2025 Volume 68 Issue 2 Pages 71-83
Long-haul flights often perform step-climb, where the cruising altitude is increased in steps as fuel is consumed, to increase fuel efficiency. However, in oceanic airspace, which is procedural rather than radar-controlled, intended step-climbs can be blocked by potentially conflicting traffic, sometimes for extended periods of time. Airspace design that facilitates operators to achieve their ideal flight plan trajectories, including step-climb profiles, will increase overall operational efficiency. This paper provides the results of simulation experiments of North Pacific Oceanic airspace, in which operators may plan flexible routes considering winds aloft, with the following two objectives: 1) to establish and validate a framework for the fast-time simulation of flexible route airspaces in which flights perform step-climb operations, and 2) to identify high-demand areas in the target airspace and clarify where the airspace design could be modified to improve flight efficiency and airspace capacity. In the validation, calculated minimum fuel and minimum flight time routes were compared with actual flown trajectories in terms of flight time and lateral and vertical profiles. The calculated minimum fuel routes were closest to the actual trajectories and had sufficient accuracy for the objectives of this paper. In the simulation experiments, potential loss of separation (PLOS) was used to identify high demand areas, and it was found that variation of step-climb locations of flights due to varying departure mass reduces PLOS duration. The identification of high PLOS areas in this study will serve to inform concepts to reduce PLOS and increase step-climb opportunities, such as airspace design to disperse traffic flow.
