A failure that big isn't a mechanical defect on all engines, otherwise other airlines would've already caught acute engine cannibalism. Either an individual defect in construction or laziness from the ground crew, who replaced used compressor shafts with surplus TSR2 ones

Bit early to draw conclusions. The damage looks interesting as it seems to only have involved the low pressure section and the fan, but without a closer look it is hard to say.

EK413 wrote:

jumbojet wrote:

bunumuring wrote:

Hey guys,
Qantas temporarily grounded its A380s immediately after QF32.
I assume Air France has NOT done the same thing after this incident?
Thanks,
Bunumuring

Don't think so. There currently are AF A380's in flight.

Which really concerns me & convinces me to steer clear of AF when travelling. The event of AF66 would've warranted grounding the entire AF A380 & perform checks of the fleet.
Guess safety isn't a priority at AF?

EK413

Perhaps the complete EA-fleet of A380's should be grounded then.

If the engine failure/break-up occured over Greenland then what are the chances that they will be able to locate any of the major parts?

beachview wrote:

B747forever wrote:

EK413 wrote:

Which really concerns me & convinces me to steer clear of AF when travelling. The event of AF66 would've warranted grounding the entire AF A380 & perform checks of the fleet.
Guess safety isn't a priority at AF?

EK413

If there really was a concern for a fleet wide problem do you think the pilots and crew would risk their lives and fly? I am sure AF know what they are doing, and dont need a a.nutter to teach them about safety.

Half the engine is GONE! How is that not a concern?

I too was VERY surprised they did not ground the fleet!

Because they have millions of hours of engine data. Given the decadeish that the a380 has been flying, this is one freak accident. Unless current data beings to show this could have a negative effect on other birds, there's not much they can do until they find the root cause. There's also the business side that would probably have grounding the aircraft be near catastrophic for them.

Planetalk wrote:

I'm surprised by your lack of rigour in this discussion Zeke, you'd normally be mauling someone for making statements such as 'the probability is zero' which is clearly nonsense. The theoretical probablity of an engine failing is very low, but it is not zero, and that is why they are designed to fail in certain ways, which this one seems not to have done.

As you know, for a long time engines on ETOPS flights were subject to more stringent maintenance requirements than on 4 engine aircraft making the same journey. So all else equal, it would be absolutely true that any individual engine failing is more likely on a 4 engine plane than a 2 engine. This has generally always been accepted, 4 times a very small number may be a very small number, but it is still bigger than 2 times a small number.

In reality of course, it is fairly insignificant because we haven't seen either a 4 holer or twin crashing due to losing all engines and you're equally safe on either.

Saying that engine reliability had nothing to do with the sudden dominance of twins is a rather bold statement as well, given that it was the emergence of ETOPS that played a large part in sealing the A340s fate...

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). The converse is also true, a serviceable engine has no influence over a failed engine. Have a search for yourself for the mathematical proof of mutually exclusive independent events and you will see that the probability is zero.

In terms of ETOPS, it applies to all aircraft these days. If it was as yourself and other are suggesting that the more engines installed on an aircraft the higher the risk, you would expect regulators to impose greater restrictions on trijets and quads. The exact opposite is actually true, the risk assessment made by regulators is twins must apply ETOPS procedures when they are 60 minutes away from a suitable airport, and quads its 3 times that amount, they have to apply ETOPS when they are 180 minutes from a suitable alternate. The regulators certainly do not buy into the notion that quads etc are less safe, or have a higher risk. In terms of engine stress, quads generally are not put to their power plant limits on takeoff as much as twins as they have greater margin 3 engine out than twins to with one engine out.

The fate of the A340 had very little to do with reliability, who has said they dropped the A340 because it was unreliable ? The aircraft proved to be very reliable over its history,and never involved in a fatal accident. Boeing said many things about quads in the past when Airbus was offering the A340, then they turned around and launched the 747-8. Reminds me of when Boeing was saying you should buy Boeing aircraft because they are made of metal, and Airbus makes plastic planes. Of you should buy Boeing aircraft because with FBW the pilot is not in control of the aircraft.

