System/subsystem failures interrupt availability and operations. Consequences can be costly and may be safety critical. Patterns of failures are typically described by the well-known bathtub curve: first a period of decreasing failures (usually for new equipment), then a period of random failures followed by increasing failures due to wear. Traditionally, maintenance is carried out to reduce failures and ensure availability. Maintenance can be preventive (PM), or repair (RM) after equipment failure. The type of maintenance is based on the type of failures on the bathtub curve. However, recent studies reveal that complex systems/subsystems do not follow the bathtub curve. They are more likely to suffer from random failures. It can be shown that preventive maintenance has no effect on random failures in improving reliability, in fact PM may increase failures. Also, random failures are not age related. Complex systems tend to have an initial phase of increasing failures for new equipment, followed by random failures with no wear out. Such awareness has led some to abandon preventive maintenance (it may have its place for equipment/components in identified wear out phases). The question then becomes, what needs to be done to ensure availability. New techniques such as predictive or on-condition maintenance are needed as part of Reliability Centered Maintenance (RCM). This paper/presentation discusses the P-F Curve (P is the point where failure may be detected before occurrence) and failure modes and effects analysis (FMEA) in determining how equipment may fail and its consequences. RCM implementation for complex systems is discussed.