JAM747
Topic Author
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Why One Engine Fails Before The Others?

Thu Mar 03, 2005 1:45 am

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
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RE: Why One Engine Fails Before The Others?

Thu Mar 03, 2005 1:54 am

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
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RE: Why One Engine Fails Before The Others?

Thu Mar 03, 2005 2:05 am

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
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RE: Why One Engine Fails Before The Others?

Thu Mar 03, 2005 2:08 am

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
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RE: Why One Engine Fails Before The Others?

Thu Mar 03, 2005 4:54 am

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

Here http://www.readbookonline.net/readOnLine/1157/
Happiness is not seeing another trite Ste. Maarten photo all week long.
 
redflyer
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RE: Why One Engine Fails Before The Others?

Thu Mar 03, 2005 7:10 am

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?
My other home is a Piper Cherokee 180C
 
citationjet
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RE: Why One Engine Fails Before The Others?

Thu Mar 03, 2005 7:51 am

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;731,732,733,734,735,737,738,739;741,742,743,744,747SP;752,753;762,763;772,773.
 
backfire
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RE: Why One Engine Fails Before The Others?

Thu Mar 03, 2005 8:01 am

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
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RE: Why One Engine Fails Before The Others?

Thu Mar 03, 2005 5:27 pm

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? Big grin
I thought I was doing good trying to avoid those airport hotels... and look at me now.
 
jfkaua
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RE: Why One Engine Fails Before The Others?

Fri Mar 04, 2005 10:05 am

now why the hell would you sensor the word bloody? lol
 
Newark777
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RE: Why One Engine Fails Before The Others?

Fri Mar 04, 2005 12:17 pm

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

Harry
Why grab a Heine when you can grab a Busch?
 
FredT
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RE: Why One Engine Fails Before The Others?

Fri Mar 04, 2005 8:05 pm

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

Seriously tongue-in-cheek,
/Fred
I thought I was doing good trying to avoid those airport hotels... and look at me now.
 
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HAWK21M
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RE: Why One Engine Fails Before The Others?

Fri Mar 04, 2005 9:45 pm

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 Big grinD
regds
MEL
I may not win often, but I damn well never lose!!! ;)
 
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HAWK21M
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RE: Why One Engine Fails Before The Others?

Fri Mar 04, 2005 9:50 pm

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  goldmedal 
regds
MEL
I may not win often, but I damn well never lose!!! ;)
 
captjetblast
Posts: 286
Joined: Thu Aug 30, 2001 5:59 am

RE: Why One Engine Fails Before The Others?

Thu Mar 10, 2005 5:09 am

"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
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RE: Why One Engine Fails Before The Others?

Thu Mar 10, 2005 7:07 am

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
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RE: Why One Engine Fails Before The Others?

Thu Mar 10, 2005 7:51 am

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
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RE: Why One Engine Fails Before The Others?

Thu Mar 10, 2005 9:31 am

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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