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In the past few years much of the global ATM research community has proposed advanced systems based on Trajectory-Based Operations (TBO). The concept of TBO uses four-dimensional aircraft trajectories as the base information for managing safety and capacity. Both the US and European advanced ATM programs call for the sharing of trajectory data across different decision support tools for successful operations. However, the actual integration of TBO systems presents many challenges. Trajectory predictors are built to meet the specific needs of a particular system and are not always compatible with others. Two case studies are presented which examine the challenges of introducing a new concept into two legacy systems in regards to their trajectory prediction software. The first case describes the issues with integrating a new decision support tool with a legacy operational system which overlap in domain space. These tools perform similar functions but are driven by different requirements. The difference in the resulting trajectories can lead to conflicting advisories. The second case looks at integrating this same new tool with a legacy system originally developed as an integrated system, but diverged many years ago. Both cases illustrate how the lack of common architecture concepts for the trajectory predictors added cost and complexity to the integration efforts.

Recent research has increased focus on the conceptual design, development and use of air-and ground-based aircraft trajectory prediction capabilities to support advanced Air Traffic Management concepts. In both the United States and Europe, the sharing of fourdimensional trajectory information between many automation systems will be necessary for successful operations. Understanding the functional and performance differences between disparate trajectory predictors is critical for enabling this system interoperability. Documented capabilities for four existing trajectory predictors were compared to identify commonalities and differences. For effective comparison, it was first necessary to abstract the prediction capabilities of each trajectory predictor. Three abstraction techniques were developed. The first separated the description of modeled aircraft behavior from the associated mathematical models used to integrate the predicted trajectory. The second defined a conceptual boundary between the trajectory predictor and its client application. The third eliminated the use of domain specific terminology. The abstraction techniques proved not only beneficial for comparing trajectory prediction capabilities, but also for defining trade-offs between the compatibility and accuracy of disparate TPs to achieve system interoperability.

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This paper develops guidance algorithms suitable for 4D-trajectory-based airspace operations. A previous paper by the same authors proposed a 4D-trajectory-based operational concept for terminal area operations. The concept consists of ground-side automation for synthesis of 4D trajectories and flight-deck-side automation for tracking the 4D-trajectory clearances. Whereas the previous paper dealt with the ground-side automation, the current paper deals with the flight-deck-side automation. The guidance algorithms are part of the flight automation necessary to realize the 4D-trajectory-based operations. The guidance algorithm design is based on the principles of feedback linearization and pole-placement techniques from feedback control theory. 4D trajectories are assumed to be designed using lower-fidelity models such as Base of Aircraft DAtabase (BADA) by ground-side automation. The guidance algorithms in the flight-deck automation on the other hand use higher-fidelity models to track the 4D trajectories. The guidance algorithm computes pitch attitude and throttle commands necessary to continually track a 4D trajectory. Closed-loop simulations using the high-fidelity TSRV aircraft model obtained from NASA Langley indicate very good tracking performance with time-tracking errors less than 1 second. Simulations demonstrate robustness to wind and temperature uncertainties. The guidance implemented on a pair of aircraft also demonstrate the capability to maintain along-trail separation.