Re: Boeing naming convention for 777

Date:         16 Aug 99 19:02:54 
From:         Pete Mellor <pm@csr.city.ac.uk>
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Regarding FADECs, see the bottom of the message.

On 7 Aug 1999, Karl Swartz wrote:

> >Point taken. But my understanding is that the heaviest available
> >current "ER" versions are quite a bit heavier than the earliest ones.
>
> Boeing's web page lists the MGTOW range for the 777-200(ER) as being
> from 580,000 lbs up to 656,000 lbs.  UA has some of the first ones built
> and theirs are all good for 632,500 lbs -- not the heaviest, but a lot
> closer to the top of the scale than to the bottom.
>
> >Perhaps someone can correct me if I'm wrong, but I understand that
> >bringing earlier builds up to the best currently-available standard
> >would certainly involve more than just a paper upgrade.
>
> So far as I know, it really is just a paper upgrade as far as the
> airframe is concerned.  You might need to upgrade engine thrust, but
> the AW&ST Source Book has identical physical dimensions and weights
> for the range of 777 engines from any given engine manufacturer so
> I'd guess that even that is little more than a paper upgrade -- you'd
> need to change the programming of the FADECs or something similar.

Not quite. My understanding is that the FADEC, together with its software,
is supplied by the engine manufacturer, and is in nothing to do with the
airframe manufacturer. This makes sense, since the FADEC is intimately
bound up with the design of the engine. Even if (as is very likely) the
writing of the FADEC software is subcontracted to a specialist software
house, it would be written to the engine manufacturer's specification.

This is one of the reasons (I guess) why it is rather difficult to obtain
details of the design of FADECs, and of FADEC software.

If the engine manufacturer needs to upgrade the FADEC software to match
an upgraded model of the engine to deliver increased thrust, then I agree
that this would be less of a problem than the modifications to the engine
hardware, but (I hope!) would still involve considerable additional
testing to meet the certification requirements.

The airframe manufacturer would need to take account of any changes to
the interfaces between the FADEC and the thrust control levers, autothrust,
engine start-up controls, and cabin air supply controls (and any other
means by which the aircraft systems affect the engine function).
I would guess that modifications to the FADEC would be made in such a way
as to minimize any changes to these interfaces.

Pete Mellor, CSR, City Univerity, London.
----------------------------------------
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