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From: stadler@Apple.COM (Andy Stadler)
Newsgroups: rec.aviation
Subject: Guided Tour of UAL Maint. Ops Center (long)
Message-ID: <56785@apple.Apple.COM>
Date: Fri, 30 Aug 91 11:50:28 PDT
Organization: Apple Computer Inc., Cupertino, CA
Lines: 145


Yesterday, I was lucky enough to be given a personally guided tour of United's
Maintenance Operations Center (MOC) at San Francisco.  The MOC is the head-
quarters of UAL's worldwide maintenance operations.  Other repair centers, of
varying sizes, exist around the world, but this is the center of it all.  It
was one of those friend of wife of a co-worker deals, but the upshot was that
three of us were escorted through the entire complex for about two hours.

As we entered the frontmost, huge building, our guide informed us of some of
the numbers involved.  There are three basic levels of service provided.  Over-
night work is basic checkout, cleanup, and simple repairs.  A moderate level
of service can be provided to repair major broken items, or to complete items
which periodic inspection, repair or replacement.  Airliners don't get "annuals"
of the kind we are used to;  They undergo FAA-approved cyclic repair on an
ongoing basis.  Finally, the airplanes are brought approximately once every
four years for a major teardown and rebuild.  The San Francisco MOC sees about
400 aircraft visits per year, and the engine shop will process about 800-900
engines in that period.

We started by walking through the repair shops.  United repairs or maintains
almost all parts and subsystems locally.  The only exceptions are proprietary
hardware which a manufacturer wishes to repair themselves, or an item which a
subcontractor can do more cheaply and better.  I asked if that meant avionics
and the answer was no, actually it happens more at the other end.  For example,
a local metal shop does a very good job with aluminum seat rails.  The MOC
maintains a large store of flight-ready parts, so typically a broken part is
replaced immediately from stores, and the broken part is repaired in sequence
in the shop.

The shops complex is, in a word, amazing.  For every single part you can think
of, there is a shop.  Flight surfaces shop.  Galley shop.  Seats & Upholstery
shop.  Life raft shop.  Hydraulic systems shop.  Brake shop.  Instruments shop.
Avionics shop.  There's even a Coffee Maker Shop.  It just went on and on.

The ostensible purpose of our visit was to discuss data-processing opportuni-
ties, so we looked at the parts tracking system.  For every part, there is a
tag which indicates flyable status, repair status, history, etc.  Every single
part has a complete history log - hours flown on which airplanes, repairs made,
etc.  United maintains a separate part number for every single piece of each
type of aircraft.  For the entire fleet, there are 350,000 unique kinds of
parts.  And this is for a Boeing + Douglas fleet only.  No TriStars, no AirBus.
Each technician, by the way, is qualified on a part-by-part basis.

Next we stepped out into the "narrow-body bays".  These are giant hangers where
the bulk of the work is done.  Most of these are left over from prop days, and
you can see how some jets fit better than others.  We saw one bay which was more
than big enough for the fuselage and wing, but the door was too low for the 
vertical tail.  United's solution was to build a special tractor rig which
elevates the nosewheel (lowering the tail), wheels the aircraft in, and then
levels it when the tail is inside the doorway.  Each bay is designed for a
specific type of airframe.  United builds its bays with permanent scaffoldings
which close around the airframe after it is parked, providing excellent access
to all surfaces.  There are also a few bays which are unconfigured, using move-
able platforms to provide more flexibility for unscheduled work.

Every airplane which comes in has a set of required maintenance operations,
plus a list of squawks, and finally a painstaking inspection to turn up any
other problems.  Once you have a pile of repair orders, how do you schedule
the work?  Currently, it's done -manually-.  A maintenance scheduler literally
shuffles the slips into an order which hopefully takes into account all 
dependencies limits dead time.

Airplanes which come in for major teardown/rebuild used to take about 20-25
days to do, but as airframes age and more inspections are required, that time
is rapidly escalating - it's now 50-60 days for older models such as DC-8's,
727s, and older 737's and 747's.  United is growing so rapidly that normal
purchasing is not really helping - the older airplanes keep flying.  The MOC
used to handle repairs for a number of outside airlines, but they are so full
these days that it's a thing of the past.  We learned that United is actively
seeking a site for a second MOC.  The new Denver airport is a possibility, but
as United's Atlantic business grows, the east coast becomes more and more
enticing.