RJWNL wrote:

It is my understanding that engines in cruise run at fairly constant settings and the electronics maintain these rather than chasing certain performance parameters? Otherwise this could momentarily cause higher/variable loading, during turbulence for example?

I have seen a few failures where thrust in increased to the maximum for an enroute step climb. Turbulence normally does not require full thrust application.

Btblue wrote:

Quite unbelievable - those are some amazing photos and video, total disintegration of the engine. Really lucky the debris flew outward and not inward. Just look at the state of that engine, I've not seen anything quite that bad for a fair old while. Surprised the rest didn't go with it, they're like any engine, designed to shear off with too much vibration?

Looks like the complete fan unit ( fan, fan cowling, ? guide vanes behind the fan blades too?...) has "vanished".
( looks like you can see the entry to the 1st LP compressor stage?)

could this be an issue like the "detaching" LP <> Fan Shaft on GenX1/2 engines from a couple of years ago?
( afair remember caused by changed surface coating technique? There the designed in fail save mechanism was
to let the LP turbine move aft into a "brake by collision" with the stator vanes condition
to avoid RPM runaway to 200% "idle")

B747forever wrote:

EK413 wrote:

jumbojet wrote:

Don't think so. There currently are AF A380's in flight.

Which really concerns me & convinces me to steer clear of AF when travelling. The event of AF66 would've warranted grounding the entire AF A380 & perform checks of the fleet.
Guess safety isn't a priority at AF?

EK413

If there really was a concern for a fleet wide problem
do you think the pilots and crew would risk their lives and fly? I am sure AF know what they are doing, and dont need a a.nutter to teach them about safety.

Qantas didn't think twice and grounded their fleet moment the QF32 incident occurred and had their entire fleet inspected! To add to this carriers with RR powered A380's performed inspections.
So to sum it up yeah it's concerning and AF haven't taken the corrective action.

EK413

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.

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.

Its easy to say that in hindsight,recomendations could have been made from France.

Close up picture of #4 engine



https://twitter.com/OlivierJoffet/statu ... 2933198848

cc2314 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.

Its easy to say that in hindsight,recomendations could have been made from France.

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

EK413

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.

As it was an uncontained failure they couldn’t be sure if there was additional damage to the aicraft.

qf789 wrote:

Close up picture of #4 engine



https://twitter.com/OlivierJoffet/statu ... 2933198848

Looking at the closeup today, which way would the debris have been thrown? Up/down? It looks like it exploded and managed to virtually clear the wing, engine #3 and more importantly the main fuselage. What are the chances of that? Very lucky for AF, Airbus and all on-board.

It looks like something seized up and stopped rotating without warning, and the energy build-up did the rest.

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.

At this point it was a 3 and a half engined aircraft. You land as soon as possible with that kind of damage

qf789 wrote:

Close up picture of #4 engine

https://twitter.com/OlivierJoffet/statu ... 2933198848

What could cause such a clean rip off?

Blotto 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.

At this point it was a 3 and a half engined aircraft. You land as soon as possible with that kind of damage

Even worse would be if the damage compromised the pylon connecting the engine to the wing. I'd assume of the engine were to have fallen off mid flight due to turbulent conditions, the pilots couldn't correct for such a great weight imbalance.

I'm kind of surprised they pylon stayed on. Aren't they designed to separate from the wing in extreme events? I'm sure the aircraft is designed to fly with a pylon and engine gone.

[img]9[/img]

KarelXWB wrote:

https://twitter.com/cypheristikal/statu ... 7622089728

Is that flap track fairing damaged on the right side of the picture??? So you have damage on the O/B leading edge spat where parts went over the wing and damage under the wing also.


It would be interesting to know if the engine is seized or not.

pugman211 wrote:

Is that flap track fairing damaged on the right side of the picture???

Looks like it:


https://twitter.com/cypheristikal/statu ... 7622089728

KarelXWB wrote:

pugman211 wrote:

Is that flap track fairing damaged on the right side of the picture???

Looks like it:

Indeed. Even aft of that area in the close-up, I see some dark protruding thing on the flap track fairing that does not look too normal to me...

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.

