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	+ Home Search Aviation Systems		01.15.08 Division Highlights Contents Tactical Automatic Altitude Resolutions Added Areas of research in robust optimization of arrival sequencing and scheduling identified Performance Based Services Meeting at Langley Airport Surface Modeling Technical Interchange Meeting Tactical Automatic Altitude Resolutions Added: The Tactical Separation Assisted Flight Environment (TSAFE) conflict detection capability is being extended to include resolution maneuvers for automated separation assurance. A basic simulation capability now can take control of flights to simulate the execution of tactical resolution maneuvers issued by TSAFE. The simulation accounts for maneuver delays (10 seconds) and basic maneuver dynamics such as turn rates and vertical acceleration limits (0.05 g). Three categories of resolution maneuvers have been implemented and tested using an archived operational error database: 1) blocking an altitude change known to cause a loss of separation, 2) a temporary altitude clearance in which an aircraft stops temporarily on its way to its ultimate cleared altitude, and 3) a change to the cleared altitude. (An operational error is an actual loss of separation in the national airspace system attributed to a controller error.) Early results show that 68 of 100 operational errors were avoided by issuing a tactical altitude resolution maneuver to one of the aircraft involved in the conflict. The next step is to allow maneuvers to be issued for both flights simultaneously. + Back to Top Areas of research in robust optimization of arrival sequencing and scheduling identified: A literature review is now complete on robust optimization of arrival sequencing and scheduling. The review covers three areas: aircraft trajectory prediction / uncertainty, empirical studies of arrival runway operations, and arrival scheduling. In addition, the review contains expert opinion from Eurocontrol, George Mason University, University of California at Berkeley, and L-3 Communications. The review uncovered several unrealistic assumptions in earlier research. In particular, past work either ignored the uncertainty of runway threshold crossing times for arrivals or used inappropriate distributions. Some of these findings can be attributed to ignoring arriving aircraft in airspace near destination airports. Furthermore, it is difficult to determine how to predict the 4-D trajectory of an arrival aircraft in terminal airspace without a more complete understanding of pilot or air-traffic-controller behavior. Data from empirical studies of arrival runway operations can create more realistic assumptions for robust arrival scheduling decision-support tools. These data will focus on rush periods when air traffic controllers aim to maximize the number of arriving aircraft, and quiet periods when aircraft are routed more or less directly to arrival runways. Planning has begun on a new research effort to identify large sets of empirical data (radar tracks or GPS measurements), from the trajectories of all different types of aircraft, as they descend from metering fixes to runway thresholds. + Back to Top Performance Based Services Meeting at Langley: The leaders of the Performance Based Services (PBS) research area met at NASA Langley to review task plans and progress for fiscal year 2008. A plan to conduct a test at the NASA Langley Air Traffic Operations Lab was discussed and a draft was written. This test will evaluate self-separation algorithms with varying aircraft communication and surveillance capabilities. Requirements from other focus areas, such as Separation Assurance and Trajectory Prediction Synthesis and Uncertainty, can be included. In reviewing progress on the development of communication, navigation, and surveillance models, the team discussed a simulation involving the Airspace Concept Evaluation Simulation (ACES) tool at Ames. This simulation will evaluate Advanced Airspace Concept logic with different levels of aircraft surveillance range. The team will pursue working together with the Ames staff to determine if this ACES test can support PBS work. + Back to Top Airport Surface Modeling Technical Interchange Meeting: The Aerospace Operations Modeling branch hosted a meeting with Sensis on their new airport surface model named the Surface Traffic Limitations Enhancement (STLE). The branch is considering this model for integration with the Airspace Concept Evaluation System (ACES), which is a simulation of the air transportation system. The current airport surface model in ACES simulates the flow of traffic in all the ramps, taxiways, and runways using a single queue. On the other hand, the STLE can simulate movement of individual aircraft on individual ramps, taxiways, and runways. In addition to simulating the traffic movement in detail, it allows direct modeling of the operations needed to separate and manage the traffic. Whereas the STLE engineering requirements were discussed at this meeting, a follow up meeting will discuss its software requirements. + Back to Top
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