Optimal Aircraft Trajectories to Minimize the Radiative Impact of Contrails and CO2

The rapid growth of air traffic in the Asia Pacific region in the last decade has brought about the need for more sustainable modes of flight. A key initiative is the development of a Next Generation Air Traffic Management (NG-ATM) system which allows aircraft to fly optimal trajectories. Besides fuel- and time-related costs, other considerations for optimal routing include emissions, noise and contrails. Multi-Objective Trajectory Optimisation (MOTO) allows the generation of optimal trajectories with regards to these objectives, with dynamic weights depending on the phase of flight. Contrails are a major contributor to aviation's total Radiative Forcing (RF), being more significant than that of CO2. In particular, when formed in areas of low temperature and high relative humidity, contrails are known to persist for hours, spreading and eventually transitioning into cirrus clouds. Contrails trap heat by reflecting the long-wave infra-red radiation emitted by the earth back to its surface, producing positive RF. However, the albedo of contrails also reflects the incoming shortwave radiation from the sun, resulting in a negative component of RF. The impact of contrails, quantified by its associated RF, is thus not merely a function of environmental parameters but also a function of time. In this paper, a MOTO algorithm is used to generate optimal trajectories that minimize the radiative impact of contrails and CO2, while minimizing flight time and fuel burn. A case study of a transcontinental flight from Paris to Beijing is presented to demonstrate the feasibility of such an algorithm in providing strategic and tactical trajectory optimization capabilities.