Abstract: Due to the absence of actual operation and historical maintenance data for the new type of aircraft components,their lifespans are assumed as uncertain variables to study the block replacing policy based on uncertainty theory.Meanwhile, considering the different maintenance requirements and stock tolerance limits, the block replacing models with three optimizing criteria are proposed to search the optimal replacing period: a. the expected value model to minimize the average cost within a block replacing period; b. the chance value model to minimize the average replacing cost beyond the budget; c. the key value model to ensure that the average replacing cost below the budget exceeds the constraint of a given confidence. Finally, numerical examples are given to prove the validity of the proposed model.

Key words: block replacing policy, uncertainty theory, stock tolerance limit, expected value model, chance value model, key value model