Aircraft fuel system diagnostics using digraphs

Faults within any system will decrease its functionality, with the worst case scenario being complete system failure. When faults do occur it is imperative they can be diagnosed and ultimately rectified as quickly as possible, minimising the effects of such a failure. In the case of a commercial aircraft system efficient diagnosis can optimise the time to return the aircraft to service, thus allowing less disruption to passenger travel. For a military air vehicle diagnosis of the status of the system can mean that missions can be altered or aborted given the faults detected. With the increasing complexity of modern day systems, designed for reliability, it is usually several items that are required to fail before catastrophic or complete system failure is experienced, thus diagnosis of multiple faults is important. In addition, for the most effective diagnosis, detection needs to happen in real time. A method of finding faults or combinations of faults as they occur is the subject of this paper. The approach uses sensor readings to assess the state of the system. The method of digraphs is used to diagnose the faults by considering deviations in the sensor readings from the expected system state. Digraphs allow a means to represent the propagation of inputs through a system, reflecting the relationships and interactions between the components. The primary research has shown the applicability of using the digraph based approach for fault diagnosis on a simulated test stand of an aircraft fuel system. The analysis has assumed steady state conditions although guidelines have been provided for use for dynamic behaviour. The technique has shown potential for extension for diagnosis to the real aircraft fuel system.