One of the complicating factors when detecting and resolving aircraft-to-aircraft conflicts is trajectory prediction uncertainty, which can cause conflicts to be detected without sufficient time to resolve them. Previous work by the authors showed this situation occurs most often in Center Airspace when an aircraft is between about 10 nmi before its top-ofdescent point and its arrival fix at the edge of the terminal area. This paper explores a pair of enhanced vertical conflict detection ranges (buffers) for aircraft descending to their meter fix that could provide enough coverage to catch potential losses for multiple types of uncertainty while limiting the increase in false alerts. The specific uncertainties examined include the predicted wind speed, cruise speed, descent speed, top-of-descent location, and the combination of all of those uncertainties plus uncertainty in aircraft fuel weight prediction. Performance metrics include false alerts, missed alerts, losses of separation, number of resolutions issued, and the total system delay caused by aircraft flying conflict avoidance maneuvers. Results show that these vertical buffers reduce the number of losses of separation for arriving aircraft from 207 to 12. However, using the vertical buffers increases the number of resolutions issued by 50% and doubles the delay accrued by aircraft flying conflict resolution maneuvers. Results also suggest that a smaller buffer (80% size) could be used to gain most of the same benefit as the full buffer with less additional delay, while alternative methods might be best suited to remove the last few loss of separation cases during descent. Further, improving the trajectory prediction accuracy combined with a vertical buffer significantly reduced the number of losses of separation, resolutions issued, and delay accrued.
The effects of selecting conflict resolution maneuvers based on minimum delay are compared to resolution selection based on minimum fuel burn. The algorithm used in this study is designed to support an automated separation assurance capability for next generation air traffic management systems. The algorithm resolves detected conflicts that are projected to be between three and twenty minutes prior to loss of separation. A total of nine fast-time simulations were conducted, each representing thirty six hours of traffic on a "low weather," high volume day with mixed aircraft types, flight phases and conflict geometries. The test matrix varied airspace region and resolution selection criteria. System-wide effects such as the number of conflicts, fuel burn, delay, and maneuver type are analyzed and compared to the same metrics when maneuvers are selected based on delay. When selecting resolutions based on fuel burn, the cumulative fuel burn of the system decreases by 27% and the delay increases by 25% when compared to resolutions selected based on minimum delay. Results indicate that speed maneuvers are the most efficient when selecting resolutions based on minimum fuel burn. Horizontal and vertical maneuvers were executed with similar frequency when comparing delay and fuel burn.
A conflict resolution algorithm is introduced that enables a user to specify the degree to which fuel economy is prioritized relative to airborne delay, analogous to the "cost index" setting in flight management computers. Fast-time simulations of current-day traffic levels in two regional airspaces under nominal weather conditions are simulated to evaluate the benefit of modifying a conflict resolution algorithm to select resolution maneuvers based on minimum cost. The study employs the use of a parameter to represent the relative importance of fuel burn price to delay price. Additionally, the price of fuel burn and delay relative to one another is varied from the nominal in order to illustrate the differences in the algorithmic behavior should the delay or fuel price increase. Results show the lowest total operational cost occurs when the relative importance of delay to fuel burn price is equally weighted. Overall, minimizing fuel burn when selecting resolutions based on cost results in a lower operational cost than minimizing delay. The sensitivity of total operational cost to resolution types is presented. Implications of these findings for advanced separation assurance concepts are discussed.
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