the invention relates to a method and an associated device making it possible to avoid guidance command input errors by the crew . since the course and the radial are linked by different relationships depending on whether the aircraft is approaching or moving away from a point , the procedures from air traffic control may be given either in course or in radial , and since the fms system can also require the input of one of the two values , the number of possible different combination creates a situation of ambiguity that is prejudicial to the safety of the flight . to resolve this problem , the invention proposes a systematic display in text mode and / or in graphic mode of the input datum and of the other for verification by the crew .