A method is provided for inferring the aircraft intent of an aircraft from an observed trajectory. Aircraft performance data relating to that type of aircraft is retrieved from memory, along with atmospheric conditions along the observed trajectory. An initial set of candidate aircraft intents is generated. Each aircraft intent provides an unambiguous description of how the aircraft may be flown that allows a determination of an unambiguous resulting trajectory. A computer system calculates a trajectory defined by each candidate aircraft intent and forms a cost function from a comparison of each calculated trajectory to the observed trajectory. An evolutionary algorithm evolves the initial candidate aircraft intents, wherein the evolutionary algorithm uses a multi-objective cost function to obtain a cost function value that measures the suitability of each candidate aircraft intent.