Abstract: An improvement to a Flight Management System (FMS) for an aircraft is described. The improvement comprises: a system coupled to the flight management system for accepting flight data information, including a required time of arrival, and for generating therefrom an estimated arrival time and deriving from the estimated arrival time a signal representative of the required airspeed needed to allow the aircraft to reach a particular point at the required arrival time; and a system for receiving the signal and for generating an output signal for modifying the actual airspeed of the aircraft to correspond to the required airspeed. The signal is derived by applying to the actual airspeed a correctional factor which is a function of the estimated arrival time and the required arrival time. The correctional factor is generated from the ratio of the difference of the estimated arrival time and the required arrival time to the required arrival time.