We next walked outside across the tarmac into the wide-body hangar.  This
hangar is less structured - it's basically a huge building with rigging hanging
from the ceiling.  How huge?  Well, yesterday, the following were parked fully
inside:  747-200.  DC-10.  Two 727's.  747-SP.  And there was room for another
DC-10 and at least two 737's.  We got to climb aboard the 747-200, which was
in the final stages of a major rebuild.  It was amazingly shiny (new paint)
and the interior was immaculate.  I had sort of hoped it would be in a more
disassembled condition but it was still pretty neat.  I did of course sit in
the cockpit and make vroom-vroom noises, but there were tags on many of the
controls - "don't touch this".  We also got to poke around a bit into the 
galley and cargo areas.

Looking at the 747-SP got us talking about aircraft procurement.  United got
its fleet of 8 -SP's from Pan Am, one of which had originally come from another
airline and is a one-of-a-kind, which means that they have two fleets - a fleet
of seven and a fleet of one.  Remember that each fleet means a separate set of 
maintainance procedures, a seperate set of parts lists, etc, etc....  An inter-
esting note is that United was -very- unhappy with the SP's in general, as
delivered, and spent quite a bit of time on each one getting it up to their
fleet standards.  In general, they set fairly high standards for flying
condition of their aircraft.  This causes some problems when new aircraft are
delivered.  For tax purposes, United takes delivery of its Boeing jets in
Vancouver BC, flies them down to SFO, and (if all goes as corporate HQ would
like it to) immediately puts them into service.  In reality, however, United
literally returns many of the new aircraft after the 3 hour "test flight".  I
was surprised that you could find things in a simple three hour flight that
Boeing's QA couldn't find in it's postmanufacture phase, but in fact they do.

Another (long) walk took us to the engine shop.  First we entered the engine
test building.  There are two test cells, each with universal rigs for all of
the different engines United flies with.  Every engine is tested here before
it leaves the MOC.  The actual cells are heavily insulated, and unmanned when
an engine is running.  The engine tests are operated by an HP minicomputer,
which has saved a tremendous amount of money because it used to take 30 minutes
to run the engine manually through all of its tests, and the computer can do it
in less than 10 - this saves quite a bit of fuel.

Next to the test cells is a power cogeneration plant.  All of the electrical
and steam needs, plus extra power sold back to PG&E, is generated by a turbine
equivalent to a single DC-10 engine.  The plant runs on natural gas OR jet
fuel - convenient given its on-airport home.

Finally we entered the engine shop, where engines are torn down, repaired and
rebuilt.  Fairly major work is done locally, including re-machining of parts,
blade disk balancing, etc.  The engine building includes a complete, large-
scale machine shop capable of just about anything.  Taken together with the
smaller machine shops scattered around the MOC, they represent the largest job
shop in the Bay Area, and the average job size is...  one.

We took a quick look at the parts retrieval system - one of those wonderfully
baroque systems with pneumatic tubes and little robotic carts driving all over
the complex.  We asked about turnaround times.  For a real rush, a part can 
conceivably be in a mechanic's hand in ten minutes from his/her request.  Other
priority levels are 30 minutes, 1 hour, or 1 day.

Finally we entered the central maintenance scheduling center.  From here, all
United repairs worldwide are coordinated.  The system is tied in with the air-
craft scheduling system (although that's done elsewhere) so that airplanes can
be re-routed based on repair needs.  There are 12 smaller maintenance centers
worldwide, but all the work they do, and decisions of where to send each plane
for which repairs, all come out of a single room at SFO.  We also saw the
"crisis center", a room reserved for major "events".

Well that was about it.  Anyone who lives in the bay area has driven past the
giant "United Airlines" building just north of the airport.  But you have to
go inside, and walk around, to really realize just how huge the complex is.  If
you were to walk around the perimeter of the building, you would have traversed
about two miles - zigzagging around, I think we certainly did.  No wonder we
saw bikes and trikes everywhere.  I came away pretty amazed at the scale of
what they do.  And do, and do, and do...  24 hours a day.

--Andy      stadler@apple.com