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LHR27C
Topic Author
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Average Overall Engine Life? (after Overhauls)

Fri Jul 31, 2009 12:28 pm

Hi all

I'm doing some research into engine lifes and wondered if anyone could help me with the following question: how long, on average, do engines physically last before they're scrapped? To be clear here - I'm aware that every x number of years the engine comes off the wing and gets overhauled, often with so many parts replaced it's almost as good as new, but - treating it as still the same engine, how long until the actual unit is scrapped relative to the aircraft it was first delivered on, or would it in theory last as long as necessary while there was still demand for the powerplant and a supply of spare parts?

Take as an example an old DC-10 delivered say 30 years ago powered by CF6s. Are those original engines still likely to be around, albeit with most of their parts replaced many times, and they will only go to the scrapheap at roughly the time the aircraft is retired? I suppose in this example the answer would probably be that given so many DC-10s have been retired, the powerplant "base" for the remaining fleet will consist of the newer engines only, even if there are some surviving 30 year old DC-10s still in service (i.e. their original engines, being older and costing more to overhaul, would have been scrapped fairly early when retirements began to pick up).

Hope the question makes sense,

LHR27C
Once you have tasted flight, you will walk the earth with your eyes turned forever skyward
 
tdscanuck
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RE: Average Overall Engine Life? (after Overhauls)

Fri Jul 31, 2009 3:09 pm



Quoting LHR27C (Thread starter):
I'm doing some research into engine lifes and wondered if anyone could help me with the following question: how long, on average, do engines physically last before they're scrapped?

There's essentially no limit. It's an economic problem, not a physical one, since very part is replaceable.

I've heard tell of JT-8 engines where the only original part is the data plate.

Tom.
 
MarkC
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RE: Average Overall Engine Life? (after Overhauls)

Sat Aug 01, 2009 2:44 am

An engine really does not have a life. All the major rotating parts have life limits. Maybe 20,000 cycles depending upon the model. Blades would eventually wear out. The static parts only really get replaced if they are beyond economic repair. Your major cases, which would be all the heavy exterior parts would typically never be replaced as repair would almost always be cheaper.

The majority of your engine cases, especially long haul engines would last the life of the aircraft.

Mark
 
ex52tech
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RE: Average Overall Engine Life? (after Overhauls)

Sat Aug 01, 2009 4:04 pm

I worked in a CF-6 overhaul shop, there were a few new cases introduced, due to some cracking issues where it wasn't possible to repair them anymore, but many of the heavier frames, or cases could be repaired or metal sprayed (built up), and then machined back to original specs.

Turbine disks, were life limited parts, then had to be replaced, but most older engines are as Tom stated, the case that the data plate is attached to is the only original part from that serial numbered engine, although some of the other cases and parts from that original engine may still be out there on other engines.

As recently as 2000, I worked on some JT9-7As that were built new in 1969 or 1970. The forward section of the airplane they were hanging off of is now in the Air and Space museum in D.C.
"Saddest thing I ever witnessed....an airplane being scrapped"
 
LHR27C
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RE: Average Overall Engine Life? (after Overhauls)

Sun Aug 02, 2009 9:23 pm

Thanks guys, that's roughly what I expected.
Once you have tasted flight, you will walk the earth with your eyes turned forever skyward
 
EcuadorianMD11
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RE: Average Overall Engine Life? (after Overhauls)

Tue Aug 04, 2009 11:56 pm



Quoting MarkC (Reply 2):
An engine really does not have a life.

I know the feeling.............

Is there a specific jet engine that is considerably more durable than the others?
I mean GE compared to RR for instance, on modern jet liners?

Ecuadorian MD11.
A lot of people need to be offended on a regular basis I always felt, and I�´m the very boy to do it! - Billy Connolly
 
tdscanuck
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RE: Average Overall Engine Life? (after Overhauls)

Sun Aug 09, 2009 4:20 pm



Quoting EcuadorianMD11 (Reply 5):

Is there a specific jet engine that is considerably more durable than the others?

The JT-8 is known for being pretty bullet-proof, as are the modern incarnations of the RB211. But it's all a matter of degrees...even a "bad" modern engine is extremely durable.

Quoting EcuadorianMD11 (Reply 5):
I mean GE compared to RR for instance, on modern jet liners?

In grossly general terms, RR tends to build for durability, GE tends to be a balance, and PW tends to go for absolute performance. But they're all very very small differences.

Tom.
 
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Pellegrine
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RE: Average Overall Engine Life? (after Overhauls)

Mon Aug 10, 2009 12:48 pm



Quoting Tdscanuck (Reply 1):
There's essentially no limit. It's an economic problem, not a physical one, since very part is replaceable.

I've heard tell of JT-8 engines where the only original part is the data plate.

