Traditionally, landing aircraft approach a runway by ‘stepping’ down from the cruising level to the ground (blue path). At each step, the pilots have to alter the thrust of the engines to level out the aircraft. New technology means that airlines can work with air traffic control and airports to create a much smoother descent to the runway, cutting out the stepping procedures and cutting fuel use and noise at the same time (green path). In fact, airlines estimate that each continuous descent approach can save 150kg of jet fuel (around 500kgs of CO2 ). A major drawback of CDA operations is the reduction of airport and/or Terminal Manoeuvring Area (TMA) capacity, since vertical separation strategies between conflicting aircraft become more complex for the ATC. In order to partially overcome this issue, ATC may issue time requirements to aircraft to meet certain waypoints (such as in the TMA entry, initial approach fix, final approach fix, etc.). This time requirements increase the complexity to compute the descent trajectory, especially if an optimisation of the trajectory is sought. GTD’s onboard fast optimiser for CDA calculates descent profiles minimizing the use of engine thrust and speed brakes while meeting ATC time requirements. This optimisation process is launched each time the actual trajectory deviates from a certain error threshold from the intended one. Thus, a new optimal flight profile is re-planned.
