Eliminating the Altitude-for-Direction Rule and implementing reduced Vertical Separation Minimum in the U.S

Abstract

This paper discusses the feasibility of eliminating the Altitude-for-Direction (AFD) rule and implementing Reduced Vertical Separation Minimum (RVSM) at higher altitudes in the United States. Both actions would provide meaningful benefits to airspace users: eliminating the AFD rule permits more efficient altitude profiles, while RVSM would provide more altitudes for traffic management, potentially reducing the number of traffic flow restrictions in congested airspace. Implementation of automation as part of the Federal Aviation Administration’s Free Flight Phase 1 and 2 programs, and development of procedures as part of the Operational Evolution Plan, are expected to facilitate these changes. Simulation scenarios were derived from real traffic scenarios to represent eliminating the AFD rule and implementing RVSM. The numbers of URET conflicts (predicted separation less than roughly 1700 feet vertical (with 2000-foot vertical minimum) and 12 nmi lateral) occurring in high altitude sectors are compared to assess the feasibility of the changes. Eliminating the AFD rule in large contiguous areas of less dense airspace is promising and warrants further study. The number of additional conflicts generated by eliminating the rule in dense airspace makes elimination there uncertain. In contrast, there was a significant drop in the number of conflicts observed in dense airspace when the runs were made with RVSM. There were indications that the additional altitudes from RVSM greatly facilitate the handling of traffic in dense airspace.