Prof John-Paul Clarke, Director of the Georgia Tech Air Transportation Laboratory (photo: W. Litant)
Thu 5 Feb 2009 – Researchers in the US have developed a traffic optimization procedure that could potentially reduce national commercial aviation fuel consumption and CO2 emissions by up to 6 percent, based on a saving of more than one billion gallons a year. Known as En Route Traffic Optimization, the procedure involves new algorithms that allow air traffic controllers to determine how to assign aircraft to the most direct and efficient routes possible while maintaining comfortable safety margins between aircraft.
The study is published this week in a report by the Partnership for AiR Transportation Noise and Emissions Reduction (PARTNER), the US multi-university aviation environmental research group led by the Massachusetts Institute of Technology’s (MIT) Department of Aeronautics and Astronautics, which is funded by the FAA, NASA, Department of Defense, Department of Transport and Transport Canada.
Currently, aircraft are assigned to predefined routes to both ensure safety and minimize complexity for controllers. However, this often results in aircraft being assigned to paths that are far from the cruise altitudes and speeds that are optimal for fuel efficiency and over routes that are, point to point, longer than they could be. This results in flight delays, unnecessary fuel burn and environmentally detrimental emissions. It has been estimated that air traffic congestion in the US costs the aviation industry around $6 billion a year, with a further $4 billion impact upon the value of collective passenger time.
The report says that given the forecast growth in aviation over the next decade there is an urgent need for air traffic control decision-support or automation tools to address the problem of congestion in the National Airspace System.
According to Dr John-Paul Clarke, Director of the Georgia Tech Air Transportation Laboratory and principal investigator for the project, the FAA is planning to test the procedure in the coming year at one of the FAA’s regional air traffic control centres. “This is a potential win-win situation – reduced fuel consumption, emissions, congestion and time wasted, all without changing a thing on the aircraft or the fuel they burn,” he said.
The research is being funded by the FAA’s Office of Environment and Energy. “While safety and technical limitations make some transportation inefficiencies inevitable, the FAA is aggressively alleviating them wherever possible and practical,” commented Dr Lourdes Maurice, the agency’s Chief Scientist for the Environment. “PARTNER’s research is key to identifying and developing new technologies and procedures that make this possible.”
The report proposes methods to investigate and quantify the economic and environmental benefits of optimization tools that en route air traffic controllers could use and, more specifically, develops mathematical models for conflict-free optimal trajectories over a volume of airspace and for continuous descent arrivals (CDAs). Computational studies are presented to demonstrate savings due to proposed algorithms using traffic through Cleveland Air Routes Traffic Control Center, one of the most congested airspaces in the US.
The researchers also determine the environmental benefits in terms of the change in the amount of emissions that are produced by aircraft. Fuel burn data has been made available through an on-going non-disclosure agreement with Boeing, and using Base of Aircraft Data (BADA) in the case of other aircraft where this data is not available.
The report contains two main sections. The first covers en route traffic optimization and develops static and dynamic conflict resolution algorithms to optimally route aircraft. The methodology developed allows for simultaneous aircraft heading and speed changes to resolve conflicts. The manoeuvres are determined so that the fuel burn incurred due to the changes are minimized. A significant characteristic of the proposed approach is that the manoeuvres are identified in only a few seconds, which enables implementation of the developed methodology in real-time traffic flow management.
The second section considers arriving aircraft only and describes a speed-change based optimization procedure for use in a CDA context.
CDA is a procedure defined as a descent from a higher altitude continuously without extended level segments and with the engine throttle setting at idle most of the time. Previous research by Prof Clarke and others have shown CDAs to reduce fuel use, in turn reducing emissions, and reducing noise over portions of the descent profile. However, he says in the report, there are numerous issues to address before CDA can become a prevalent procedure.
Chief among these issues is making sure aircraft arrive at the ‘metering point’, the point at which aircraft begin to follow the same flight path to fly a CDA, with the necessary time interval. Typically, a procedure named the Tool for the Analysis of Separation and Throughput (TASAT) is used to determine the time spacing required at the metering point. However, an aircraft’s flight plan does not often align with the calculated CDA separation. By issuing speed changes to the series of flights participating in the CDA procedure during the en route travel portion of the flight, small adjustments to an aircraft’s estimated time of arrival at the metering point can be made.
To aid this, the researchers have developed and tested a program it calls the En route Speed Change Optimization Relay Tool (ESCORT), which has produced results in line with expectations, they say, during CDA flight tests.
The report says more research needs to be carried out to link the two separate optimization programs. “If they are not considered together, it is possible that fuel savings en route will be offset if CDA procedures cannot be implemented,” its authors conclude. “Furthermore, an optimization program that assigns arrival times and spacing for CDAs might yield infeasible solutions if aircraft are unable to achieve arrival times due to conflicts en route.”
Georgia Tech is one of nine universities collaborating in PARTNER’s research to develop breakthrough aviation technologies, operations and policies in the areas of aviation emissions, noise and alternative fuels.
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