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Parametric optimisation software package for trajectory shaping under constraints

Final Report Summary - POTRA (Parametric optimisation software package for trajectory shaping under constraints)

Executive summary:

One of the integrated technology demonstrators around which the CLEAN SKY Joint technology initiative (JTI) is articulated is the Systems for green operations (SGO) which focuses on all-electrical aircraft equipment and systems architectures, thermal management, capabilities for 'green' trajectories and mission and improved ground operations to give any aircraft the capability to fully exploit the benefits of SES.

In particular, the SGO aims at defining new approaches for the management of trajectory and mission for an overall optimisation of the aircraft and systems by implementing the following two concepts:

- Green trajectories, based on more precise, reliable and predictable three-dimensional (3D) flight path, optimised for minimum noise impact and low emission, including agile trajectory management, in response to meteorological hazard.
- A green mission from start to finish, with management of new climb, cruise and descent profiles, based on new aircraft performances database which includes noise parameter and allows multi-criteria optimisation (noise, emissions, fuel, time), including management of weather conditions which could negatively impact the aircraft optimum route and results in additional fuel consumption.

The POTRA project has been devoted to analyse and develop the following points:

- overview of the state of the art of collocation optimisation techniques;
- definition of the theoretical problem to solve;
- specification of the numerical optimisation techniques applicable to the problem;
- developing of a numerical optimisation software package;
- define the validation methodology and perform numerical simulations.

As a result of this project a tool has been developed with the following functionalities:

- 4D trajectories (e.g. emulate CCB, FRA, CDO, point to point);
- considered trajectory constraints;
- aircraft dynamics and operational weights;
- fly over fixes with altitude bands (user defined, SIDs and STARs);
- altitude bands at each trajectory segment between fixes;
- direct operations cost;
- fuel consumption;
- flight duration (CI);
- noise charges (noise stations).

Project context and objectives:

Due to the increase of flights during the last decades it has been necessary to define new routes and ways of flying. In order to overcome the limitations in existing procedures a new concept was envisaged, called Area navigation (RNAV). This concept is defined by International Civil Aviation Organisation (ICAO) as 'A method of navigation which permits aircraft operation on any desired flight path within the coverage of the station-referenced navigation aids or within the limits of the capability of self-contained aids, or a combination of these'. That means that the pilot is able to fly from waypoint to waypoint if the navigation system in the aircraft is able to compute these waypoints using the navaids in the area where it is flying. With this new concept the avionics industry has developed new systems in order to adapt the aircrafts to this new way of flying.

At the same time the number of routes and the flexibility of these routes have been increased.

New Air traffic service (ATS) routes, flight procedures in the terminal area, and departure, approach and arrival procedures have been defined as a consequence of the RNAV concept. The RNAV concept was complemented with the introduction of the required navigation performance concept that defines the level of performance that should fulfil the navigation on board the aircraft to flight the RNAV procedures, and both concepts have been recently enhanced by ICAO with the new concept of Performance-based navigation (PBN).

In spite of the fact that the RNAV has introduced new routes and more flexibility to the usage of the airspace, the Air traffic management (ATM) is still a very complex and highly regulated system. A substantial change in the current ATM paradigm is needed because this system, responsible for sustainable, efficient and safe operation in civil aviation, is reaching the limits of its capabilities. Its capacity, efficiency, environmental impact and flexibility should be improved to accommodate airspace user requirements and the forecasted demand growth.

These inefficiencies are caused by many restrictions currently in use. The need to fit aircraft trajectories to ATM system requirements makes them difficult to be optimised and, therefore, generally suboptimal flight profiles are being flown. This results in higher operational costs and higher emissions due to non-minimal fuel consumption (e.g. air traffic is responsible for 2 % of CO2 global emissions).

The SESAR programme establishes that in the mid and long term the air navigation will be based mainly on Global navigation satellite system (GNSS). Those systems will allow the aircrafts to fly more accurate routes with high integrity that will be traduced into a more flexible and less restricted airspace. The need of computing and flying 4D optimal routes will be essential in order to have less fuel consumption and emissions and a more efficient airspace.

The following paragraphs analyse the current problem of route optimisation and the proposed study to be undertaken in the scope of POTRA.

The work done in the context of POTRA has covered the following issues:

- definition of the problem to solve;
- analysis of the optimisation methods, basically it will be analysed and compared the direct method with Gauss-Lobatto collocation techniques, Legendre collocation techniques (pseudospectral) and hybrid method;
- based on the conclusions of the first analysis an optimiser will be selected;
- with the methodology and optimiser selected a software package will be developed in order to solve the optimum trajectory problem.

The problem to solve will be analysed and studied as general as possible and the implementation will done from the simplest to the most complex. This step by step implementation will be as follows (in all the steps flight envelope and weight restrictions are considered):

- optimisation of vertical profile;
- optimisation of horizontal profile with winds;
- optimisation of 4D profile;
- optimisation of 4D profile with phases (climb, descend and stepped climb in route);
- optimisation of 4D profile with phases and departure constrained (SID);
- optimisation of 4D profile with phases, departure (SID) and arrival constrained (STAR);
- optimisation of 4D profile with phases, departure, arrival and route waypoints constrained.

Project results:

The main result of the project is the development of a tool capable of computing optimal trajectories considering the following:

- calculation of the optimal flight between two airports;
- calculation of the optimal command along SID from an airport;
- calculation of the optimal command along STAR to an airport;
- customisation of the aircraft parameters;
- edition of the route intermediate points;
- edition of the noise measuring stations;
- plotting 2D graphics;
- generation of output files.

Potential impact:

The expected improvements that can be obtained with the new methods of optimisation are the following:

- Better 4D optimal trajectories: These methods allow obtaining the 4D trajectories. That means that the optimisation is not done in two steps, horizontal and vertical but in one step, therefore the computed trajectory is better in terms of optimal solution of the problem.
- Lower fuel consumption and emissions: These methods minimise the cost function, therefore new cost functions can be implemented and trajectories that minimise the fuel consumption, emissions or noise can be obtained.
- Guidance law: As an output of the solution this methods provide the guidance law of certain parameters, this guidance law could be injected in the Flight management system (FMS) of an aircraft and fly exactly the optimised trajectory. This will be traduced in more optimal and greener ways of flying.

In summary those methods give a new vision and way of optimising aircraft trajectories and could be the basis of new concept of flying and optimising the resources of the airlines and the airspace.

E-mail: Jesus Cegarra , Luis Javier Alvarez

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