Re: Development of MD-11?

Date:         03 Feb 98 19:53:04 
From:         "P. Wezeman" <>
Organization: The University of Iowa
References:   1 2 3 4
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Karl Swartz (kls@ohare.Chicago.COM) wrote:
[different engines in same plane]

> The simple answer is they don't.  FedEx has some 727s which have had the
> #1 and #3 engines replaced with JT8D-217C engines, similar to those on
> the MD-80 family, while retaining the original JT8D-17A in the center
> position.

> The problem is that you need to have spares and maintenance programs for
> each type of engine.  It's bad enough having different engine types on
> different planes.

	I have wondered about this. Back when Boeing was going to build
a new version of the 747, the engine maker suggested that it could use
a mix of B777 size engines on the inner pylons and B747 size engines
on the outer pylons. Boeing insisted on a new engine of intermediate
size. It seemed to me that if an airline already operated B777's or
Airbus A330's with big engines, and B747, B767, MD11, A300, A310 or
anything else with engines of that size, then they could order a
B747-500 or 600 with engines which they already used and maintained,
whereas with the intermediate sized engines they would have to stock a
whole new set of spare parts. Further, the market for both large and
smaller engines is intensely competitive, with all three manufacturers
aggressively improving performance and life. In contrast, the
intermediate size engine would be a collaboration between two builders
and would be the only one of its class, a sellers market. Both builders
would have every incentive to concentrate development efforts on their
other engines.
	One disadvantage of mixed engines is that I suppose all engine-out
performance figures would have to be figured for the worst case, with
one of the larger engines inoperative. This could result in a lower
maximum take-off weight for the same airframe.

                        Peter Wezeman, anti-social Darwinist

                             "Carpe Cyprinidae"