KarelXWB wrote:

What could cause such a clean rip off?

Larger engines are designed to be split between the fan and the hot section. It allows for the hot section or fan to be replaced or repaired independently. It also allows the engine to be transported easier as the fan can be transported flat on a pallet and the hot section on a smaller stand.

caverunner17 wrote:

I'd assume of the engine were to have fallen off mid flight due to turbulent conditions, the pilots couldn't correct for such a great weight imbalance.

The weight with one engine missing is not that great, they can be flown with complete fuel imbalance.

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

I think the QF incident would also have at least some impact on the captains decision. Kudos to the designers though, after such an event, still holding on to half the engine..

EK413 wrote:

but in the event of medical or weather operations control would influence the decision based on alternate airports, ground support, recovery etc.

Not at all, there is no shared dispatch model under EU OPS, the decision (and responsibility) is up to the captain. People on the ground have no control or responsibility over a flight. They can make suggestions which you can take onboard or reject, it is up to the captain.

As to if it was an emergency or not that will come out in the report, if the damage has been secured it becomes non normal situation rather than an emergency. Most times aircraft divert an emergency does not need to be declared.

We don't know if this is a one-off incident or something that may affect all such engine models. While it would be an excessive act to 'ground' all aircraft with this engine, it would be prudent after an early determination of what caused this failure to cycle around those aircraft for a more extensive mx check between flights. That is most likely what will happen. That may mean some cancelled flights by their operators but that can be mitigated.
As to keeping the passengers on the plane and not allowing them to leave, it was unknown at the time how long it would take to get a replacement aircraft(s), transfer those pax and all their stuff, maintain security, at a tiny and reletively isolated airport and terminal, so despite the discomfort it was the only thing to do.

zeke wrote:

caverunner17 wrote:

I'd assume of the engine were to have fallen off mid flight due to turbulent conditions, the pilots couldn't correct for such a great weight imbalance.

The weight with one engine missing is not that great, they can be flown with complete fuel imbalance.

Wasn't that the cause of AA191 where the engine came detached on the DC10?

EK413 wrote:

B747forever wrote:

EK413 wrote:

Which really concerns me & convinces me to steer clear of AF when travelling. The event of AF66 would've warranted grounding the entire AF A380 & perform checks of the fleet.
Guess safety isn't a priority at AF?

EK413

If there really was a concern for a fleet wide problem
do you think the pilots and crew would risk their lives and fly? I am sure AF know what they are doing, and dont need a a.nutter to teach them about safety.

Qantas didn't think twice and grounded their fleet moment the QF32 incident occurred and had their entire fleet inspected! To add to this carriers with RR powered A380's performed inspections.
So to sum it up yeah it's concerning and AF haven't taken the corrective action.

EK413

"Damn it, we're going to crash!"

uta999 wrote:

qf789 wrote:

Close up picture of #4 engine



https://twitter.com/OlivierJoffet/statu ... 2933198848

Looking at the closeup today, which way would the debris have been thrown? Up/down? It looks like it exploded and managed to virtually clear the wing, engine #3 and more importantly the main fuselage. What are the chances of that? Very lucky for AF, Airbus and all on-board.

It looks like something seized up and stopped rotating without warning, and the energy build-up did the rest.

Very interesting.

caverunner17 wrote:

Wasn't that the cause of AA191 where the engine came detached on the DC10?

The reason that became uncontrollable was not the weight of the engine, some slats retracted on one side creating an aerodynamic roll moment that could not be corrected at low speed.

zeke wrote:

caverunner17 wrote:

Wasn't that the cause of AA191 where the engine came detached on the DC10?

The reason that became uncontrollable was not the weight of the engine, some slats retracted on one side creating an aerodynamic roll moment that could not be corrected at low speed.

Interesting. Learned something new today!

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.

Yes but with wing damage and hydraulics leaking out, possible control issues. Is it really worth the risk?

