Multi-objective optimisation of aircraft flight trajectories in the ATM and avionics context

Performing the paradigm shift to 4D-Trajectory-Based Operations will involve several procedural improvements. High planning predictability allows better usage of airspace and dropping some of today's constraining factors. Efficiency improves by flying aircraft specific optimized procedures. By usage of sophisticated models and planning algorithms, total system's performance will come close to global optimum. This paper describes a new and powerful way of modeling 4D airspace incorporating traffic, weather, restricted areas and any other objects existing/moving in 4D airspace. The model represents these objects in a way allowing very fast conflict detection and resolution in order to find a feasible and efficient global solution.

A global airspace model for 4D-rajectory-based operations

The growth in traffic increased the pressure on the environmental sustainability of air transport. In this context, many research effort has been devoted to minimise the environmental impact in the different phases of flight. Continuous descent operations, ideally performed with the engines at idle from the cruise altitude to right before landing, have shown to reduce fuel, noise nuisance and gaseous emissions if compared to conventional descents. However, this type of operations suffer from a well known drawback: the loss of predictability from the air traffic control point of view in terms of overfly times at the different waypoints of the route. Due to this loss of predictability, air traffic controllers require large separation buffers, thus reducing the capacity of the airport.
Previous works investigating this issue showed that the ability to meet a controlled time of arrival at a metering fix could enable continuous descent operations while simultaneously maintaining airport throughput. In this context, the planning and guidance functions of state-of-the-art flight management systems need to be modernised. On-board trajectory planners capable to generate an optimal trajectory plan satisfying time constraints introduced during the flight are seldom, mainly because the real-time optimisation of aircraft trajectories is still elusive. Furthermore, the time scale and spatial resolution of the wind forecasts used by these trajectory planners are far from being adequate to generate accurate flight time predictions. Finally, there exist guidance strategies capable to accurately comply with time constraints enforced at a certain fix in the trajectory plan, yet they are not specifically designed to minimise the environmental impact.
This PhD thesis aims at investigating fast optimisation techniques to enable real-time updates of the optimal trajectory plan subject to time constraints during the descent; wind networking concepts to generate more accurate and up-to-date wind forecasts and, consequently, time predictions; and more robust an efficient guidance strategies to reduce the environmental impact at the maximum extent while complying with the time constraints of the trajectory plan. 
First, the feasible time window at a metering fix that could be achieved during a descent requiring neither thrust nor speed brakes usage is quantified as a function of the aircraft states (altitude, distance to the metering fix and airspeed), aiming to assess the feasibility of guidance strategies that take advantage of time and energy management concepts. Then, the performance of four of these guidance strategies is compared in terms of environmental impact mitigation and ability to satisfy operational constraints. Results from the comparison reveal that model predictive control, a strategy based on a frequent re-calculation of the optimal trajectory plan during the execution of the descent, is the most robust in terms of energy and time deviation at the metering fix, providing at the same time excellent environmental impact mitigation figures. However, the execution time required to solve a rigorous trajectory optimisation problem at each re-calculation instant remains a critical limitation for practical applications. In order to address this issue, a variant of the model predictive control strategy that allows for fast updates of the optimal trajectory plan based on parametric sensitivities is proposed, which shows analogous results yet halving the time needed to update the optimal trajectory plan. Finally, the potential benefits of using wind observations broadcast by nearby aircraft to reconstruct the wind profile downstream right before updating the optimal trajectory plan when using model predictive control is also investigated. Promising results show that the combination of model predictive control with wind networking concepts could enable optimal descents without degrading the capacity of the airport.

Optimal trajectory management for aircraft descent operations subject to time constraints

This research project aimed to develop innovative Multi-Objective Trajectory Optimisation (MOTO) and Dynamic Airspace Management (DAM) models and tools to enhance the performance of Air Traffic Management (ATM) and Air Traffic Flow Management (ATFM) syste

A novel air traffic management decision support system

Within the present air traffic management (ATM) system, a desired high capacity rate of continuous descent operations, flown from top-of-descent to final approach, is not yet feasible during daytime operations at the major airports. A concept of operations is described aiming at reducing the aviation environmental impact through better planning and predictability in the (extended) terminal area. This should enable a higher rate of Continuous Descent Approach (CDA) profiles while maintaining at least the same rate of Continuous Climb Departures. The work was performed within the ERAT project (Environmentally Responsible Air Transport), sponsored by the European Commission. The project aims to achieve enhanced climb and descent services as defined by SESAR and for implementation of operational improvements in the short to medium term. Key elements in the concept of operation for medium to high density CDA operations are time based operations using Controlled Time of Arrival (CTA), applying advanced arrival management and trajectory prediction, as well as integrated controller support tools. The evaluations have definitely proven benefits of the concept regarding predictability and efficiency. The concept and the advanced arrival management tool that have to support the concept seem to cater for possibilities to reach higher efficiency.

Implementing time based CDA operations in a medium-high density ATM environment

The expected future growth in aviation requires more efficient and environmentally sustained operations. The present paper presents the results of a concept evaluation to increase the rate of Continuous Descent Approaches. This work was carried out within the frame of the EU sponsored 6FW project ERAT (Environmentally Responsible Air Transport). The project facilitates in enhanced climb and descent services as defined by SESAR and aims for operational improvements for implementation in 2015. The concept of operation attempts to achieve medium to high density CDA operations applying time based operations. It is based on an advanced arrival management (AMAN) system that supports Controlled Time of Arrival (CTA) operations.

Staffan Törner

Papers

Implementing time based CDA operations in a medium-high density ATM environment

Real Time ATC simulation of Time Based CDA operations