Maintenance scheduling for multicomponent systems with hidden failures

This paper develops a maintenance policy for a multicomponent system subject to hidden failures. Components of the system are assumed to suffer from hidden failures, which can only be detected at inspection. The objective of the maintenance policy is to determine the inspection intervals for each component such that the long-run cost rate is minimized. Due to the dependence among components, an exact optimal solution is difficult to obtain. Concerned with the intractability of the problem, a heuristic method named “base interval approach” is adopted to reduce the computational complexity. Performance of the base interval approach is analyzed, and the result shows that the proposed policy can approximate the optimal policy within a small factor. Two numerical examples are presented to illustrate the effectiveness of the policy

Cost based risk analysis to identify inspection and restoration intervals of hidden failures subject to aging

The analytical model presented in this paper aims to study possible maintenance strategies considering risk constrains, to preserve or assure availability of hidden functions of a repairable unit in aircraft systems considering ageing effect. The paper discusses two known strategies for hidden failure management aviation and other high risk industries, namely Failure Finding Inspection (FFI), and a combination of a series of FFI and restoration after a specific number of FFI cycles ( i.e., FFI-Rs strategy). Based on discussions, the paper introduces a new approach named Dynamic Failure Finding Inspection strategy (DFFI) to assure the acceptable level of risk and also the unit's hidden function availability continuously . The paper presents analytical methods to estimate optimal FFI, and optimal thresholds for restoration of degradation (refreshing risk level) within FFI-Rs strategy. It also discusses criteria used to select appropriate thresholds to change the FFI intervals within DFFI strategy, i.e. reducing inspection intervals after specific thresholds, to reduce the risk. The method is based on the mean proportion of time i.e. (Mean Functional Dead Time, MFDT) that the unit is not functioning during the inspection intervals and the average unavailability behavior within the restoration/discard period. The proposed method considers inspection, repair, and restoration times, and takes in to account costs associated with inspection, repair, restoration, potential losses due to non-availability of aircraft due to maintenance downtime or accident often caused multiple failures.Validerad; 2011; 20090912 (aliahm