I'm thoroughly amused by all those anti Air France posts. We don't even know what happened, but surely the pilots are to blame for an engine disintegrating in mid-air, of course; just like we should blame AF for destroying all types of planes it flies, right? By this kind of logic, we should have stopped boarding AA/US a long time ago, since they totalled MDs, Boeings and even Airbuses. Jasum.
If you read up on the problems that did affect AF cockpit culture in the early 2Ks (lots of skygods à la PanAm) and culminated in the 447 crash, you will see that they instituted a full reform of the crew standards. Does this change right away? Of course not. Must we stop flying AF? See my first point.

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, then the whole of the fan sheared off from its shaft due to the sudden contact with the damaged cowling and then the fan together with the weakened cowling broke off and fell away under the wing, contacting the bottom of the wing as it went.

Keith2004 wrote:

SCAT15F wrote:

Surprised no one has brought this up yet but you better believe those passengers and crew were really glad they were on a 4 engine aircraft.

Long live 4 Engines 4 Long Haul! (3 works too)

3 - already extinct
4 - endangered

This is the second time this has happened to this particular 4 engined aircraft,

Ohoh! I was waiting for that one...

Different engine, different component, different airline. Complete nonsense to suggest a link.

rbavfan wrote:

Btblue wrote:

Here's a side on view of the engine without cowlings etc. Appears the whole of the front section has been taken away (coloured brown in the photo).

It would apear that the fan sroud thats composite and supposedly tested to survive fan failure, does not survive.

It's designed to survive a couple of fan blades departing... not the entire fan coming off!

SomebodyInTLS wrote:

Keith2004 wrote:

SCAT15F wrote:

Surprised no one has brought this up yet but you better believe those passengers and crew were really glad they were on a 4 engine aircraft.

Long live 4 Engines 4 Long Haul! (3 works too)

3 - already extinct
4 - endangered

This is the second time this has happened to this particular 4 engined aircraft,

Ohoh! I was waiting for that one...

Different engine, different component, different airline. Complete nonsense to suggest a link.

I know that, and it is just as nonsensical to say that 4 engine 4 the long-haul is somehow safer because of this incident, yes different engine types, but 2 engine long haul planes of varying engine types have not had incidents those 2 A380s had.

All I was saying was that 3/4 engine aircraft (regardless of engine type) have had more incidents with engines in flight than 2 engine long haul aircraft, could just be coincidental, but no reason to have false sense of security with more than 2 engines

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:


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

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

Keith2004 wrote:

but 2 engine long haul planes of varying engine types have not had incidents those 2 A380s had.

All I was saying was that 3/4 engine aircraft (regardless of engine type) have had more incidents with engines in flight than 2 engine long haul aircraft, could just be coincidental, but no reason to have false sense of security with more than 2 engines

Twins have had many uncontained engine failures, the engine does not know what sort of airframe it is installed on.

https://aviation-safety.net/database/db ... Event=ACEU

zeke wrote:

Planetalk wrote:

I'm surprised by your lack of rigour in this discussion Zeke, you'd normally be mauling someone for making statements such as 'the probability is zero' which is clearly nonsense. The theoretical probablity of an engine failing is very low, but it is not zero, and that is why they are designed to fail in certain ways, which this one seems not to have done.

As you know, for a long time engines on ETOPS flights were subject to more stringent maintenance requirements than on 4 engine aircraft making the same journey. So all else equal, it would be absolutely true that any individual engine failing is more likely on a 4 engine plane than a 2 engine. This has generally always been accepted, 4 times a very small number may be a very small number, but it is still bigger than 2 times a small number.

In reality of course, it is fairly insignificant because we haven't seen either a 4 holer or twin crashing due to losing all engines and you're equally safe on either.

Saying that engine reliability had nothing to do with the sudden dominance of twins is a rather bold statement as well, given that it was the emergence of ETOPS that played a large part in sealing the A340s fate...

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). The converse is also true, a serviceable engine has no influence over a failed engine. Have a search for yourself for the mathematical proof of mutually exclusive independent events and you will see that the probability is zero.

