Evolution of the United States National Airspace: The Move Towards Performance-Based Navigation

The Transition from Ground-Based Navigation Aids to Satellite-Based Navigation

As the FAA entered the 21st Century, the agency faced a new paradigm in aviation. Revenues from passenger flight taxes and operations fees have dropped. The airline industry is transitioning from mostly hub and spoke operations dominated by large airlines using large aircraft to a highly competitive, regional point to point operations dominated by low cost carriers flying regional jets. This new environment has increased the number of daily operations yet the FAA’s workforce has contracted. Traditionally, one of FAA’s major funding streams came from passenger taxes. As the cost of flights has dropped, funding levels have dropped. In a word, the FAA has to learn to do more with less.

Currently the FAA’s national airspace is actually a system of systems. For navigation and landing  purposes, the FAA maintains a highly redundant, overlapping system of VORs, ILSs, DMEs, NDBs, marker beacons, and numerous lighting systems. As mentioned previously, this comprises over 3,000 individual pieces of equipment. The cost to maintain and operate such a large system is enormous. In fiscal year 2004, this cost the FAA more than $300,000,000. The fastest growing portion of the FAA budget is operations. Budgetary reality is that something has to change. As satellite navigation technology matures, the FAA must begin to plan the transition from a ground-based navigation infrastructure.

The FAA has begun  developing transition strategy to assess the current state of the NAS and to determine what the best combination of navigation aids is to serve aviation’s needs, and the path or paths the transition  can take. The transition will be a slow and arduous process, gaining insight into constantly evolving requirements and needs.

The first step of this evolution is to fully implement satellite-based navigation. As satellite navigation becomes more of the standard, conventional ground based navigation aids will continue to be phased out. Eventually, there will probably be a network of ground based navigation aids in place in case of a catastrophic problem with satellite-based solutions. This will not replicate the capability of the operating NAS, it will be in place to ensure the safe operation or aircraft until satellite navigation can be restored.

The transition to Satnav is dependent upon the increased service provided over existing ground-based Navaids in instrument meteorological conditions with operations continuing in the presence of interference. The FAA is not in a position to support the development and deployment of Satnav and to also re-capitalize the entire existing ground-based infrastructure, making Satnav just another layer of navigation. The FAA is recommending the sustainment of a reduced number of existing Navaids to provide both a redundant and backup capability for en route navigation, non-precision approach, and precision approach. Redundancy is defined as being able to navigate apart from the airway structure using area navigation (RNAV). A backup capability is dependent on flying directly between retained ground-based Navaids.

The FAA will sustain a network of DMEs to provide a redundant RNAV capability. A reduced set of VORs and long-range NDBs will be retained to support a backup capability. At least one ILS will be retained at airports where this service is provided today, unless the ILS is not necessary, as part of the backup service and traffic use does not justify a requirement for continued and uninterrupted service. These actions effectively reduce the threat to air transportation from disruption of Satnav services. The continued development and deployment of spectrum diversity (L1 and L5 frequencies on the GPS satellites) as well as improved anti-jamming capability adequately addresses the issue of unintentional interference. The exact mix of ground-based Navaids will need to be defined by specific locations and time for removing systems so that the users can assess the impact to their operation and plan their investments in Satnav.

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