NOx, fuel consumption and time effects of flight path angle during descent

Abstract

Due to factors affecting flight operation and air traffic management, such as air traffic separation, avoidance of traffic from congested areas, or facilitating separation with crossing traffic, as well as environmental constraints, aircraft cannot always use optimum descent profiles and perform stair step descent or low level flight. This leads to vertical flight inefficiencies and thereby an increase in fuel consumption and NOx emissions. In order to address the negative impact of vertical flight inefficiencies, particularly in the descent phase, descending at constant flight path angles has been identified as an efficient approach procedure by aviation organizations and researchers. This procedure is defined as continuous descent approach. In this study, an evaluation of continuous descent approach and various flight path angles, in relation to conventional approaches, is investigated and the comparative results are given in terms of NOx emissions, fuel consumption, and descent duration. As a result, a strong inverse proportion between flight path angle and fuel consumption is found. As expected, an analogous strong inverse relationship is also found for flight path angle and NOx emissions, not only from reduced fuel usage, but also from the changed exhaust gas temperature due to lower power settings thanks to the continuous descent approach. It can also be seen that the descent duration could be less for steeper flight path angles.