1. A computer-implemented method of generating a description of aircraft intent expressed in a formal language that provides an unambiguous description of an aircraft's intended motion and configuration during a period of flight, comprising: obtaining a description of flight intent corresponding to a flight plan spanning the period of flight; ensuring that the flight intent description is parsed to provide instances of flight intent, each instance of flight intent spanning a flight segment with the flight segments together spanning the period of flight; for each flight segment, generating an associated flight segment description that comprises one or more instances of flight intent, wherein each instance of flight intent provides a description of the aircraft's motion in at least one degree of freedom of motion thereby closing the associated at least one degree of freedom of motion and/or provides a description of the aircraft's configuration to close at least one degree of freedom of configuration; identifying flight segments where not all degrees of freedom are closed and completing the identified flight segments by adding one or more instances of flight intent to close all degrees of freedom; and collating the flight segment descriptions thereby providing a description of aircraft intent for the period of flight expressed in a formal language.