I'd have no problem being on that flight. If ever there was a contingency likely to have been previously looked at every which way to Thursday, it's losing an engine; I very much doubt there were many decisions to make that hadn't been pre-planned, reviewed and signed off by everyone involved long before this incident.

What is interesting, as mentioned up-thread, is that both pumps failed. As the initial report said that the aircraft was signed off after they'd been replaced, the failure mode seems likely to be due to the pumps themselves rather than an external factor, excepting perhaps bad maintenance.

Does anyone know the details of the pump system on this engine, and whether any common factor could lead to dual pump failure?

Are you implying that once the twin is airborne, that proposition no longer applies?

If not, could you explain the significance of your proviso that it "hasn't yet taken off"?

If there exists a definition of (and a way of measuring) "safety" that renders a 4-engined aircraft flying on 3 "safer" than a twin flying on both, it's not immediately obvious what that definition/metric would be.

Strictly speaking, some aircraft don't even need the fourth engine to get airborne. I've operated a three-engine ferry on a four-engined aircraft without any drama. No passengers or crew of course. Also, four engine performance caters for an engine failure after V1 and before rotate so, to be utterly pedantic, a 747 doesn't even need the fourth engine to get airborne; the fourth engine merely needs to get the aircraft to v1!

- I just cannot resist pointing out that the subsequent engine failure would result in only a 33% loss of available power or a 25% loss of full power? Thus after 2 failures, 'Mr 4' is in the same boat (no pun intended) as 'Mr 2' after 1.

Exactly my point.

So, given that the starting point for the comparison is an all-engines-operating twin vs a 4-engined aircraft with one failed, the argument seems to be that the likelihood of an engine failure on the twin is higher than the likelihood of one of the 3 remaining engines failing on the quad.

That's counter-intuitive.

Paddy & Mick were en-route to XYZ in a 4 engined a/c. The captain came on the rail and apologised for "an engine failure, but no problem they would continue and arrive 1 hour late. Please enjoy the refreshments." Paddy & Mick thought this a great idea to have 1 hour more Guinness time. Later the captain came on again to inform them of a "2nd engine failure, but no problem, they would continue and arrive 2 hours late. Please enjoy the refreshments." Paddy and Mick could now look forward to 2 hours of extra Guinness time. A short while later the captain came on again with grave news. "a 3rd engine failure, but no problem, they would continue and arrive 4 hours late. Enjoy the refreshments." Paddy & Mick thought enough Guinness was enough and Paddy made the very astute observation that "good Lord Mick, I hope the other engine doesn't stop otherwise we'll be up here for ever."

I've flown ETOPS on 2 donks and would be far more wary of diverting 3 hours on 1 engine to 'nearest suitable' than continuing en-route on 3 .

One of our B727's lost an engine over El Paso and our op specs said we could continue with two engines, not land at nearest suitable airport as our twin jets. They landed at LAX and found one engine missing. It was found on someones property near El Paso. I was asked to fly our Jetstar on three engines from BUR to LAX for maintenance and refused because BUR has fairly short runways and terrain and it was just to save higher maintenance cost of having it fixed there.

It is the captains call how to handle it so let him decide. If it is legal decide if it is safe. A lot of things are legal but not necessarily as safe as erroring on the side of caution.

And also wrong

Given that all engines have the same probability of failure and are independent entities (so one failure does not cause another) an aircraft with 3 engines has more likelihood of an engine failure than an aircraft with two engines. If you like the aircraft has three tickets in the failure lottery compared with two tickets in the failure lottery.

The EFFECT of the failure may be more profound on the twin engined aircraft. Though even there some 4 jets reduced to two could be in a worse position than a twin reduced to one. An A340 with both engines out on one wing would be a little less capable than an A330 with one engine failed.

Thanks for the confirmation, Ian, I was beginning to doubt my sanity. :O

I flew around for years on 3 engines - a complete non -event - a bit like this thread.

Mainly DC10s, but with a smattering of TriStars of various flavours.

