En Route and Traffic Flow Management

En Route Speed Optimization to Implement Continuous Descent Arrivals

Continuous Descent Arrival (CDA) is a procedure defined as a descent from a higher altitude continuously without extended level segments and with engine throttle setting at idle most of the time. While CDAs have been shown to save up to 1000 lbs. of fuel per flight, in turn reducing emissions, and reducing noise over portions of the descent profile, there are numerous issues to address before CDA can become a widespread 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 CDA, with the necessary time interval. The ATL uses its fast-time simulator 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. This shortcoming is the current motivation for CDA considerations in en route spacing. 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 (ETA) at the metering point can be made.

The above figure shows a screen shot of flights participating in a CDA flight test in April 2007. Although there are only 19 flights shown, one can imagine how difficult it would be to adjust the en route speeds of the flights involved, making sure each adjustment is relatively small yet optimal for fuel burn using manual methods. By incorporating speed changes into an optimization formulation, and also pursuing a more accurate Trajectory Predictor than what is currently available, the minimum amount of speed change necessary to arrange flights to fly a CDA can be found. This en route speed optimization research, in conjunction with the trajectory predictor that provides accurate Estimated Times of Arrival will be tested in the Atlanta airspace during the fall of 2008. Current work on this project will be presented at a conference sponsored by the American Institute of Aeronautics and Astronautics in August.

En Route Conflict Resolution with Weather Inclusion

Air traffic delays due to congestion in the National Airspace System (NAS) are a source of unnecessary cost to airlines, passengers, and air transportation dependent businesses. Congestion is estimated to cost the aviation industry, passengers, and shippers approximately $10 billion per year. This cost can be further segregated into a $6 billion impact upon direct airline operating costs and a $4 billion impact upon the value of collective passenger time.

Delays also have an environmental cost. Because of congestion, aircraft are often forced to fly far from the cruise altitude and/or the cruise speed for which they are designed. Such sub-optimality results in unnecessary fuel burn and gaseous emission that give rise to environmental concerns both globally and locally at ground level. The significant magnitude of air traffic delays presently observed is an indication that the current air traffic control infrastructure is not capable of handing current traffic levels. 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 NAS.

This research develops mathematical models for conflict-free optimal trajectories over a volume of airspace. The Air Transportation Laboratory (ATL) has completed computational studies and demonstrated savings due to proposed algorithms using traffic through Cleveland Air Route Traffic Control Center (ARTCC), one of the most congested airspaces in the US. In addition, the ATL is developing weather models to be included in the simulations so that solutions for aircraft avoiding each other and inclement forecasted weather can be modeled in real time.

The ATL has determined the environmental benefits in terms of the change in the amount of emissions that are produced by aircraft. The fuel burn is determined using data for aircraft performance and fuel burn that has been made available through an on going nondisclosure agreement with Boeing, and using Base of Aircraft Data (BADA) in the case of other aircraft where this data is not available.

About Clayton Tino