.
 
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Re: AF66 CDG-LAX (A388-F-HPJE) diverts to Goose Bay (YYR) with reports of suspected damage to leading edge above #4 engi

Mon Oct 02, 2017 3:17 pm

zeke wrote:
2Holer4Longhaul wrote:
You do realize that double engine failure at cruise altitude is extremely rare, and (to my knowledge) unheard of on modern 2-holers, right? Look at the 767, 777, A330, 757, A320 family, and 737.


They do happen, BA 777 into LHR, SQ A330 to PVG, BI 787 into MNL.


Also on my mind is DL 777

Is this a coincidence that all this events are RR related? One is T800, same on DL 777, one T700 and last is T1000
 
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Re: AF66 CDG-LAX (A388-F-HPJE) diverts to Goose Bay (YYR) with an uncontained engine failure to #4 engine

Mon Oct 02, 2017 3:31 pm

Sometimes it's good to have 4 engines.
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Re: AF66 CDG-LAX (A388-F-HPJE) diverts to Goose Bay (YYR) with an uncontained engine failure to #4 engine

Mon Oct 02, 2017 4:00 pm

flyingclrs727 wrote:
I can't understand why they diverted to such a remote airport? It's a 4-engined aircraft. It still had 3 good engines. An A380 with 3 engines running isn't required to land at the nearest suitable airport. It would have been easier to get accommodations and flights to their final destinations for them if they had diverted to JFK.


A certain BA captain would have opted to continue all the way to LAX, just to end up with a low fuel situation and diverting into SFO . . .
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Re: AF66 CDG-LAX (A388-F-HPJE) diverts to Goose Bay (YYR) with an uncontained engine failure to #4 engine

Mon Oct 02, 2017 4:11 pm

Finn350 wrote:
Here is a little thought experiment: there is one A380 and two B777 flying with all the engines having the same failure rate. Now is there same probability that one of the four engines in the A380 fails as that one of the four engines in the two B777 fails?

The answer to that is dependent on the definition of "failure rate".
For an airframe as a whole, an accident rate is defined as "per 1,000 hrs flown"
For an engine, the defined failure rate may appear similar, and yet slightly different; i.e. "per 1,000 hrs" but this is applied per engine.

Thus a B777 might fly a total of 21,000 hrs, and the engine clock on each engine registers 21,000 hrs, but that engine type will register 42,000 hrs trouble-free service.
If that same B777 then suffers a single engine failure and subsequently crashes, the airframe will have a failure rate of 1 in 21,000 hrs, but the engine type will have a failure rate of 1 in 42,000 hrs (per engine), corresponding to the fact that the second engine was in perfect working order up to the moment the B777 hit the ground

To answer your question; yes, in theory one of your B777s would have an engine failure at exactly the same time the A380.
The whole essence of the 4-engine vs 2-engine argument, is what happens next? The A380 (on 3 engines) has the luxury of considering it's options, and may even continue on to it's original destination. The B777 struggling along on 1 engine is most likely looking for the first opportunity to reach terra firma. A further consideration is what happens if the unthinkable happens - a second engine failure. For the A380, this would be quite bad news, and much more so if the double engine failure was on the same side, resulting in asymmetric thrust. Meanwhile, on the B777 glider - I'll let you do the math.(*)

(*) Ok, so it is also possible that the second engine failure on the B777, happens to the second B777, giving us two single-engine B777s. But that's another can of spaghetti.
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Re: AF66 CDG-LAX (A388-F-HPJE) diverts to Goose Bay (YYR) with an uncontained engine failure to #4 engine

Mon Oct 02, 2017 4:25 pm

PW100 wrote:
flyingclrs727 wrote:
I can't understand why they diverted to such a remote airport? It's a 4-engined aircraft. It still had 3 good engines. An A380 with 3 engines running isn't required to land at the nearest suitable airport. It would have been easier to get accommodations and flights to their final destinations for them if they had diverted to JFK.


A certain BA captain would have opted to continue all the way to LAX, just to end up with a low fuel situation and diverting into SFO . . .


