The purpose of this manual is to guide facility managers through the Failure Mode, Effects and Criticality Analysis (FMECA) process, directing them how to apply this type of analysis to a command, control, communications, computer, intelligence, surveillance, and reconnaissance (C4ISR) facility. These facilities incorporate several redundant systems used to achieve extremely high availability that require specialized tools, which are described in this manual, to conduct an accurate analysis. The information in this manual will provide the facility manager the necessary tools needed to conduct a realistic approach to establish a relative ranking of equipments' effects on the overall system. The methods used in this manual have been developed using existing concepts from various areas. These methods include an easy to use evaluation method to address redundancy's affect on failure rates and probability of occurrence. Because a C4ISR facility utilizes numerous redundant systems this method is very useful for conducting a FMECA of a C4ISR facility. Examples will be provided to illustrate how this can be accomplished by quantitative (with data) or qualitative means (without data). Although heating, ventilation and air conditioning (HVAC) systems are used as examples, the FMECA process can be applied to any electrical or mechanical system.