bergkampsticket
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How Much Of A Plane Surives Its Lifespan?

Tue May 29, 2012 10:32 pm

Apologies in advance if this is in the wrong part of the forum and thus is most likely a stupid question but today I paid a visit tothe National Museum of Flight in Scotland where I was able to board an old BA BAC 1-11 G-AVMO, as well as Concorde G-BOAA. Both of these aircraft served for around 30 years and I was wondering with all the required replacements and part changes, as well as refurbs and so on, how much of an aircraft retiring after so many years would remain throughout its lifespan.
Sure it'll depend on a plane by plane basis but I'd be intriegued to get an idea.
 
tdscanuck
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RE: How Much Of A Plane Surives Its Lifespan?

Wed May 30, 2012 1:58 am

Quoting bergkampsticket (Thread starter):
Both of these aircraft served for around 30 years and I was wondering with all the required replacements and part changes, as well as refurbs and so on, how much of an aircraft retiring after so many years would remain throughout its lifespan.

Generally the wiring harnesses, ducts, piping, primary structure, and flight control surfaces will last the entire life (assuming no damage). Many components are on-condition maintenance and, assuming they didn't fail, may still be original (gauges, avionics boxes, interior panels, lights).

Some things are known consumables or life-limited parts and almost certainly won't be new: tires, brakes, landing gear, engines, filters.

Some things are known offenders for requiring replacement and, just statistically, probably aren't original: sensors, seals, actuators, windows, etc.

Tom
 
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lightsaber
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RE: How Much Of A Plane Surives Its Lifespan?

Fri Jun 01, 2012 7:22 am

The keel (if the aircraft has one) and the wingbox (with patches/repairs) stay with the aircraft.

I do wonder if Cargolux's last RR powered 747Fs will have one engine on the life of the airframe. The RB211-524G/H-T was an amazingly mature engine when the last were delivered. However, that would be the exception, not the rule. I recall one RB211 powered BA 742 retired/scrapped with one original engine still on the wing, but that was an early airframe retirement. (I think there were two in that situation, but perhaps my memory faded.)   

Quoting tdscanuck (Reply 1):
Generally the wiring harnesses

I agre with most of your well written reply. However, some new aircraft have the wiring harnesses replaced at a set interval. (IIRC, Original A380 plan, but I believe the switch to copper wire changed that). That can be cheaper than inspecting/testing. Note: That could be airline specific. I'm actually aware of more than a few older aircraft that had the bulk of the wiring replaced (usually harness specific due to known issues). TWA 800 was the inspiration to start looking at rule changes.

http://www.keybridgeti.com/videotraining/manualdl/25827.PDF

But in general, more is spent on the aircraft replacing parts over its life than was originally spent.

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Faro
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RE: How Much Of A Plane Surives Its Lifespan?

Fri Jun 01, 2012 8:36 am

Quoting lightsaber (Reply 2):
But in general, more is spent on the aircraft replacing parts over its life than was originally spent.

You mean total lifetime parts-replacement costs (undiscounted) is greater than total ex-factory acquisition price? Would you have a rough multiple in mind?


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tdscanuck
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RE: How Much Of A Plane Surives Its Lifespan?

Fri Jun 01, 2012 12:55 pm

Quoting faro (Reply 3):
You mean total lifetime parts-replacement costs (undiscounted) is greater than total ex-factory acquisition price?

Yep.

Quoting faro (Reply 3):
Would you have a rough multiple in mind?

I'd guess something like 2-3 but that's just a wild guess on my part.

Tom.
 
smartt1982
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RE: How Much Of A Plane Surives Its Lifespan?

Sun Jun 03, 2012 1:07 pm

Quoting lightsaber (Reply 2):
TWA 800 was the inspiration to start looking at rule changes.

This is something that I have been confused about, I know that document mentions about moisture and vibration as the cause of deterioration in wires, I never realised it would have that much of an effect.

I could never understand how wires which were out of sight and not being manhandled get so worn/exposed.

In a recent Safety refresher we were told there may even be spills of various liquids on the wire which would could help start a fire, how would this happen? (as in how it would spills etc. get in there?)
 
zanl188
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RE: How Much Of A Plane Surives Its Lifespan?

Sun Jun 03, 2012 2:20 pm

Quoting tdscanuck (Reply 4):
Quoting faro (Reply 3):
Would you have a rough multiple in mind?

I'd guess something like 2-3 but that's just a wild guess on my part.

It's also one of the reasons why OEMs can take a loss on the original sale & still make a profit on the program.

