After a system's functions have been defined, the next step is to define all the ways in which each function can fail, which is defined as a Functional Failure. For each function, the analysis team should consider each reasonable way in which a function could fail.
The following example shows one possible function and a related Functional Failure for a cooling tower:
Functional Failure: Unable to produce 500 gallons per minute of water due to failure of one supply pump.
Function: Provide 500 gallons per minute of water at a maximum of 90 degrees Fahrenheit under all ambient conditions.
The following item is defined as a requirement for failures according to the SAE Standard JA1011, "Evaluation Criteria for Reliability-Centered Maintenance (RCM) Processes":
All the failed states associated with each function shall be identified.
