Indirect approaches to individual aircraft structural monitoring

At present, aircraft structural integrity is maintained by equally applying to an entire fleet knowledge obtained during the design phase and/or from a fleet sample and by introducing conservative assumptions, load surveys, costly inspections and maintenance procedures to safeguard airworthiness. Several investigations have highlighted the significant variations in individual aircraft usage and have indicated the inadequacy of applying 'conservative' assumptions and updating the assumptions by monitoring a fleet sample. They have, in addition, suggested the importance of individual aircraft tracking (IAT). IAT can be achieved by fitting each aircraft with strain gauges to monitor critical component loads directly, but maintaining a large number of strain gauges entails high operational costs. Affordable IAT can be achieved by analysing recorded flight parameters to indicate usage, loads and fatigue indirectly. This paper reviews the key investigations into indirect IAT structural monitoring methods.