This wasn't something like a high oil temperature. When the captain looked out of the window, he probably didn't need to go through a MEL to divert. Objectively, the risk of collateral damage seems significant enough. At some point the wing pylon lets go the engine. Apparently this failure was enough to break the shaft nevertheless. Apparently something came off, created instability and a full HPT disintegration. Something I hope to never experience on a big twin above a dark, cold, lonely place. I see myself sitting in a seat, intensively listening to the remaining engine..

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Re: AF66 CDG-LAX (A388-F-HPJE) diverts to Goose Bay (YYR) with an uncontained engine failure to #4 engine

Mon Oct 02, 2017 4:32 pm

Several pictures, including this one:
Image


. . . clearly show that the fandisk/hub/drum had failed.

Here you can see that the fandisk/hub/drum is one single component:

Image

Click here for lrage


At this moment we do not know if this was the first part to fail or not. However:
* there does not seem to be evidence for shrapnel/high energy debris;
* wing/slat damage is most likely the result of cowling separating during the event, and blown by 900 km/hr airstream into the wing;
* the retaining nut holding the fan disk/drum onto its driving shaft is still intact;
* the fandisk/drum fracture shape is in line with traditional initial fatigue followed by high torisional overload fracture.

This all suggests that the fan disk assembly (including all fan blades) left the engine fairly intact. Which would support the theory that the fandisk/drum was the PFI (Primary Failed Item).

Heavy rotating engine parts (such as compressor and turbine disks) like this fan disk cannot be made fail safe. Continued airworthiness is therefore assured by applying both a) intense inspection programs, and b) absolute life limits, usually in terms of engine cycles.

A failure of life-limited part of this magnitude would most certainly lead to a (dramatic) reduction in certified life-limit. I expect this to be published probably before the end of the week.

First step would be to analyze the actual P/N and S/N of the fan disk/drum, and determining its number of accumulated flight cycles. Emergency AD should be issued within one or two weeks, limiting the number of cycles allowed on this P/N.
Unless it can be demonstrated by Engine Alliance and/or Air France maintenance that something else was the root cause. It seems unlikely that would be accomplished in such short time frame.

It will be determined when it was last NDT inspected. It will be determined if any repair process were applied to the part, during overhaul but also during manufacturing.

PW100
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Re: AF66 CDG-LAX (A388-F-HPJE) diverts to Goose Bay (YYR) with an uncontained engine failure to #4 engine

Mon Oct 02, 2017 5:16 pm

Holy Cowl !
 
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Re: AF66 CDG-LAX (A388-F-HPJE) diverts to Goose Bay (YYR) with reports of suspected damage to leading edge above #4 engi

Mon Oct 02, 2017 7:31 pm

Newbiepilot wrote:
Planetalk wrote:

An engines status is considered to be serviceable or unserviceable, not both, ie the engine status is mutually exclusive. Engines are also considered to be independent, because the status of each engine is independent of the status of another engine, if you have a failure of one engine it does not mean the other will fail (some engines need to be removed a number of times from the wing for repair over their life, and some engines do not get removed at all).


That's not entirely true. The design objective is to make engine failures entirely independent events, but that is not totally true. For example one factor could be a mechanic accidentally using APU oil instead of engine oil and the result of successive engine failures is higher due to a common cause. Contaminated fuel can also increase the probability of engine failures, since if one engine gets contaminated fuel, others will be getting the same fuel. There's also the possibility of one engine causing damage to the other with an uncontained failure. A manufacturing defect (often referred to as an escapement) can affect multiple engines and the same airplane may have close to sequential serial number engines. Fuel leaks can affect multiple engines. There's a reason for all the enhanced ETOPS procedures regarding maintenance.

Any failure modes that can cause multiple engines to fail will likely be catastrophic under a failure mode and effects analysis and therefore be required to have probabilities lower than 1E-9. A single engine failure is not a catastrophic event so it can have a higher probability like 1E-7 or 1E-5, but a common failure cause will have the highest risk and therefore must have the lowest probability of happening.


