Increases to the capacity of the National Airspace System (NAS), and reduction of delayed and cancelled flights, can be achieved by increasing the landing and takeoff capacity of the runways at the nation's busiest hub airports. NASA and the FAA are evaluating the feasibility of increasing runway capacity through reduced wake vortex separation distances between aircraft in the arrival and departure flows. Traditionally three methods have been used to determine safe wake vortex separation distances: (i) flight test experiments, (ii) historic operational data, and (iii) analytical models. This paper describes the WAVIR toolset, developed by the National Aerospace Laboratory NLR (the Netherlands), for evaluation of wake vortex separation distances. WAVIR is an analytic tool that uses stochastic models for wake vortex generation, wake vortex encounter, aircraft separation, and pilodaircraft response to an encounter of varying magnitudes. The WAVIR tool provides the ability to evaluate the feasibility of different separation distances between fleets of heterogeneous aircraft under different operational, weather and wind conditions. The approach is applied to evaluate the safety related to current practice single runway arrivals.
In today's operations, a limiting factor for runway throughput and the spacing between aircraft on final approach is the required minimum separation. This is either a minimum radar separation or a wake turbulence separation. The latter is based on ICAO's definition of wake turbulence categories and minima, sometimes with local adaptations.EUROCONTROL, in the context of SESAR Project 6.8.1, investigates concepts for flexible and dynamic use of wake turbulence separations that could replace the static and to some extent suboptimal ICAO Wake Turbulence (WT) classification scheme.Given certain separation criteria, the actual spacing between aircraft as controlled by ATC is fluctuating along the approach, with a general tendency to compress due to differences in the ground speed of leader and follower aircraft. To account for this compression of the spacing, ATC applies a 'spacing buffer' when setting up the sequence.From a survey of the current practice of separation delivery at major airports in Europe, it appeared that this spacing buffer on average decreases from roughly 1.5 NM at 10 NM before the threshold to 0.5 NM at the runway threshold. It was furthermore observed that there is a considerable variation in the actual spacing, with a standard deviation of 0.5 NM at the threshold.For getting the most benefit from more optimized and flexible separation criteria while maintaining safety, it is therefore considered necessary to also optimize the separation delivery. For this, more accurate information on and prediction of the aircraft approach speed and -related to thistime to fly a certain distance is required. This paper presents a data driven model to predict approach speed and time to fly dependent on actual headwind conditions and aircraft type.The model has been developed using radar data in combination with weather data. The performance of the model has been assessed in terms of Root Mean Square Error (RMSE) of time to fly and have been compared to static (aircraft specific but wind independent) speed profiles. Dependent on the headwind condition, the actual time to fly from 10 to 0 NM varies between 200 and 300 seconds. The RMSE when using the model varies between 5 and 10 seconds, which is about a 40% improvement compared to predictions using the static speed profiles. Furthermore, the variance of the error is reduced which helps to prevent significant over or underestimation of the actual time to fly.The results of this study are used by SESAR and EUROCONTROL in the development of the Leading Optimised Runway Delivery (LORD) tool to support Air Traffic Controllers to optimize the delivery of separation.
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