Maintenance schedule of aircraft fleet based on stochastic crack growth and structural risk

In recent years, one of the probability approaches, stochastic crack growth analysis (SCGA), has been successfully applied to structural risk evaluation of aircraft fleet. The structural risk evaluated by SCGA provides a criterion to plan the preventive maintenance schedule. In this paper, a fatigue control point of an upper stringer angle in central fuselage of the aircraft is taken as an example to study the procedures of defining inspection schedule. The crack propagation curves under usage variation spectrums are computed by crack growth code. The results of crack growth analyses are validated by a coupon test. By SCGA, the dispersion of usage severity is determined quantitatively from the crack growth curves. To determine the dispersion of crack growth rate due to material property variations, the material variance coupon test is performed. The crack growth curves under specific risk levels are obtained by the total log standard deviation and median curve. Finally, by introducing the reliability centered maintenance analysis (RCMA), the inspection intervals can be planned under the design risk ranged from 1.0 × 10^-8 to 5.0 × 10^-8 loss per hour.