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http://en.wikipedia.org/wiki/Fault_model

A fault model is an engineering model of something that could go
wrong in the construction or operation of a piece of equipment. From
the model, the designer or user can then predict the consequences of
this particular fault. Fault models can be used in almost all branches
of engineering.

A fault model in an Aerospace context is a set of structured information which helps users or systems to identify and isolate a problem that occurs on an engine, Line-replaceable unit (LRU), or Auxiliary power unit
(APU) during a flight. Associated with this fault model may be a
suggested repair procedure along with references to Aircraft
maintenance manuals (~ Light maintenance manual ).