Management of Aging Aircraft using Deterministic and Probabilistic Metrics -

Aging aircraft can be effectively managed by a combination of deterministic and probabilistic metrics. The deterministic metric provides a damage index for each aircraft relative to the full-scale test. This indexing method based on crack initiation or crack growth, may not be singly sufficient to support fleet management decisions at a time when the fleet is aging. To ensure safety of fleet, a probabilistic metric has to be developed, specifically when there are deviations in operations of the fleet from the fullscale test, when significant findings are observed across fleet aircraft, or when immediate fleet actions such as inspection plans have to be formulated for safety of fleet aircraft. This paper first provides a brief discussion on deterministic metrics and their limitations. The probabilistic metrics are discussed next, specifically paying attention to the single flight probability of failure. In this context, risk analysis and assessment of aging aircraft are discussed in general with focus on engineering and management challenges in carrying out this effort. The engineering challenges emerging from lack of substantial service data and analytical limitations of existing methods are elaborated. The management challenges due to the dynamic nature of calculated risk values, decisions with respect to acceptable levels of risk, immediate fleet actions and future planning are discussed. The paper concludes with a section on promising technologies on the horizon that will provide prognosis capability to make proactive decisions to ensure flight safety.