Analysis of the wake vortex encounter risk under reduced vertical separation enabled by geometric altimetry

As the current requirements of at least 1000 ft vertical separation between aircraft in en-route airspace are mainly determined by the limited accuracy of barometric altimetry, a study has been performed whether these separation minima might be reduced to 500 ft with usage of geometric altimetry. Thus, allowing smaller nominal vertical distances between flight paths, it is to be expected that the risk (in frequency of occurrence and severity) of wake vortex encounters increases. The present study, using a comparative fast-time simulation of traffic at European level for two full-day scenarios, indeed confirms a relative encounter risk increase by a factor of 3 to 4 across all severities (as expressed by the magnitude of the circulation encountered), with this factor being largely independent of the wind situation. Consequently, the exploration of mitigation means such as conditional application of reduced vertical separation or tactical wake conflict prediction tools should be undertaken as part of further development of the concept.