Air ground collaboration through delegated separation: Results of simulations for arrivals to closely spaced parallel runways

Abstract

Delegated separation is an air traffic management concept in which responsibility for separation from one or more aircraft is assigned to the flight crew by an air traffic controller, in specific tactical situations, to improve operational efficiency in the National Airspace System (NAS). One example of delegated separation that is used in today's Air Traffic Control (ATC) system is visual separation, during which which controllers request that pilots accept responsibility for separation by direct visual contact with another aircraft. Delegated separation procedures using emerging display technology which brings information on nearby traffic to the flight deck have been explored for more than three decades. With the advent of Automatic Dependent Surveillance — Broadcast (ADS-B) and Cockpit Displays of Traffic Information (CDTI) the possibility of using delegated separation procedures, even when other aircraft cannot be seen, is now a practical possibility. In this human-in-the-loop (HITL) simulation, 12 airline pilots flew a series of scenarios to assess the acceptability of delegated separation during closely spaced parallel approaches. The operations concept is that pilots use the information available on a CDTI in a manner that is directly analogous to the use of out-the-window visual contact when visual separation is being used. Range, closure rate and aircraft wake category were displayed, and a method for highlighting the traffic to follow (TTF) was available. Vertical situation information, including lead aircraft altitude history, was provided to support wake avoidance judgments. When pilots were cleared for the instrument approach with delegated separation responsibility, they were free to choose a spacing interval that they judged to be safe. Lead aircraft to follow were Large, Heavy and Boeing 757 aircraft, requiring pilots to consider the possibility of wake encounter in making a separation judgment. Ownship was assumed to be in the Large wake category. The simulated scenarios were instrument approaches to closely spaced parallel runways, performed in marginal visual meteorological conditions with a ceiling of approximately 1200 ft and a visibility of 5 miles. Confederate air traffic controllers provided real-time communications, traffic point out, and control instructions to the pilots. Lead aircraft trajectories were scripted, and their communications were assumed to be on another radio frequency. A confederate pilot performed pilot monitoring duties. The simulated weather conditions precluded actual visual contact with the lead aircraft until breaking out underneath the overcast layer at about 2.5 miles from the runway threshold. Pilots reported that the information available on the CDTI was sufficient to perform the separation task, workload for the arrival task was within acceptable limits, and that they would be willing to perform this task in actual operations with the CDTI as implemented in this study, with respect to Large aircraft as leaders. However, some pilots raised concerns when following lead aircraft for which additional spacing would normally be provided by controllers due to their wake category. Objective spacing performance showed improvement over the baseline case. The observed baseline and delegated separation spacing distributions were applied to a fast-time simulation to estimate the arrival throughput benefits that may result from the application of these procedures. Fast time simulation data for two cases are reported. The first case used observed separation from the simulation for Large leaders and standard separation behind Heavy and Boeing 757 leads. The second case used observed separation for all leaders. Even when restricted to Large leaders, significant benefits were computed compared to the no-delegation condition with a single arrival stream as would be required under the weather conditions simulated.