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Blog
Chronic or Rogue Parts
There are certain parts or components
that manifest the same recurring problems or write-ups over and over
again within a certain period. Such parts or are said to be
exhibiting ‘chronic’ or ‘rogue’ histories. Maintenance folks
have often called these offenders ‘Hangar Queens’ due to their
frequent visits to the shop.
TYPICAL PATTERN
The typical pattern is that initially the shop will return the part
to service with a ‘Could not duplicate’, or ‘No trouble
found’, or that corrective actions did not eliminate the pesky,
recurring write-up. This
may occur a few times before the part is declared ‘chronic’ or
‘rogue.’ A simplistic definition for these parts is that they
pass all the required Maintenance Manual tests and inspections, but
do not last on the aircraft. Most shops or airlines establish a
baseline, rule of thumb to make the determination that a part is
chronic or rogue; for example, if a certain serial number part
exhibits 3 removals in a six month period. These baselines vary
widely depending on the family of parts, ATA chapter, and/or the
airline or shop policy.
REALITY CHECK
I’ve had the sad experience to hear some end users of these parts
express some pretty inflammatory remarks regarding the practices of
the maintenance folks who repair these parts. This is sad because
this uninformed view does not accommodate the reality that these
parts will, and do exist, but until they are identified, the
maintainers are doing everything according to the approved data and
their training. In fact the maintainers take great pride in their
art, and are the first to self-inflict umbrage when they learn that
previous attempts to repair a part have failed. The real work and
test of the maintainers starts after the part has been identified as
chronic or rogue. Myopic critics abound too, on the side of the
shops who must fix these units, about the operator’s methods. The
uniformed critic needs to ask two questions: What causes this
phenomenon, and what is typically done to address it?
CAUSES
The causes of chronic or rogue parts generally fall into these
categories
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Variation: Variation in the manufacturing
process: Anyone who has studied statistics in manufacturing
will be familiar with the term “Variation.” The holy grail
in manufacturing is to eliminate such variation in the product.
Manufacturers with Six-Sigma processes for example, are said to
exhibit the least variation in the product. Regardless,
variation exists in any process, and that variation may exhibit
itself in a particular serial number that will eventually end up
on someone’s chronic list. To be totally honest in this tech
log, I’d have to acknowledge that variation exists in the maintenance
process as well. A manufacturer may have produced a flawless
part, but later during maintenance, a technician may have
accomplished a poor solder joint repair or improperly crimped a
wire for example. These could lead to intermittent failures.
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Intermittent Failures: This
is the bane of maintainers. These faults seemingly
manifest themselves randomly, and of course, rarely in
the shop. There are many causes which may include the following:
Variation in the manufacturing or maintenance process as
previously discussed; undetected wear; corrosion; abuse such as
being dropped or mishandled; ESD damage; severe events such as
lightning strikes, hard landings, landing gear collapse, or
collisions with ground vehicles; coffee, water, lavatory leaks
or other spills; failure of other parts in the system such as an
over-voltage condition, etc.
-
Software: This is quite
specialized, but it does happen. Many parts are controlled by
software and interact with other systems similarly controlled by
software. Such software is routinely updated, and occasionally
the new software causes the system to act in unforeseen ways.
This naturally causes the pilots to write-up the system, and the
aircraft technicians to take corrective, remove-and-replace
actions; of course the shops can find nothing wrong with the
units. It may be months before the operator or manufacturer
correlates the failures with the new software, and in the
meantime, the rogue list has grown significantly.
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False indicators: Sometimes
the problem does not lie with the part, but with the airplane.
Do rogue or chronic problems exist on the aircraft side? Of
course they do, you silly wabbit. I’ve seen some problems
on aircraft that defy troubleshooting logic and whose final fix
may not occur until months later. In the mean time multiple
removals of the same part may have occurred, and the repair shop
is being asked what are they doing about the spikes in removals
or chronic lists?
FIXING CHRONIC OR ROGUE PARTS
Remember that these parts all pass the tests required by the
maintenance manuals, and I’ve never met a manual that had a
troubleshooting section that addressed all problems. Fixing
it will require a mixture of experience, logic, the process of
elimination, and sometimes just plain old dumb luck. For those with
experience in the area, the process starts with coming up with a
written plan. Here’s a sampling of some common techniques
that may be used in the plan.
