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2.4 Optimal Fault Diagnosis
State-of-the-Practice
Fault diagnosis at PMS
• Runtime Costs. The runtime costs of the current diagnostic approach are high compared to
the automated approaches suggested in the next chapter. Many people are involved and that
means high labor costs. Also, the fixed costs of having the help desks up and running.
• Explanation Facility. Nowadays, the ability to explain the causes of a failure only consists
of the job sheets. However, usually these do not contain enough detail to understand a specific
failure.
• Adaptability. In case of a design change, all the artifacts that support the service engineer,
and are related to the particular subsystem, require re-implementation. This includes fault
isolation procedures, technical drawings, Symptom-Cause-and-Solution sheets and the Erroron-solution
database. This means that the Adaptability is not well addressed in the current
approach.
2.4.3 The Goals of a New Approach
The above shows that not all attributes are present in today’s practice. Therefore, it can be concluded
that the current approach is not able to meet the definition of a perfect fault diagnosis process. The
most striking flaws are speed of diagnosis, inaccuracy, uncertainty and inflexibility. The main cause
of the inability to achieve a desired presence of these items is that information is not at the right
time, at the right place, in a suitable form for diagnosing. Another flaw that is caused by a lack of
information is the reason that accuracy of the current practice cannot be determined.
Employees that develop the system, as well as service engineers, all have valuable knowledge
that is important for the diagnostic process. The artifacts described in Section 2.2 aim to record this
knowledge. However, these are not able to cope with the increased complexity. It is more and more
important to use data from the log. The interpretation of this data, that is specific for each particular
version of the system, requires information that is hard to record. Service engineer are supposed
to interpret this data, but it cannot be expected that employees have enough information in order to
use their own, time consuming and error-prone, human interpretation, for each produced diagnosis.
For these reasons, this lack of information, makes that the current approach is not fast, accurate and
flexible.
The new proposed approach should make better use of information in the organization. An
automated approach is a mean to achieve this. This automated approach should be able to improve
accuracy, speed of diagnosis, decrease uncertainty, and offer more flexibility in case of a design
change. An approach that allows for validation of the presence of these items is in favor above
other. This way, it is possible to improve fault diagnosis with respect to higher dependability. The
next chapter shows the possible automated approaches. The items of Section 2.4.1 are used as
criteria for the rationale to choose the most optimal approach.
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