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JAM747
Topic Author
Posts: 524
Joined: Thu Feb 03, 2005 12:17 am

Why One Engine Fails Before The Others?

If all the engines on an airliner have the same hours and flew in the same conditions why does one fail before the others? Sometimes the remaining engines can fly for many more hours. I hope this is not a silly question

oly720man
Posts: 5813
Joined: Fri May 21, 2004 7:13 am

RE: Why One Engine Fails Before The Others?

Depends what fails. There are many components in an engine and they are not absolutely identical. One engine might run slightly hotter than another, or vibrate slightly more than another and after a period of time it will cause a component failure.
wheat and dairy can screw up your brain

FredT
Posts: 2166
Joined: Thu Feb 07, 2002 9:51 pm

RE: Why One Engine Fails Before The Others?

A good position to start thinking about it: Why won't two matches thrown in a rapid river together end up in anywhere near the same spot?
I thought I was doing good trying to avoid those airport hotels... and look at me now.

LeanOfPeak
Posts: 496
Joined: Thu Oct 21, 2004 2:18 am

RE: Why One Engine Fails Before The Others?

Frankly, identical is a myth.

In design, you have a bell curve that defines probabilities of failures, with a point at which the part is most likely to fail and the odds tapering off from that point of the part failing before then or lasting past that point. This variability is due to manufacturing tolerances, material imperfections, etc. The acceptable risk of failure varies with how critical the part is, but when that threshold is reached, the part is replaced or refurbished.

The parts are replaced or refurbished when the odds of failure are so infinitesimal that the odds of having two simultaneous failures are practically immeasurable.

SlamClick
Posts: 9576
Joined: Sun Nov 23, 2003 7:09 am

RE: Why One Engine Fails Before The Others?

For the best answer read "The One Horse Shay" by Oliver Wendell Holmes.

Happiness is not seeing another trite Ste. Maarten photo all week long.

redflyer
Posts: 3905
Joined: Thu Feb 24, 2005 3:30 am

RE: Why One Engine Fails Before The Others?

Another good analysis would be the UA DC-10 flight back in July '89 that had a catostrophic failure in Engine #2 (tail) and lost all hydraulic pressure, which disabled the control surfaces causing the plane to make a crash landing in Sioux City, Iowa.

I read in the NTSB report at the time that the engine had a failure because the fan-disk core (which was recovered in a corn field months afterward) had a tiny, hairline crack in it that had resulted during the manufacturing process. That engine and core had been in service since their original date of manufacture back in 1971. It's been a while, but I don't recall hearing about any other fans from the same manufacturing batch having the same problem.

So, since the production methods were identical, why did one engine end up with the crack while the others in the production batch didn't?

Now, I'm sure someone will elaborate on this incident further so, just to cover my bases ahead of time, if other engines from the same production batch did end up having the same manufacturing defect, the next logical question would be why did this particular engine fail first? Was it perhaps because it had the most hours in service?
A government big enough to take away a constitutionally guaranteed right is a government big enough to take away any guaranteed right. A government big enough to give you everything you need is a government big enough to take away everything you have.

citationjet
Posts: 2573
Joined: Sun Mar 09, 2003 2:26 am

RE: Why One Engine Fails Before The Others?

In a light fixture in your house that has two identical light bulbs, both installed new. Many months later one burns out, yet the other one continues to burn much longer. Both have seen the same service, but have different lives. Would you be surprised that one burns out earlier than the other?
Boeing Flown: 701,702,703;717;720;721,722;731,732,733,734,735,73G,738,739;741,742,743,744,747SP;752,753;762,763;772,773,788.

backfire
Posts: 3467
Joined: Fri Oct 06, 2006 8:01 am

RE: Why One Engine Fails Before The Others?

Scientists call it chaos theory.

Two situations which are apparently the same to the eye will inevitably differ at the microscopic level. As you look closer and closer you will find more and more differences between the two, and these minute differences will gradually cause differences at the observable level.

This ability for almost-undetectable differences in starting conditions to affect outcomes in the everyday world is also known as the 'butterfly effect'.

The theory is that tiny air currents produced when a butterfly flaps its wings are enough to completely change the way in which a weather system develops - so the weather in the USA really can depend on whether a butterfly is airborne in Hong Kong...

FredT
Posts: 2166
Joined: Thu Feb 07, 2002 9:51 pm

RE: Why One Engine Fails Before The Others?

