Defining requirements for advanced PHM technologies for optimal reliability centered maintenance

Condition based maintenance plus (CBM+) can be described as optimal condition based maintenance (CBM) procedures defined by applying the principles and process of reliability centered maintenance. This approach offers a rigorous and disciplined method, based on the system FMECA, to determine the least cost maintenance policy and procedures that are consistent with acceptable levels of safety and readiness, applying available prognosis and health management tools. It is argued that the same process is the preferred method to define requirements for advanced PHM technologies based on RCM derived capability gaps, preferably accounting for synergies with concurrent continuous (maintenance) process improvement. There may be synergies in coupling this process with Continuous Process Improvement programs, such as NAVAIR's AIRSPEED. In discussing this proposed approach, several issues are addressed. The first is the question of interdependence between incommensurable safety, affordability and readiness objectives and metrics. The second is the problem of uncertainty in the FMECA failure modes and probabilities until the system and equipment has accumulated considerable service history, while still subject to the emergence or aggravation of failure modes by mission exposure, component deterioration, quality escapes and intentional configuration change. In practice it may be necessary to fall back on less rigorous (semi)qualitative methods to target innovation. In any case, more adaptable PHM architectures are needed to mitigate inevitable uncertainty in requirements.. Note: the terms equipment health management (also, more specifically, engine health management) [EHM] and prognostic health management (or prognosis and health management) [PHM] are used with little distinction in this paper, but in general PHM is restricted to methods generating estimates of remaining useful life.