Flighty From United States of America, joined Apr 2007, 7932 posts, RR: 3 Reply 1, posted (5 years 9 months 2 days 20 hours ago) and read 2868 times:
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 From Canada, joined Jan 2006, 12709 posts, RR: 81 Reply 2, posted (5 years 9 months 2 days 19 hours ago) and read 2850 times:
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.
Flighty From United States of America, joined Apr 2007, 7932 posts, RR: 3 Reply 3, posted (5 years 9 months 2 days 18 hours ago) and read 2836 times:
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.
Tdscanuck From Canada, joined Jan 2006, 12709 posts, RR: 81 Reply 5, posted (5 years 9 months 2 days 16 hours ago) and read 2802 times:
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.
NA From Germany, joined Dec 1999, 10054 posts, RR: 11 Reply 6, posted (5 years 9 months 2 days ago) and read 2716 times:
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.
Zkpilot From New Zealand, joined Mar 2006, 4749 posts, RR: 10 Reply 7, posted (5 years 9 months 1 day 17 hours ago) and read 2657 times:
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.
RoseFlyer From United States of America, joined Feb 2004, 9166 posts, RR: 52 Reply 9, posted (5 years 9 months 6 hours ago) and read 2542 times:
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!