Quoting bergkampsticket (Thread starter):
Sure it'll depend on a plane by plane basis but I'd be intriegued to get an idea.

Whatever you do, don't take a "set in stone" rule away from this thread. For example: It's not common to replace primary structure but there are circumstances where it has happened. Such as bombed TWA 707 got a new nose, AC DC-9 that burned at CVG gave up its wing to a NW DC-9, etc
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tdscanuck
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RE: How Much Of A Plane Surives Its Lifespan?

Sun Jun 03, 2012 4:35 pm

Quoting smartt1982 (Reply 5):
I could never understand how wires which were out of sight and not being manhandled get so worn/exposed.

The airframe is constantly in motion (vibration & flex), which causes wires to move minutely. Maintenance elsewhere on the aircraft (especially above) often generates small debris (shavings, dust, etc.) that falls down into the bundles and, over time, can wear away the wires. Post TWA800 inspections showed way more FOD and wear than was expected on some aircraft.

Quoting smartt1982 (Reply 5):
In a recent Safety refresher we were told there may even be spills of various liquids on the wire which would could help start a fire, how would this happen? (as in how it would spills etc. get in there?)

Other than the galleys and lavs (and sometimes not even then) the floor isn't waterproof). Spills in the cabin will eventually end up in the bilge. On the way there they go through the floor and cargo hold sidewalls...right where a bunch of the wire bundles go.

Tom.
 
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DarkSnowyNight
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RE: How Much Of A Plane Surives Its Lifespan?

Sun Jun 03, 2012 5:25 pm

Quoting faro (Reply 3):

You mean total lifetime parts-replacement costs (undiscounted) is greater than total ex-factory acquisition price? Would you have a rough multiple in mind?

Not sure what the breakdown is, but consider that even cheaply acquired freighters, let's say a 1990's vintage 767-322 just as example, will be worked on by mechanics making in the low $20 - to high $30s per hour, and a fair bit of them. This MX is not just for heavy letter checks either, but everything from post-flight to nightly inspections as well.

Additionally, parts are very expensive as well. If you own a car, you might not be used to the idea of a $200 light fixture, $60 latch, or a $5,000 brake build-up, but small items like that do get replaced on time (WTL) and condition, and over the 20 - 40 year life of an airframe, will add up.

Both of the above factors are compounded by the fact that relative to cars (as an example) airliners are always in work. Inspections occur very frequently as well as regulatory agencies encouraging pilots to write up items in their log books. It's reasonable to assume that a given airliner (not in storage) is looked by MX at least once a day.

And then you get things like D-checks, which even when sent overseas to be done by cheaper labor, still cost millions per trip.

Based on that, I would say it of course depends on the total life of a frame (F9's 318's vs 5X DC-8-73s for example), I think anywhere from 2 to 7 times the original cost is a good starting point.

Quoting smartt1982 (Reply 5):
This is something that I have been confused about, I know that document mentions about moisture and vibration as the cause of deterioration in wires, I never realised it would have that much of an effect

Both of these things cause or enhance corrosion in metals.
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Faro
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RE: How Much Of A Plane Surives Its Lifespan?

Sun Jun 03, 2012 8:43 pm

Quoting Darksnowynight (Reply 8):
Based on that, I would say it of course depends on the total life of a frame (F9's 318's vs 5X DC-8-73s for example), I think anywhere from 2 to 7 times the original cost is a good starting point.

Wow, quite a multiple; I guess controls over maintenance costs are more important than negotiating discounts on initial acquisition...


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ssteve
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RE: How Much Of A Plane Surives Its Lifespan?

Mon Jun 04, 2012 3:42 am

Quoting tdscanuck (Reply 1):
Some things are known consumables or life-limited parts and almost certainly won't be new: tires, brakes, landing gear, engines, filters.

Landing gear? How often?
 
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RE: How Much Of A Plane Surives Its Lifespan?

Mon Jun 04, 2012 2:43 pm

Quoting faro (Reply 3):
You mean total lifetime parts-replacement costs (undiscounted) is greater than total ex-factory acquisition price?

Planes are used over a long time. Many parts are replaced multiple times. After some time production will slow done and you will have expensive low volume production or high cost for storing finished good.
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imiakhtar
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RE: How Much Of A Plane Surives Its Lifespan?

Mon Jun 04, 2012 5:24 pm

Quoting SSTeve (Reply 10):
Landing gear? How often?

Ultimately, it depends on usage and flight cycles but generally, a landing gear on current generation aircraft will need to go in for overhaul at around the 10 year interval.

PK maintenance overhaul their 747 Classic landing gears every 6 years or so.
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