Re: maintenance (was Re: pair (sorry, couldn't resist the pun))

From: (Harry Funk)
Organization: Honeywell Systems & Research Center
Date:         02 Dec 92 13:18:59 PST
References:   1 2 3
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In article <airliners.1992.60@ohare.Chicago.COM> (Gary Bisaga) writes:
>In article <airliners.1992.40@ohare.Chicago.COM>, weiss@wright.SEAS.UCLA.EDU (Michael Weiss) writes:
>|> primarily).  He said that DC-10s are notorious for repairs being all-day
>|> operations, whereas Boeing's 737-300 and -400, 747-300 and -400, 757, and 767
>|> have self-diagnostic systems that go so far as to direct the location of the
>|> repair instructions down to the page, turning the repairs into a half-day

>Nor would I - but you're comparing apples to oranges.  The other aircraft you
>mention probably have much more extensive electronic maintenance aids since
>most have much more extensive avionics in general.  It wouldn't surprise me
>if there was also more electronic diagnosis.

>The MD-11, of course, is just as highly outfitted with electronics as any
>of those others - and the FMC design is newer as well, if I'm not mistaken -
>so a comparison with the MD-11 would almost certainly be different.

I agree.  There are several factors involved here:
	  how often does stuff break or require scheduled maintenance,
	  how well is the fault isolated by on-board or off-board
	    maintenance aiding systems,
	  how well does the documentation aid you in further isolating and
	    subsequently rectifying the fault, 
	  how difficult does the design of the aircraft make it to perform
	    the directed operations.

The MD-11 has a Centralized Fault Display System (CFDS), which serves as a
gateway to the BIT information provided by other avionics.  ARINC report
604 describes the characteristics of a CFDS system.  The 747-400 (but not
older versions of the 747, nor the 757/767) has a Central Maintenance
Computer, which takes the individual reports provided by the avionics,
merges them to form a consistent picture, which it provides to the
maintenance tech by means of a fault message.  The message is associated
with a entry point into the (paper) maintenance documentation fault tree.
Airbus has a similar system.  B777 will have a similar system.  These last
three are all (I think) ARINC Report 624 (On-board Maintenance System)

The more advanced systems, such as those found on the B747-400, A320/340
and B777, are quite difficult to build, since a change in the design of any
reporting subsystem may affect the design/operation of the CMC.  During
flight test, when things change rapidly, the CMC changes as the sum of all
the subsystem changes (best case - worst case is that the changes

"I am not, have never been, and hope never to be, a spokesperson for 

Harry A. Funk     Principal Research Scientist        Voice: (612)-782-7396
Honeywell Systems and Research Center             FAX:       (612)-782-7438
3660 Technology Dr.   MS:MN65-2500           Inet:
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