na
Posts: 9170
Joined: Sun Dec 12, 1999 3:52 am

Boeing Serial-no. Oddity

Thu Sep 13, 2007 2:13 am

I found something strange in the succession of serial-numbers from Boeing aircraft. Why are, in the same fleet, higher (later) numbers used on older aircraft while newer aircraft carry lower numbers?

Just one example of this are
SIA 747-400Fs

9V-SFA (1994): serial-no. 26563
9V-SFB (1994): 26561
9V-SFC (1995): 26560
9V-SFD (1995): 26553
9V-SFE (1996): 28263
9V-SFF (1997): 28026
9V-SFG (1998): 26558
9V-SFJ (2001): 26559

Very odd is that SFE and SFF seem to be from a later order as the serial-no is much higher (by more than 1500 frames) and the later built SFG and SFJ have low numbers again, SFJ even a number lower than SFA built 6 years earlier. What is the sense behind that?
I noticed the same with Korean Airs 744s, while LHs 744s serial-numbers are linear with age.
 
dutchjet
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RE: Boeing Serial-no. Oddity

Thu Sep 13, 2007 2:38 am

Quoting NA (Thread starter):
found something strange in the succession of serial-numbers from Boeing aircraft. Why are, in the same fleet, higher (later) numbers used on older aircraft while newer aircraft carry lower numbers

It depends upon when the aircraft was ordered.......an aircraft ordered in 1995 but delivered in 2000 would carry a lower serial number than an aircraft ordered in 1997 and delivered in 1998.

Thus, with respect to the SQ aircraft that you mentioned, SFE/SFF were probably ordered separately from the other 744Fs that you list.

There is a method to the madness!
 
na
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Joined: Sun Dec 12, 1999 3:52 am

RE: Boeing Serial-no. Oddity

Thu Sep 13, 2007 2:49 am

There must be a method to the madness, I agree.

That SFE/SFF are from a later order seems clear, but why were they built earlier than -apparently- identical airplanes of the same fleet ordered earlier? Why weren´t the earlier numbers used first? Maybe the specifications of the aircraft are a bit different, SFG/SFJ differing from the others? I can´t think of any other sensemaking reason.
 
dutchjet
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Joined: Sat Oct 14, 2000 6:13 am

RE: Boeing Serial-no. Oddity

Thu Sep 13, 2007 2:54 am

Quoting NA (Reply 2):
That SFE/SFF are from a later order seems clear, but why were they built earlier than -apparently- identical airplanes of the same fleet ordered earlier?

Why were they built earlier? Because thats what customer SQ requested and negotiated. Boeing does not swap serial numbers around.....the numbers for the later delivered airplanes were already assigned.
 
tdscanuck
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RE: Boeing Serial-no. Oddity

Thu Sep 13, 2007 3:07 am

Quoting NA (Thread starter):
Why are, in the same fleet, higher (later) numbers used on older aircraft while newer aircraft carry lower numbers?

Serial number should be assigned at the time the aircraft definition is defined. That has only a very loose connection with the manufacturing order.

Tom.
 
na
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Joined: Sun Dec 12, 1999 3:52 am

RE: Boeing Serial-no. Oddity

Thu Sep 13, 2007 3:08 am

You mean, in this example, Boeing had already assigned serial-no.26558 to be line-number 1173 when SIA suddenly wanted more freighters built earlier, so 28263 could become line-no.1094? Didn´t know that Boeing fixes these numbers to line-numbers sometimes already many years before its been built.

Thanks for the answer.
 
Rivet42
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RE: Boeing Serial-no. Oddity

Thu Sep 13, 2007 3:18 am

You need to understand that there is no direct relationship between frame numbers and build sequence. Frame numbers are allocated as aircraft are ordered, regardless of when they might be build and delivered. Thus, whilst I don't have the data to hand at present, SQ Cargo most likely added aircraft to their initial order at a later date (or two later dates, judging by the two higher but unrelated frame numbers), but managed to negotiate earlier delivery of those two aircraft - possibly as a result of another 747 customer delaying or cancelling an order thereby freeing up slots on the production line.

Personally, I don't pay much attention to Boeing frame numbers, my records are based on the line number, as this - also unique for each production line - gives a true(r) sequence of build, and, more or less (though not always), delivery. On my database the frame number is merely a reference field, which holds no significance other than to indicate order sequence (which is pretty much meaningless in itself).

Riv'
I travel, therefore I am.
 
tdscanuck
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RE: Boeing Serial-no. Oddity

Thu Sep 13, 2007 3:50 am

Quoting NA (Reply 5):
You mean, in this example, Boeing had already assigned serial-no.26558 to be line-number 1173 when SIA suddenly wanted more freighters built earlier, so 28263 could become line-no.1094?

No, I mean they didn't know that S/N 26558 would be L/N 1173 at the time they assigned the S/N. Definition of the airplane (which sets the serial number) is a whole separate process from when it gets built (which sets the line number). An aircraft at Boeing gets a variable number and serial number before it gets a line number.

Tom.
 
MEA-707
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RE: Boeing Serial-no. Oddity

Thu Sep 13, 2007 10:23 am

Quoting NA (Reply 5):
Boeing had already assigned serial-no.26558 to be line-number 1173

Adding to Toms fine explanation; when they assigned serial nr 26558, they put a delivery date (at least something like a month or a quarter) , specifications and finance schemes etc. in the contract.
As monthly production goes up and down overyears, they had no clue it would become 1173 til about a year before delivery BUT they knew they approximate delivery date.
nobody has ever died from hard work, but why take the risk?
 
na
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RE: Boeing Serial-no. Oddity

Thu Sep 13, 2007 6:36 pm

OK, that makes sense. Thank you.