Thanks for the interesting information. Just to note, it wasn't actually my post you were quoting :smile:
 
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Re: AF66 CDG-LAX (A388-F-HPJE) diverts to Goose Bay (YYR) with an uncontained engine failure to #4 engine

Mon Oct 02, 2017 7:36 pm

One thing to point out ... these engines are designed to contain a failure like this.

From the apparent lack of damage elsewhere on the airplane, it's a fair guesstimate that's exactly what it did ... then the damage from the containment + the airflow removed the affected parts from the airframe. (they were at *cruise*, that's darned fast)
 
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Re: AF66 CDG-LAX (A388-F-HPJE) diverts to Goose Bay (YYR) with an uncontained engine failure to #4 engine

Mon Oct 02, 2017 7:51 pm

I'm not sure I buy that guesstimate. In UA323 / Sioux City the entire fan disk took off, and yeah, it doesn't spray shrapnel, it just takes off in however many directions there are pieces, but if there's something in it's way, it's bad news.
 
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Re: AF66 CDG-LAX (A388-F-HPJE) diverts to Goose Bay (YYR) with an uncontained engine failure to #4 engine

Mon Oct 02, 2017 7:52 pm

litz wrote:
One thing to point out ... these engines are designed to contain a failure like this.

From the apparent lack of damage elsewhere on the airplane, it's a fair guesstimate that's exactly what it did ... then the damage from the containment + the airflow removed the affected parts from the airframe. (they were at *cruise*, that's darned fast)


Boy oh Boy, really.

I really get stressed out by people who make comments stated as fact, when they obviously have no knowledge of real engine design or failure modes.

ENGINES ARE NOT DESIGNED TO CONTAINED THIS TYPE OF FAILURE.
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Re: AF66 CDG-LAX (A388-F-HPJE) diverts to Goose Bay (YYR) with reports of suspected damage to leading edge above #4 engi

Mon Oct 02, 2017 7:52 pm

ZEDZAG wrote:
zeke wrote:
2Holer4Longhaul wrote:
You do realize that double engine failure at cruise altitude is extremely rare, and (to my knowledge) unheard of on modern 2-holers, right? Look at the 767, 777, A330, 757, A320 family, and 737.


They do happen, BA 777 into LHR, SQ A330 to PVG, BI 787 into MNL.


Also on my mind is DL 777

Is this a coincidence that all this events are RR related? One is T800, same on DL 777, one T700 and last is T1000

Can you post some informational link? Most accidents that happened to twins would (and have) happened to quads just as easily.
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Re: AF66 CDG-LAX (A388-F-HPJE) diverts to Goose Bay (YYR) with an uncontained engine failure to #4 engine

Mon Oct 02, 2017 8:03 pm

PW100 wrote:
Several pictures, including this one:
Image


. . . clearly show that the fandisk/hub/drum had failed.

Here you can see that the fandisk/hub/drum is one single component:

Image

Click here for lrage


At this moment we do not know if this was the first part to fail or not. However:
* there does not seem to be evidence for shrapnel/high energy debris;
* wing/slat damage is most likely the result of cowling separating during the event, and blown by 900 km/hr airstream into the wing;
* the retaining nut holding the fan disk/drum onto its driving shaft is still intact;
* the fandisk/drum fracture shape is in line with traditional initial fatigue followed by high torisional overload fracture.

This all suggests that the fan disk assembly (including all fan blades) left the engine fairly intact. Which would support the theory that the fandisk/drum was the PFI (Primary Failed Item).

Heavy rotating engine parts (such as compressor and turbine disks) like this fan disk cannot be made fail safe. Continued airworthiness is therefore assured by applying both a) intense inspection programs, and b) absolute life limits, usually in terms of engine cycles.

A failure of life-limited part of this magnitude would most certainly lead to a (dramatic) reduction in certified life-limit. I expect this to be published probably before the end of the week.

First step would be to analyze the actual P/N and S/N of the fan disk/drum, and determining its number of accumulated flight cycles. Emergency AD should be issued within one or two weeks, limiting the number of cycles allowed on this P/N.
Unless it can be demonstrated by Engine Alliance and/or Air France maintenance that something else was the root cause. It seems unlikely that would be accomplished in such short time frame.

