Failure mode describes how something fails. Failure mode effects describe failure local effects that provide evidence of failure at the component level ( see Fig. 2-15).

Figure 2-15: Black Box Component Model

With the black box equipment model, given that all inputs are present, failure to provide output the desired function must reflect an internal fault (failure inside the black box). Failure must occur inside the hot model, or one or more inputs, using a functional block diagram construction, must be missing. Reliability engineering models failure. Failure must be adequately defined to address with scheduled maintenance.

Failure characterization and development is part engineering, part art. Failure modes describe how components fail. Components are made of parts. Part failures cause component failure. Part failure is conventionally described as an engineering failure mechanism. Parts are the lowest discernible element in the equipment hardware hierarchy chains. The part is the atom of the equipment the lowest detail level. Failed parts are the elements maintenance activities must identify and correct. Rework or replace addresses failed component parts. Replacing or reworking parts corrects failures.

This hardware hierarchy ( see Fig. 2-16) and failure description can be summarized this way. It

• differentiates components into parts

• details components failure effects as failure modes

• describes part failure for analysis

• explains part failure completely

• provides

  • failure (mode)

  • cause

  • symptom

  • local effects

  • hidden failure (or evident)

  • risk exposure

Figure 2-16: Hardware Hierarchy

Failures may or may not be evident; often they are hidden. Symptoms...