A method of applying a “Heading Then Merge Behind” (HTMB) guidance directive sent by an air traffic control center to an aircraft comprising a flight management system, the flight management system making it possible to automatically follow the trajectory of an active flight plan. The method includes reception and validation of the directive by the flight management system, confirmation by the pilot of the aircraft of the application of the directive, creation by the flight management system of a flight plan incorporating the directive, activation by the pilot of the flight plan incorporating the directive, so that the directive is executed automatically by the flight management system while following the trajectory of the flight plan incorporating the directive.