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From 1978 to 1996, the annual number of flights in the United States handled by radar controllers in the Federal Aviation Administration’s (FAA) en route centers increased from 28.1 million to 40.4 million. (En route centers control all airspace except that below 10,000 feet within 50 miles of major airports.) During those years, controllers received no new automation tools that significantly changed how they kept aircraft under radar control safely separated, and it is still a largely manual process. Today’s automation attaches the aircraft call sign to the correct radar position symbol and moves it across the radar display; prints a paper flight strip at each sector that will handle an aircraft; and provides a human-machine interface for manipulating the display and for entering and retrieving data. The current automation does little to predict close approaches between aircraft or to figure out aircraft maneuvers to avoid them. To enable controllers to handle the significant growth in traffic, the FAA has reduced the size of individual sectors (divisions of flight space) and imposed restrictions on flight paths. Many sectors today are so small that the controllers spend a lot of time simply handing off control of aircraft from one sector to another. The small sector size limits the amount of airspace they have for maneuvering aircraft to resolve conflicts, or for merging them with other arriving aircraft. Consequently, controllers must either coordinate maneuvers frequently with adjacent sectors, or wait until aircraft are under their control and carry out last-minute, and often exaggerated, maneuvers. There is airspace in the eastern United States where sectors have been made as small as feasible, and controllers will have difficulty handling any significant growth in traffic. There are several forms of flight restrictions for creating structured traffic environment for controllers. The FAA specifies the routes that aircraft must fly into, out of, and between busy airports. These required routes cause the airspace users to fly longer routes, and prevent them from changing their route to take advantage of changing wind conditions. The FAA also places restrictions on the altitude profiles that can be flown, thereby causing additional fuel penalties to users. Safety is of paramount importance in the operation and enhancement of the air traffic control system. In the last 35 years, there has never been a midair collision between two aircraft under radar control caused by an error of the air traffic control system. This record is remarkable, given the manual nature of the process. It is also an indication of the very demanding safety requirements levied on decision-support systems intended to reduce the effect of current flight restrictions. Here it is important to distinguish the air-traffic term "conflict" from "collision." En route controllers are required to keep all aircraft separated by either a specified horizontal or vertical separation. When two aircraft are on flight paths that will bring them closer than these specified separations, they are said to be in "conflict," and the controller must issue instructions to the pilots that will keep them separated. The FAA is developing a decision- support system called Conflict Probe that will help preserve safety, increase the capacity of saturated air spaces, and reduce the costs from flight restrictions. MITRE is helping develop Conflict Probe by making a prototype called the User Request Evaluation Tool (URET) available for an extended evaluation at two of the FAA’s en route control centers, where it is used on a daily basis by controllers at operational sectors. Conflict Probe provides an electronic display of aircraft flight plans, similar to that of the paper flight strips, but it automatically keeps this display updated as aircraft enter and leave the sector. It also includes a situation display on which current positions and future paths of aircraft, along with details of conflict situations, can be shown graphically. Conflict Probe maintains trajectories of future paths for all aircraft and continuously searches for conflicts. When Conflict Probe detects a conflict between two aircraft, it selects a single sector for notification and displays a visual alert to that sector. Conflict Probe usually detects conflicts 10 to 15 minutes in advance. In current manual operation, controllers recognize and take action to resolve conflicts later (about five minutes before the conflict). Detecting conflicts earlier allows the controller to explore several alternative resolutions, use less disruptive maneuvers, and resolve several conflicts in one maneuver. Conflict Probe also provides a trial-planning capability. The controller
can easily create an amended flight plan for an aircraft to resolve
a potential conflict and submit it for checking. Conflict Probe graphically
displays the proposed flight plan with color coding to indicate the
conflict status. If the flight plan resolves the displayed conflict
and does not create any new conflicts, the route is displayed in green.
If the flight plan has a conflict, the route is displayed in red or
yellow, depending upon the predicted closest separation between aircraft.
Because Conflict Probe sends warnings earlier than controllers currently resolve conflicts, it often happens that one or both aircraft in a conflict are not yet under the control of the sector that has been notified of the alert. If the controller at the notified sector wishes to take early action, he or she needs to coordinate with an adjacent sector. Conflict Probe incorporates a graphical sector-to-sector coordination capability to facilitate this coordination. This important capability lends a distributed aspect to the Conflict Probe decision-support system. MITRE is also researching an aid to help controllers resolve identified conflicts. This aid could ultimately be incorporated into Conflict Probe. The controller identifies the two-aircraft conflict for which he or she wants the aid to develop candidate resolutions. The aid evaluates a comprehensive set of maneuvers including climbs, descents, left turns, and right turns for each aircraft, and certain combinations of maneuvers for both aircraft. The system then displays a list of all maneuvers that are conflict free (maneuvers that resolve the original conflict but also contain no other conflicts). There is no implication that the controller should select a particular one from the list, or even that he should select any one from the list. It is not possible for the Conflict Probe system to be aware of all practical considerations that need to be taken into account in selecting a resolution. Nevertheless, the list of conflict-free resolutions provides assistance to the controller in resolving a conflict because it contains maneuvers that are conflict free for a greater time into the future than the tactical resolutions controllers develop manually today. And the controller can more quickly arrive at a conflict-free resolution than he would without this list. Controllers enthusiastically received the URET capabilities during live, but off-line, evaluations conducted at the FAA’s Indianapolis Center in 1996. Based on favorable results of these evaluations, the FAA asked MITRE to install a second copy of the system at the Memphis Center and to make the URET capabilities available on-line at all sectors in Indianapolis and Memphis Centers. As of December 1998, over 500 controllers have been trained in the use of URET and the system is available for use 19 hours each day in en route airspace covering Indiana, Ohio, Kentucky, Tennessee, and West Virginia. Much valuable feedback has been obtained from the field evaluations and many improvements have been incorporated in response to controller comments. The FAA has a contract in place with a commercial contractor to develop and deploy at seven FAA centers a limited production version of URET that will reduce some restrictions placed on airspace users. Current plans call for URET to be in place by the end of 2002. (The contents of this material reflect the views of The MITRE Corporation. Neither the Federal Aviation Administration nor the Department of Transportation makes any warranty or guarantee, or promise, expressed or implied, concerning the content or accuracy of the views expressed herein.) For more information, please contact Alvin McFarland using the employee directory. |
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