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Check all the available data for
correlation. For example: Are the parts coming from a single
aircraft tail number; was there an event such as a new Service
Bulletin or software revision that coincided with the rise in
removals; is there a particular phase of flight that the problem
manifests (cruise, landing or takeoff); was there any
maintenance event that occurred in the history of the unit that
seemed to usher in the rise of removals (such as a repair or
replacement of anything); etc.
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Shake and bake: Subjecting
the part to environmental extremes, is commonly called ‘shake
and bake’. This may involve putting the part into a freezer
and then testing the part, putting the part in an oven then
testing, and/or inducing a vibration during testing to see if
anything fails. In fact this whole process can get quite
sophisticated when you try to replicate the hot, cold,
pressurized/unpressurized, or vibration environment that the
particular part operates in.
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Under the magnifying glass:
This means examining the suspected part under a microscope or
magnification of some strength to look for flaws that may not
otherwise be detected with the naked eye.
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Swapping parts: With the
operator’s or airline’s permission, this involves swapping a
subassembly from one unit into another and seeing if the problem
follows. If the chronic unit comes back again, at least you’ve
eliminated that subassembly from the list of possibilities, and
the list narrows.
-
Replace suspected parts:
Although the shop doesn’t see hard failures, you can at least
make a logical, educated estimate that the problem comes from a
certain area in the unit, and simply replace a few parts. Some
call this ‘shotgunning’, but sometimes it really works. This
can get expensive, however, particularly if it does not yield
immediate results.
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Flight testing: After a
major effort to fix the problem, it may be possible to put the
part on a flight test or operational aircraft accompanied
typically by an engineer on the flight deck. If the part fails
again, at least the engineer can gather more information as to
the operational profile and crew procedures in affect at the
time of failure; valuable insight.
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Shoot the horse for crying out
loud! There comes a time in the life of a chronic or rogue
unit where the combination of operational delays or
cancellations, parts replaced, and labor costs reach a point
where you could have purchased a new or aftermarket replacement
part. Of course this means removing the rogue from service.
This is difficult sometimes, because maintainers hate to give
into a challenging problem. Management simply has to make this
call, and in fact it may turn out to be the most cost effective
solution.
WHAT SHOULD YOU DO WITH ROGUE PARTS
THAT YOU’VE DECIDED TO REMOVE FROM SERVICE?
The obvious answer is to scrap the part. There are some in our
industry however, that may try to salvage any value from the part,
and recoup their losses by selling it on the aftermarket. This is
unethical, and depending on the part, unsafe. The most
unscrupulous of these persons would send the part to an unwitting
repair station with the knowledge that the part is going to pass the
routine tests. Now with a fresh 8130-3, the part is on its way to
the aftermarket to start a new life with a new operator as a chronic
unit. Fortunately, these types of persons who engage this activity
are in a very small majority.
CAN’T WE ALL JUST GET ALONG?
Before I get off this soapbox and turn in my laser-pointer and lapel
mike, a few words: As I alluded to earlier, as regards chronic or
rogue parts, tempers can flare on both sides of the Operator-Shop
relationship. Allegations of poor quality at the Shop, or poor
troubleshooting at the operator’s aircraft abound in this arena.
Exacerbating this is when the operator is experiencing operational
delays or cancellations (a source of passionate debate at any
operator), or making warranty demands on the shop for the rogue’s
performance, and it may not be the shop’s fault! My humble wisdom:
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Operator: First acknowledge that
occasionally you’ll own a part that becomes a rogue or chronic
unit. Don’t be so fixated on turn-times, warranty claims, or
allegations of poor quality that you actually dis-incentivize
the shop from doing a proper job in addressing the rogue.
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Shop: Don’t get in the habit of
writing off all those ‘no trouble found’ responses to the
operator’s perceived lack of troubleshooting skills at their
aircraft. If you see a chronic part developing, don’t be so
fixated on turntime goals that you don’t accomplish a proper
job of addressing the problem.
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Both: To the degree that most
operators really want to encourage an atmosphere where their
vendors are partners and team members, the environment should be
characterized by a lack of fear to express problems, and for
both parties to put aside the emotions and roll up their sleeves
to fix the problem. Fortunately, most of you are just such
players.
There are all kinds of deeper, more
profound information regarding this subject, but this is just a
primer on the issue...
Over ‘n out.
10/1/04
Roy Resto
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VP Technical Operations,
FAA-DAR
Phone: 414 875-2191
Fax: 414 875-0200
royboy@mbtrepair.com
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