Or, paraphrasing Terry Pratchett: If all the weather here is caused by a butterfly flapping its wings in the Amazonas, isn't it about bl**dy time someone finds that butterfly and makes sure it stops flapping?
I thought I was doing good trying to avoid those airport hotels... and look at me now.

jfkaua
Posts: 972
Joined: Tue Aug 31, 2004 7:42 am

RE: Why One Engine Fails Before The Others?

now why the hell would you sensor the word bloody? lol

Newark777
Posts: 8283
Joined: Thu Dec 02, 2004 6:23 am

RE: Why One Engine Fails Before The Others?

This has turned into a very deep conversation, and it started with a simple engine failure.

Harry
Why grab a Heine when you can grab a Busch?

FredT
Posts: 2166
Joined: Thu Feb 07, 2002 9:51 pm

RE: Why One Engine Fails Before The Others?

Jfkaua,
to avoid upsetting oversensitive Americans. It's your b****y fault!

Seriously tongue-in-cheek,
/Fred
I thought I was doing good trying to avoid those airport hotels... and look at me now.

HAWK21M
Posts: 30120
Joined: Fri Jan 05, 2001 10:05 pm

RE: Why One Engine Fails Before The Others?

 Quoting Backfire (reply 7):Two situations which are apparently the same to the eye will inevitably differ at the microscopic level. As you look closer and closer you will find more and more differences between the two, and these minute differences will gradually cause differences at the observable level.

Well & Simply put D
regds
MEL
I may not win often, but I damn well never lose!!!

HAWK21M
Posts: 30120
Joined: Fri Jan 05, 2001 10:05 pm

RE: Why One Engine Fails Before The Others?

 Quoting Backfire (reply 7):Two situations which are apparently the same to the eye will inevitably differ at the microscopic level. As you look closer and closer you will find more and more differences between the two, and these minute differences will gradually cause differences at the observable level.

Well & Simply put
regds
MEL
I may not win often, but I damn well never lose!!!

captjetblast
Posts: 289
Joined: Thu Aug 30, 2001 5:59 am

RE: Why One Engine Fails Before The Others?

"If all the engines on an airliner have the same hours and flew in the same conditions why does one fail before the others?"

This tends to be untrue as time passes, as some engines are replaced and maybe others not. So it is not uncommon to find an aircraft with its engines having different running hours.

airplay
Posts: 3369
Joined: Sat Oct 25, 2003 1:58 am

RE: Why One Engine Fails Before The Others?

Most of the engine failures I've seen on modern airliners are the result of poor maintenance. Maintenance is the variable.

The design of airplanes including the engine are pretty conservative and forgiving. However, you never have just one person doing the servicing on the airplane and/or engine.

All it takes is a single mistake during servicing to cause accelerated wear or a condition couducive to failure.

So the chances of an engine failing increases a great deal the first time the cowls are cracked....

A/c train
Posts: 674
Joined: Sun Jun 10, 2001 7:57 am

RE: Why One Engine Fails Before The Others?

I'd agree with Airplays experience entirely there, the odd few now and then are manufacturing defects which end up in warranty claims, but classic things such as wiring looms chafing on pipes/ducts are a result of poor mx, whn the a/c was delivered there was adequate clearance between duct and loom, when the pipe was changed, the p-clip was undone, someone drops a stand off and loses it, doesnt replace it and the clearance gone, 50 cycles later and a load of vibration, you get an IFSD.
I give an example, new a/c off the production line 2 engines "zero hours in service", first flight, left engine has 1.9 CTA (Switzerland)">BB vib, the right has 0.2, the bearings, pipes, labyrinth seals etc etc are all given a good shaking and wear begins too occur quicker, small seeps from seals = more engine oil uplifts, engine begins too run hotter and burns a little more oil. Fan trim balance carried out and Vib gone.
The left engine is coming off wing earlier than the right. But the same may happen too the left, it could all come down too a filler seal not seated correctly !!
its a 'how longs a piece of string' question, but I agree with maintenance being the variable.
regds a/c
p.s, cant get rid of the CTA swiss thing so ignore !

flyabunch
Posts: 446
Joined: Fri Nov 05, 2004 1:42 am

RE: Why One Engine Fails Before The Others?

Why do two identical automobiles have different lives? In the real world, there is no such thing as identical.

If you look at the complexity of a modern jet engine, it is absolutely remarkable that they are as dependable as they are. I salute those who keep them flying. You are the true heroes of aviation to me.

Thanks,

Mike

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