What is the VOR MON?
The Very High Frequency Omni-directional Range (VOR) Minimum Operational Network (MON) provides a conventional navigation backup service in the event of a loss of Global Positioning System (GPS) signal. The MON includes the minimum number of geographically situated VORs in the contiguous United States (CONUS) necessary to provide coverage at and above 5,000 feet above ground level. Additionally, the MON supports International Oceanic Arrival Routes and mission critical military use.
On December 15, 2011 the FAA published in the Federal Register a notice of proposed policy and request for comments (76 FR 77939) on the FAA's proposed strategy for gradually reducing the current VOR network to a Minimum Operational Network (MON) as the National Airspace System (NAS) transitions to performance-based navigation (PBN) as part of the Next Generation Air Transportation System (NextGen). The FAA announced that, as part of a NAS Efficient Streamlined Services Initiative, the number of conventional navigational aids (NAVAIDs) would be reduced while more efficient Area Navigation (RNAV) routes and procedures are implemented throughout the NAS. The FAA noted its intention to convene a working group to assist in developing a candidate list of VORs for discontinuance using relevant operational, safety, cost, and economic criteria. Interested parties were invited to participate in the review of this policy and planning effort by submitting written comments on the proposal. The FAA reviewed all 330 comments received and on August 21, 2012, published in the Federal Register the disposition of the comments on the notice of proposed policy (77 FR 50420).
The following criteria were used by the FAA to determine which VORs would be retained as a part of the MON:
- Retain VORs to perform Instrument Landing System (ILS), Localizer (LOC), or VOR approaches supporting MON airports at suitable destinations within 100 nautical miles (NM) of any location within the CONUS. Selected approaches would not require Automatic Direction Finder (ADF), Distance Measuring Equipment (DME), Radar, or GPS.
- Retain VORs to support International Oceanic Arrival Routes.
- Retain VORs to provide coverage at and above 5,000 ft above ground level (AGL).
- Retain most VORs in the Western U.S. Mountainous Area (WUSMA), specifically those anchoring Victor airways through high elevation terrain.
- Retain VORs required for military use.
- VORs outside of the CONUS were not considered for discontinuance under the VOR MON Implementation Program.
The following considerations were used to supplement the VOR MON criteria above:
- Only FAA owned/operated VORs were considered for discontinuance.
- Co-located DME and Tactical Air Navigation (TACAN) systems will generally be retained when the VOR service is terminated.
- Co-located communication services will be relocated or reconfigured to continue transmitting their services.
How does the VOR MON support aviation?
The MON will enable pilots to revert from PBN to conventional navigation for approach, terminal and en route operations in the event of a GPS outage and supports the NAS transition from VOR-based routes to a more efficient PBN structure consistent with NextGen goals and the NAS Efficient Streamlined Services Initiative.
The VOR MON is designed to enable aircraft, having lost Global Navigation Satellite System (GNSS) service, to revert to conventional navigation procedures. The VOR MON is further designed to allow aircraft to proceed to a MON airport where an ILS or VOR approach procedure can be flown without the necessity of GPS, DME, ADF, or Surveillance. Of course, any airport with a suitable instrument approach may be used for landing, but the VOR MON assures that at least one airport will be within 100 NM.
FAA Contact: Leonixa Salcedo, VOR MON Program Manager
Tel.: (844) 4-VORMON; (844) 486-7666