na
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Service Life 747Classic Vs 744 Vs 748I

Sat Mar 15, 2008 12:09 pm

I wonder if the 744 and the coming 748I are constructed to make more flights than the 747 Classics, if they are built to last longer.
 
Flighty
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RE: Service Life 747Classic Vs 744 Vs 748I

Sat Mar 15, 2008 10:58 pm

Well service life is really measured in hours, not cycles for a normal 747. The Japanese domestic 747 fleet probably has more landings and takeoffs than any 747 will get, ever. Most 747s can last 50 years at only 2 cycles per day.

So, we can say it won't be a matter of physical durability. The 744 has nothing that would suggest it can take any less than 100,000 or 150,000 hours. But the problem is fuel burn and maintenance costs.

Over time, new technology 773ER got invented. This means an older 744 is nearly obsolete in terms of fuel costs and maintenance bills. The jets are fine, but a superior product has been invented. Therefore, durability has not been an important issue.

Nobody wants to use a 747 for 35 years anymore, even though it WILL last that long. I have no doubt you could D-check a 742 and have it run reliably today until 2020. The aircraft IS that durable. But who would want to? And who will want to use a 748-I in 2040? Probably no one. They could, but they will choose not to.
 
tdscanuck
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RE: Service Life 747Classic Vs 744 Vs 748I

Sun Mar 16, 2008 12:24 am



Quoting Flighty (Reply 1):
So, we can say it won't be a matter of physical durability. The 744 has nothing that would suggest it can take any less than 100,000 or 150,000 hours.

Except the fact that it's aluminum, and aluminum fatigues. I'm not sure what the design service life is for the 747-400, but fatigue will eventually take down the structure no matter how well you maintain it.

Quoting Flighty (Reply 1):
I have no doubt you could D-check a 742 and have it run reliably today until 2020. The aircraft IS that durable.

If you ran a 747-200 at normal airline rates until 2020, your D-check would be incredibly expensive because of all the structural repairs. So the plane isn't exactly that durable...you're just rebuilding it during checks. There are JT8D's around where the only original part is the data plate. You could say that's an extremely durable engine, but it's really not the same engine you started with. Same situation if you take an aircraft way past its fatigue life.

Tom.
 
Flighty
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RE: Service Life 747Classic Vs 744 Vs 748I

Sun Mar 16, 2008 12:51 am



Quoting Tdscanuck (Reply 2):
Same situation if you take an aircraft way past its fatigue life.

I'm sure, granted I don't know jack about repairing aircraft. But I can say that UPS kept its 741 over 35 years. NW kept their DC-10s over 30 years.

At the tail end (after 20 yrs, say), it really doesn't matter. The aircraft are obsolete and worth next to nothing. Whether they continue flying, or not, is of very little importance. The most important thing is years 0-15, and then 15-25 if all is going well. After that, sure you can keep "it" running. But it probably won't make any sense.

Look at Iran Air. That's as good an answer as any. They run 30 year old Boeings. Saha Air runs 50 year old Boeings. It can be done, if there is no other option.
 
LockstockNL777
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RE: Service Life 747Classic Vs 744 Vs 748I

Sun Mar 16, 2008 2:50 am



Quoting Flighty (Reply 3):
Look at Iran Air. That's as good an answer as any. They run 30 year old Boeings. Saha Air runs 50 year old Boeings. It can be done, if there is no other option.

I do believe those aircarft have a really low cycle or hour count, the 707´s of Saha practicly "new" (if I´m not mistaken)

btw: are there any real structural changes to the fuselage when comparing the classics with the -400 and -8i?
 
tdscanuck
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RE: Service Life 747Classic Vs 744 Vs 748I

Sun Mar 16, 2008 3:10 am



Quoting Flighty (Reply 3):
But I can say that UPS kept its 741 over 35 years. NW kept their DC-10s over 30 years.

UPS is low hour/low cycle compared to a commercial carrier, so that may explain part of their longevity. Douglas is a whole other situation...Douglas had a very different design philosophy when it came to fatigue than either Airbus or Boeing. As a result, they age better (structurally, anyway).

Quoting LockstockNL777 (Reply 4):
btw: are there any real structural changes to the fuselage when comparing the classics with the -400 and -8i?

I suspect they change alloys a lot, but I doubt that the actual detailed arrangement is that different. If you look in the fuselage of a 777 and a 707 the design concept is pretty much the same. Mostly, they play around with the frame/stringer/shear-tie arrangement.

Tom.
 
na
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RE: Service Life 747Classic Vs 744 Vs 748I

Sun Mar 16, 2008 7:23 pm



Quoting Flighty (Reply 1):
And who will want to use a 748-I in 2040? Probably no one. They could, but they will choose not to.

I assume that in the light of sky-rocketing fuelprices the ever-increasing need to find alternative fuels will lead to even shorter service life of current types. I doubt that by 2040 we will see 777s or A330s in service still. A state-of-the-art 773ER built in 2008 could be obsolete as early as 2020.
 
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Zkpilot
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RE: Service Life 747Classic Vs 744 Vs 748I

Mon Mar 17, 2008 2:32 am

The aircraft itself can last a long time, it is the engines where the issue occurs... Trying to get parts for classics is becoming more and more differcult by the day... so unless re-engine (which simply isn't economic anymore for a classic) then it comes down to engine life.
56 types. 38 countries. 24 airlines.
 
Viscount724
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RE: Service Life 747Classic Vs 744 Vs 748I

Mon Mar 17, 2008 3:35 am



Quoting Flighty (Reply 3):
UPS kept its 741 over 35 years. NW kept their DC-10s over 30 years.

BA operated some of their original 747-100s (delivered when they were still BOAC) for up to 28 years.
 
roseflyer
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RE: Service Life 747Classic Vs 744 Vs 748I

Tue Mar 18, 2008 1:42 pm

The 747 was designed as a 20,000 cycle airplane. That does not mean it can't fly more, but rather the components that are designed to last the lifetime of the airplane are tested so that engineers are 95% confident that 95% of the components will last the lifetime of the airplane. As far as I know, this number has not changed with any of the design iterations on the 747.
If you have never designed an airplane part before, let the real designers do the work!

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