In terms of ETOPS, it applies to all aircraft these days. If it was as yourself and other are s
uggesting that the more engines installed on an aircraft the higher the risk, you would expect regulators to impose greater restrictions on trijets and quads. The exact opposite is actually true, the risk assessment made by regulators is twins must apply ETOPS procedures when they are 60 minutes away from a suitable airport, and quads its 3 times that amount, they have to apply ETOPS when they are 180 minutes from a suitable alternate. The regulators certainly do not buy into the notion that quads etc are less safe, or have a higher risk. In terms of engine stress, quads generally are not put to their power plant limits on takeoff as much as twins as they have greater margin 3 engine out than twins to with one engine out.

The fate of the A340 had very little to do with reliability, who has said they dropped the A340 because it was unreliable ? The aircraft proved to be very reliable over its history,and never involved in a fatal accident. Boeing said many things about quads in the past when Airbus was offering the A340, then they turned around and launched the 747-8. Reminds me of when Boeing was saying you should buy Boeing aircraft because they are made of metal, and Airbus makes plastic planes. Of you should buy Boeing aircraft because with FBW the pilot is not in control of the aircraft.

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.

When speaking to reliability I was in no way referring to safety, I thought it was clear I meant that with increased engine reliability, and the introduction of very long ETOPS routes, the need for 4 engined planes greatly reduced. I don't think there's much debate about that.

Please don't turn this into Boeing versus Airbus Zeke, completely irrelevant and unnecessary, resist, for once. Nor is anyone questioning the captain's authority by pointing out they will use all resources at their disposal and work as a team with ground ops to form a decision when it is advantageous. Chill

You can see damage to engine 3’s TR area in the photos above.

EK413 wrote:

B747forever wrote:

EK413 wrote:

Which really concerns me & convinces me to steer clear of AF when travelling. The event of AF66 would've warranted grounding the entire AF A380 & perform checks of the fleet.
Guess safety isn't a priority at AF?

EK413

If there really was a concern for a fleet wide problem
do you think the pilots and crew would risk their lives and fly? I am sure AF know what they are doing, and dont need a a.nutter to teach them about safety.

Qantas didn't think twice and grounded their fleet moment the QF32 incident occurred and had their entire fleet inspected! To add to this carriers with RR powered A380's performed inspections.
So to sum it up yeah it's concerning and AF haven't taken the corrective action.

EK413

Did BA or Korean ground their 777 fleets after their uncontained engine fires? It would actually be quite an unusual thing to do.

EK413 wrote:

B747forever wrote:

EK413 wrote:

Which really concerns me & convinces me to steer clear of AF when travelling. The event of AF66 would've warranted grounding the entire AF A380 & perform checks of the fleet.
Guess safety isn't a priority at AF?

EK413

If there really was a concern for a fleet wide problem
do you think the pilots and crew would risk their lives and fly? I am sure AF know what they are doing, and dont need a a.nutter to teach them about safety.

Qantas didn't think twice and grounded their fleet moment the QF32 incident occurred and had their entire fleet inspected! To add to this carriers with RR powered A380's performed inspections.
So to sum it up yeah it's concerning and AF haven't taken the corrective action.

EK413

No. Very different situation

- new aircraft
- new engine
- significant damage to the aircraft

In this case, as others mentioned, the engine has been flying for a decade so there is no reason to suspect a systematic design or manufacturing issue. The aircraft even less so.

This is obviously an unusual failure, so one can assume the rest of the fleet is safe. That said, I'm sure there were a lot of heads stuck in engines around the world last night just to have a check.

Okcflyer wrote:

You can see damage to engine 3’s TR area in the photos above.

Where did you see this? I checked the last three pages of this thread but didn't find such a picture.

zeke wrote:

the engine does not know what sort of airframe it is installed on.

This made me laugh. Funny but very useful comment....

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.

Planetalk wrote:

Yes engine failures are independent events, and one failing does not increase the odds of another failing.

Thank you, something we agree on.

Planetalk wrote:

The chance of an engine failing is the sum of the individual odds across the number of engines on the plane.

That is not correct, see your previous comment, "engine failures are independent events, and one failing does not increase the odds of another failing"

Planetalk wrote:

No-one said 4 engine planes are higher risk.

From earlier in this thread which is what I initially replied to "the fact that 4engine aircraft have a higher probability of experiencing this sorta thing, which is a big part of the reason airlines and OEMs moved away from them in the first place?"