Remember the L1011 that took off from MIA over the Caribbean losing oil on all three engines, shutting two down and had to restart them because the last one was seizing? I think it was Delta a long time ago. Mechanic didn't replace O rings with his oil change.

Bubbers -

https://en.wikipedia.org/wiki/Easter...nes_Flight_855

Many years ago I took off single engine in a twin, from an oiled sand island strip and ferried it across the sea. All legal and above board. I'm still here.

Good grief!! You've brought back memories of those horrendous Two Engines Inoperative charts (DC-10). You went into them at the pre-flight planning stage to determine if you might have to limit zero fuel mass, so that you didn't have to jettison so much fuel to avoid going splash, leaving not enough to reach dry land.

Fortunately, this proved to be irrelevant on trans-Atlantic routes so for us it was only ever a base-check questionnaire teaser.

Shows how much thought does go into the ramifications of continued flight with engines inoperative, though.

Yes, and you did read me right: Two engines inoperative.

3 engine cruise on a 4 engine airplane, big yawn.
 

I think I'll take my crew rest now. Wake me 90 minutes out.

;-)

Decision Making Process:


lose engine...worry for 12 hours get close to home.

or

lose engine, dump fuel return to land at airport I just took off from, where the weather is about the same as when I took off, go to hotel, go see a play and get a nice dinner.

Attempt trip next day.

there are many considerations in any situation

23,000 hrs with no real engine failures just a precautionary shut down to avoid hydraulic contamination makes me feel very fortunate. I still treat each flight the same not expecting my luck to last. Flying one, two, three and four engine aircraft I have never lost an engine. I did once when I was showing my cousin how you could take a J3 Cub to altitude and stop the prop and get it windmilling again by diving it but I was young and stupid so had to dead stick it back to the airport and prop it on the runway to taxi in so they would rent to me again when I was 19.

One other time in a Jetstar they forgot to put oil in one engine and we had to shut it down. It was of course the number two engine again so lost normal hydraulics. My chief pilot was flying and I said we lost oil pressure on number two engine and he said it is just a indication problem. I said the low oil pressure light is on, we are going to destroy our engine if we don't shut it down. He reached over and shut it down and said don't tell the controllers. We only flew 20 miles but when he landed the only hydraulics we had was electrical pump. He heard it working so turned the switch off. I was a bit irritated by then but as we were approaching a line of AC and needing to turn saw our pressure drop to minimum so showed him the pressure was almost zero so was going to turn the pump back on. Thank God I got an airline job.

All a very interesting read on ones take of eng failures in 4 eng planes.

Just off topic a little as it's going round in circles anyway it's obvious to me that the biggest & ugliest flying machine in the air 2day the A380 Dugong has 4 engines for one main reason, they needed x amount of thrust to move such a large mass thru the air & they couldn't get it with just 2 (3 would have meant a totally diff airframe design).

4 engines for the A380 was needed there where no other options not 'cause of 'just in case'
With large engines now producing somewhere around 105000lbs of thrust or so we could almost have a very large SE Airliner carrying hundreds of pax but we don't see anything like that on the drawing board for very obvious reasons.
Safety in numbers:)

I've posted before about a DC-10 that lost #1 at 0200 out of KHI, and after a sequence of diversion plans, pressed on up the Persian Gulf and beyond (DXB-KWI-BEY) to finally make a daylight landing at ATH. I believe he set some sort of record. :eek:

Award of the day for "bleedin' obvious"... The point though is it needs the grunt to get into the air; however once it's up there in the cruise it certainly does NOT need all that grunt. Why, only the other day I was flying one from DXB to Australia and at top of climb I calculated that an engine failure would mean descending to FL170 or thereabouts (gross weight around 540,000kgs) However, two hours later the engine out profile is much rosier... And with all that gas:p

Although I think the incident was handled well and according regulations and procedures, let’s not forget:

4 engines have double the probability of an engine failure than 2 engines.

3 engines still have a higher probability of one failing than a twin.

Engines working on higher cruise thrust have a higher probability of failure again.