What about the shafts? After how long do they get replaced?
We fly JETS, we don't fly donkeys. Citizenship/Residence::: Washington DC, US; Vaud, CH; Providenciales, TCI (hence my avi)
 
tdscanuck
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RE: Average Overall Engine Life? (after Overhauls)

Tue Aug 11, 2009 2:00 am



Quoting Pellegrine (Reply 7):
What about the shafts? After how long do they get replaced?

I think shafts are on-condition, not LLP's, so there would be some kind of inspection in the overhaul manual and, as long as the shafts passed, you could keep using them. If they're LLP's you'd just replace them when their life is up.

Tom.
 
grandtheftaero
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RE: Average Overall Engine Life? (after Overhauls)

Tue Aug 11, 2009 4:35 pm



Quoting EcuadorianMD11 (Reply 5):
Is there a specific jet engine that is considerably more durable than the others?

As with any engineered system, durability is traded with other figure of merits. If one engine is less or more durable than a competing design, it's probably not due to lack of workmanship, but probably because it was designed that way.

A good example is the CFM56 family of engines. Designed for short/medium haul routes, longer time-on-wing and higher durability are usually more desirable than cruise performance in these engines. Among many other things, blade clearances are larger, cooling passages are simplified, and turbine inlet temperatures are lower. This leads to a more durable engine at the cost of performance and fuel economy.

Just throwing that out there. When you compare X and Y engine (or and engineered system) it's important to realize that the benefits and drawbacks were carefully traded at the drawing board.
 
planemaker
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RE: Average Overall Engine Life? (after Overhauls)

Tue Aug 11, 2009 11:40 pm



Quoting GrandTheftAero (Reply 9):
A good example is the CFM56 family of engines. Designed for short/medium haul routes, longer time-on-wing and higher durability are usually more desirable than cruise performance in these engines.

CFM56-3 Engine Sets New World's Record for Time On-Wing
06.15.1997

LE BOURGET - A CFM56-3 engine powering a Boeing 737-500 with Braathens S.A.F.E. reached 19,855 cycles without a single shop visit, setting a new world's record for time on wing. The previous record of 19,841 cycles was held by a CFM56-3 engine in service with Southwest Airlines.

The CFM56-3C1 engine, which entered Braathens' fleet in October 1991, was removed after nearly six years of service due to life-limited parts in the core. The airline may soon break its own record as there are six additional -3 engines in its fleet that have logged more than 18,000 cycles without a shop visit.

A CFM56-3 engine in service with Germania Flug is poised to set yet another time-on-wing record by year's end. The engine has been in service with the German charter and regional carrier since 1988 and has logged more than 28,000 engine flight hours without a shop visit. If the engine stays on wing for 30,000 hours, Germania will have set a new world's record.
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grandtheftaero
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RE: Average Overall Engine Life? (after Overhauls)

Thu Aug 13, 2009 12:25 pm



Quoting Planemaker (Reply 10):
The previous record of 19,841 cycles was held by a CFM56-3 engine in service with Southwest Airlines.



Quoting Boeing767mech (Reply 11):
American Airlines has set a time on wing record for a GE CF6-80C2 engine - logging more than 40,000 flight hours and nearly 10 years of continuous on-wing operation on a Boeing 767 aircraft.

Here we see another difference when it comes to bookkeeping. Since the CFM56 is designed for shorter flights, the majority of the engine deterioration comes from going from ground idle to full power back to ground idle several times a day. In this case it makes more sense to keep track of cycles instead of hours.

In a CF6, the process of going from ground idle to full power back to ground idle may only occur once a day, but these engines spend most of their operating time at cruise. Here it makes more sense to keep track of hours.
 
tdscanuck
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RE: Average Overall Engine Life? (after Overhauls)

Fri Aug 14, 2009 12:44 am



Quoting GrandTheftAero (Reply 12):

In a CF6, the process of going from ground idle to full power back to ground idle may only occur once a day, but these engines spend most of their operating time at cruise. Here it makes more sense to keep track of hours.

Both engines track hours and cycles all the time...it's not a bookkeeping difference. However, the technical differences you note are why the short-range engine gets the cycle record and the long-range engine gets the hour record.

A short-range engine will burn out its cycles long before it can ever break the hours record, and vice versa for the long-range engine.

Tom.
 
grandtheftaero
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RE: Average Overall Engine Life? (after Overhauls)

Mon Aug 17, 2009 7:31 pm



Quoting Tdscanuck (Reply 12):
Both engines track hours and cycles all the time

Indeed. From a technical standpoint, both hours and cycles are book kept. But as you alluded to, depending on the mission of the aircraft/engine you will either exceed hour limits or cycles limits first. Maintenance contracts are written with this in mind. In other words, the time between overhauls for a CFM may be stated in cycles, whereas the time between overhauls for a CF6 may be stated in hours. That's what I was speaking to.

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