It will be determined when it was last NDT inspected. It will be determined if any repair process were applied to the part, during overhaul but also during manufacturing.

PW100


100 agree with your post.

I struggle with the failure mode as fatigue cracking should have failed on take off.

I am left at this time with a bearing issue, but probably fatigue, will be waiting for initial report with interest.
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Re: AF66 CDG-LAX (A388-F-HPJE) diverts to Goose Bay (YYR) with an uncontained engine failure to #4 engine

Mon Oct 02, 2017 8:11 pm

keesje wrote:
Sometimes it's good to have 4 engines.


If this had happened to a twin, the single good engine would have still enabled the plane to land safely.
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Newbiepilot
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Re: AF66 CDG-LAX (A388-F-HPJE) diverts to Goose Bay (YYR) with reports of suspected damage to leading edge above #4 engi

Mon Oct 02, 2017 8:15 pm

Planetalk wrote:
Newbiepilot wrote:
Planetalk wrote:

An engines status is considered to be serviceable or unserviceable, not both, ie the engine status is mutually exclusive. Engines are also considered to be independent, because the status of each engine is independent of the status of another engine, if you have a failure of one engine it does not mean the other will fail (some engines need to be removed a number of times from the wing for repair over their life, and some engines do not get removed at all).


That's not entirely true. The design objective is to make engine failures entirely independent events, but that is not totally true. For example one factor could be a mechanic accidentally using APU oil instead of engine oil and the result of successive engine failures is higher due to a common cause. Contaminated fuel can also increase the probability of engine failures, since if one engine gets contaminated fuel, others will be getting the same fuel. There's also the possibility of one engine causing damage to the other with an uncontained failure. A manufacturing defect (often referred to as an escapement) can affect multiple engines and the same airplane may have close to sequential serial number engines. Fuel leaks can affect multiple engines. There's a reason for all the enhanced ETOPS procedures regarding maintenance.

Any failure modes that can cause multiple engines to fail will likely be catastrophic under a failure mode and effects analysis and therefore be required to have probabilities lower than 1E-9. A single engine failure is not a catastrophic event so it can have a higher probability like 1E-7 or 1E-5, but a common failure cause will have the highest risk and therefore must have the lowest probability of happening.


Thanks for the interesting information. Just to note, it wasn't actually my post you were quoting :smile:


Sorry for misquoting you since it was actually Zeke's words. I'm not sure how that happened.
 
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Re: AF66 CDG-LAX (A388-F-HPJE) diverts to Goose Bay (YYR) with an uncontained engine failure to #4 engine

Mon Oct 02, 2017 8:39 pm

So what is the prognosis on the airframe likely to be? From initial appearance, there is limited damage to the structural components -- at least nothing that can't be fixed/replaced. I presume fixing these issues, plus a new engine and she'll be back in service within a few months?
 
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UAL747422
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AF66: what exactly happened?

Mon Oct 02, 2017 9:08 pm

Air France flight 66 was a regularly scheduled flight from CDG-LAX. Due to an uncontained engine failure in the number 4 engine, the plane diverted to Goose Bay. I'm sure that this is all over A.net, but what exactly happened to cause the engine to disintegrate? The A388 has had engine problems before, like Qantas flight 32. I believe the fan blade cracked, triggering the engine to fall apart. I also am aware that it is very early in the investigation, and much is still unknown. I'd be intrested to hear all thoughts.

UAL747422
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m1m2
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Re: AF66 CDG-LAX (A388-F-HPJE) diverts to Goose Bay (YYR) with an uncontained engine failure to #4 engine

Mon Oct 02, 2017 9:11 pm

Regarding Goose Bay (CYYR) being a "remote airport", it's not actually in a large city, but it has very long runways, the shortest over 9500' and the longest over 11000'. Add to that the fact that there are still large hangars there from the days when there was a very large American Air base there and this may also be a reason for landing there. I'm not certain an A380 would fit in those hangars, but from being there myself, it looks as though at least one of them would be large enough to house this aircraft provided the owner will make it available.