A 4-holer flying with only 2 has less performance than a twin on one hole, per design.

A 4-holer is not ETOPS certified, thus when losing the second hole, is in uncharted territory and on a full blown emergency.

That leads me to conclude that if you lose an engine on a 4-holer, you can continue, but you would be best advised to get into a 60min circle of a suitable airport within a reasonable time. This is not regulation, but looking at the situation from the above side, continuing over extended waters or high terrain on 3 holes might be legal and economic, but certainly not the safest solution.

(I remember faintly that on 3-holers we had en exemption for 120min until we had to be within 60min of a suitable airport, that makes some sense)

Just wondering...
 

... what if the An-225 loses an engine?

Glofish
 

Glofish, your conclusions are not applicable - you're now into another universe with probability stats if you start to look at two engine failures on a four engine aircraft on the same flight.

You probably have a far higher chance of being hit by a meteorite.:)

As an industry we generally don't do, if, if, if and if and that's what is being done in this thread - there is no evidence that there is a problem here nor that engine out flight has been dealt with other than with successful outcomes.

The statistical probability calculations argue that we've more chance of an engine failure in a 3 or 4 engine aircraft etc - well, that's good, the 747 gets "safer" after it's engine failure. :)

Don't forget that the engine failure stats/data on which ETOPS was founded did not include many failures such as the engine stopping due to a gearbox malfunction etc - the engine had stopped and it was not possible to start it again but as it wasn't a "core engine" problem it didn't count :ugh:

PS there are regs to be complied with if you lose another engine including drift down on two ..... at high weights on two engines most aircraft like the 747, A340 etc need a drift down altitude of circa 10-15,000 feet - there is still a safety net.

My only personal experience of prolonged flight with an engine inop was on a DC10 trans-atlantic. We soon noted a very significant increase in oil consumption, due due breakdown of the labyrinth seals for the windmilling engine. However, we soon established the oil loss to be at at a constant and predictable rate and on this basis continued to destination while closely monitoring oil contents.
No sweat, no drama.

No argument with the meteorite analogy, but you're missing the point. While Glofish's conclusions might be debatable, his statements on probability are demonstrably correct re 3 engines vs 4 (see also Ian W's earlier post).

Yes, of course the a priori probability of two successive, unrelated engine failures in the same flight is extremely low (in effect it's a very small number multiplied by an almost as small number).

But we're talking instead about the conditional probability of a second failure given that one engine has already failed. Since the probability of something that has already happened is 100%, we are now talking about one small number, not two small numbers multiplied together.

Good introduction to Conditional Probability here:

https://en.wikipedia.org/wiki/Conditional_probability

DaveReidUK
 

Need to read what I wrote;

I was debating his conclusions !

Didn't say he was wrong on those statements (indeed I agreed with them) in the first part of the post re : engine failure on a "four engine aircraft", engine failure on a "three engined aircraft" and engine failure on a "two engined aircraft" (had all three happen)

but, the argument moved on to apply some interesting conclusions to another completely different scenario and the getting inside a 60 minute circle (why 60) from an airport because you're down to three engines !!

Having spent considerable time on one engine after an engine failure on a twin (more than once) and also on three engines after engine failure on a quad (more than once) I know where I'd rather be. Remember, this thread is about continuing with three engines on a four engine aircraft in a world that allows almost unlimited flight on one engine with circa 350 people down the back.

I've asked twice already but I'll try again, have there been problems with continuing on three engines - any examples ? I know someone mentioned a constellation a couple of pages back but.....

GBS

Your last question is a rhetoric one. I could just as much ask stupidly if continuing with only one on a twin was that much of a problem .... examples EY and a Kenian a few years back and nothing happened either.

I was debating the risk present when deciding to legally continue on three with a 4-holer.

1. I did not read or hear anyone considering the increased risk of failure on the remaining engines due to higher rpm and egt. Why would we derate on T/O if not to increase lifetime and cruising for 12 hours on higher rpm and egt certainly reduces lifetime and increases risk of something turning sour.
2. i pointed at the fact that when you lose the second engine on a 4-holer you are in a less comfortable situation than with a twin losing its first, simply because the latter's power ratio is better on one and its systems are more specifically designed to handle such a situation (ETOPS).

