Page 9 - Volume 15 Number 2

groups better understood the necessity of maintaining multiple forms of navigational systems. Yes, VOR stations are costly, have range limitations and require maintenance. Thus, some will be allowed to fade into history. However, a Minimum Operational Network (MON) of them will remain for the foreseeable future.
VORs Evolution to MON
In late 2011, the FAA published its first notice for public comment related to its proposal to draw down the VOR network within the Continental U.S. (CONUS) to a MON. After the normal process of comment evaluation, proposals and notices was complete, a plan for transitioning to NextGen navigation systems was published by the FAA in July 2016. It included a plan for transitioning to PBN and for establishing a VOR MON. Phase I of that plan was to run from Fiscal Year (FY) 2016-2020. Before Phase I began, the FAA owned 957 VORs. Another 100 non-federal VORs were also in operation around the U.S. Some VORs were decommissioned during Phase I, but the primary goal during that time was to remove, replace or amend affected Instrument Flight Procedures (IFP), which would allow for more widespread VOR decommissioning during Phase II. By the time you read this, Phase II will have already begun and is currently scheduled to run through 2030. During Phase II, the federal VOR count will fall to 589, but without a significant loss of capability for the average user (see Figures 1 and 2, opposite page).
The creation of the VOR MON was a well thought out plan, allowing critical VORs to remain and for an expansion in service volume in many of those. Additionally, a network of Minimum Operational Network Airports (MONA, also known as “Safe Landing Airports”) was established to ensure that, in the event of a widespread GPS outage, all aircraft operating within CONUS would be within 100 nautical miles
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of an airport with a VOR or ILS approach procedure that does not require GPS, Radar Coverage, DME or ADF to legally fly. Of course, any suitable airport or approach procedure that is even closer at the time of total GPS signal loss may be utilized.
Should They Stay or Should They Go?
It is important for us, as pilots, to fully understand what defines the VOR MON network and what VOR capability changes have developed to facilitate it. First, what criteria was used for decommissioning versus retention decisions? Beyond those VORs used to support ILS, LOC or VOR approaches at Safe Landing Airports, additional factors were applied. Any VOR falling into the following categories will be retained:
= VORs which support international oceanic routes
= A sufficient network of VORs to provide coverage at/above 5,000 feet AGL
= VORs in the Western U.S. Mountainous Area (WUSMA) which anchor Victor Airways through high elevation terrain
= Any VOR required for military use
= All VORs outside of CONUS
Additionally, no non-FAA VORs were considered for decommission as part of the VOR MON plan. Yet, those VORs are not part of the VOR MON network either. So, they can be thought of as VORs in addition
to the VOR MON. However, since they are not FAA owned, they could be subject to decommission by their owner/operators at any time. Fortunately, all DME, TACAN and communication capabilities will be retained and reconfigured as necessary, even if the VOR they are co-located with is to be decommissioned. This will not only protect the integrity of DME and TACAN units, but also important communications services, such as Hazardous Inflight Weather Advisory Services (HIWAS) and Remote Communications Outlets (RCO).
Conclusion
With the transition to VOR MON and the Safe Landing Airports networks, the FAA has begun implementing some charting changes related to both (specifically, refer to Figure 3). To facilitate the reduction in VOR numbers within CONUS, while retaining a VOR network with consistent reception capabilities at/above 5,000 feet AGL, two new Standard Service Volumes (SSV) are being added to VORs on the retention list. While these new SSVs do not require major equipment changes, they do represent a change in the SSVs many of us have learned and memorized during initial and recurrent instrument training. Specifically, for High VORs, a 70- nautical-mile SSV will now exist between 5,000 feet and 14,500 feet Above Transmitter Height (ATH). For Low VORs, the same 70-nautical- mile SSV will extend from 5,000 feet
Figure 3: Charting example (with descriptions) of a MON Airport on a NOAA (government) Low Enroute IFR chart. (Source: faa.gov)
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