From the damage I see in the pictures posted here, I would imagine this aircraft could be back in service within a couple of weeks. The flap canoe is easy to change and the leading edges can also be changed, or the dents NDT'd, patched if within limits and then sent to a maintenance base to be repaired. Probably the biggest challenge would be getting a replacement engine shipped to YYR.
Last edited by m1m2 on Mon Oct 02, 2017 9:15 pm, edited 1 time in total.
 
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UAL747422
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Re: AF66 CDG-LAX (A388-F-HPJE) diverts to Goose Bay (YYR) with an uncontained engine failure to #4 engine

Mon Oct 02, 2017 9:12 pm

I personally think the reason for this incident was a cracked fan blade that gave way, causing the cowling to break away. At least that's what I think, it is still very early in the investigation to know...

Although, UA232 has catastrophic engine failure due to a fan blade that broke, just saying. I think when Turbofan engines are being made they melt the titanium fan blades three times before being used, correct me on any of this information.
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UAL747422
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Re: AF66 CDG-LAX (A388-F-HPJE) diverts to Goose Bay (YYR) with an uncontained engine failure to #4 engine

Mon Oct 02, 2017 9:14 pm

keesje wrote:
Sometimes it's good to have 4 engines.


Agreed. Although, the 777 can travel on one engine for a couple of hours.
"I think we could build a better one" -William Boeing
 
m1m2
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Re: AF66 CDG-LAX (A388-F-HPJE) diverts to Goose Bay (YYR) with an uncontained engine failure to #4 engine

Mon Oct 02, 2017 9:19 pm

A cracked fan blade wouldn't take the whole fan disk with it, it most definitely would damage the cowling, but it wouldn't cause the damage we see to the fan disk here. That and the design requirement is that if a single blade fails it has to stay within the engine. This is tested during manufacture. That brown layer shown in some of the "complete" engine pictures is the fan containment case, it's made of Kevlar to be extremely strong.
 
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Re: AF66 CDG-LAX (A388-F-HPJE) diverts to Goose Bay (YYR) with reports of suspected damage to leading edge above #4 engi

Mon Oct 02, 2017 9:27 pm

Finn350 wrote:
The correct calculation is inverse of the none of the engines failing, that is 1 - (1- P)^N, where N is the number of engines and P probability for a single engine failure. This assumes that engine failures are not dependent on each other.


Well the real divide is how many engines can you loose without being directly SOL and things going unmitigateable pear shaped .
That is ONE for the twin and probably two for the quad.


for PR purposes the probablities were wrongly stated as making a Twin better than a Quad
for some number "N" of hours between failures for an engine type
a twin would show N/2 while a quad would show N/4 for one engine out.
Now for a Twin two engines out ( dead ) is (N/2)*N while for the Quad ( 3rd out) it is (N/4)*(N/3)*(N/2)
( any objections?)

where in reality the Twin just became "good enough" ...
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sasd209
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Re: AF66: what exactly happened?

Mon Oct 02, 2017 9:28 pm

Well clearly the front fell off...


www.imdb.com/title/tt3332068/
 
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TheRedBaron
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Re: AF66 CDG-LAX (A388-F-HPJE) diverts to Goose Bay (YYR) with an uncontained engine failure to #4 engine

Mon Oct 02, 2017 9:29 pm

Thanks to Karel, PW100, Zeke and other for the very useful info. Seeing the pictures AF is very lucky that no shrapnel or parts it the fuselage, and damage was very localized. I bet they have a lot of people on this event to see exactly why this happened. And we can argue add infinitum of why twins are as safe as quads, but I bet If I saw this kind of damage on a twin in the middle of Greenland, Id be shitting on my pants.
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RobertS975
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Re: AF66 CDG-LAX (A388-F-HPJE) diverts to Goose Bay (YYR) with an uncontained engine failure to #4 engine

Mon Oct 02, 2017 9:34 pm

Prost wrote:
I can’t imagine a scenario where someone denied entry to Canada is allowed in the US.


Actually, it is quite easy to imagine the scenario... just about any US citizen with an arrest record over the past 5 years would not be allowed into Canada under ordinary circumstances. This situation was obviously not ordinary!
 
