How much fuel and time can be saved in a perfect flight trajectory? Continuous cruise climbs vs. conventional operations

Continuous climb, cruise and decent operations (referred as continuous operations) may contribute to significantly reduce fuel and emissions. Nevertheless, it is obvious that the introduction of such procedures at large scale is not possible with the current air traffic management concept of operations, since flying at constant altitudes is one of the key aspects to strategically separate flows of aircraft. This paper tries to quantify what would be the potential savings of flying such optimised vertical profiles. A multiphase optimal control problem is formulated and solved by means of numerical optimisation. Optimal conventional trajectories (subject to realistic air traffic management practices and constraints) are compared with optimal continuous (and ideal) operations, only subject to aircraft performance constraints. Results show that the continuous cruise phase can lead to fuel savings between 1% and 2% of the total trip fuel for an Airbus A320. Interestingly, continuous operations show also a reduction of trip times between 1% and 5% of the total trip time, depending on the trip distance between origin and destination airports.