BLACKSBURG, Va., Aug 11, 2000 --- Two Virginia Tech engineers, working under the auspices of the Federal Aviation Administration's (FAA) Air Transportation Center of Excellence for Aviation Operations Research (NEXTOR) are calling for a change in the way air traffic controllers perform their work in order to help alleviate the enormous time delays air travelers are now experiencing.
"Efforts to augment the current capacity by building new airports or by expanding existing ones are expensive, time consuming, and environmentally controversial," say Toni Trani and Hanif Sherali, Virginia Tech professors of civil and environmental engineering and industrial and systems engineering, respectively.
Instead, they believe that there are efficiency measures that could be adopted to improve air traffic control procedures.
Trani and Sherali, are the lead faculty members at Virginia Tech who are involved with NEXTOR. Virginia Tech, in conjunction with the University of California at Berkeley, the Massachusetts Institute of Technology, and the University of Maryland, comprise the center, started in 1996. Sherali, a member of the National Academy of Engineering, is an authority on solving transportation network flow problems, optimal resource allocation of airport gates, and how to best locate high speed exits at busy runways. Trani has been developing aviation related computer models to improve the capacity of airports.
Together, they have written a paper "Integration of Simulation Models to Evaluate the National Airspace System," to be published in The Journal of Transportation Engineering. They describe the "critical bottleneck in the air traffic control system" to be in the airspace that is 60 nautical miles around an airport.
Specifically, they are concerned with the airport terminal area where three types of air traffic control activities occur: aircraft sequencing operations that control the traffic inside the airport terminal area; runway operations that control aircraft landings and departures; and taxiway operations that guide aircraft from the gate to the runway for departures or vice versa for arrivals.
Each of these activities has its own type of air traffic controller. Final approach controllers are responsible for aircraft sequencing. Local controllers work on runway operations. Ground controllers are responsible for taxiway operations.
Trani and Sherali, along with their former student Hojong Baik, a post-doctoral student, propose that the three operational components be coordinated as one task. They have developed three pieces of computer software: the Aircraft Sequencing Problem (ASP) for runway operations; the Network Assignment Problem (NAP) for taxiway operations; and the Simulation Model (SM) for addressing communication activities in the airport ground transportation network. (This analysis was Baik's dissertation.)
With ASP, Trani explains "the guiding principle is that if arrivals and departures are sequenced intelligently, then an enhanced system will accrue."
For example, air traffic controllers try to maintain a minimum of five nautical miles when a heavy aircraft leads a smaller one. This distance is equivalent to about 196 seconds in time. If the sequence is switched so that the smaller aircraft leads the heavy one, the required distance between the two aircraft is reduced to three nautical miles or about 75 seconds. Although this switch might not be possible in each instance, it would save some 100 seconds when feasible. At a busy airport like Atlanta where more than 900,000 operations are handled each year, the savings in time could prove significant.
Using the results of their studies to date with ASP, the Tech engineers are using these initial conditions for solving the NAP problem.
With taxiway operations, landing aircraft have higher priority over departing and taxiing aircraft. The rationale is that arrivals are both costly and safety critical from a fuel consumption and operational point of view. For the same reason, the runway operation has a priority over the ground taxiing.
But Trani, Sherali, and Baik believe that by using ASP and obtaining the optimal runway operational sequence, they can also reduce the time connected with taxiway operations.
The third part of the overall equation for increasing efficiency at the nation's airports is the communication congestion due to controller work load. "For instance, even after a departing flight is ready to taxi, the flight could be delayed at the gate until it obtains a taxiing clearance from the ground controller," the three researchers say.
They have developed the SM to portray the pilot-controller communication process. This model provides very detailed information about the dynamic status of things such as flights, local controllers, and ground controllers. It also includes other pertinent information such as the aircraft's speed, acceleration, position, etc. at every time interval of simulation. This model is unique because for the first time it includes pilot-controller data link logic in an airport simulation model. Baik was responsible for the computer implementation of the model.
Add'l contact:
Lynn Nystrom
540-231-4371
tansy@vt.edu
Journal
Journal of Transportation Engineering