Abstract: To meet the requirements of interactive diagnosis and isolation of civil aircraft troubleshooting, a test-maintaince signed directed graph (TMSDG) method with test and maintenance information is proposed by introducing the fault probability, unmeasured status and test nodes in signed directed graph (SDG). A procedure of interactive diagnosis based on TMSDG is proposed. First, according to initial symptoms, an initial suspect set is reasoned. Then, an optimal binary diagnosis tree with the minimal expected test cost is developed considering fault probability and testing cost, and the initial suspect set can be further isolated using the binary diagnosis tree. The complicated status association and fault-test dependency of a complex system fault can be modeled and interactively diagnosed by the proposed method. Finally, a fault diagnosis model of an aircraft engine bleed system is built up with the proposed method. The case results prove the effect and utility of this model, which suggests that the method may be suitable for application in aircraft on-site fault diagnosis and isolation.

Key words: SDG, interactive diagnosis, test cost, test sequence, diagnosis binary tree