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Re: AF66 CDG-LAX (A388-F-HPJE) diverts to Goose Bay (YYR) with an uncontained engine failure to #4 engine

Mon Oct 02, 2017 9:36 pm

UAL747422 wrote:
keesje wrote:
Sometimes it's good to have 4 engines.


Agreed. Although, the 777 can travel on one engine for a couple of hours.


Every ETOPS ( ICAO/EASA/FAA defnition) Twin is supposed to do that.
Murphy is an optimist
 
ubeema
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Re: AF66 CDG-LAX (A388-F-HPJE) diverts to Goose Bay (YYR) with an uncontained engine failure to #4 engine

Mon Oct 02, 2017 10:16 pm

I am not a math or stats wiz so I appreciate the heated but classy exchange on the probability of engine failures of this group:
Zeke
Planetalk
Finn350
TheLark
NewbiePilot

Thanks guys for staying adults.
 
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ikolkyo
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Re: AF66: what exactly happened?

Mon Oct 02, 2017 10:24 pm

There is already a whole thread on this.
 
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Re: AF66: what exactly happened?

Mon Oct 02, 2017 10:43 pm

ikolkyo wrote:
There is already a whole thread on this.

.... that is addressing twins vs quads and many things other than 'AF66: what exactly happened?' ....
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crownvic
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Re: AF66: what exactly happened?

Mon Oct 02, 2017 11:03 pm

It hit a drone...I mean a flock of seagulls...really?????
 
LAXLHR
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Re: AF66 CDG-LAX (A388-F-HPJE) diverts to Goose Bay (YYR) with an uncontained engine failure to #4 engine

Mon Oct 02, 2017 11:09 pm

PW100 wrote:
flyingclrs727 wrote:
I can't understand why they diverted to such a remote airport? It's a 4-engined aircraft. It still had 3 good engines. An A380 with 3 engines running isn't required to land at the nearest suitable airport. It would have been easier to get accommodations and flights to their final destinations for them if they had diverted to JFK.


A certain BA captain would have opted to continue all the way to LAX, just to end up with a low fuel situation and diverting into SFO . . .


HAHAHAHAHA! nice one :-) Yes the BA Captain of the 744 LAX-LHR that lost an engine on take-off but decided it was a go all the way to LHR, but gave up and diverted to MAN....haha, oh so close :-).
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Newbiepilot
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Re: AF66 CDG-LAX (A388-F-HPJE) diverts to Goose Bay (YYR) with an uncontained engine failure to #4 engine

Mon Oct 02, 2017 11:19 pm

caverunner17 wrote:
So what is the prognosis on the airframe likely to be? From initial appearance, there is limited damage to the structural components -- at least nothing that can't be fixed/replaced. I presume fixing these issues, plus a new engine and she'll be back in service within a few months?


3-4 weeks most likely. The pylon is damaged and those structural parts can take a few weeks to fabricate replacements. I expect Air France has a spare engine so all the parts on the pylon and any airframe damage will take a few weeks.
 
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Re: AF66 CDG-LAX (A388-F-HPJE) diverts to Goose Bay (YYR) with an uncontained engine failure to #4 engine

Mon Oct 02, 2017 11:20 pm

I really shouldn't speculate based on a couple photos and the thinnest of evidence, but here goes anyway...

I'm going to suggest that you almost have to postulate some sort of crack, large or small, in the fan disk. I could see a bearing failure seizing the shaft and causing the fan to twist off, maybe, but wouldn't it do just as much damage to the LPC and LPT? and while I grant you they can't be seen directly in those photos, I would have expected some sort of visible havoc in the rear of the engne, at least enough to post a photo from the ground, and I haven't seen any. A single fan blade failure should have been contained. Some sort of catastrophic fan case failure? yeah, maybe, but I would have expected such an event to be a little more drawn-out as blades take their leave. If you throw a disk crack into the mix, though, it's easier to imagine the entire fan twisting off and (luckily) exiting without hitting much of anything else.

Now I'll wait for the real experts with real evidence to figure out what actually happened. :-)
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keesje
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Re: AF66 CDG-LAX (A388-F-HPJE) diverts to Goose Bay (YYR) with an uncontained engine failure to #4 engine

Mon Oct 02, 2017 11:37 pm

WIederling wrote:
UAL747422 wrote:
keesje wrote:
Sometimes it's good to have 4 engines.