Planetalk wrote:

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.

That is not correct, see your previous comment, "engine failures are independent events, and one failing does not increase the odds of another failing"

What people are mixing up here is probability of something happening in the future, and for mutually exclusive independent events like engine failures that is zero, and historic rates of failure (which is generated by hindsight), which are measured in terms of failures per thousands of hours of the population of engine. What happens with the historic rates is they also tend to zero as the number of engines in the population increase and the number of hours flown increase.

What people also get wrong is they see a historic failure rate of say 0.0002 per 1000 hours for an engine and they say that if you have two engines the failure rate is 2x0.0002, and 4 engines it is 4x0.0002, i.e. the failure rate is twice as high on a quad. However this is not correct, for every 1000 hours a twin flies the engines do 2000 hours, and on a quad 4000 hours. 2x0.0002/2000, and 4 engines it is 4x0.0002/4000 is the same rate 0.0002 per 1000 hours. Intuitively this makes sense as we dont expect a Genx installed on a 787 or a 748 to have different historical failure rates per 1000 hours flown, and as more engines are built, and more they are flown the failure rate will tend more towards zero, the denominator, being the number of hours the engine is flown increases much faster than number of failures occur, and engines improve as a result of in service experience. The other factors that reduce engine failure rates are maintenance and trend monitoring, engines are repaired or removed from service before they fail.

There is over 500 GP7200s in service, they all contribute over 7000 hours a day to the number of hours flown to the engine population, the population of engines does not know where they are installed (ie position), the airline, the route etc. Each engine is independent of the next.

zeke wrote:

Planetalk wrote:

Yes engine failures are independent events, and one failing does not increase the odds of another failing.

Thank you, something we agree on.

Planetalk wrote:

The chance of an engine failing is the sum of the individual odds across the number of engines on the plane.

That is not correct, see your previous comment, "engine failures are independent events, and one failing does not increase the odds of another failing"

Planetalk wrote:

No-one said 4 engine planes are higher risk.

From earlier in this thread which is what I initially replied to "the fact that 4engine aircraft have a higher probability of experiencing this sorta thing, which is a big part of the reason airlines and OEMs moved away from them in the first place?"

Planetalk wrote:

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.

That is not correct, see your previous comment, "engine failures are independent events, and one failing does not increase the odds of another failing"

What people are mixing up here is probability of something happening in the future, and for mutually exclusive independent events like engine failures that is zero, and historic rates of failure (which is generated by hindsight), which are measured in terms of failures per thousands of hours of the population of engine. What happens with the historic rates is they also tend to zero as the number of engines in the population increase and the number of hours flown increase.

What people also get wrong is they see a historic failure rate of say 0.0002 per 1000 hours for an engine and they say that if you have two engines the failure rate is 2x0.0002, and 4 engines it is 4x0.0002, i.e. the failure rate is twice as high on a quad. However this is not correct, for every 1000 hours a twin flies the engines do 2000 hours, and on a quad 4000 hours. 2x0.0002/2000, and 4 engines it is 4x0.0002/4000 is the same rate 0.0002 per 1000 hours. Intuitively this makes sense as we dont expect a Genx installed on a 787 or a 748 to have different historical failure rates per 1000 hours flown, and as more engines are built, and more they are flown the failure rate will tend more towards zero, the denominator, being the number of hours the engine is flown increases much faster than number of failures occur, and engines improve as a result of in service experience. The other factors that reduce engine failure rates are maintenance and trend monitoring, engines are repaired or removed from service before they fail.

There is over 500 GP7200s in service, they all contribute over 7000 hours a day to the number of hours flown to the engine population, the population of engines does not know where they are installed (ie position), the airline, the route etc. Each engine is independent of the next.

Zeke, you keep making the same mistake regarding probabilities. Read the post by TheLark above. Yes obviously any single engine, whether installed on a twin or a quad has the same individual chance of failing which is what you keep saying. But no-one has questioned that. 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. Unless you are saying that engines know why are on a four engine plane and somehow become individually less likely to fail than when they are on a twin?

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.