A method for managing speed constraints of a flight plan of an aircraft, the method includes the following steps: identifying a current flight phase, determining CAS speed profile, the speed profile establishing a behavior of the aircraft with respect to a speed setpoint, determining a Mach speed profile, the Mach speed profile establishing a behavior of the aircraft with respect to a Mach setpoint, the Mach setpoint being a speed setpoint transcribed into an equivalent Mach number, determining a Cross-Over altitude, the Cross-Over altitude being an altitude of transition from an automatic control of the aircraft according to the CAS speed profile to an automatic control according to the Mach speed profile, determining an end-of-applicability criterion of the speed profile and of the Mach speed profile.