Agreed. Although, the 777 can travel on one engine for a couple of hours.


Every ETOPS ( ICAO/EASA/FAA defnition) Twin is supposed to do that.


It's not so much one engine going poeff. This happening on a twin, I would listen & watch the remaining engine as if my life depended on it. I would wonder why #1 failed, something obviously went wrong. Is that something relevant for #2? On a polar ETOPS 330 flight..

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Dalmd88
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Re: AF66 CDG-LAX (A388-F-HPJE) diverts to Goose Bay (YYR) with an uncontained engine failure to #4 engine

Mon Oct 02, 2017 11:42 pm

N14AZ wrote:
peterinlisbon wrote:
It looks to me like one or more of the low-pressure blades must have come loose and cut into the cowling whilst spinning at high speed like a circular saw

But in such a scenario, wouldn't you expect some shrapnels hitting the fuselage? That's what happened in case of VH-OQA:

Image
Source: http://www.mromanagement.com/feature/ge ... ne-failure

Anyhow, too early to speculate. They will find out...

A lot of that has to do with which side of the aircraft the engine is on. Due to the direction of rotation of the parts, fuselage damage is more likely if the engine is on the left side of the plane.
 
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Re: AF66 CDG-LAX (A388-F-HPJE) diverts to Goose Bay (YYR) with an uncontained engine failure to #4 engine

Tue Oct 03, 2017 12:00 am

PITingres wrote:
I really shouldn't speculate based on a couple photos and the thinnest of evidence, but here goes anyway...

I'm going to suggest that you almost have to postulate some sort of crack, large or small, in the fan disk. I could see a bearing failure seizing the shaft and causing the fan to twist off, maybe, but wouldn't it do just as much damage to the LPC and LPT? and while I grant you they can't be seen directly in those photos, I would have expected some sort of visible havoc in the rear of the engne, at least enough to post a photo from the ground, and I haven't seen any. A single fan blade failure should have been contained. Some sort of catastrophic fan case failure? yeah, maybe, but I would have expected such an event to be a little more drawn-out as blades take their leave. If you throw a disk crack into the mix, though, it's easier to imagine the entire fan twisting off and (luckily) exiting without hitting much of anything else.

Now I'll wait for the real experts with real evidence to figure out what actually happened. :-)

There will be much to be learned from examining the fracture surface of the drum/disc. Such fractography is very mature, but the piece needs to get to the PWA East Hartford lab for that unless the French decide to take back to France. Until then, any comments are speculative, but in any event, one possible root cause is a minute inclusion or hard alpha particle in the titanium that would propagate a fatigue crack leading to a critical length and then overload, etc. which can happen at cruise speed. If this is the case, then the odds of similar failure any time soon are pretty low since the titanium is indeed triple melted to minimize such flaws, the billets, etc. non-destructively inspected, etc. Unfortunately, the system and inspections cannot catch flaws below a certain size that may still be problematic. The JETQC (Jet Engine Titanium Quality Committee) of the FAA is on top of this and the provenance of the billets is closely tracked to end products, so if this proves to be the case, the titanium producer will perform RCCA and other suspect parts will be recalled.
 
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Re: AF66 CDG-LAX (A388-F-HPJE) diverts to Goose Bay (YYR) with an uncontained engine failure to #4 engine

Tue Oct 03, 2017 12:03 am

Newbiepilot wrote:
caverunner17 wrote:
So what is the prognosis on the airframe likely to be? From initial appearance, there is limited damage to the structural components -- at least nothing that can't be fixed/replaced. I presume fixing these issues, plus a new engine and she'll be back in service within a few months?


3-4 weeks most likely. The pylon is damaged and those structural parts can take a few weeks to fabricate replacements. I expect Air France has a spare engine so all the parts on the pylon and any airframe damage will take a few weeks.


Can't Airbus take a pylon in production for one of the A380's in production and divert it to the Air France plane? It's not as if airlines are in a big rush to get their new A380's delivered.

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