Re: What's in a model number? (MD-95 Structural Specs)

From:         Stefano Pagiola <spagiola@worldbank.org>
Organization: World Bank
Date:         04 Dec 95 01:14:53 
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Don Stokes <Don.Stokes@vuw.ac.nz> wrote:
>Thinking about MDD's rather limited product range, vs Boeing's pretty much
>complete range of >100pax aircraft (and Airbus's not-quite-as-complete but
>still better than MDD's)...
>
>How much commonality is there between Boeing models that wouldn't be there if
>you ran a mixed fleet -- eg is there a significant advantage to flying an
>all-Boeing fleet, say 737s & 757s vs flying a mixed fleet (eg A319s instead of
>737s)?

Well, there's commonality across similar vintages of the 737, and to a
slightly smaller degree between them.  Pilots can be cross-qualified on
the 757 and 767, so there is commonality in pilots there (Delta was the
first to use this in practice, as I recall).  The 747-400 has a fair amount
in common in terms of avionics with the 767.

In terms of strict commonality, the picture isn't all that impressive.
Engines differ, as you noted.  Pilot qualification differs except across
some of the types.

But there is an overall picture here that we should not forget.  Beyond
strict commonality there is a great commonality in many matters of design
philosophy and the like.  One poster in another thread noted that Ansett
crews didn't like the BAe 146 partly because "everything worked
differently."  When it all comes from Boeing, yu can expect most things
to work in a given way, and that's a non-negligible advantage.

That said, if you're an airline picking your next wonderjet, there are
other factors you consider.  (1) Even when a family covers an entire range,
some of its members may not cover a particular niche as well as members
of a competing family.  Airbus widebodies have a wider fuselage, and hence
cargo capacity, than the 767.  If you want a high-capacity "long thin
routes" widebody right now, you can't get one from Boeing and have to
settle for the A340 or MD-11.  The MD-90 has very good hot-and-high
performance (which helped sway Saudia to it, even though it had never
operated a Douglas airliner before).  So the advantage of commonality may
be outweighed by a better fit to your airline's particular requirements.
(2) When you're talking of largish fleets, you can afford to have pretty
dissimilar fleets. You'll need so many pilots anyway that commonality with
other types in the fleet isn't quite as important (except under exceptional
circumstances, eg LH's desire to have their A340 crews fly A320s on the
last segment of some long South America trips).

Stefano