This puts you on a higher risk situation than on a twin for two reasons, therefore my conclusion that continuing over extended waters or terrain might not be the best solution. As simple as that.
I think that it is certainly possible to continue, but some 4-hole jockeys seem a little too enthusiastic about this capability. Just some points to maybe consider a little bit closer.

I can assure you power is increased on the remaining engine on the twin.

Having had an engine failure with a depres at the same time on a twin due air system redundancy problems I'll have to disagree with your comments on ETOPS redundancy - won't even get into ETOPS "dispatch" criteria

Give me lots of hydraulic, electric and air systems any day - this is where the argument goes wrong ...... i.e. viewing the failure of the "power" plant in isolation - n.b. the development of the ETOPS statistical debate was made by ignoring engine failures caused by anything that wasn't a "core" engine fault.

Bottom line is they kept diversion and delay compensation costs to a min and arrived at destination only 5 hours late. Apparently the economic engine is much more important than engine #4.

GSD

If you want to compare with a Twin, your choice, but then again a Twin with a failure lands asap!! So comparison falls short.

I am saying that just because a 4-holer has more redundancy and is not legally bound to land, considering what i mentioned above, it is not automatically a good choice to continue over ........ but i realise i am talking against a 4-hole wall.:confused:

And so they were not affected by flight and duty time limits.

Glofish,

- I think we'll have to differ on that one. Can't get my head around three is riskier than one ... after you've lost one.

LAND ASAP is almost academic over the Pacific, Poles etc when the nearest usable is 1500+ miles away - 1500+ on one is a long way.... no, if I had the "choice" I'd rather have three.

Like you (I'm guessing) I've got quite a few thousand hours on wide body twins doing ETOPS (which I enjoyed and have no problems with) - but you can't beat starting with four :ok:

Isn't probability of losing 2 engines the same on quad or twin?
I mean.. probably the engines and plane don't know how many are fitted.

Except that doing that on a twin wins you a headline title, on a quad only a pprune topic.

Hi Dufo ... unless I'm mistaken .... according to DaveReidUK and his point on Conditional Probability ...... you're right!

"Risk" is a combination of two factors - the likelihood of something happening, and the seriousness of the consequences if it does.

It's perfectly legitimate to agree to differ on the degree of weighting that you attach to each of these factors.

Clearly you are correct in that the consequences of losing your one remaining engine on a twin are considerably more serious than the consequences of losing a second engine on a 4-engined aircraft.

Equally, Glofish is correct in saying that the likelihood of losing a second engine is higher (albeit still extremely remote) when there are 3 potential candidates than when there is only one.

DaveReidUK

Been doing risk assessments for years - It's not the definitions, it's the application of logic.... but I now understand where they come from - I could be wrong but I think Glofish may fly a wide body twin on ETOPS so it's a bit rich and quite incredible he makes the comments below ... no cred I'm afraid

Glofish said:

Let me raise a different issue. The plane eventually had to divert to Kuwait -- presumably because it could not manage the additional 530 miles to Dubai. Unless Baghdad is an acceptable diversion destination for an EK A380, this means that for the roughly 1000 miles prior to reaching Kuwait, this bird had no good diversion airports available. Does anyone think this might represent sketchy decisionmaking?

No............................:ok:

Sir: If I read your short answer correctly, the availability of diversion airports along the flight path plays no role in decisionmaking as to whether to continue a 3 out of 4 flight?

They didn't make "an emergency landing due to desperate fuel shortage"

they made a planned landing within the duration of their SAFE fuel reserves......saved their pax a huge amount of delay and inconvenience...saved the operator a fortune and probably gave time for logistics to organise the last 450-mile shuttle "home"
as a mere industry outsider, I can only see positives in this decision.....had they been in a two-engined machine, I would have looked at it somewhat differently.

they weren't...I didn't. :p