Impact of Wake Vortex Deformation on Aircraft Encounter Hazard

A safe revision of current aircraft separation minima requires detailed knowledge of the vortex decay and its effect on encountering aircraft. The wake vortex system generated by an aircraft rolls up to a pair of counter-rotating vortices. They deform with growing vortex age due to the long-wave Crow instability, and they later break up into vortex rings. However, most encounter flight simulations to date simply consider the vortex decay by a reduction in circulation strength but not by vortex deformation. This paper investigates the impact of wake vortex deformation on the hazard and risk of aircraft encounters by means of mass encounter flight simulations. Different methods to model aging vortices are compared in terms of their ability to adequately reproduce the vortex-induced aircraft response. The results show that the vortex deformation affects the response of encountering aircraft and maycause an increased hazard in terms of bank angle upsets. It should therefore be incorporated in vortex simulation models. The encounter risk, which describes the frequency of hazardous encounters, decreases with the vortex age. The decrease is significant for large deformations and vortex rings; however, it is lower than expected for small deformations. This result provides the potential to reduce current separation minima.