UA1175 emergency landing Honolulu

[NWA SLF]

Are statistics available showing how many 3 engine wide bodies (DC-10, MD-11, L1011) suffered two engine failures in flight and landed due to one engine remaining? I know of the Eastern maintenance issue where they lost all 3 but were able to get one restarted after cooling enough to free the engine so it would turn but it was going down if not close to an airport). I also know of multiple 747 hull losses with 2 engine failures on one side (ElAl, China) and numerous 707/DC-8 losses due to two engine failures. Wasn't the 767 finally allowed ETOPS due to proven reliability of other wide bodies plus domestic flights. Notice how many fewer fatal accidents there have been as the industry has moved from quads to twins. Engine problems we see in the latest designs are a concern - pushing the envelope too far in order to compete on fuel economy just like the JT9D was a stretch on the first 747s.

[EDML]

Well, Eastern L1011 was a maintenance error (missing gaskets) - that would have been the same on 2,3 or 4 engines.


All losses of 2 engines on the same side of a 4 holer have been connected and caused by an uncontained failure of one engine (or ripping of one engine and hitting the other one).


I never heard of any failure of 2 engines on a modern jet on the same aircraft due to different reasons. It is either connected (uncontained failure) or maintenance related (Eastern L1011).


Marcus

[panda-k-bear]

Originally Posted by TURIN

FAA now assert ETOPS standards for all large aircraft. That's why ETOPS now means ExTended OPerationS instead of Extended Twin OPerationS.

And there was me thinking it meant Engines Turn Or Passengers Swim

[oldchina]

Polar Bear Repellent.

Is it required for some ETOPS?
Would you feel better having it ?
Get out of your comfy chair and imagine. Are they hungry ?

[ethicalconundrum]

Since this thread has migrated a bit into the 2 vs 4 engine and ETOPS concerns, I will share a little of what likely influenced decisions on 2 engine jets over the past decade. I'm an EE by trade, but much of my work involves load determination and speeds/feeds. I've been using some interesting tools which have been developed very well since the late 80s in stochastic process(probability), and Poisson distributions.

Without going all into the math of it, the stochastic process attempts to build a model of two or many more independent, and random variable events or outcomes. If we consider the failure of engines to be both random and independent(one engine not taking out the other, contaminated fuel, etc) events, there is a model using the MTBF that will provide an index or deflection point that will give some indication of likelhood(I know, that's a lot of qualifiers).

I did a quick google(because I had no idea) of jet engine MTBF and came up with a number of inflight shutdowns of less than 0.01 per 1000 hours for EDTO > 180 min, 0.02 per 1000 hours for EDTO < 180 min, and 0.05 per 1000 hours for EDTO < 120min. Note, that this is not really the MTBF, but is the best I can find without going wild. Based on independent probabilities for a flight of 3 hours, I came up with a probability of 1.6e-9 (.0000000016).

While this sounds very small, taken into account all the various flight events we have around the world each year, this is a reachable event. I'm actually kind of surprised it hasn't happened - yet. I suspect there is not an actual independence at play, because should one engine fail on a jet, the flight will not typically proceed as planned, and the change in event duration window would be cut way down, unless over water. Even in cases of over water, the destination may be inland, and I'm guessing that an engine shutdown over water would mean diversion to the closes landing point, notwithstanding destination. So, that - and several other things would certainly influence the decline of the dual engine failure probability.

[lomapaseo]

I never heard of any failure of 2 engines on a modern jet on the same aircraft due to different reasons. It is either connected (uncontained failure) or maintenance related (Eastern L1011).


Marcus

Well a few have occurred. Most were not in ETOPs operation (e.g birds).

Taking into account independent failures the quad is 2.5 times more (than a twin) likely to lose two or more in an ETOPS flight. However the numbers are so low that all other failure conditions beyond the powerplants alone drive the FEDs to make rules.

The passenger can pick and choose but their choices are getting more and more limited by the science of the aircraft designer and the operator's needs

[BRE]

An uncontained failure can take out other parts. Would you rather have two or four of these potential bombs?

[BRE]

Originally Posted by stilton

A 707 without a doubt, it can fly a lot further
after losing two engines

Is that so?

My understanding is that in both cases, for the V2 scenario, a single engine out is considered. This means that a 4-holer must be able to climb out safely on three engines, whereas a twin must on one. Hence one engine on a twin has considerably more thrust reserves than two on a quad.

[number0009]

Originally Posted by lomapaseo

Single engine failure, fan blade contained within the engine cases.

Anybody else notice that close to 90% of the inlet nose cone is missing? Not a simple blade failure.
......

[lomapaseo]

Anybody else notice that close to 90% of the inlet nose cone is missing? Not a simple blade failure.

The photos show one complete blade and the tip of another. It's the tip that skids forward into the soft skin of the cowl and cuts a slash in the inner cowl.
It's the extent of these slices that is important and the ability to sustain the boom noise and the rundown vibration.

