Navigation system autonomy and integration in NextGen: Challenges and solutions

For strategic air traffic management, NextGen foresees the use of negotiated 4-D trajectories. With the separation margins envisioned in NextGen, navigation errors can result in a loss of separation within a time that is shorter than the time needed to resolve the conflict through trajectory negotiation. A gap exists between the time to conflict that the situation can be resolved through trajectory negotiation and the time to conflict at which TCAS starts to provide collision avoidance guidance. To limit the situations in which TCAS must provide collision avoidance guidance, the challenge is to minimize the encounter probability in the time domain where negotiating 4-D solutions is not practical. To support the pilot with self-separation, ADS-B enabled Conflict Detection and Resolution (CD&R) concepts are being developed. To realize a situation in which the pilot assesses options generated by the CD&R system and selects the one to be executed by the GNC system, integration between these two systems is required. The integration needs to address the autonomy of the system functions, the associated role of the pilot and the resulting information requirements. The work discussed in this paper has focused on the design of a concept for the computation and execution of conflict prevention maneuvers with a high degree of trajectory (outer- loop) predictability and the presentation of the result to the pilot in such a way that it can be used both for manual and supervisory control. The basis for this approach is the use of conflict probes for the CD&R function. Based on the location and extent of the predicted conflict space(s), a set of trajectories are continuously computed and presented to the pilot. The pilot can assess the different trajectories relative to the constraints and select the most appropriate one. A number of examples are provided to illustrate the concept.