Analysis of the Aircraft to Aircraft Conflict Properties in the National Airspace System

*† ‡ The primary function of administering the United States’ National Airspace System (NAS) is the air traffic controller task of actively monitoring assigned aircraft and resolving the conflicts (i.e. losses of minimum separations between aircraft) anticipated some time in the future. To mitigate the safety risks of increased traffic growth and effectively designing automation to aid in the separation management task, knowledge of the characteristics or properties of the conflicts is required. This paper reports on a comprehensive study that has examined these properties by collecting traffic data from all 20 NAS en route centers, developing software models to determine these events, implementing experimental design techniques to calibrate them, validating the models by comparing to advanced operational systems, and presenting detailed graphical and statistical analysis of the results. I. Introduction In the United States, the overall system of managing and controlling air traffic is known as the National Airspace System (NAS), which is administered by the Federal Aviation Administration (FAA). Detailed procedures involving restrictions on routing, speeds, and altitudes are an integral part of the NAS. These restrictions severely reduce the amount of aircraft traffic that NAS can accommodate, yet are needed to ensure the high level of safety required. At the heart of these operations is the human air traffic controller who must synthesize many pieces of timely information including radar surveillance information and flight data. Their fundamental responsibility is to ensure the safety of the aircraft flying within their regions of airspace in the most efficient means possible. To accomplish this, air traffic controllers actively monitor their aircraft and then resolve any conflicts (i.e., loss of minimum separation between aircraft or restricted airspace) predicted some time into the future. Furthermore, these resolutions are administered by air traffic controller voice instructions via radio transmissions to the aircraft. In the current system, there are automation systems that aid the air traffic controller mainly in the monitoring part of the task such as the ground based tactical and strategic conflict probes. In the en route centers, typically managing the aircraft above 18,000 feet, the Host Computer System’s (HCS) Conflict Alert function provides tactical alerts. The upgrade to the HCS, still under development, called the En Route Automation Modernization (ERAM), replaces Conflict Alert with several categories of alerts with the basic function requiring a minimum of 75 seconds warning. The User Request Evaluation Tool (URET), developed by MITRE Corporation’s Center for Advanced Aviation System Development, is an example of a strategic conflict probe in operation in the en route centers. It predicts conflicts up to 20 minutes in the future with typically a minimum warning of five minutes. Even with the aid of ground-based conflict probes, the task of separating aircraft will become increasingly difficult, since most air traffic service providers in the United States and Europe anticipate significant growth in air traffic. The growth is expected to out pace the capacity limits of the aviation systems, resulting in greater congestion and inefficiency. The interagency Joint Development Planning Office (JPDO) in the United States foresees a traffic demand increase by 2025 up to three times the number of flights of today’s traffic. 1 Given the need for enhanced safety and efficiency, broad categories of advances in ground and airborne automation are required. The JDPO, as established in their charter under the “Vision-100” legislation (Public Law 108-176) signed by President G. W. Bush in December 2003, has mandated a next generation operational concept of the NAS for 2025. 1 This next generation