[old,not bold]

FAA now assert ETOPS standards for all large aircraft. That's why ETOPS now means ExTended OPerationS instead of Extended Twin OPerationS.

Hmmm.....not quite as simple as that, in my understanding (which is getting increasingly addled); EDTO covers all aircraft, ETOPS regs cover twins as a subset.

If someone comes along to say that's not right either I won't be at all surprised. But for the moment, here's EASA's take on it all;

AMC 20-6 rev. 2
Extended Range Operation with Two-Engine Aeroplanes ETOPS Certification and
Operation

[vapilot2004]

I recall it was decided nearly two decades ago that engine reliability no longer drives the ETOPS argument of 2 v 4 engines. Considerations of inflight fire suppression capabilities and weather diversions outweighed the turbine reliability concerns. Can anyone point to an incident or accident where an ETOPS twin lost both power plants due to engine failure? I cannot.

Thus, the statistics hold true where they state: there's a small chance you might lose one, but the odds go well into the stratosphere when we run the probability on losing two. ETOPS certified aircraft systems, capabilities, procedures, and maintenance practices are all designed to handle the loss of one engine with practically no demonstrated loss in safety margins.

I guess for some, the question remains, are we on borrowed time, or is this issue not worth debating considering the reliability of modern turbine engines?

[ethicalconundrum]

The other part of the probability equation is the risk-based management of outcome. Back in my field, if one of my networks goes down, we have a workaround that may delay some users from getting their data in 1/2 second, or 1.5 second. Meh - our ability to accept the loss of one system is much more tolerant than aviation. There used to be several quality ideals that were put forth, like SixSigma, and Five-9s, etc. Most of them have been replaced by the moving target of continuous process improvement. Aviation uses this, and it's one of the foundations of the US aircraft AD system.

Lastly, the two things about probability is that its a best guess, based on what we think is valid input data. In many cases, choosing valid input data is critical, and margin bands for probabilities(sometimes called the R^2 value), or chi-square of variability is an important factor(low R^2 factor means that the measured statistic has a wide variability, or poor prediction of event(s)). Second, all probabilities are not static! This is a common failing. Process control, product changes, systemic changes, and more constantly change the probability data. So, what I gave only a few minutes ago, may not be remotely accurate once the latest gen engines hit the market. A whole new plot of data will be done for that.

[ph-sbe]

Originally Posted by NWA SLF

I also know of multiple 747 hull losses with 2 engine failures on one side (ElAl, China)

The ElAl incident in Amsterdam was not caused by an engine failure. It was caused by fuse pin failures. All four engines were producing full thrust and when the pins failed the number 3 engine broke free and slammed into the number 4. In that process, the leading edge of the wing and some hydraulic systems were damaged. The crew was able to line up with the runway, but lost control when deploying flaps.

Engine failure had nothing to do with this.

[DaveReidUK]

Originally Posted by ph-sbe

The ElAl incident in Amsterdam was not caused by an engine failure.

Nor, indeed, was the other cited accident (assuming it's a reference to the China Airlines -200F).

[Start Fore]

Still, I'll stick to my 4 burner ta very much.

[NWA SLF]

You may not call it an engine failure but the FAA did. Specifically they stated that the loss of 2 engines on one side of a 4 engine airplane should not result in loss of control. It did not matter to them if the fan failed, turbine failed, or in the China and ElAl cases the entire engine falls off. The fuse pins were designed to let the engine fall off in the case of a very hard landing preventing a fire. Due to a design error they failed resulting in 2 hull losses and one major damage (NWA failure on landing in Tokyo). But we are getting way off the subject. I remember responding to somebody's statement that 3 engine airliners were going to return due to recent engine failures (not hull losses) on twin engine wide bodies - after 30+ years of wide body twins flying with no hull losses due to both engines failing. However there have been hull losses of 4 engine planes resulting from loss of power from both engines on one side.

[Bahrd]

Originally Posted by ethicalconundrum

Without going all into the math of it, the stochastic process attempts to build a model of two or many more independent, and random variable events or outcomes. If we consider the failure of engines to be both random and independent(one engine not taking out the other, contaminated fuel, etc) events, there is a model using the MTBF that will provide an index or deflection point that will give some indication of likelhood(I know, that's a lot of qualifiers).

I wonder whether it makes sense (in order to increase independence) to mount the engines drawn from different production lots.
The recent PW's troubles seem to suggest so.

[Hokulea]

My apologies for posting here, I'm not a pilot and can't add to the technical discussion, but thought some might be interested in some footage that has been shown on a local TV station regarding the engine that failed. I haven't seen this posted before:

Flight makes emergency landing - Honolulu, Hawaii news, sports & weather - KITV Channel 4

At around the 1:30 mark you get a good view of the front of the failed engine while still in flight. To my completely untrained eye, the engine has been shut down and the blades are windmilling but causing a lot of vibration.

Not sure if this is useful but thought I'd share in case it hadn't been seen by people on this thread before. Thanks for indulging me.

[Capn Bloggs]

Impressive, Hokulea. Also for the effect on the pax.