Systems and methods for diagnosing an engine or an aircraft are described herein. Flight data of at least one of the engine and the aircraft is obtained. A graph-based representation modeling a mathematical relationship between parameters of at least one of the engine and the aircraft is obtained. The graph-based representation has a plurality of permutations. Output data for the plurality of permutations is generated based on the flight data. The output data for the plurality of permutations is compared and a fault is detected based on a discrepancy in the output data. A signal indicative of the fault is outputted in response to detecting the fault.